OQ COR 09W: Cathodic Protection Remediation-

Corrosion Specialist

Study Guide
INTRODUCTION

Cathodic protection systems along the pipeline must be tested and maintained to
ensure adequate protection against corrosion. The pipeline system has many
test stations, casings, rectifiers, foreign line crossings, isolation flange kits and
test points that allow pipeline personnel and the Corrosion Specialists to monitor
these levels. As a result of annual surveys, bi-monthly rectifier/critical bond
readings, Close Interval Surveys and other tests, remedial measures must be
taken to correct the changing conditions along the pipeline. This module will
attempt to describe in moderate detail the procedures necessary to remedy some
of the basic problems encountered while maintaining our cathodic protection
systems. According to the DOT and BP’s OMER I Manual these tasks are
required. It is beyond the scope of this training to describe in detail every
scenario that may be encountered while trying to maintain adequate levels of
cathodic protection. For the purposes of this training module, a brief description
for installing impressed current and sacrificial groundbeds, installing/checking
isolation flange kits, rectifier maintenance and troubleshooting and the handling
of shorted casings will be given. The Rectifier/Critical Bonds, the Conducting an
Annual Survey and the Perform General Pipeline Repair Activities Study Guides
should serve as additional references to this guide.

CORROSION BASICS

Before we get into the remediation process, let’s discuss some basic corrosion
principles that may help you to understand the need for cathodic protection.
Corrosion by definition is the deterioration of a substance (usually a metal), or
its properties, as a result of its reaction with its environment.

Figure No. 1 – Corrosion that occurred on an unprotected buried steel pipeline.

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All metallic corrosion is electrochemical in nature, and is the result of direct
electrical current flow.

Consider a flashlight battery, composed of a positive terminal (connected to the

graphite post), and a negative terminal (connected to the zinc container) and the
space between the graphite post and the zinc container is filled with an
electrically conductive paste, called an "electrolyte".

By using the concept that current flows from positive to negative through the
circuit external (termed "conventional current flow concept"), corrosion of the zinc
case is caused by the flow of DC current from the zinc case, through the
electrolyte to the graphite post, and completing the electrical circuit through the
external connection from the positive terminal through the light bulb, and back to
the zinc case, where it started. (Some people call this "conventional current"
flow, or "positive charge" flow, which is in the opposite direction to electron flow).

Since this current flows from the zinc into the electrolyte, it causes the zinc to
corrode.... to be eaten away by corrosion. In this case, the resulting current flow
(as electron flow in the meta llic circuit) would be from the more active metal (the
anode) to the less active metal (the cathode). An oxidation (corrosion) reaction
would occur at the anode and a reduction (cathodic protection) reaction would
occur at the cathode. Just like the cathodic protection systems installed along
the pipeline, the anodes corrode or are consumed. They in turn produce and
electrical current that helps to protect the pipeline from external corrosion.

All metals exist in nature in their lowest energy level. This state of existence is
referred to as the "ore" state of the metal. For most metals, this is not a very
usable state. By refining, they become a very useful material (i.e. carbon steel
for our pipelines and ASTs).

It takes a different amount of energy to refine each kind of metal from its ore. Part
of the refining energy stays within the metal following the refining process. The
more energy it takes to refine the metal, the more that is stored inside the
material. Basically, this is what happens when we take a refined metal like our
pipeline (carbon steel) and bury it in the ground. The pipeline will want to revert
back to its original form (iron ore). As it rusts/corrodes the energy that it retained
from the refining process is released.

OUR DEFENSES

Cathodic protection and coatings are used in combination with one another to
reduce or eliminate corrosion. Cathodic protection is used to turn the pipeline
into a cathode. We are basically raising the pipe’s electrical potential high
enough so that it will not theoretically corrode. Cathodic protection helps the
pipeline retain the energy from the refining process. We accomplish this by
installing impressed current (groundbeds and rectifiers) and sacrificial cathodic
protection systems (magnesium anodes) at various locations along the pipeline.

Coatings are our mainline defense against corrosion. It is used to prevent the
pipeline from coming in contact with an electrolyte (soil, water, etc.). If the
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pipeline is 100% coated, then one leg of the corrosion cell is eliminated (no
electrolyte). Much like the same concept in the fire triangle, if there isn’t any
Oxygen, the fire cannot sustain itself. Since achieving a 100% coated pipeline is
not possible, cathodic protection is used in conjunction with coatings to reduce
the potential of a corrosion related leak.

For the purpose of this study guide, we are going to focus on the cathodic
protection aspects for corrosion prevention.

CATHODIC PROTECTION GENERAL OVERVIEW

The typical components for cathodic protection systems include anodes

(impressed or galvanic), rectifiers, High Molecular Weight Polyethylene
(HMWPE) cable and a low resistance backfill material typically referred to as
coke breeze. The rectifiers are supplied with AC power. The AC is then
converted to DC through a rectifying element (diodes or a selenium stack). The
DC voltage is then directed to some type of anode configuration that produces
DC current (amps). The DC current then travels through the soil to areas along
the pipeline that are exposed to the soil via holidays or holes in the coating. This
DC current is what prevents the pipeline from corroding. The DC current then
travels through the pipeline back to its source (the rectifier) to complete the
circuit. Each rectifier has the ability to protect miles and miles of pipeline. The
area of protection or influence may be dependent on the following factors:

® Coating condition – The better the condition of coating, the greater the
area of influence from the cathodic protection system.
® Soil Resistivity – The lower the soil resistivity, the greater the area of
influence from the cathodic protection system.
® Anode Configuration – The number, arrangement (deep well or
distributed) and placement of anodes affect the area of influence.
® Type of Anode Material – different anode materials and sizes affect the
overall output of the groundbeds.
® Foreign Structures – The lower number of foreign pipeline/structures in
the vicinity of groundbed, the greater the area of influence.

See the Figure No. 2 on the following page for an example of a typical cathodic
protection system:

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 ANODES-Galvanic

There are basically two types of anodes used in the cathodic protection of
pipelines, galvanic and impressed current. Galvanic anodes (magnesium, zinc,
etc.) are typically connected directly to the pipeline via an exothermic weld. This
welding procedure is the same procedure used to attach cathodic protection test
leads to the pipeline. One of the advantages to using a sacrificial anode is that it
does not require an external current source to operate. However, the anode’s
driving potential and current capacities are limited. The anode can be laid either
vertically or horizontally. See Figure Nos. 3 & 4 below for typical installation
details:

Cott shunt to measure anode current COTT

.001Ω

BP Anodes

Test lead for taking PSPs.

Cott “Big Fink”

Test Station

Native Backfill
Cathodic Protection Warning Tape

Pipeline
Spliced connections to anode header cable

Magnesium anodes vertically installed to a depth of 3-5 feet

below the pipeline.

Figure No. 3 – Typical magnesium anode array that has been vertically installed.

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 COTT

Cott shunt for measuring anode current

.001Ω

BP Anodes
Test lead for taking PSPs.

Cott “Big Fink”

Test Station

Native Backfill

Pipeline
Cathodic Protection Warning Tape

Spliced connections to anode header cable

Magnesium anodes horizontally installed to a depth of
3-5 feet below the bottom of the pipeline.

Figure No. 4 – Typical magnesium anode array that has been horizontally installed.

Galvanic anodes will typically arrive from the manufacturer encapsulated inside a
paper bag that has been lined with plastic. Before the anodes are placed inside
the excavation, it is imperative that the plastic lined bag be removed from the
anode. Otherwise, the anodes will not function. Usually galvanic anodes used
along our pipeline will come pre-packaged with a specialized backfill material. A
five-gallon bucket of water should be poured on the anodes prior to backfilling.
The water will help the anodes activate.

Galvanic anodes should be installed a depth of 3-5 feet below the pipe. These
depths will generally reduce the amount of seasonal current variation that results
from changing moisture contents within the soil.

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Maintenance of galvanic anode installations are usually performed to determine
whether or not the anode header cables or individual anode leads have been
exposed, damaged (by third party or otherwise) or splice failure. Third party
damage can be reduced by locating not only the pipeline but by locating any
cathodic protection component in the vicinity of the excavation.

If for example, a magnesium anode array is showing a decrease in output and

the anode array should have plenty of life left, a broken header cable or broken
anode lead wire my be reason. The anode header cable can be located using a
conductive method (Metrotech or other conductive locator), an over the line
survey or even excavation. Once the break is located, the break should be
repaired with the proper splice kit or a high voltage splice suitable for below
grade applications.

Typical Uses

Galvanic anodes can be used for a variety of applications along the pipeline.
Generally, they are used in situations where small amounts of Cp current are
required and in location that have low soil resistivity. If a large amount of current
is required, an impressed current CP system is recommended. The following
scenarios are examples of typical galvanic anodes installations:

Ø Hot-spot protection
Ø Small areas on well-coated lines
Ø Valve installation
Ø Shorted casings that cannot be cleared
Ø Areas of electrical shielding
Ø Electrical grounding
Ø Stray current interference

However, before using any of the above applications, all design considerations
(soil resistivity, coating condition, current requirements, easement limitations,
etc.) should be explored.

Vertically Installed Impressed Current Anodes

There are a multitude of impressed current anodes out on the market today.
Some of the most popular anodes are mixed-metal oxides, graphite, high silicon
cast iron and platinum. The type and size of anodes used varies greatly from
environment to environment. The anodes can either come bare or prepackaged
depending on the application. All design considerations should be used in the
selection of anodes.

Impressed current cathodic protection systems are usually installed in these two
arrays, surface anode groundbeds (SAGB) and deep anode ground beds
(DAGB). In a SAGB, the anodes can be either laid vertically or horizontally.
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 Their orientation is usually determined by subsurface conditions or right of way
(ROW) restrictions. Figure No. 5 below illustrates the typical installation details
for a vertically installed anode. The anode type, size, diameter and depth should
be determined by the Corrosion Specialist or a company approved engineering
firm.

Native backfill

36 Minimum
Cathodic protection
ground cover
warning tape

Splice connection
to header cable
B
Dimension ‘A’ = Depth of
anode per specs.
Well tamped calcined
coke breeze A
Dimension ‘B’ = Anode to be
C Centered in backfill.

Impressed current
Anode per specs. Dimension ‘C’ = Length of
anode per specs.

