STEAM

The steam distribution system is the essential link between the steam generator and the steam user.

This Tutorial will look at methods of carrying steam from a central source to the point of use. The central source might
be a boiler house or the discharge from a co-generation plant. The boilers may burn primary fuel, or be waste heat
boilers using exhaust gases from high temperature processes, engines or even incinerators. Whatever the source, an
efficient steam distribution system is essential if steam of the right quality and pressure is to be supplied, in the right
quantity, to the steam using equipment. Installation and maintenance of the steam system are important issues, and
must be considered at the design stage.
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Steam system basics

From the outset, an understanding of the basic steam circuit, or 'steam and condensate loop' is required - see Figure
10.1.1. As steam condenses in a process, flow is induced in the supply pipe. Condensate has a very small volume
compared to the steam, and this causes a pressure drop, which causes the steam to flow through the pipes.

Fig.
10.1.1 A typical basic steam circuit
The steam generated in the boiler must be conveyed through pipework to the point where its heat energy is required.
Initially there will be one or more main pipes, or 'steam mains', which carry steam from the boiler in the general
direction of the steam using plant. Smaller branch pipes can then carry the steam to the individual pieces of
equipment.

When the boiler main isolating valve (commonly called the 'crown' valve) is opened, steam immediately passes from
the boiler into and along the steam mains to the points at lower pressure. The pipework is initially cooler than the
steam, so heat is transferred from the steam to the pipe. The air surrounding the pipes is also cooler than the steam,
so the pipework will begin to transfer heat to the air.

Steam on contact with the cooler pipes will begin to condense immediately. On start-up of the system, the
condensing rate will be at its maximum, as this is the time where there is maximum temperature difference between
the steam and the pipework. This condensing rate is commonly called the 'starting load'. Once the pipework has
warmed up, the temperature difference between the steam and pipework is minimal, but some condensation will
occur as the pipework still continues to transfer heat to the surrounding air. This condensing rate is commonly called
the 'running load'.

The resulting condensation (condensate) falls to the bottom of the pipe and is carried along by the steam flow and
assisted by gravity, due to the gradient in the steam main that should be arranged to fall in the direction of steam
flow. The condensate will then have to be drained from various strategic points in the steam main.

When the valve on the steam pipe serving an item of steam using plant is opened, steam flowing from the distribution
system enters the plant and again comes into contact with cooler surfaces. The steam then transfers its energy in
warming up the equipment and product (starting load), and, when up to temperature, continues to transfer heat to the
process (running load).

There is now a continuous supply of steam from the boiler to satisfy the connected load and to maintain this supply
more steam must be generated. In order to do this, more water (and fuel to heat this water) is supplied to the boiler to
make up for that water which has previously been evaporated into steam.

The condensate formed in both the steam distribution pipework and in the process equipment is a convenient supply
of useable hot boiler feedwater. Although it is important to remove this condensate from the steam space, it is a
valuable commodity and should not be allowed to run to waste. Returning all condensate to the boiler feedtank closes
the basic steam loop, and should be practised wherever practical. The return of condensate to the boiler is discussed
further in Block 13, 'Condensate Removal', and Block 14,'Condensate Management'.

The working pressure

The distribution pressure of steam is influenced by a number of factors, but is limited by:

 The maximum safe working pressure of the boiler.

 The minimum pressure required at the plant.

As steam passes through the distribution pipework, it will inevitably lose pressure due to:

 Frictional resistance within the pipework (detailed in Tutorial 10.2.

 Condensation within the pipework as heat is transferred to the environment.

Therefore allowance should be made for this pressure loss when deciding upon the initial distribution pressure.

A kilogram of steam at a higher pressure occupies less volume than at a lower pressure. It follows that, if steam is
generated in the boiler at a high pressure and also distributed at a high pressure, the size of the distribution mains will
be smaller than that for a low-pressure system for the same heat load. Figure 10.1.2 illustrates this point.

Fig. 10.1.2 Dry saturated steam -

pressure/specific volume relationship
Generating and distributing steam at higher pressure offers three important advantages:

 The thermal storage capacity of the boiler is increased, helping it to cope more efficiently with fluctuating
loads, minimising the risk of producing wet and dirty steam.
 Smaller bore steam mains are required, resulting in lower capital cost, for materials such as pipes, flanges,
supports, insulation and labour.
 Smaller bore steam mains cost less to insulate.
Having distributed at a high pressure, it will be necessary to reduce the steam pressure to each zone or point of use
in the system in order to correspond with the maximum pressure required by the application. Local pressure reduction
to suit individual plant will also result in drier steam at the point of use. (Tutorial 2.3 provides an explanation of this).

