Interval/Frequency and Extent of Inspection
due date may exceed the typical half-life interval used in a more conventional analysis
Piping Installation
The purpose of installation inspection is to verify that the piping is clean and safe for operation, and
to initiate plant inspection records for the piping systems
piping is installed correctly
correct metallurgy
supports are adequate
exterior attachments
flanged and other mechanical connections are properly assembled
pressure-relieving devices satisfy design requirements
This installation inspection should document base-line thickness measurements to be used as initial
thickness
Piping Service Change
Inspection intervals shall be established for the new service condition
review of applicable pressure relieving device settings
If both the ownership and the location of the piping are changed, the piping shall be inspected
before it is reused
Piping Inspection Planning
piping classification scheme in 6.3.4 is based on the consequence of a failure
Setting Inspection Intervals without the Use of RBI
the corrosion rate and remaining life calculations
the piping service classification
the applicable jurisdictional requirements
judgment of the inspector, the piping engineer, the piping engineer supervisor, or a materials
specialist(based on operating conditions, previous inspection history, current inspection results, and
conditions)
owner/user or the inspector shall establish inspection intervals for thickness measurements and
external visual inspections
For Class 1, 2, and 3 piping, the period between thickness measurements for CMLs or circuits should
not exceed one-half the remaining life or the maximum intervals recommended in Table 1,
whichever is less
Type of Circuit Thickness Measurements Visual External
Class 1 5 years 5 years
Class 2 10 years 5 years
Class 3 10 years 10 years
Class 4 Optional Optional
Injection points a 3 years By class
Soil to Air Interfaces b — By class
Class 4 piping are left to the determination of the owner/user
For piping that is in non-continuous service, the interval between thickness measurements may be
based on the number of years of actual service
inspection interval shall be reviewed and adjusted as necessary after each inspection or significant
change in operating conditions and/or inspection results
Interval/Frequency and Extent of Inspection
Piping Service Classes
All process piping systems shall be categorized into different piping classes except for piping that has
been planned based on RBI.
focused on piping systems that
may have the highest potential consequences if failure or loss of containment should occur
Classifications should be based on potential safety and environmental effects should a leak occur
Class 1
Flammable services that can auto-refrigerate and lead to brittle fracture
Pressurized services that can rapidly vaporize during release
Hydrogen sulfide (greater than 3 % weight)
Anhydrous hydrogen chloride
Hydrofluoric acid
Flammable services operating above their auto-ignition temperature
Class 2
includes the majority of unit process piping and selected off-site piping
on-site hydrocarbons that will slowly vaporize
below the boiling point but above the flash point
on-site hydrogen, fuel gas, and natural gas
on-site strong acids and caustics
Class 3
either flammable but do not significantly vaporize i.e. below the flash point,
Services that are potentially harmful to human tissue but are located in remote areas may be
included in this class
on-site hydrocarbons that will not significantly vaporize during release such as those operating
below the flash point
off-site distillate and product lines to and from storage and loading
tank farm piping
off-site acids and caustics
off-site hydrogen, fuel gas and natural gas
Other lower risk hydrocarbon piping
Class 4
nonflammable and nontoxic
steam and steam condensate;
air;
nitrogen;
water, including boiler feed water or stripped sour water;
lube oil, seal oil;
ASME B31.3, Category D services;
plumbing and sewers
Interval/Frequency and Extent of Inspection
Extent of Visual External and CUI Inspections
external visual inspection for potential CUI is also to assess insulation condition and shall be
conducted on all piping systems susceptible to CUI
Damaged insulation at higher elevations may result in CUI in lower areas remote from the damage.
RT or insulation removal and visual inspection is normally required for this inspection at damaged or
suspect locations
Other NDE assessment methods may be used where applicable
If the inspection of the damaged or suspect areas has located significant CUI, additional areas should
be inspected and, where warranted, up to 100 % of the circuit should be inspected.
several factors may affect the likelihood of CUI to
include:
a) local climatic conditions,
b) insulation design and maintenance,
c) coating quality,
d) service conditions
An exact accounting of the CUI inspection targets is not required
the owner/user may confirm inspection targets with operational history or other documentation
remaining life of over 10 years or that are adequately protected against external corrosion need not
be included for the NDE inspection
condition of the insulating system or the outer jacketing, such as a cold-box shell, should be
observed periodically by operating or other personnel
Extent of Thickness Measurement Inspection and Data Analysis
It is not the intent of this Code that every established CML needs to be measured each time.
A statistical sampling of active CMLs may be monitored
Some CMLs may be documented as inactive and therefore do not need to be measured and would
not be considered overdue.
should include data for all the various types of components and orientations (horizontal and
vertical) found in each circuit
CMLs to be monitored at each inspection shall be determined by the inspector in consultation with a
piping engineer and/or corrosion specialist
Point-to-Point Method
An analysis method, whereby the corrosion rate, remaining life and re-inspection interval is
determined for each individual CML
During a re-inspection of a piping system, all of the CMLs may be re-inspected or only those that are
coming due
is generally not possible to apply a statistical analysis with the point-to-point method since
it difficult to compare corrosion rates in the circuit or between CMLs
Individual CML rates may be generated over significantly different times, when operating conditions
may have changed.
Circuit Analysis Method
properly circuitized into common corrosion mechanisms and expected rates
Interval/Frequency and Extent of Inspection
Approach is generally applicable to damage mechanisms that produce uniform and some mildly
localized corrosion environments.
Inspection and Maintenance of Pressure-relieving Devices (PRDs)
PRDs shall be tested and repaired by a repair organization experienced in pressure relieving device
maintenance
Pressure-relieving devices shall be tested and inspected at intervals that are frequent enough to
verify that the valves perform reliably in the particular service conditions
Other pressure-relieving devices (e.g. rupture disks and vacuum breaker valves) shall be inspected at
intervals based on service conditions.
determined by the inspector, engineer, or other qualified individual per the owner/user's quality
assurance system
5 years for typical process services, and
10 years for clean (non-fouling) and noncorrosive services
use a max 150 % of set pressure beyond which the valve is classified as stuck shut if it does not pop,
and the test is discontinued