Dimension ‘D’ = Diameter of

B anode column per specs.
Undisturbed earth

Figure No. 5 – Typical vertical impressed current anode installation.

Since impressed current anodes are all made up of different materials, are
different lengths, come pre-packaged or bare, they should be handled carefully.
Graphite or silicon cast iron anodes are brittle. If not handled carefully, they can
break. All anodes have lead wires that have been spliced into the anode
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material. It is for this reason the anodes should not be handled by their lead
wires. If necessary, the anodes can be lowered into vertical installation by the
lead wire only if extreme care has been taken to maintain the integrity of the lead
wire/ anode connection point.

As the vertical anode is lowered into the hole, care must also be taken to center
the anode inside of the coke breeze. First of all, an equal amount of coke breeze
should be placed around the entire anode. Secondly, an equal amount of coke
breeze should be placed above and below the anode. Finally, the coke breeze
should be well tamped prior to backfill. This minimizes the possibility of bridging
across the hole with void spaces below the bridge. These voids may increase
circuit resistance and ultimately contribute to the reduction in anode life. If any
questions ever arise during anode installation, please contact the area Corrosion
Specialist for clarification.

Horizontally Installed Impressed Current Anodes

Horizontal impressed current anode arrays are typically installed in soil

conditions that have high resistivities at the depths vertically installed anodes are
placed. The lower resistance soil combined with a larger anode surface helps to
reduce the overall groundbed resistance. This in turn yields a more efficient
groundbed that can help produce larger amounts of CP current if needed with a
longer life span.

Horizontally installed impressed current anodes should be installed in a

continuous column of coke breeze along the entire length of the groundbed. The
first and last anodes should not be placed closer than five feet from the ends of
the anode column. In addition, the anodes should be centered inside of the coke
breeze. The continual column of coke breeze allows the anodes to operate more
efficiently and extends their useful life. Like vertically installed anodes, they
should not be handled by the lead wire or mishandled in any way.

After the anodes have been placed into the coke breeze and backfilled to the
bottom of the trench, they should be spliced into a header cable using either a
two-part epoxy resin mix that can be poured into a form around the compression
crimp, or a high voltage underground taped splice. The header cable can then
be routed into the rectifier and terminated.

Horizontally installed impressed current anodes should also be installed at a

depth deep enough to reduce the amount of seasonal current variation that
results from changing moisture contents within the soil. Figure No. 6 on the
following page illustrates the typical installation details for a horizontally installed
impressed current anode.

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 Well-Tamped Earth Backfill

Splice Connection the Positive Header Cable 5’-8’

Typical
Cathodic Protection Warning Tape

Well-Tamped Coke Breeze

Undisturbed Native Soil

15’ – 20’ Typical

Figure No. 6 – Typical horizontal impressed current anode installation.

IMPRESSED CURRENT CP CABLES & SPLICES

All underground cables connected to the positi ve terminal of the rectifier are
subject to corrosion at any break in the insulation. The slightest current
discharge at any of these points will result in cable breaks. Anode header
cable’s can be cut by a third party contractor, company personnel or even
rodents. Splices at anode locations can fail prematurely due to improper slicing
techniques. Moisture usually intrudes into the spliced connection providing an
avenue for current discharge. It is for this reason that extreme care must be
taken when making splice connection, handling and backfilling cables.

When backfilling over any CP cable, care must be taken to ensure that there are
no sharp rocks or objects in the cable trench that might puncture the insulation.
The first layer of backfill over the cable should have at least 6’ of cover to protect
the cable from subsequent layers of backfill. In very rocky soil conditions, it is
recommended that sand be used for the first 6 inches of backfill over the CP
cable. Horizontal cable runs are typically buried to a depth of at least 24 inches.

Prior to making the splice, remember that a high compression crimp or

exothermic connection should be used. Split-bolt connections are NOT permitted
unless they are to be used as a temporary emergency repair.

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Field applied splices must be made absolutely waterproof. A watertight splice
can be achieved by taping after the application of insulating putty. The insulating
putty will cushion against any sharp corners that may exists from the
compression crimp, followed by a liberal coat of “Scotch Kote”, four layers of
rubber tape, one more coat of “Scotch Kote”, and finally, four coats of a high
quality electrical tape. Remember to gradually increase the overlap area from
each successive wrap over the cable’s insulation so that at least 2” have been
covered by the time the splice has been completed. Cable repairs and splices
can also be coated with a two-part epoxy resin splice kit by 3M or equivalent.
See Illustration No. 7 below and No. 8 on the following page for typical high
voltage below grade splice repair procedures:

Step 1 – Connect Anode to Header Cable Step 2 – Apply electrical insulating putty.

Step 3 – Apply “Scotch Kote”

Step 4 – Apply multiple coats of “Rubber Tape”

Step 5 – Reapply “Scotch Kote” Step 6 – Apply multiple coats of electrical tape

Illustration No. 7 – Below grade high voltage splice

repair using a taped system

Step 7 – Reapply “Scotch Kote”

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Step 1 – Place mold around spliced connection & Step 2 – Break the separation between the two
tape the ends. components and thoroughly mix until a consistent
color is achieved and snip off corner.

Step 3 – Pour mixed epoxy resin into mold Step 4 – Plug and tape over the fill location.
until it completely covers the spliced Let the epoxy resin cure prior to backfilli ng.
connection

Illustration No. 8 – Typical splice kit application procedures

RECTIFIER REPAIR, REPLACEMENT & INSTALLATION

Various standards for rectifier installations are used by pipeline companies. The
installation practices will vary depending on local codes or conditions and even
individual Corrosion Specialist preferences. The installations examples given in
this study guide are to be used as general guidelines. The Area Corrosion
Specialist should be consulted for specific site details. See Illustration No. 9, 10
and 11 on the following pages for typical rectifier installations.

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 Illustration No. 11

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Many of the above installations may even have junction boxes for the positive
leads from the anodes or a looped positive header cable. Some installations
may have a negative junction box. In either case, the junction should be
mounted below or adjacent to the rectifier. See Illustration No. 12 below for an
example.

C D 3 4
B 2
5
A 1
F 6

STRUCTURE ANODE
(-) (+)

Illustration No. 12 Post-mounted rectifier with positive junction box installed below the rectifier

RECTIFIER TROUBLESHOOTING

As with any mechanical or electrical device, a good maintenance program will

greatly reduce the need for troubleshooting. Even so, to prevent costly down
time, it is also necessary to be able to quickly find the cause of the failure and
repair the inoperative rectifier.

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Basic Maintenance Considerations

Simple, common sense upkeep will help keep a rectifier in good working order.
Keeping the paint touched up prevents corrosion of the sheet metal enclosure
and a little periodic lubrication of the hinges and catches will insure their proper
operation. Nicks and dents should be taken care of, not only for appearance
sake, but to prevent eventual rust-through.

It is imperative that rectifiers be allowed to cool properly. They should be

mounted away from heat producing equipment and away from ventilator
exhausts that hamper their cooling and could cause premature failure of the
stacks or transformers. Screens are placed in the enclosures of convection-
cooled rectifiers to allow airflow across these heat-producing components.
Allowi ng screens to become blocked by weeds, insects, or debris will prevent
proper airflow needed for cooling. Never leave the manual lying on the bottom
screen to block off the ventilating area!

Oil immersed rectifiers radiate heat from the sides of the enclosure, so room
should be allowed for this radiation to take place. Thick mastics or other heavy
coatings should never be applied to the sides of the tank. This will insulate the
tank allowing heat build-up, which becomes detrimental to the power
components inside.

The oil should be checked periodically for contamination and for dielectric
strength. Contamination can cause dielectric breakdown or chemical
deterioration of certain components. Periodic checks should be made for
moisture in the bottom of the tank and drained off if necessary.

All rectifier enclosures, whether air or oil cooled, should be properly grounded.
Ungrounded cases are a potential shock hazard. A technician standing on damp
ground could be seriously injured or killed if a short existed in the rectifier,
causing an above ground potential on the case.

Ground rods should be driven adjacent to the rectifier and a good electrical bond
made between the rod and the case.

One of the most importance points in a good maintenance program is record

keeping. With a good set of records, including past history, a technician cannot
only tell how a rectifier is presently performing, but can many times predict a
failure. Some of the items to record are: A.C. input voltage, stack A.C. input
voltage, D.C. output voltage and current, and transformer tap settings. With
these readings the technician can diagnose problems in all the basic rectifier
components as well as the rectifier’s load circuit. Changes from one set of
readings to the next provide the key to the problem and its solution.

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Component Description – Troubleshooting Preliminary

To troubleshoot, one must first have a working knowledge of the individual parts
and their relation to one another.

To gain such knowledge, let us follow the order in which they appear, starting at
the A.C. input of the rectifier:

The input lightning arrestor may be the first component on the input side of the
rectifier. Lightning arrestors come in a wide variety of sizes, shapes, and forms;
however, most are essentially a set of gapped points across which an arc current
may travel when a voltage surge is great enough in magnitude. Failure of the
arrestor itself is unlikely to directly cause failure of other components following it,
but if the arrestor is destroyed, it leaves the rest of the rectifier circuit vulnerable
to the other voltage surges. Arrestors may be tested, but the equipment needed
to do this is seldom available in the field. Usually, a visual inspection is adequate
to determine if the arrestor is good or bad.

The circuit breakers are the next components in line after the arrestors. A circuit
breaker is a mechanical switch with either a magnetic or thermal trip element. It
is designed so that excessive current through the trip element will open the
mechanical contacts. The switch has two modes of failure, “short” or “open”.
The contacts may weld in the closed position, or an open may develop because
the contacts have burned away or the trip element in series with the contacts has
an open. Voltage or continuity checks can be made across breakers to
determine if one of these inoperative conditions exist.

Following the circuit breakers is the transformer. It consists of two coils of wire
wound around a laminated iron core. One winding, called the “primary”, has the
input voltage applied to it. This in turn induces voltage into the other winding,
called the “secondary”, through a magnetic coupling in the core. Taps placed at
intervals on the secondary allow different voltages to be selected for setting the
rectifier output. The transformer is very rugged and is not failure prone, but
lightning or inadequate insulation can cause failure. If the primary should
develop an open, there will be no voltage induced into the secondary to be
applied to the rectifier stack. If the secondary has an open between the two taps
being used for the stack supply voltage, no voltage will exist across those taps or
any taps that span the open. If the open is beyond the tap setting being used,
however, as long as no further failure develops, the transformer may be used as
is within the range excluding the open. If a short develops in either winding, the
result will be excessive currently in the winding that will eventually cause failure
of the transformer a nd or breaker.