Note: It is sometimes thought that running a steam boiler at a lower pressure than its rated pressure will save fuel.
This logic is based on more fuel being needed to raise steam to a higher pressure.

Whilst there is an element of truth in this logic, it should be remembered that it is the connected load, and not the
boiler output, which determines the rate at which energy is used. The same amount of energy is used by the load
whether the boiler raises steam at 4 bar g, 10 bar g or 100 bar g. Standing losses, flue losses, and running losses are
increased by operating at higher pressures, but these losses are reduced by insulation and proper condensate return
systems. These losses are marginal when compared to the benefits of distributing steam at high pressure.

Pressure reduction
The common method for reducing pressure at the point where steam is to be used is to use a pressure reducing
valve, similar to the one shown in the pressure reducing station Figure 10.1.3.

Fig. 10.1.3 Typical pressure reducing valve station

A separator is installed upstream of the reducing valve to remove entrained water from incoming wet steam, thereby
ensuring high quality steam to pass through the reducing valve. This is discussed in more detail in Tutorial 9.3 and
Tutorial 12.5.

Plant downstream of the pressure reducing valve is protected by a safety valve. If the pressure reducing valve fails,
the downstream pressure may rise above the maximum allowable working pressure of the steam using equipment.
This, in turn, may permanently damage the equipment, and, more importantly, constitute a danger to personnel.

With a safety valve fitted, any excess pressure is vented through the valve, and will prevent this from happening
(safety valves are discussed in Block 9).

Other components included in the pressure reducing valve station are:

 The primary isolating valve - To shut the system down for maintenance.
 The primary pressure gauge - To monitor the integrity of supply.
 The strainer - To keep the system clean.
 The secondary pressure gauge - To set and monitor the downstream pressure.
 The secondary isolating valve - To assist in setting the downstream pressure on no-load conditions.

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Standards and wall thickness
There are a number of piping standards in existence around the world, but arguably the most global are those derived
by the American Petroleum Institute (API), where pipes are categorised in schedule numbers.

These schedule numbers bear a relation to the pressure rating of the piping. There are eleven Schedules ranging
from the lowest at 5 through 10, 20, 30, 40, 60, 80, 100, 120, 140 to schedule No. 160. For nominal size piping 150
mm and smaller, Schedule 40 (sometimes called 'standard weight') is the lightest that would be specified for steam
applications.

Regardless of schedule number, pipes of a particular size all have the same outside diameter (not withstanding
manufacturing tolerances). As the schedule number increases, the wall thickness increases, and the actual bore is
reduced. For example:

 A 100 mm Schedule 40 pipe has an outside diameter of 114.30 mm, a wall thickness of 6.02 mm, giving a
bore of 102.26 mm.
 A 100 mm Schedule 80 pipe has an outside diameter of 114.30 mm, a wall thickness of 8.56 mm, giving a
bore of 97.18 mm.

Only Schedules 40 and 80 cover the full range from 15 mm up to 600 mm nominal sizes and are the most commonly
used schedule for steam pipe installations.

This Tutorial considers Schedule 40 pipework as covered in BS 1600.

Tables of schedule numbers can be obtained from BS 1600 which are used as a reference for the nominal pipe size
and wall thickness in millimetres. Table 10.2.1 compares the actual bore sizes of different sized pipes, for different
schedule numbers.

In mainland Europe, pipe is manufactured to DIN standards, and DIN 2448 pipe is included in Table 10.2.1.

Table
10.2.1 Comparison of pipe standards and actual bore diameters.
In the United Kingdom, piping to EN 10255, (steel tubes and tubulars suitable for screwing to BS 21 threads) is also
used in applications where the pipe is screwed rather than flanged. They are commonly referred to as 'Blue Band'
and 'Red Band'; this being due to their banded identification marks. The different colours refer to particular grades of
pipe:

 Red Band, being heavy grade, is commonly used for steam pipe applications.
 Blue Band, being medium grade, is commonly used for air distribution systems, although it is sometimes
used for low-pressure steam systems.

The coloured bands are 50 mm wide, and their positions on the pipe denote its length. Pipes less than 4 metres in
length only have a coloured band at one end, while pipes of 4 to 7 metres in length have a coloured band at either
end.

Fig. 10.2.1 Red band, branded pipe, - heavy grade

 Fig. 10.2.2 Blue band, branded pipe, - medium grade, between 4-7 metres in
length
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Pipe material
Pipes for steam systems are commonly manufactured from carbon steel to ASME (ANSI) B 16.9 A106. The same
material may be used for condensate lines, although copper tubing is preferred in some industries.

For high temperature superheated steam mains, additional alloying elements, such as chromium and molybdenum,
are included to improve tensile strength and creep resistance at high temperatures.

Typically, pipes are supplied in 6 metre lengths.

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Pipeline sizing
The objective of the steam distribution system is to supply steam at the correct pressure to the point of use. It follows,
therefore, that pressure drop through the distribution system is an important feature.

Liquids
Bernoulli's Theorem (Daniel Bernoulli 1700 - 1782) is discussed in Block 4 - Flowmetering. D'Arcy (D'Arcy Thompson
1860 - 1948) added that for fluid flow to occur, there must be more energy at Point 1 than Point 2 (see Figure 10.2.3).
The difference in energy is used to overcome frictional resistance between the pipe and the flowing fluid.

Fig. 10.2.3
Friction in pipes
Bernoulli relates changes in the total energy of a flowing fluid to energy dissipation expressed either in terms of a
head loss hf (m) or specific energy loss g hf (J/kg). This, in itself, is not very useful without being able to predict the
pressure losses that will occur in particular circumstances.

Here, one of the most important mechanisms of energy dissipation within a flowing fluid is introduced, that is, the loss
in total mechanical energy due to friction at the wall of a uniform pipe carrying a steady flow of fluid.

The loss in the total energy of fluid flowing through a circular pipe must depend on:
L = The length of the pipe (m)
D = The pipe diameter (m)
u = The mean velocity of the fluid flow (m/s)
μ = The dynamic viscosity of the fluid (kg/m s=Pa s)
ρ = The fluid density (kg/m)
ks = The roughness of the pipe wall* (m)
*Since the energy dissipation is associated with shear stress at the pipe wall, the nature of the wall surface will be
influential, as a smooth surface will interact with the fluid in a different way than a rough surface.

All these variables are brought together in the D'Arcy-Weisbach equation (often referred to as the D'Arcy equation),
and shown as Equation 10.2.1. This equation also introduces a dimensionless term referred to as the friction factor,
which relates the absolute pipe roughness to the density, velocity and viscosity of the fluid and the pipe diameter.

The term that relates fluid density, velocity and viscosity and the pipe diameter is called the Reynolds number, named
after Osborne Reynolds (1842-1912, of Owens College, Manchester, United Kingdom), who pioneered this technical
approach to energy losses in flowing fluids circa 1883.

The D'Arcy equation (Equation 10.2.1):

Equation 10.2.1
Where for equation 10.2.1 using
SI based units:

hf = Head loss to friction (m)

f = Friction factor (dimensionless)
L = Length (m)
u = Flow velocity (m/s)
g = Gravitational constant (9.81 m/s2)
D = Pipe diameter (m)

Where for equation 10.2.1 using

Imperial based units:

hf = Head loss to friction (ft)

f = Friction factor (dimensionless)
L = Length (ft)
u = Flow velocity (ft/s)
g = Gravitational constant (32.17 ft/s2)
D = Pipe diameter (ft)
Interesting point
Readers in some parts of the world may recognise the D'Arcy equation in a slightly different form, as shown in
Equation 10.2.2. Equation 10.2.2 is similar to Equation 10.2.1 but does not contain the constant 4.

Equation 10.2.2
The reason for the difference is the type of friction factor used. It is essential that the right version of the D'Arcy
equation be used with the selected friction factor. Matching the wrong equation to the wrong friction factor will result
in a 400% error and it is therefore important that the correct combination of equation and friction factor is utilised.
Many textbooks simply do not indicate which friction factors are defined, and a judgement must sometimes be based
on the magnitudes quoted.

Equation 10.2.2 tends to be used by those who traditionally work in Imperial units, and still tends to be used by
practitioners in the United States and Pacific rim regions even when metric pipe sizes are quoted. Equation 10.2.1
tends to be used by those who traditionally work in SI units and tends more to be used by European practitioners. For
the same Reynolds number and relative roughness, the 'Imperial based friction factor' will be exactly four times larger
than the 'SI based friction factor'.
Friction factors can be determined either from a Moody chart or, for turbulent flows, can be calculated from Equation
10.2.3, a development of the Colebrook - White formula.

Equation 10.2.3
Where:

f = Friction factor (Relates to the SI Moody chart)

ks = Absolute pipe roughness (m)
D = Pipe bore (m)
Re = Reynolds number (dimensionless)
However, Equation 10.2.3 is difficult to use because the friction factor appears on both sides of the equation, and it is
for this reason that manual calculations are likely to be carried out by using the Moody chart.