The rectifier stack changes the A.C. to D.C. by inverting alternate halves of the
A.C. wave form, making all portions of the wave form electrically unidirectional.
Selenium or silicon semiconductors accomplish this. These semiconductors may
fail in an open or shorted condition. If they are open, the output of the rectifier
will be either half its previous output or zero, depending on whether half or all of
the stack currently which will burn up wiring or the transformer if the breakers do
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not trip in time (with low tap settings this is possible because of the high
secondary current, but relatively low reflected primary current).

Another mode of failure of selenium is “aging”, which is a gradual failure that

decreases the output of the stack with the same amount of A.C. applied to it. If
left alone, these stacks will eventually fail completely.

Fuses are placed in a rectifier to protect the more expensive components. A fuse
consists of a low melting point metal element, which is designed to carry specific
current. Current exceeding the rating creates excessive heat, which melts the
element, opening the circuit it is protecting.

Meters are used in a rectifier to indicate the amount of D.C. voltage and current
present in the output. They consist of a coil of very fine wire through which a few
milliamps of current flow when it is energized. Magnetic fields caused by current
flow in the coil attempt to align the coil with a permanent magnetic field, with the
amount of meter deflection being proportional to the current through the coil.
Delicate instruments such as these are susceptible to damage from voltage or
current surges left continuously in the circuit, therefore, switches are usually
recommended to remove the meters from the circuit when not being read. The
movements may be damaged or ruined completely giving the technician a false
indication of trouble in another component. To verify reading of the output
meters, use portable meters of known accuracy and compare readings.

Troubleshooting – Basics

An adequate inspection and maintenance program will greatly reduce the

possibility of rectifier failure. Rectifier failures do occur, however, the field
technician must know how to find and repair troubles quickly to reduce rectifier
down time.

Troubleshooting Equipment

Equipment required for troubleshooting need not be elaborate, but must be

adequate to do the job. A multimeter, such as the Simpson 260 or Triplett 630, is
relatively inexpensive and is valuable for reading AC and DC voltages and DC
current up to 10 amperes. This meter may also be used to measure resistance
and to determine whether short circuits or open circuits exist, (other than ground-
bed resistance). A milli voltmeter may be used for checking rectifier DC current
by measuring the millivolt drop across the shunt on the rectifier panel. In addition
to necessary small tools, every technician’s kit should include a heavy shorting
cable and several jumper cables about three feet long with booted alligator clips.

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Precautions

The following precautions should be observed when troubleshooting rectifiers:

1. TURN THE RECTIFIER OFF when handling components within the

rectifier. Open the disconnect switch ahead of the rectifier as well as the
internal circuit breakers.

2. Be careful when testing a rectifier that is in operation. Most rectifiers are

located in isolated areas and an injured technician may be far from help.
Some companies insist that their technicians stand on a rubber mat and
wear rubber gloves when working on electrical equipment.

3. Consult the rectifier’s wiring diagram before starting to troubleshoot.

4. Make certain that the meters used in troubleshooting are properly

connected. The voltmeter should be connected across the points where
the voltage is to be measured, while the ammeter should be placed in
series with the circuit being tested. A milli voltmeter should be connected
across the terminals on the rectifier shunt. Correct polarity must be
observed when using DC instruments. Turn the rectifier off before using
an ohmmeter to avoid harming the instrument.

Troubleshooting Procedures

Most rectifier troubles are simple and do not require extensive detailed trouble
shooting procedures. Most common problems are: blown fuses, faulty meters,
loose terminals, open ground bed leads and lightning damage. These troubles
are usually found by a simple visual examination of the rectifier.

For more difficult trouble, however, it is usually better to systematically isolate the
rectifier components until the defective part is found. This amounts to trading a
difficult problem for several simpler ones. This may be done as follows (please
refer to Illustration No. 13 for Point locations.

1. Check to see whether voltage is being supplied to the rectifier by placing

the leads from an AC voltmeter across the line side of the circuit breaker
at Points A.

2. Check across the load side of the circuit breaker at Points B to determine
whether it is defective. The voltage should be the same as that at Points
A.

3. Check the input change taps (Point C) for loose connections and to verify
that the tap change bar (or lead) is adjusted for the correct input voltage.

4. With an AC voltmeter or light check or light, check the transformer

secondary winding (at Points D and E) to determine whether voltage is
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 present. Voltage may be measured between any of the secondary taps.
The entire secondary winding may be measured between the Number 4
course tap and the Number 5 fine taps. If the circuit breaker trips,
indicating a short circuit, the transformer may be isolated from the DC
circuit by removing the secondary tap changing link bars (Point D and E).
If the circuit breaker continues to trip, look for visible shorts between the
transformer leads. If it holds, the short is not in the transformer, but in the
DC circuit.

5. Measure the AC voltage supplied to the rectifier stack (Points F and G).
This voltage should be the same as that measured at the transformer
secondary, but not at the stack AC terminals, check the leads from the
transformer to the stack as follows: Place the AC voltmeter leads between
Point D on the transformer secondary and Point G on the stack. If no
voltage is present, the lead between Points E and G is probably open.
Verify by measuring the AC voltage between Points E and F. If voltage is
present between these points, the open is between Points E and G.
Replace the defective lead.

6. If the circuit breaker trips, the stack may be isolated from the rest of the
DC circuit by removing one of the DC leads at either Point H or Point J. If
the breaker continues to trip, the stack is defective and should be
replaced.

7. If AC voltage is supplied to the stack, check the DC output voltage with a

DC voltmeter. If DC voltage is present but is much less than expected,
the stack testing procedure of Section 5 may be used to determine
whether the stack is aged. If the DC voltage is about half than expected,
turn the unit off and feel the individual plates in the stack(s). If part of the
plates are warm, and part are cold, the stack has an open circuit and is
half-waving. If the stack assembly consists of more than one stack, check
the connecting leads for opens. This may be done readily by paralleling
the suspected lead with a jumper cable.

8. If the circuit breaker does not trip when a DC lead on the stack is
removed, but does trip when it is connected, the short circuit is probably in
the external ground-bed or structure leads. This may be verified by
removing one of the external DC leads from the rectifier and turning the
rectifier on again.

9. If DC voltage is present at the stack, but not at the rectifier output

terminals, check for loose connections or open leads between Points H
and K. This may be done by measuring the DC voltage between Points J
and K or between H and L.

10. If DC voltage is present at the rectifier output terminals, but no current is

flowing, there is an open in one of the external DC leads.

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Illustration No. 13 – Typical single phase rectifier wiring diagram

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 11. Faulty meters may cause the rectifier to appear defective when it is
actually all right. The meters may be checked with portable meters known
to be accurate.

12. The meter switches may be checked with an ohmmeter or, after consulting
the wiring diagram, jumper wires may be placed across the switch
terminals. (Care must be taken not to short across both switch terminals
at the same time on units equipped with combination voltammeters).

13. Some rectifiers are equipped with a filter for noise interference or to
improve conversion efficiency. If it is suspected that the choke is
defective, it may be effectively taken from the circuit by placing a heavy
jumper lead across the choke leads.

The capacitors in an interference filter are individually

fused. Capacitors usually fail by shorting. If the capacitor
fuse is blown, replace with a new fuse and turn the unit on
again. If the fuse blows again, the capacitor is defective
and should be replaced. The unit may be safely operated
without the capacitor. When the fuse is open or removed,
the defective capacitor is not in the circuit.

14. Lightning arrestors in rectifier may be isolated by removing them from the circuit.
The rectifier will operate without them.

Troubleshooting Tips
Many rectifiers problem are relatively obvious to the experienced technicians upon
physical examination. The obvious should never be overlooked! Loose connections,
signs of arcing, strange odors, etc., indicate troubles, which do not require elaborate test
procedures to uncover. Some helpful troubleshooting tips to follow:

1. If no output voltage or current is present, the trouble and remedy may be:

a. Breaker Tripped (or Fuse Blown)

i. If apparently due to steady overload, reduce the output slightly.
ii. If the breaker trips repeatedly even with the output reduced, the
cause may be a short circuit in some component. Isolate the
component as described before and repair or replace.
iii. If the breaker trips occasionally for no obvious reason, the cause
may be:
Ø Temporary overload due to soil moisture changes.
Ø Line voltage surges, or wrong line voltage connections.
Adjust the rectifier for operation at the proper line voltage
for the location.
Ø Intermittent short circuits. Isolate the component as
described before. Check for loose brackets or
connections. Check with ohmmeter while moving leads,
etc. (Make certain power is turned off when using the
ohmmeter.)
Ø Thermal breaker may be affected by sun heat. Install a
shield or shade.
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 b. No AC line voltage. Check with light or AC voltmeter. Do not overlook the
possibility that service to the rectifier may have been interrupted.

c. Open Circuit in Some Component or Connection

i. Check all connections, especially the AC voltage selector (dual

input units only), fine and course transformer tap adjustments and
stack connections.
ii. Rectifier stacks. Use an AC voltmeter to see if voltage is applied
to the stacks. If so, they may be open-circuited and should be
checked with an ohmmeter and possibly re-placed. (Note: An
ohmmeter check is not a valid test for determining whether
selenium stacks are aged). If multiple stack arrangements are
used, check leads between stacks for opens. On silicon stacks,
disconnect each silicon diode and check individually with an
ohmmeter for forward and reverse resistance. A bad silicon diode
is either shorted or open, so the ohmmeter check is valid here.

d. Defective meters or meter switches. Follow the procedure or Paragraph 11,

of the Troubleshooting Section.

e. Defective Transformer. If AC line voltage is applied to the primary, but none

is present in the secondary, check to see whether there is an audible hum
coming from the transformer.

i. If so, the primary is operating, but the secondary is probably open.

ii. Check the above conclusions by isolating the transformer and
checking the DC resistance of the windings with an ohmmeter.
Ø Secondary should have generally less than 1ohm
resistance.
Ø Primary should have perhaps 1-10 ohms resistance.
Ø If either is quite high, that winding is effectively an open
circuit and the transformer will have to be replaced. (It is
difficult to make internal repairs on a defective
transformer.) Make certain that the high resistance is in
the winding and not in some connection lug.

f. Circuit breaker (or thermal overload protector). If the contacts do not close,
they should be repaired or the breaker replaced.