On an SI style Moody chart, the friction factor scale might typically range from 0.002 to 0.02, whereas on an Imperial
style Moody chart, this scale might range from 0.008 to 0.08.

As a general rule, for turbulent flow with Reynolds numbers between 4000 and 100000, 'SI based' friction factors will
be of the order suggested by Equation 10.2.4, whilst 'Imperial based' friction factors will be of the order suggested by
Equation 10.2.5.

Equation 10.2.4 - 'SI based' friction factors

Equation 10.2.5 - 'Imperial based' friction factors

The friction factor used will determine whether the D'Arcy Equation 10.2.1 or 10.2.2 is used. For 'SI based' friction
factors, use Equation 10.2.1; for 'Imperial based' friction factors, use Equation 10.2.2.

Example 10.2.1 - Water pipe

Determine the velocity, friction factor and the difference in pressure between two points 1 km apart in a 150
mm constant bore horizontal pipework system if the water flowrate is 45 m³/h at 15°C.

In essence, the friction factor depends on the Reynolds number (Re) of the flowing liquid and the relative roughness
(kS/d) of the inside of the pipe; the former calculated from Equation 10.2.6, and the latter from Equation 10.2.7.

Reynolds number (Re)

Equation 10.2.6
Where:

Re = Reynolds number  
ρ = Density of water = 1000 kg/m
u = Velocity of water = 0.71 m/s
D = Pipe diameter = 0.15 m
μ = Dynamic viscosity of water (at 15°C) = 1.138 x 10-3 kg/m s (from steam tables)
From Equation 10.2.6:
The pipe roughness or 'ks' value (often quoted as 'e' in some texts) is taken from standard tables, and for 'commercial
steel pipe' would generally be taken as 0.000045 metres.

From this the relative roughness is determined (as this is what the Moody chart requires).

Equation 10.2.7
From Equation 10.2.7:

The friction factor can now be determined from the Moody chart and the friction head loss calculated from the
relevant D'Arcy Equation.

From the European Moody chart (Figure 10.2.4),

Where: ks/D = 0.0003 Re = 93585: Friction factor (f) = 0.005

 Fig.
10.2.4 'SI based' Moody chart (abridged
From the European D'Arcy equation (Equation 10.2.1) :

From the USA / AUS Moody chart (Figure 10.2.5),

Where: ks/D = 0.0003 Re = 93 585 Friction factor (f) = 0.02
 Fig.
10.2.5 ‘Imperial based’ Moody chart (abridged)
From the USA / AUS D'Arcy equation (Equation 10.2.2):

The same friction head loss is obtained by using the different friction factors and relevant D'Arcy equations.

In practice whether for water pipes or steam pipes, a balance is drawn between pipe size and pressure loss.
 Top

Steam
Oversized pipework means:

 Pipes, valves, fittings, etc. will be more expensive than necessary.

 Higher installation costs will be incurred, including support work, insulation, etc.
 For steam pipes a greater volume of condensate will be formed due to the greater heat loss. This, in turn,
means that either:
- More steam trapping is required, or
- Wet steam is delivered to the point of use.

In a particular example:

 The cost of installing 80 mm steam pipework was found to be 44% higher than the cost of 50 mm pipework,
which would have had adequate capacity.
 The heat lost by the insulated pipework was some 21% higher from the 80 mm pipeline than it would have
been from the 50 mm pipework. Any non-insulated parts of the 80 mm pipe would lose 50% more heat than
the 50 mm pipe, due to the extra heat transfer surface area.

Undersized pipework means:

 A lower pressure may only be available at the point of use. This may hinder equipment performance due to
only lower pressure steam being available.
 There is a risk of steam starvation.
 There is a greater risk of erosion, waterhammer and noise due to the inherent increase in steam velocity.

As previously mentioned, the friction factor (f) can be difficult to determine, and the calculation itself is time
consuming especially for turbulent steam flow. As a result, there are numerous graphs, tables and slide rules
available for relating steam pipe sizes to flowrates and pressure drops.

One pressure drop sizing method, which has stood the test of time, is the 'pressure factor' method. A table of
pressure factor values is used in Equation 10.2.2 to determine the pressure drop factor for a particular installation.

Equation 10.2.8
Where:

F = Pressure factor
P1 = Factor at inlet pressure
P2 = Factor at a distance of L metres
L = Equivalent length of pipe (m)
Example 10.2.2
Consider the system shown in Figure 10.2.6, and determine the pipe size required from the boiler to the unit
heater branch line. Unit heater steam load = 270 kg/h.
 Fig. 10.2.6 System
used to illustrate Example 10.2.2
Although the unit heater only requires 270 kg/h, the boiler has to supply more than this due to heat losses from the
pipe.