2. If maximum DC output voltage at rated DC current is only about half what it

should be, the trouble may be:

a. Rectifier may be connected for higher input voltage than that being used.
b. Half the stacks or plates open-circuited, making the unit operate as half-
wave, rather than full-wave rectifier.
c. Badly aged stacks.
d. In a three-phase unit, in addition to the above, one phase may:
i. Be open circuited, in which case the current in one AC line will be
considerably less than that in the other two.
ii. Have stacks that are more aged than the other two.

e. Low line voltage.

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 3. VARIABLE TRANSFORMER CONTROL

a. Some rectifiers may be equipped with a variable transformer in lieu of the

standard tap and link bar arrangement for output adjustment. The variable
transformer will provide step-less, infinite control of the output of the rectifier.

Troubleshooting the variable transformer will be the same

as the procedure for the main transformer. A.C. input
voltage should be checked across terminals one and four.
Output A.C. voltage can be checked across terminals one
and three. Control knob should be at maximum rotation.
Output voltage of the variable transformer should be the
same as the input voltage. If no A.C. voltage is present on
the output terminals of the variable transformer, check for
open winding or damaged, dirty or worn wiper brush.

CASED CROSSINGS

Historically, carrier pipelines have been installed inside sections of larger pipe
under railroads and highways that bore heavy traffic. The purpose was threefold.
The larger pipe, termed a casing, was supposed to bear the brunt of the traffic
impact load, preventing damage to the carrier pipe. The casing was supposed to
carry any flammable fluids or gasses away from the traveled roadway and
thereby prevent any fire or explosion that might occur if the vapors should be
ignited by traffic. The pipe could be removed and repaired, or replaced, without
disturbing the roadway. End seals were used in an effort to prevent water and
other contaminates from entering the annulus between the casing and the carrier
pipe and causing corrosion due to differential aeration or any other type of
corrosion that could occur without cathodic protection. A vent pipe was added
near one or both ends of the casing to vent fluids and vapors to the atmosphere.

With the advent of cathodic protection as a supplemental form of corrosion

control on coated pipelines, the bare pipe casing absorbed a large amount of
cathodic protection current if it was shorted to the pipeline. Non-conductive
spacers that would withsta nd the load of the pipe were used to electrically isolate
the carrier pipe from the external casing. The casing pipe size was normally
increased to four inches larger than the carrier pipe to allow room for the
spacers. Improved end seals were used in an effort to keep water and
contaminates out of the annulus between the carrier pipe and the casing, and to
help prevent the carrier pipe from shorting to the casing.

Even with the improvements in modern construction techniques and the products
on the market today, we are still faced with situations where the carrier pipe and
the casing are shorted together. Unfortunately, over time the casing and carrier
pipe may become shorted. In other words, the casing and carrier pipe are
contacting each other at one or more points. When this happens it becomes very
difficult to cathodically protect the section of pipeline inside of the casing. As a
result, all shorted casings shall be monitored for leaks until the shorted condition
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has been corrected or the casing has been removed. Typically, shorted casings
are identified during annual cathodic protection surveys.

During the annual cathodic protection surveys, casing-to-soil (CSP) and carrier
pipe-to-soil potentials (PSP) are taken at every location that casings exist.
Shorted conditions can usually be identified by having identical or very similar
potentials on the casing and the carrier pipe. However, it should be noted that
additional testing should be performed by the Corrosion Specialist to make the
final determination. These locations should be highlighted during the annual
surveys.

Methods For Controlling Corrosion At Cased Crossings

Due to the complexity of the corrosion problems associated with casings, no
single method of controlling corrosion inside of casings is practical; therefore, a
combination of corrosion control methods must be utilized to assure an effective
corrosion control program. For a more detailed description on the repair
methods associated at cased crossings please see the “Cathodic Protection
Remediation-Advanced” Study Guide.

The methods used for the control of corrosion within casings are: Coatings; End
seals; Electrical isolation; Cathodic Protection; and Inhibitors.
Coatings

Pipeline coatings must be considered as the main line of defense against

corrosion of the carrier pipe within a casing. Pipeline coatings are used to
provide a protective barrier between the pipe surface and the environment.

The coatings used within a casing must provide the following properties if
corrosion protection of the carrier pipe is to be obtained:

1. The coating must have a high electrical resistance at the time of

installation and maintain this resistance over time. This is
particularly important where cathodic protection will be used to
supplement the coating.

2. A coating must be holiday free if complete corrosion control is to

be achieved. A holiday may be defined as a defect that allows the
pipe surface to be subjected to the environment.

3. The coating must exhibit sufficient mechanical properties to

withstand the stress exerted during the installation of the carrier
pipe and subsequent stresses for the life of the installation. Most
coating damage is encountered during the insertion of the carrier
pipe into the casing. The dielectric casing insulators are usually
spaced in accordance with the pipe/casing diameter, coating
thickness and type, etc.

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Casing End Seals
Casing End Seals are used to prevent the migration of foreign matter from the
environment outside of the casing into the annulus space of the casing. They
must provide a positive seal and be able to support the weight of the carrier pipe
and all additional stresses incurred after backfilling. The seal must be made of
nonconductive materials to insure electrical isolation of the casing and carrier
pipe.

Approved casing seals are Thunderline ‘Link Seals’ and ‘CANUSA or RAY-
CHEM’ heat-shrink casing end seals. The Canusa Casing Seal kit (CSK) forms a
waterproof seal that is resistant to vibration, impact, corrosive gases, and
thermo-dynamic effects resulting from the expansion and contraction of carrier
and casing pipes, flanges and mechanical couplers. The CSK consists of several
components including; a heat shrinkable one -piece wraparound sleeve, a
polypropylene support skirting, and a roll of filament tape. Depending on the
specific application, several optional items may also be included in each kit. The
sleeve is made of a cross-linked polyolefin sheet coated with a layer of anti-
corrosion adhesive. It features the patented "Snap-fit" closure that allows for fast
and simple installation without the need for special tools or equipment. The CSK
is available in 500mm (20") or 860mm (34") widths to fit almost all casing/carrier
pipe size combinations.

Casing Isolators

Electrical isolation of the carrier pipe from the casing must be achieved and
maintained if protection of the carrier pipe is expected. The following methods
are employed:

® The carrier pipe’s coating must maintain electrical isolation of the carrier
pipe from the environment, as well as from the casing. If this is not done,
current may discharge from all anodic points and/or may cause a shorted
condition if allowed contact with the casing.

® Casing insulators are used to assure electrical isolation of the casing by

centering the carrier pipe within the casing. Insulators must exhibit high
dielectric properties if the electrical isolation is to be maintained over time.
Typically these insulators are made of a high-density polyethylene, and
are typically installed at five feet intervals. The insulators must maintain
sufficient compressive and tensile strength to withstand the stresses
exerted during the initial construction and for the life of the system.

Casing Fillers
Casing fillers are generally made of a substance that is not electrically
conductive and somewhat impervious to moisture. Casing fillers are intended to
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eliminate (by displacement) the corrosive environment within the casing annulus.
The filler material must be compatible with the carrier pipe coating. The most
commonly used casing filler materials are the low melting point waxes or
petrolatum. These materials have been used in the oil and gas industry for over
forty years. They do not require priming, gelling agents, extremely high
installation temperature, or exotic installation equipment and techniques.

Hot installed casing fillers are delivered to the casing job site in a heated tanker
truck and pumped down the casing vent as a hot liquid. As the material cools, it
firms up to a wax consistency, forming a high dielectric, anti-corrosive barrier
between the casing and the carrier pipe.

Water tends to accumulate in the casing by condensation or by leaks in the end

seals or the casing itself. Oxygen in the water tends to create a potentially
corrosive environment in the casing. If the casing is filled with a high dielectric
material, the water is displaced and any new water with oxygen is prevented
from entering the casing annulus. Casing fillers may reduce the possibility of
corrosion within the casing.

The most significant contribution of casing fillers is the ability to discourage the
effects of atmospheric corrosion. Even in the absence of ground water in the
casing annulus, moisture and condensation are usually present in the
atmosphere of the casing annuals. The moisture in conjunction with the oxygen
present in the casing may result in the corrosion of the carrier pipe at holidays
and other damaged areas of the coating. By developing a barrier between the
casing and carrier pipe the filler acts as an additional coating material that will
decrease the possibility of corrosion of the carrier pipe.

Filling a Cased Crossing

Determine if the vents are clear and open into the casing. To determine if the
vents are clear and the casing filler will be able to flow into the casing, blow air
through one vent and out the other. If the casing has not been prepared for filling,
the best method is to excavate the casing ends and remove the casing vents to
check the hole size in the casing and to inspect the vent pipes to be sure that
they are clear of obstructions. After this investigation has been made, reattach
the vent pipes to prepare for the filling process.

It is virtually impossible to fill a casing with only one vent, especially if the casing
contains water. The filling of casings with one vent should not be attempted,
since the success is questionable. It is Amoco's intent to install vents on both
ends before casing filler is injected.

Check the end seals to assure that they are intact and able to hold the casing
filler without allowing it to leach into the environment outside the casing.
Remove the water from the casing annulus if possible either through blowing the
casing out with a compressor or by exposing each end of the casing, removing
the end seal and link seals. This will allow the water to drain.

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For best results, the casing should have one top vent on the high end and one
bottom vent on the low end. The vent should be welded to the casing and not
mechanically coupled. It is possible to receive satisfactory results if other
combinations of the vent locations are used, but it is not recommended. All vent
pipes that are installed during new installations, or as a result of repair
procedures, are to be 3 inches in diameter with at least 1½-inch openings in the
casing wall for ease in filling. The casing filler can now be pumped into the
annular space. Consult the Area Corrosion Specialist for the volumes required at
each casing. Please see Illustration No. 14 for a detail of the typical cased
crossing being filled.