The allowance for pipe fittings

The length of travel from the boiler to the unit heater is known, but an allowance must be included for the additional
frictional resistance of the fittings. This is generally expressed in terms of 'equivalent pipe length'. If the size of the
pipe is known, the resistance of the fittings can be calculated. As the pipe size is not yet known in this example, an
addition to the equivalent length can be used based on experience.

 If the pipe is less than 50 metres long, add an allowance for fittings of 5%.
 If the pipe is over 100 metres long and is a fairly straight run with few fittings, an allowance for fittings of 10%
would be made.
 A similar pipe length, but with more fittings, would increase the allowance towards 20%.

In this instance, revised length = 150 m + 10% = 165 m

The allowance for the heat losses from the pipe

The unit heater requires 270 kg/h of steam; therefore the pipe must carry this quantity plus the quantity of steam
condensed by heat losses from the main. As the size of the main is yet to be determined, the true calculations cannot
be made, but, assuming that the main is insulated, it may be reasonable to add 3.5% of the steam load per 100 m of
the revised length as heat losses.

In this instance, the additional allowance =

Revised boiler load = 270 kg/h + 5.8% = 286 kg/h

From Table 10.2.2 (an extract from the complete pressure factor table, Table 10.2.5, which can be found in the
Appendix at the end of this Tutorial) 'P' can be determined by finding the pressure factors P 1 and P2, and substituting
them into Equation 10.2.8.
 Table
10.2.2 Extract from pressure factor table (Table 10.2.5)
From the pressure factor table (see Table 10.2.2):

P1 (7.0 bar g) = 56.38

P2 (6.6 bar g) = 51.05

Substituting these pressure factors (P1 and P2) into Equation 10.2.8 will determine the value for 'F':

Equation 10.2.8.

Following down the left-hand column of the pipeline capacity and pressure drop factors table (Table 10.2.6 - Extract
shown in Table 10.2.3); the nearest two readings around the requirement of 0.032 are 0.030 and 0.040. The next
lower factor is always selected; in this case, 0.030.

Tab
le 10.2.3 Extract from pipeline capacity and pressure factor table (Table 10.2.6)
Although values can be interpolated, the table does not conform exactly to a straight-line graph, so interpolation
cannot be absolutely correct. Also, it is bad practice to size any pipe up to the limit of its capacity, and it is important
to have some leeway to allow for the inevitable future changes in design.

From factor 0.030, by following the row of figures to the right it will be seen that:

 A 40 mm pipe will carry 229.9 kg/h.

 A 50 mm pipe will carry 501.1 kg/h.

Since the application requires 286 kg/h, the 50 mm pipe would be selected.

Having sized the pipe using the pressure drop method, the velocity can be checked if required.

Where:
Viewed in isolation, this velocity may seem low in comparison with maximum permitted velocities. However, this
steam main has been sized to limit pressure drop, and the next smaller pipe size would have given a velocity of over
47 m/s, and a final pressure less than the requirement of 6.6 bar g, which is unacceptable.

As can be seen, this procedure is fairly complex and can be simplified by using the nomogram shown in Figure 10.2.9
(in the Appendix of this Tutorial). The method of use is explained in Example 10.2.3.

Example 10.2.3
Using the data from Example 10.2.2, determine the pipe size using the nomogram shown in Figure 10.2.7.

Inlet pressure = 7 bar g

Steam flowrate = 286 kg/h

Minimum allowable P2 = 6.6 bar g

Method

 Select the point on the saturated steam line at 7 bar g, and mark Point A.
 From point A, draw a horizontal line to the steam flowrate of 286 kg/h, and mark Point B.
 From point B, draw a vertical line towards the top of the nomogram (Point C).
 Draw a horizontal line from 0.24 bar/100 m on the pressure loss scale (Line DE).
 The point at which lines DE and BC cross will indicate the pipe size required. In this case, a 40 mm pipe is
too small, and a 50 mm pipe would be used.
 Fig.
10.2.7 Steam pipeline sizing chart - Pressure drop
Sizing pipes on velocity
From the knowledge gained at the beginning of this Tutorial, and particularly the notes regarding the D'Arcy equation
(Equation 10.2.1), it is acknowledged that velocity is an important factor in sizing pipes. It follows then, that if a
reasonable velocity could be used for a particular fluid flowing through pipes, then velocity could be used as a
practical sizing factor. As a general rule, a velocity of 25 to 40 m/s is used when saturated steam is the medium.

40 m/s should be considered an extreme limit, as above this, noise and erosion will take place particularly if the
steam is wet.

Even these velocities can be high in terms of their effect on pressure drop. In longer supply lines, it is often necessary
to restrict velocities to 15 m/s to avoid high pressure drops. It is recommended that pipelines over 50 m long are
always checked for pressure drop, no matter what the velocity.

By using Table 10.2.4 as a guide, it is possible to select pipe sizes from known data; steam pressure, velocity and
flowrate.
 Table
10.2.4 Saturated steam pipeline capacities in kg/h for different velocities (Schedule 40 pipe)
Alternatively the pipe size can be calculated arithmetically. The following information is required, and the procedure
used for the calculation is outlined below.

Information required to calculate the required pipe size:

u = Flow velocity (m/s)

vg = Specific volume (m³/kg)
s = Mass flowrate (kg/s)

= Volumetric flowrate (m³/s) = ms x vgFrom this information, the cross sectional area (A) of the pipe can be
calculated:
Rearranging the formula to give the diameter of the pipe (D) in metres:

Example 10.2.4
A process requires 5 000 kg/h of dry saturated steam at 7 bar g. For the flow velocity not to exceed 25
m/s, determine the pipe size.

Where

Therefore, using:

Since the steam velocity must not exceed 25 m/s, the pipe size must be at least 130 mm; the nearest
commercially available size, 150 mm, would be selected.

Again, a nomogram has been created to simplify this process, see Figure 10.2.6.

Example 10.2.5
Using the information from Example 10.2.4, use Figure 10.2.6 to determine the minimum acceptable pipe
size
Inlet pressure =</TD 7 bar g
Steam flowrate = 5000 kg/h
Maximum velocity = 25 m/s
Method:

 Draw a horizontal line from the saturation temperature line at 7 bar g (Point A) on the pressure scale to the
steam mass flowrate of 5 000 kg/h (Point B).
 From point B, draw a vertical line to the steam velocity of 25 m/s (Point C). From point C, draw a horizontal
line across the pipe diameter scale (Point D).
 A pipe with a bore of 130 mm is required; the nearest commercially available size, 150 mm, would be
selected.

Fig.
10.2.8 Steam pipeline sizing chart - Velocity
Sizing pipes for superheated steam duty
Superheated steam can be considered as a dry gas and therefore carries no moisture. Consequently there is no
chance of pipe erosion due to suspended water droplets, and steam velocities can be as high as 50 to 70 m/s if the
pressure drop permits this. The nomograms in Figures 10.2.5 and 10.2.6 can also be used for superheated steam
applications.

Example 10.2.6
Utilising the waste heat from a process, a boiler/superheater generates 30 t/h of superheated steam at 50 bar
g and 450°C for export to a neighbouring power station. If the velocity is not to exceed 50 m/s, determine:

1. The pipe size based on velocity (use Figure 10.2.8).

2. The pressure drop if the pipe length, including allowances, is 200 m (use Figure 10.2.9).

Part 1

 Using Figure 10.2.8, draw a vertical line from 450°C on the temperature axis until it intersects the 50 bar line
(Point A).
 From point A, project a horizontal line to the left until it intersects the steam 'mass flowrate' scale of 30 000
kg/h (30 t/h) (Point B).
 From point B, project a line vertically upwards until it intersects 50 m/s on the 'steam velocity' scale (Point
C).
 From Point C, project a horizontal line to the right until it intersects the 'inside pipe diameter' scale.

The 'inside pipe diameter' scale recommends a pipe with an inside diameter of about 120 mm. From Table 10.2.1 and
assuming that the pipe will be Schedule 80 pipe, the nearest size would be 150 mm, which has a bore of 146.4 mm.

Part 2

 Using Figure 10.2.7, draw a vertical line from 450°C on the temperature axis until it intersects the 50 bar line
(Point A).
 From point A, project a horizontal line to the right until it intersects the 'steam mass flowrate' scale of 30 000
kg/h (30 t/h) (Point B).
 From point B, project a line vertically upwards until it intersects the 'inside pipe diameter' scale of
(approximately) 146 mm (Point C).
 From Point C, project a horizontal line to the left until it intersects the 'pressure loss bar/100 m' scale (Point
D).

The 'pressure loss bar/100 m' scale reads about 0.9 bar/100 m. The pipe length in the example is 200 m, so the
pressure drop is:

This pressure drop must be acceptable at the process plant.