Illustration No. 14 – Typical cased crossing being filled

Shorted Casing Repair Procedures

After determining the presence of a shorted casing, procedures must be
implemented to correct the problem. Most shorted casings can be cleared by
following the procedures for shorted casing repair:
1. Prior to Excavation:

i. Locate, notify and coordinate work with all underground

utilities in the area of the work site.

ii. Contact all necessary utilities, companies, and agencies to

obtain any permits required, before beginning work.

iii. Contact and coordinate work with the property owners and
tenants.
OQ Task – Cathodic Protection Remediation Advanced
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 iv. Determine the low end of the casing if possible. Expose the
low end first.
2. Excavation:

i. Excavate the site in a safe manner. Attain safe working

conditions in accordance with all Federal, State, and BP
requirements. Examples: Shoring or sloping of bell-hole
walls, barricades, signs, flagman, monitoring devices, etc.
ii. Exercise caution when digging around a pipeline.

iii. Hand excavate around and under the pipeline. This is to

ensure that damage to the coating or the pipe does not
occur.
3. After excavation:

i. Remove old end seals, and test leads. Vents may also need
to be removed if they are plugged or in bad condition.

ii. Drain the casing annulus of any electrolyte that may be

present.

iii. Remove all solids, such as sludge and mud, from the
annulus of the casing. This may be accomplished by
washing with fresh water under pressure. To accomplish this
properly, one end of the casing should be sealed to
withstand the water pressure.

4. The water line should be attached to the same end of the casing by way of
a temporary vent or nipple. Existing vents may be used if their condition is
such that they were not previously removed.
5. Inspect the pipeline and casing condition.

6. Check the pipeline for coating damage and disbonded coating.

7. If the casing needs to be trimmed to ensure sound coating, install a shield

not less than 0.2 inches thick between the casing and the carrier pipe to
avoid damage of the coating and pipe.

8. Inspect the pipeline for corrosion. If corrosion damage is found, make the
necessary repairs. If repair of the pipeline is not possible and the extent of
the corrosion damage is severe, replace the pipe. (See the procedures for
new installation in Section VIII, Pipeline Construction and Maintenance)

9. If there is no corrosion damage severe enough to require replacement of

the pipeline, recoat the pipeline with an approved coating material.

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10. New 3" vents must be installed on each end of the casing to
accommodate the pumping of casing fillers. The vent on the low end of
the casing should be installed off the bottom and the vent on the high side
should be installed off the top of the casing.
11. Lift, center, stabilized and seal both ends of the casing.

12. Lift with air bags. The use of air bags reduces the possibility of damage to
the pipeline. The stress exerted on the pipeline is spread over a larger
area of the pipe.

13. Center the carrier pipe in the casing to allow the installation of casing
insulators and link seals.

14. Stabilize the carrier pipe outside of the casing with sand or cement filled
bags.
15. Install the appropriate nonmetallic casing insulators.

16. Seal the pipe/casing annulus space with an appropriate link seal.

17. Apply an approved coating material to vent pipes (up to grade level) link
seal bolts and casing test leads at the point of the exothermic welds.

18. Backfill the work area restoring it to the proper compaction and shape.
Repair any pavement if disturbed. Please see the Completed Casing
Installation in Illustration No. 15 on the following page.

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OQ Task – Cathodic Protection Remediation Advanced
32
ISOLATION FLANGE KITS – Insulating Devices
Isolation flange kits (IF), unions and other isolating devices are installed at
various locations along the pipeline. This section defines the meaning and the
intent of electrical isolation in the application and control of cathodic protection.
General guidance on the various types of isolation devices and their
recommended installation procedures will follow.

The connotation of "electrical separation" means to remove any direct metal-to-

metal contact between the two structures. It should be noted that an electrical
path still exists through the earth between the two structures. However, this type
of structure-to-structure connection usually has enough resistance to maintain
isolation.

IF Kit Purposes
One of the problems associated with Cathodic Protection (CP) deals with
ensuring that the CP current generated by the various CP systems installed
along the pipeline remains on the pipeline or any other structures intended to
receive that current. If the pipeline is not insulated from its end points or
attachments, the CP current will usually take the path of least resistance (usually
bare structures) to any structure in the area that remains electrically continuous
to the pipeline. The bottom line is any structure that is electrically continuous
with our pipeline will receive CP current. It should be up to the Area Corrosion
Specialist to determine which structures should be protected or tied to our
system.

IF kits or other insulating devices can be found at a multitude of locations along

the pipeline, at stations, terminals, foreign delivery points, motor operated valve
(MOV) conduits, etc. The Corrosion Specialist will usually determine the need
and type of isolation device required.

Insulating devices have a specific purpose. If improper materials or type of

isolation device is used, a leak or other catastrophic event could occur. It is
imperative that the Corrosion Specialist be consulted if one is unsure of the
device’s application. The list on the following page describes most of the
characteristics needed in an isolation device:

Ø All insulating materials must be flame retardant, have high dielectric

strength and be highly resistant to the flow of electric current.

Ø They must have extremely low moisture absorption and have very
low moisture vapor transmission rate.

Ø They must be strong enough to withstand the applied and operating

pressures of the system in which they are installed, yet remain
resilient enough to maintain a perfect seal without cold -flow.

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 Ø They must withstand all temperatures that they are exposed to,
retain their physical and chemical properties during their lifetime,
regardless of the exposure to their environment.

Ø They must maintain an effective seal, keeping the product within

the carrier pipe regardless of the pipe or product movement.

Ø The material must not degrade due to the product, product

contaminate, or the ravages of any other environment.

Ø Bolt insulation must be resilient enough for installation yet tough

enough that the bolt threads will not cut through the material during
installation or under normal operating conditions.

Ø Unions must have insulating material that is molded and bonded to

the union body, with a brass ring bearing surface that will prevent
damage to the material during tightening.

When ordering IF kits, the following information will be required:

ü The product and temperature

ü The pressure rating
ü The flange size (in inches)

ü The number of bolts and type (Stud bolts and/or through bolts)

ü Whether the insulation is desired to insulate the bolts from each flange
face ("insulate both sides"), or from only one flange face ("insulate one
side")

Please see the Illustration No. 16 on the following page for typical isolating
devices.

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OQ Task – Cathodic Protection Remediation Advanced
35
The follo wing steps should be used as a guideline when installing an insolated
union:

1. Check the union to see that it is complete, is not

damaged, and is of the proper size and pressure rating.

2. If the union is to replace another union already installed, remove the one
to be replaced and set it aside so it cannot be involved in the re-assembly.

3. Clean the pipe threads thoroughly and apply lubricant with graphite (anti-
sizing compound).

4. Disassemble the new insulating union. Clean and lubricate all threads.

5. Install the body part that has the threaded shoulders. Make sure it is not
cross-threaded. Run it up hand tight, then tighten it with a wrench to its
final torque. Be sure not to damage the threads on its shoulders.

6. Slip the nut on the other pipe end with the threaded end out. Move it back
from the end until it will not be in the way of the next step.

7. Install the remaining body part (Be sure the brass ring is in place behind
its shoulder). Make sure it is not cross-threaded. Run it up hand tight,
then tighten it with a wrench to its final torque. Be sure not to damage the
insulation or the brass ring.

8. Move the nut back over the body part just installed, and engage it onto the
threads of the first body part installed. Make sure it is not cross-threaded,
and tighten it hand tight.

9. Tighten the nut to its required sealing pressure. If it is an "O" ring type,
hand tightening will probably be enough. If it is a ground joint type, a
wrench will probably have to be used, but...do not over tighten, or the
insulation might be damaged. Do not use a hammer to beat on a
handlebar type of nut.

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The following steps should be used as a guideline when installing an insulated
flange kit:

1. Check insulating material kit to make sure that it is complete, is not

damaged, and is of the proper size.
2. Clean all bolting materials. Apply a graphite lubricant (anti-sizing
compound) to all the threads of the nuts and bolts that will become
engaged.

3. Align the flange faces so that they are parallel and concentric with
the boltholes in a lignment.

4. Insert two bolts on each side of the flange far enough below the midway
boltholes to hold the center gasket in place. Temporarily tighten the bolts
hand tight, and properly insert the center gasket.

5. Line up all of the bolt holes by driving two tapered drift pins in
opposite directions to each other into two diametrically opposite bolt
holes.

6. Insert the insulating sleeves into the bolt holes (except the holes which
have the drift pins). If they do not slide in easily, the flanges are not lined
up properly. Do not force sleeves into the boltholes otherwise damage
might occur.
7. Assemble the insulating material on the bolts as follows:
i. • Run one nut on each all thread bolt so that two full threads
are showing beyond the nut.
ii. • From the opposite end of the bolt, place one metal washer
and one insulating washer against the nut.

8. Insert all of the bolts with the nut and washers through the sleeves in the
flange (except in the holes where the drift pins are). Place an insulating
washer and then a metal washer on each bolt. Run a nut on the end of the
bolt. Tighten until all nuts are hand tight.

9. Torque the first two bolts at diametrically opposite locations (according to

the tightening sequence shown below) to approximately 30% of the torque
indicated. Replace the two drift pins with sleeves, washers, bolts, and
nuts. Then hand tighten. Torque the remaining bolts to 30% of their
torque value, using the tightening sequence shown.

10. Torque all bolts in their proper sequence until approximately 60% of their
final value.

11. Continue to torque all bolts in the proper sequence until all have been
properly tightened.

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 12. Install the proper cathodic protection testing facilities, including any bonds,
etc., that are required.

13. Properly seal the opening between the flange faces.

14. Properly re-coat any thermite welds, and/or any other area where the
coating was damaged.

Testing Isolation Devices

Whether or not an in-line electrical isolating device is working (with no parallel

metallic circuits or isolating devices) can be tested by the following methods:

ü Measure the potential on each side the insulating device, leaving the
reference cell in the exact same location for each reading (PSP). If there
is no potential difference, the device could be shorted. It could also be
insulated. Check the resistance across the device with an ohmmeter. If it
"zero" ohms, the device is shorted. It if reads some value of resistance, it
is not shorted.

ü Apply a cathodic protection current through a temporary groundbed on

one side of the device while measuring the potential across the device. If
there is no potential difference with the current "on" or "off", the device is
shorted.