Using formulae to establish steam flowrate on pressure drop

Empirical formulae exist for those who prefer to use them. Equations 10.2.9 and 10.2.10 are shown below. These
have been tried and tested over many years, and which appear to give results close to the pressure factor method.
The advantage of using these formulae is that they can be programmed into a scientific calculator, or a spreadsheet,
and consequently used without the need to look up tables and charts. Equation 10.2.10 requires the specific volume
of steam to be known, which means it is necessary to look up this value from a steam table. Also, Equation 10.2.10
should be restricted to a maximum pipe length of 200 metres.

Pressure drop formula 1

Equation 10.2.9.
Where:
P1 = Upsteam pressure (bar a)
P2 = Downstream pressure (bar a)
L = Length of pipe (m)
s = Mass flowrate (kg/h)
D = Pipe diameter (mm)
Pressure drop formula 2 (Maximum pipe length: 200 metres)

Equation 10.2.10.
ΔP = Pressure drop (bar)
L = Length of pipe
vg = Specific volume of steam (m3/kg)
</< td> = Mass flowrate(kg/h)
D = Pipe diameter (mm)
Where:
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Summary
 The selection of piping material and the wall thickness required for a particular installation is stipulated in
standards such as EN 45510 and ASME 31.1.
 Selecting the appropriate pipe size (nominal bore) for a particular application is based on accurately
identifying pressure and flowrate. The pipe size may be selected on the basis of:

- Velocity (usually pipes less than 50 m in length).

- Pressure drop (as a general rule, the pressure drop should not normally exceed 0.1 bar/50 m.

Appendix
Table
 10.2.5 Pressure drop factor (F) table

Tab
le 10.2.6 Pipeline capacity from pressure drop factor
 Fig
10.2.9 Steam pipeline sizing chart - Pressure drop
 Fig
10.2.10 Steam pipeline sizing chart - Velocity
Throughout the length of a hot steam main, an amount of heat will be transferred to the environment, and this will
depend on the parameters identified in Block 2 - 'Steam Engineering and Heat Transfer', and brought together in
Equation 2.5.1.

Equation 2.5.1
Where:

= Heat transferred per unit time (W)

k = Thermal conductivity of the material (W/m K or W/m °C)
A = Heat transfer area (m²)
ΔT = Temperature difference across the material (K or °C)
Χ = Material thickness (m)
With steam systems, this loss of energy represents inefficiency, and thus pipes are insulated to limit these losses.
Whatever the quality or thickness of insulation, there will always be a level of heat loss, and this will cause steam to
condense along the length of the main.

The effect of insulation is discussed in Tutorial 10.5. This Tutorial will concentrate on disposal of the inevitable
condensate, which, unless removed, will accumulate and lead to problems such as corrosion, erosion, and
waterhammer.

In addition, the steam will become wet as it picks up water droplets, which reduces its heat transfer potential. If water
is allowed to accumulate, the overall effective cross sectional area of the pipe is reduced, and steam velocity can
increase above the recommended limits.
Top

Piping layout
The subject of drainage from steam lines is covered in the European Standard EN 45510, Section 4.12.

EN 45510 states that, whenever possible, the main should be installed with a fall of not less than 1:100 (1 m fall for
every 100 m run), in the direction of the steam flow. This slope will ensure that gravity, as well as the flow of steam,
will assist in moving the condensate towards drain points where the condensate may be safely and effectively
removed (See Figure 10.3.1).

Fig. 10.3.1
Typical steam main installation
Drain points
The drain point must ensure that the condensate can reach the steam trap. Careful consideration must therefore be
given to the design and location of drain points.

Consideration must also be given to condensate remaining in a steam main at shutdown, when steam flow ceases.
Gravity will ensure that the water (condensate) will run along sloping pipework and collect at low points in the system.
Steam traps should therefore be fitted to these low points.

The amount of condensate formed in a large steam main under start-up conditions is sufficient to require the
provision of drain points at intervals of 30 m to 50 m, as well as natural low points such as at the bottom of rising
pipework.

In normal operation, steam may flow along the main at speeds of up to 145 km/h, dragging condensate along with it.
Figure 10.3.2 shows a 15 mm drain pipe connected directly to the bottom of a main.

Fig. 10.3.2 Trap pocket too

small
Although the 15 mm pipe has sufficient capacity, it is unlikely to capture much of the condensate moving along the
main at high speed. This arrangement will be ineffective.

A more reliable solution for the removal of condensate is shown in Figure 10.3.3. The trap line should be at least 25
to 30 mm from the bottom of the pocket for steam mains up to 100 mm, and at least 50 mm for larger mains. This
allows a space below for any dirt and scale to settle.