INTERFERENCE CONDITIONS & TESTING PROCEDURES

The definition of interference is the uncontrolled and undesirable flow of alternating or

direct current, that results in any of the following:

ü An induction, or fault current, of such magnitude that might be detrimental

to a person’s health, or might possibly cause damage to either facilities or
operations.

ü Corrosion damage to buried or submerged metallic structures.

ü Interference to the operation of cathodic protection systems

ü Interference with cathodic protection measurements.

Direct Current Interference

D-C interference, like other examples of corrosion, is composed of distinctive

parts. It differs from other types of corrosion in that it must have a separate
driving source, apart from the system affected that supplies the electrical current.
The structure affected must have a current pick-up area (cathode); a metallic
conductor (the wall of the pipe itself) ; a discharge area (anode) ; an electrolyte
(ionic conductor); and a return metallic path back to the source of the
interference.
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The problem might be a comparatively simple one where only two structures are
involved, or it might be complex, where several structures are involved.

The following discussion of d-c interference uses the concept of conventional

current flow...that is, current flows from positive to negative in the metallic circuit.
(This is opposite of electron flow).

Direct current interference to pipelines is caused by some foreign source of

current that enters the pipeline in a current pickup area, flows in the pipe wall,
and at another area, is withdrawn (discharged) from the pipe into the soil and
makes its way back to its source to complete its circuit.

The current pickup area is usually close to the current source. The current is
discharged into the electrolyte outside of the current pickup area. The discharge
point is usually close to a completely different structure that acts as a better
conductor for the current to return back to its source. This other structure might
have the same owner as the offending source.

The d-c interference can be caused by any source of direct current, such as:
• Rectifiers
• Sun Spot (Telluric) Activity
• D-C railroads and transit systems
• Diesel Electric Trains
• Mine operations, Elevators, and Welding Shops
• High voltage d -c transmission lines

Rectifiers
Usually there are only two pipelines involved when a rectifier is the source of
interference; however, sometimes several structures can be involved, and be
damaged as a result of only one offending source. For instance, for a cathodic
protection system, the current pickup area might be the power company
grounding system in the vicinity of the rectifier, and the discharge point(s) might
be either off of their grounding system, or a farmers metal water line, or metal
gas line, or any combination of the three.

Impressed current cathodic protection systems are the most prevalent source of
interference problems. These usually belong to a foreign company; however, if
we are not careful, we can cause interference to others, or even to some of our
own facilities.

Sun Spot (Telluric) Activity

The effect of Sun spot activity causes ionized particles (solar winds) to enter the
earth's atmosphere approximately sixty miles from the earth's magnetic poles.
These geomagnetic disturbances are more intense above 55° latitude
maximizing near the auroral zone, the point sixty miles from the magnetic poles.
The amplitudes are about evenly distributed throughout the forty-eight
contiguous states of the United States.

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The ionized particles enters the earth's ionosphere, causing a disturbance by the
movement of the ionization layers. This movement causes disturbances in the
transmission of radio waves, etc.

The particles, and the movement of the ionization layers, cause a disturbance in
the earth’s magnetic field. This magnetic field disturbance has an effect on any
metallic conductor (such as a pipeline) within its field. The longer the pipeline,
and the better its coating, the more it is effected.

The effect on a pipeline can be thought of as a coil in a d-c generator. Although

there is a potential impressed across the coil, and there is electron movement,
back and forth, in the wire as the coil rotates, if there is no completed circuit of
the coil (no Load) , no external current flows as a result of its action and reaction.
A pipeline is not a closed loop, and thus does not provide a complete circuit for
the flow of electrons.

There will be the effects of a voltage impressed on the pipeline at various

locations along the line, which will cause the pipe-to-soil potentials to increase,
and then decrease, in a distinct, patterned cycle, from normal to a value
somewhat higher, then back to a value just a little above normal, then to a new
high, then back to value above the last low, and so on, completing the upward
trend. When the upward trend is complete, the potentials will start a reverse
trend, repeating its pattern, from high to toward normal, then not quite so high
and back closer to normal, etc., until the lower trend is has reached normal, and
the total cycle is completed. This pattern repeats itself throughout each cycle,
until the disturbance has stopped.

There will also be the effects of a current flow impressed within the pipe wall.
This current seems to act as a wave of electrical energy as the electrons within
the pipe wall are moved, first in one direction, and then the other. There is no
known (recorded) example where this type of current flow has actually caused
any corrosion damage.

The magnitude of the induced current variation is proportional to the

geomagnetic activity. Each cycle period lasts from several minutes to six hours.
There might be more than one period in a single day, and there might be as
many as twenty days of some activity without cessation. The solar induced
activity is rated as "Very quiet", "Quiet", "Active", and "Major Storms".

Statistical behavior of geomagnetic activity levels has shown that, on an

average, there are about eight days per month that can be termed as "Very
Quiet". On an average, there are about four days per month that can be termed
"Active". "Major storms" reach their maximum intensity near March 21st and
September 23rd. Their minimum intensity is near June 22nd and December
22nd.

The following observations apply to a coated pipeline. The better the coating, the
more it will be effected. (Bare or poorly coated pipelines seem to be effected very
little).

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 Ø During the "Very Quiet" and "Quiet" times, field instrumentation
measurements can usually be made with no difficulty. Sometimes
there is some variance in measurements; however, this variance is
minimal, and is usually short lived.

Ø During the "Active" periods, field instrumentation measurements for

critical information might have to be suspended from a few minutes to
a few hours, for two or three days in a row, due to the sporadic nature
of the disturbance.

Ø During a "Major Storm" period, which might last from two to five days
per storm, field instrumentation measurements for critical information
will probably have to be suspended for the duration of the storm.

Analyzing field instrumentation data is very difficult, if that information is gathered

during the "Active" and "Major Storms" activity periods. Information relating to
past, present, and predicted sun spot activity, and its related geomagnetic
activity, can be obtained by communicating with:

(Forecaster on Duty: (303) 497-3171) Space Environment

Services Center Environmental Research Laboratory Boulder,
Colorado 80302

The time scheduled for all important field measurements should be based on the
predictions of the Forecaster's information.

D-C Railroads and Transit Systems

D-C railroads and transit systems use a d-c supply, usually from overhead, to
provide current to run d-c motors, which, in turn, convert their mechanical power
to the driving wheels. They use the rails they run on for the d-c return circuit to
the power station. They depend on the mechanical and electrical connectors
across each rail segment to provide a continuous return circuit. They depend on
the cross ties, setting on a raised bed of highly resistive material, like rock, to
insulate the rails from the earth, so that the current will stay within the rails,
instead of using the earth as part of the return circuit. The more modern of these
systems weld the rails together, and provide an expansion device periodically
along the rails. This greatly reduces the resistance that the old style of electrical
connection between rails had, and provides a much more dependable method of
current return, reducing the current flow through the earth to virtually nil. If there
is no current flow in the earth, there is no pick-up or discharge area for any
pipeline in the vicinity, hence, no loss of metal because of interference.

Some of the d-c railroads and transit systems, when operating, allow
some of their current return path to be through the earth. The moving
motorcar acts somewhat like a moving groundbed, raising the positive
gradient of the earth within its area of influence. This moving gradient in
the earth causes difficulty in reading and analyzing pipe-to-soil
potentials. Some questions are: "Is the pipe picking up current and
become more negative, or has the earth just become more positive, with
the pipe potential actually staying the same?"; "Is the pipe discharging
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 current and become more positive, or has the earth just changed its
potential, with the pipe potential actually staying the same?"; and "How
can I move fast enough with my instrumentation to tell the difference?”.

Diesel Electric Trains

Another type of interference that might be termed as d-c, is the moving

electrostatic field that the electric motors of a diesel electric train exhibits. As the
generators provide d-c to drive electric motors, the influence of their windings
cause an image reflection in the earth surrounding the generator section, in
addition to an influence from the d-c drive motors. This is a movi ng field of the
electrostatic type. The power supply is carried with the engine, and hence does
not use either the rails or the earth for any current return circuit, even though it
does cause potential changes in the surrounding area of the earth.

This type of interference causes metering and measurement problems, but only
during the time the engine passes through the immediate area. It might be noted
that the same conditions can also follow d-c railroads and transit systems. The
effect is usually not noticeable for systems that have some current leakage to
earth; however, it can be the most prominent factor for those systems that are
not experiencing any current leakage.

Mine Operations, Elevators, and Welding Shops

These three types of operations are similar in that they have intermittent
operations of varying d-c magnitude. Their activity and related problems are like
d-c railroads and transit systems that introduce current flow into the earth, except
their source (for all practical purposes) can be considered stationary, instead of
moving.

High Voltage d-c Transmission Lines

These electrical transmission lines transmit high voltage d-c, with normally very
low amperage, from the point of origin to near the point of use. Sixty-hertz a-c
transmission has a problem called "skin effect". The transmitted a-c wants to
crowd to the outer edge of the power line conductors, leaving much of the inside
of the conductor wires carrying very little of the load.

A-C transmission also has a reasonable amount of loss due to its transformer
action inducing power (which has to come from itself) into the surrounding media.
D-C transmission does not have near the loss a-c has. In this way, it is
considered much more efficient. The d-c usually is obtained by stepping a-c up,
by transformers, to the high voltage required, then rectifying it to d-c by the use of
huge mercury-arc rectifier tubes. At the receiving end, it is transformed back into
a-c for its continued journey to its distribution.
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D-C is transmitted over a two-wire system. That is, it has a positive wire and a
negative wire (return) to complete the circuit. It also has an excellent electrical
ground at both the transmitting end and the receiving end. There is still some
leakage to earth even in bipolar transmission. If either the positive or the
negative wire develops a fault, its place is taken by the ground return through the
electrical ground grid at each end. This causes tremendous amounts of d-c
current to flow in the earth, and acts as d-c interference to everything in its path.
It hardly affects a line crossing its corridor, but can do a great amount of damage,
in a short time, to lines lying parallel to it.

Alternating Current Interference

Sixty-hertz a-c does not normally cause corrosion on buried steel pipelines.
There is a "one-in-a-million" chance that an electrolyte loaded with oxides could
possibly form a metal-oxide rectifying element, using the pipeline as a metal
base, and converting any a -c present to d-c, thus causing corrosion. (There is no
known recorded situation of this ever happening.)
Alternating current can cause an increase in a corrosion rate if its presence (and
quantity) causes an increase in the temperature of a corrosion cell.
For most practical situations, alternating current, except for fault currents, does
not seem to cause many problems for bare or poorly coated buried pipelines.
The obvious reason for this is that the line is electrically grounded, and it is just
as easy for a-c to be discharged from the line as it is to be induced into the line.
Almost all of the a-c current continuously flowing in pipelines is induced into the
line from overhead electrical power lines; however, lightning causes much of the
instantaneous induction in the pipeline. The induction of a-c on well-coated
buried pipelines is becoming much more of a problem with the increase of
pipelines and overhead power lines.
There are three modes of coupling by which a-c voltages (or currents) can be
induced in pipelines sharing the same right-of-way as overhead high-voltage
power lines. These modes are termed conductive, electromagnetic, and
electrostatic.
Interference Measurements and Solutions for Direct Current Interference
Rectifiers, and all other types of d-c power supplies for cathodic protection, inject
current into the earth by the use of a groundbed, intending the current to spread
outward along the pipeline for a reasonable distance. As mentioned before,
when the rectifier current output exceeds a certain amount, the unit causes
interference to other underground structures in the neighborhood. When this
happens, it results in a current pickup area, and a current discharge area, on the
foreign structure affected.
If the foreign structure is long enough so as to extend outside of the groundbed
gradient, then the current discharge must be outside of this gradient. If, however,
the foreign structure lies totally within the groundbed gradient, then the current
discharge point will also be within the gradient, but at the point of least influence
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of the gradient (generally, the greatest distance from the ground bed, and most
probably toward the pipeline).
To determine if interference exists on the power company grounding system, a
series of "off-on" structure-to-soil potential tests are made on the power company
grounds and guy wires closest to the pipeline, but out of the groundbed gradient.
If interference does exist, those in the discharge area will have more negative
"off" potentials than "on" potentials. It is best, if any interference does exist, to
either reduce the current output until the interference disappears, or bond the
power ground system into the rectifier negative. Resistance should be included in
the circuit only if the current drain is considered too much. If resistance is
required, be very careful not to over-resist, and still leave some area of
discharge. Also, consider the wattage rating of the resistor used.
The most dependable way of determining if, and where, an interference problem
on another pipeline exists, is by "current chasing"; that is, by the use of "IR" drop
type test stations. By this means, both the pick-up and the discharge area can
be defined, as well as being a paramount aid in determining a solution to the
problem.
When the interference exists between two pipelines that cross each other outside
of the groundbed gradient, the discharge area is normally at the pipelines'
crossing. Usually, the easiest way of determining if an interference problem
exists, is to conduct a close interval, "on" and "off", pipe-to-soil potential test over
the offended line. The potentials should be fairly close together at and near the
crossing, but can be a greater interval away from the crossing. An example of
this type measurement is shown in Illustration No. 17.
The following methods of arresting the interference can be used, in order of
preference:
1 Reduce or remove the source
2 If the structure that has the interference problem (termed the "interfered
with" structure) is within a reasonable distance of the rectifier that is
causing the interference (termed the "interfering" structure), bond the
interfered with structure, through a negative bond box, to the interfering
rectifier. Please see Illustration No. 18 for details.
3 Bond the two lines together at the crossing, using a bond box that is
accessible, preferable by vehicle, in any weather. Be sure that both parties
have entrance to the bond box...if not, use two boxes in series (A separate
box for each company)
4 If bare or poorly coated lines are involved, coat the interfered with
structure and the interfering structure throughout the groundbed gradient,
and the interfering structure through the crossing area. (Do not coat the
Interfered with structure at the crossing!! To do so would cause the total
potential over the possible damage area to act on any small coating
defect, and cause the rate of penetration of the pipe wall thickness to be
very fast)
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 Illustration No. 17

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 Illustration No. 18

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Install a rectifier/groundbed on the interfered with structure in the location of the
interfering rectifier/groundbed.

Use multiple magnesium anode banks for electrolytic coupling between the lines in
the crossing area.

Use a combination of the above.

If, for some reason, a surface potential survey will not suffice in the pipeline-
crossing example above, then IR leads might have to be installed in order to
determine if interference does exist. If this is necessary, use spacing between the
leads that will allow the available voltmeter to read millivolts with accuracy for the
weight of the pipe of the offended line. (Remember, 10 milliamps will consume 0.2
of a pound of steel in one year.)

Install the closest test lead on each side of the crossing outside of the area of
influence of the pipe potential gradient. Use test lead wire that has no
imperfections in its' insulation (and will stay that way). Make absolutely certain the
cadweld connection is well coated.

When testing for interference that is outside of the groundbed gradient, and the
lines do not cross, it is very difficult to find a discharge point, and even then, one
cannot be sure that there is not more that the one that was found. When this event
occurs, IR test leads must be used, and must be installed outside of the groundbed
gradient. In order to do this, conduct an "on-off" P/S potential survey over the
offended line throughout the groundbed gradient area, with the spacing variable to
fit the situation, until there is no negative change in the offended lines' potential
when the rectifier is cycled (See Illustration No. 19).

Install IR drop test leads, on appropriate spacing, on each side of the offending
rectifier, just outside of the indicated groundbed gradient.

Analyze the on-off IR readings on each side of the rectifier. If there is no

interference, the IR readings in the pipeline will not change. If there is interference,
the pipeline IR readings will show current flowing away from the rectifier when it is
turned on. If there is interference, bond the line, through a bond box, to the
offending rectifier negative terminal. Adjust the current drain until the IR leads
indicate the line current, on each side, flows toward the rectifier (See Illustration
No. 20). There should not be any need to adjust the bond resistance after the first
time. If the output of the rectifier is increased, the current will increase, etc.

If possible, diodes should be used to block reverse current.

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 Illustration No. 19

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 Illustration No. 20

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Mine Operations, Elevators, and Welding Shops

Elevators and welding shops are operated from a central point. It is unlikely that
an elevator would cause a pipeline any difficulty, even if it were as close as fifty
feet away from it. Welding shops have a habit of welding all of the metal in their
shop together, so as to provide a good ground for their welding machine. In this
way, they can use a chuck, or a vise, which provides as excellent ground for their
material. Unfortunately, sometimes this also provides problems for pipelines that
are very close to the welding shop, or who cross a natural gas pipeline that
provides gas for the shop and/or surrounding buildings.

Mine operations usually have a central power source, but the hopper cars that use
that source can operate at some distance from the central location. It is very
important for the power system not to leak current into the earth in order to be
absolutely safe to personnel working in the mine. When electrical power was first
used, this was not always the case, and pipelines near the surface of the earth felt
this stray current. From this early beginni ng, mine operations got a bad reputation;
however, they have now cleaned up their act, and no known interference problems
are now evident.

High Voltage D-C Transmission Lines

Much testing has been accomplished between representatives of the HVDC

companies and various pipeline companies that might be affected by a fault in the
HVDC system. If one of the d-c transmission wires has a fault, either an open or a
ground. It is then replaced by a ground return circuit, allowing an amount of d-c
current to flow through the ground to replace the faulted wire.

Alternating Current Interference

Resistive coupling by fault currents are too unpredictable for any preventative
action to be taken. It would be unthinkable to require the moving of pipelines from
power line corridors or crossings.

There is a possibility of using a Kirk cell, or a zinc or magnesium grounding cell, for
a connection to a bare road casing or to another good electrical ground. If a good
electrical ground is not available, one should be constructed. Do not use any
electrical company's tower footings or grounding system.

Inductive Coupling: There are three primary ways of reducing a-c voltage and
current on a pipeline. These are:

1 By the use of a groundbed with, or without, diodes

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 2 By the installation of magnesium anodes at the locations of the highest a-c
P/S voltages If the a-c voltage is high enough, diodes might be installed in
the circuit to provide half-wave rectification
3 By the use of Kirk cells, or zinc or magnesium grounding cells, attached to a
bare casing, or to a BP constructed solid welded bare scrap pipe
groundbed. (See Illustration No. 21)

The use of a specially built groundbed, with diodes, will greatly reduce the a-c
voltage and current, without connecting the groundbed to the regular cathodic
protection system. The groundbed works best if neither the anodes, nor the
backfill, has any carbon content. The anodes can be high-silica cast iron, zinc, or
magnesium, and the backfill can be standard magnesium anode backfill.

It should be remembered that the diodes might fail, and leave the groundbed
connected to the pipeline.

This wouldn't hurt the a-c drainage value of the groundbed, but the groundbed
would be connected to the pipeline, and would affect the CP system.

An MOV of the correct size, shunting the diode, would afford protection for the
diode in the event of power surges, etc.

Capacitive Coupling

This type of coupling applies to sections of welded line on skids during

construction, or storage, while in close proximity to HVAC power lines. It can also
apply to short sections of isolated, extremely well coated lines buried under an
HVAC line. It is necessary, for both of the above conditions, to electrically ground
the pipe.

The line on the skids during construction must be grounded by any effective
means, such as a driven ground rod (in comparatively low resistivity, moist, soil).

The coated buried pipe can be grounded with one, or more, magnesium anodes
with a #8 AWG (Minimum size) TW insulation, lead wire.

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 Illustration No. 21
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BONDS-CRITICAL OR OTHERWISE

Critical bonds are current drain bonds if removed, would cause interference
damage to Amoco Pipeline Company structures or would disconnect one of those
structures from the cathodic protection system. These bonds are installed
between structures that were electrically isolated before bonding, and which, if not
bonded, would remain electrically isolated. It is imperative that these electrical
connections be kept in good operating condition. Maintenance problems are due
to either physical damage caused by equipment, animals, or vandals; by
insufficient wattage rating of parts used; or by faulty assembly of parts. The
installation of the critical bond boxes, etc., should include protective fencing, an
over-rating of the wattage on the parts used, surge current protective devices (if
included), and proper cleaning and tightening of current carrying connections.
These bonds should be read on the same intervals as Cathodic Protection
Rectifiers.

Bonds that are not critical are those, which if disconnected, and left that way for
some length of time, would not cause the structure to suffer metal loss. These
bonds might include some a -c drainage bonds, or bond stations installed for testing
purposes. They are important and should be maintained in the same manner as
other testing and/or bonding facilities, and checked annually.

For typical bond installations, please refer to the “Repair and Maintain Test Lead”
study guide. Remember, before establishing a bond with a foreign facility, one
must notify that company’s corrosion representative prior to installation. If
practical, a resistance bond should be installed to control the amount of current
given to the foreign pipeline company.

TESTING FOR A SHORTED CASING

Testing must be performed to determine the condition of the encased installation.

These tests will help determine the actual corrosive conditions and whether a
shorted condition exists.

Testing for Shorted Condition

P/S (Pipe-to-Soil Potentials) are measured using a copper/ copper sulfate
reference electrode. The reference is placed near the end of the casing, where
the pipe-to-soil and the casing-to-soil potential measurements are to be made. It
is very important that both the pipe-to-soil and the casing -to-soil measurements
be made at the same location without moving the reference electrode. Before
testing the casing to determine if the casing is electrically shorted to the carrier
pipe, test leads must be available. If test leads are not available, or not in good
condition, they should be installed prior to testing. Test leads will be installed
according to the test station drawings shown in figure VII-16.

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Normal Cathodic Protection Survey
1 Firmly insert the reference electrode (half cell) in the soil near the end of
the casing and attach the positive lead from the meter to the copper rod of
the half cell and the negative lead to the test lead on the carrier pipe.

2 Select the proper DC voltage range on the meter.

3 Record the reading and polarity that is displayed on the meter, in millivolts.
Note: If the positive lead is attached to the half-cell, the recorded millivolt
reading should be positive. If the polarity is reversed the reading will be
negative.

4 Repeat the process by connecting the test leads to the casing test lead. It
is a good practice to also test the casing vent, in the event that the vent is
not attached to the pipeline.

Caution: Just because the Pipe-to-Soil potential reading and the Casing-to-Soil
potential are close to each other doesn't necessarily mean that the casing is
shorted. This test does not provide definitive results as to whether a casing is
shorted, but it may indicate if further investigation is required. This should be
used as a first step in determining the condition of the casing.

The Interrupted Rectifier Method involves interrupting the rectifier and reading
the potential shifts (ON and OFF) of both the carrier pipe and the casing. In order
to perform this method, all rectifiers and bonds affecting the area should be
simultaneously interrupted. This procedure may be useful if a casing is located in
close proximity to a cathodic protection groundbed, since voltage gradients in the
area of the groundbed will affect the voltage reading on the meter.

1 Set interruption cycle, e.g., 6 seconds ON and 3 seconds OFF. This may
be set at any interval that feels comfortable to the person performing the
test.

2 Synchronize the interrupter(s).

3 Interrupt all rectifiers and bonds influencing the casing, which is to be

tested.

4 Place the reference electrode near the casing end, attach the positive lead
of the voltmeter to the reference electrode and the negative lead to the
pipeline or pipeline test lead. Record the pipe-to-soil measurement for the
ON and OFF cycles. Indicate the polarity of the readings.

5 Repeat the process by connecting the negative lead to the casing or

casing test lead. The casing vent pipe should also be tested to insure that
the vent is attached to the casing.

6 This test should be performed on both ends of the casing to insure a

continuous casing.
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 7 If the casing and the carrier pipe potentials track each other exactly (both
vary by the same degree in the same direction), the casing is likely
shorted

The Panhandle Eastern Method

The basic concept is to make the casing temporarily the anode of an impressed
current system. Then determine the electrical isolation of the carrier by
determining the potential shift of the carrier pipe. The magnitude of the reversed
current required to produce an increase in potential difference between the
carrier pipe and the casing is a measure of the net resistance between the carrier
and the casing. Normally, the casing can be driven increasingly positive with
respect to the carrier pipe. If a low resistance short circuit exists between the
casing and carrier, even large amounts of current applied to the casing will not
cause a significant separation of the carrier and casing potentials. The following
is a step-by-step procedure by which the insulating status of the casing can be
determined:

1. 1 Construct a temporary metallic structure to be used as a "groundbed".

The structure must be a minimum of 50 ft. from the casing and carrier end.
The "groundbed" should be constructed of 5 bare steel rods, 5 to 10 feet
apart in a straight line perpendicular to the pipeline.

2. Using the previously constructed temporary "groundbed" as the cathode

(connect the header cable from the groundbed to the negative side of the
DC power source). Connect the casing lead to the positive side of the DC
power source. Keep in mind that these source connections are opposite to
the normal cathodic protection installation.

3. Using one of the acceptable means of measuring current, apply varying

amounts of current from 0.5 amps to 10 amps in 0.5 amp increments. At
each current level, measure the casing to soil potential and the pipe to soil
potential at each end of the crossing. The degree, which the carrier's
potential changes, has a direct relationship to the amount of current being
applied to the casing. Note: Varying amounts of current will be necessary
to determine the insulating condition of the casing. It may not be
necessary to apply 10 amps of current to smaller diameter pipe to
effectively determine the condition. It may also require that more than 10
amps of current be applied to large diameter pipe.

After all the readings have been taken for the different values of applied current,
the resistance of the casing installation can be determined using the equation on
the following page:

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The definitions of each term of the equations 1 through 3 are listed below:

Ø PI = the steady state value of the pipe-to-soil potential, taken with

normal cathodic protection currents applied. (Record all readings in
millivolts and include polarity).
Ø Cl = the steady state value for the casing -to-soil potential, taken
with normal cathodic protection currents applied. (Record all
readings in millivolts and include polarity).
Ø P2 = the value of the pipe-to-soil potential taken with the temporary
current applied. (Record readings in millivolts for each increased
increment of current, also include the polarity)
Ø C2 = the value of the casing-to-soil potential taken with the
temporary current applied. (Record readings in millivolts for each
increased increment of current, also include the polarity).

Ø I = the value of the temporary current applied. (Record all values in

amps)
Ø R = the calculated value of resistance using formula 1 above.

After the calculations for the resistance have been made, the determination as to
the condition (shorted or not shorted) can be made. A calculated resistance
greater than 0.080 ohms may indicate an effectively insulated installation, and a
cased crossing with a calculated resistance less than 0.080 ohms may indicate
that a shorted condition may exist and corrective action may need to be taken.
Also keep in mind that the resistance calculated using formula 1 represents an
overall resistance.

Before a determination of the condition of the installation can be made from the
calculated resistance one more step must be taken. This step requires the
graphing of the information gathered during the testing. The graphic
representation will provide a visual means of identifying the condition of the
installation as well as provide documentation.

The graphing may be done manually or with any number of computer programs,
such as Lotus 123 or Microsoft Excel. Figures VII-19A through 19P illustrate
typical results for shorted and not shorted casings.

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Note: The indicated "volts per amp" is not a true resistance value, but, instead,
can be thought of as a coupling resistance. If the casing has a good metal-to-
metal contact to the carrier pipe, the carrier pipe becomes a component within
the circuit itself and is termed a direct short. If the carrier pipe is connected to the
casing through a "loose" metal-to-metal contact (such as the two metals barely
touching each other; a metal bridge of rust particles or metal slag; or a
lightning/fault current metal spike) it is termed a resistance coupling (Some
people call this a "high resistance short". If it is not shorted, but, instead,
completes its coupling through an electrolyte (dirt and/or water) inside the casing,
or through the electrolytic path outside the casing, it is termed an inductive
coupling. In Ohm's law, the formula for resistance is R = E/I, which can be stated
"volts per amp"; however, in the circuit explained above, if the carrier pipe is not
shorted to the casing, it is not a part of the circuit, except by inductance (Similar
to interference coupling). Please see figure VII-20A on the following page.

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ABNORMAL OPERATING CONDITIONS:

Listed below are components, which are part of the pipeline, and may be
subjected to pump pressure and could fail during the performance of a
maintenance and repair task:

• Failure of a control/block valve

• Stopple failure
• Launcher closure door
• Pipe failure caused by:
o Damaged or failing pipe support system
o Sagging aboveground pipe at a span
o Soil movement due to excavation
o Corrosion damage
o Mechanical damage
o Burn through during exothermic welding procedures
• Relief valve failure
• Flange gasket failure
• Weld/seam failure
• Tubing failure
• High high level tank switch failure
• High pressure switch failure

Listed below are personnel safety related failures:

• Trenching/excavation failures
• Encounter hazardous atmosphere
• Injury on the job

All of the above components can cause one or more of the following Abnormal
Operating Conditions while performing maintenance tasks

AOC: Leak
RESPONSE: Assess situation for hazards and safety, identify and isolate source of
leak if possible. Limit access to the area as much as possible. Take appropriate
immediate action to protect your self, the public, property and the environment.
Contact local Fire/Police for immediate support. Contact Team Leader and District
Manager.

AOC: Fire
RESPONSE: If fire is small in nature, use on-site fire fighting equipment to extinguish.
If fire is beyond local control, immediately call local authorities. Take appropriate
immediate action to protect your self, limit access to the area as much as possible and
call Team Leader and District Manager.

AOC: Injury on the job – Failure to follow proper safety procedures

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RESPONSE: Provide First Aid assistance and call for medical attention, if necessary.
Make sure all safety items are covered in job plan. Consider and follow all company
applicable safety rules.

AOC: Ditch cave-in. Failure to apply proper excavation/trenching/shoring procedures

and practices.
RESPONSE: Provide assistance and call for medical attention and rescue, if
needed. Make sure all excavation/trenching safety rules are considered during
job plan. A competent person must be designated for each excavation/trenching
site.

AOC: Encounter Hazardous Atmosphere – Combustible vapors/Toxic

contaminants/Oxygen deficiency.
RESPONSE: Ensure all operating and safety procedures and requirements are
followed and met to assure the protection of personnel from hazardous
atmospheres during excavation/trenching, welding/hot-work, opening of pipeline
systems or tanks, leaks, releases, emergencies and any other tasks where a
hazardous atmosphere may be present. Appropriate and/or continuous
gas/vapor monitoring shall be conducted to assure adequate assessment of
atmospheric hazards and potentials.

Additional Study Material

Ø Covered Task write up and references per the Operator

Qualification Plan
Ø Field Specialist Training Manuals
Ø A.W. Peabody’s “Control of Pipeline Corrosion”; Second Edition

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