Fig. 10.3.3 Trap pocket

properly sized
The bottom of the pocket may be fitted with a removable flange or blowdown valve for cleaning purposes.

Recommended drain pocket dimensions are shown in Table 10.3.1 and in Figure 10.3.4.
 Table
10.3.1 Recomended drain pocket dimensions
Top

Waterhammer and its effects

Waterhammer is the noise caused by slugs of condensate colliding at high velocity into pipework fittings, plant, and
equipment. This has a number of implications:

 Because the condensate velocity is higher than normal, the dissipation of kinetic energy is higher than would
normally be expected.
 Water is dense and incompressible, so the 'cushioning' effect experienced when gases encounter
obstructions is absent.
 The energy in the water is dissipated against the obstructions in the piping system such as valves and
fittings.

Fig. 10.3.5
Formation of a ‘solid’ slug of water
Indications of waterhammer include a banging noise, and perhaps movement of the pipe.

In severe cases, waterhammer may fracture pipeline equipment with almost explosive effect, with consequent loss of
live steam at the fracture, leading to an extremely hazardous situation.

Good engineering design, installation and maintenance will avoid waterhammer; this is far better practice than
attempting to contain it by choice of materials and pressure ratings of equipment.

Commonly, sources of waterhammer occur at the low points in the pipework (See Figure 10.3.6). Such areas are due
to:

 Sagging in the line, perhaps due to failure of supports.

 Incorrect use of concentric reducers (see Figure 10.3.7) - Always use eccentric reducers with the flat at the
bottom.
 Incorrect strainer installation - They should be fitted with the basket on the side.
 Inadequate drainage of steam lines.
 Incorrect operation - Opening valves too quickly at start-up when pipes are cold.

Fig. 10.3.6
Potential sources of waterhammer

Fig. 10.3.7 Eccentric and concentric pipe reducers

To summarise, the possibility of waterhammer is minimised by:

 Installing steam lines with a gradual fall in the direction of flow, and with drain points installed at regular
intervals and at low points.
 Installing check valves after all steam traps which would otherwise allow condensate to run back into the
steam line or plant during shutdown.
 Opening isolation valves slowly to allow any condensate which may be lying in the system to flow gently
through the drain traps, before it is picked up by high velocity steam. This is especially important at start-up.
 Top

Branch lines

Fig. 10.3.8 Branch line

Branch lines are normally much shorter than steam mains. As a general rule, therefore, provided the branch line is
not more than 10 metres in length, and the pressure in the main is adequate, it is possible to size the pipe on a
velocity of 25 to 40 m/s, and not to worry about the pressure drop.

Table 10.2.4 'Saturated steam pipeline capacities for different velocities' in Tutorial 10.2 will prove useful in this
exercise.

Branch line connections

Branch line connections taken from the top of the main carry the driest steam (Figure 10.3.8). If connections are
taken from the side, or even worse from the bottom (as in Figure 10.3.9 (a)), they can accept the condensate and
debris from the steam main. The result is very wet and dirty steam reaching the equipment, which will affect
performance in both the short and long term.

The valve in Figure 10.3.9 (b) should be positioned as near to the off-take as possible to minimise condensate lying in
the branch line, if the plant is likely to be shutdown for any extended periods.
 Fig. 10.3.9 Steam off-take
Drop leg
Low points will also occur in branch lines. The most common is a drop leg close to an isolating valve or a control
valve (Figure 10.3.10). Condensate can accumulate on the upstream side of the closed valve, and then be propelled
forward with the steam when the valve opens again - consequently a drain point with a steam trap set is good
practice just prior to the strainer and control valve.

Fig.
10.3.10 Diagram of a drop leg supplying a unit heater
Top

Rising ground and drainage

There are many occasions when a steam main must run across rising ground, or applications where the contours of
the site make it impractical to lay the pipe with the 1:100 fall proposed earlier. In these situations, the condensate
must be encouraged to run downhill and against the steam flow. Good practice is to size the pipe on a low steam
velocity of not more than 15 m/s, to run the line at a slope of no less than 1:40, and install the drain points at not more
than 15 metre intervals (see Figure 10.3.11).

The objective is to prevent the condensate film on the bottom of the pipe increasing in thickness to the point where
droplets can be picked up by the steam flow.

Fig. 10.3.11 Reverse

gradient on steam main
Top

Steam separators
Modern packaged steam boilers have a large evaporating capacity for their size and have limited capacity to cope
with rapidly changing loads. In addition, as discussed in Block 3 'The Boiler House', other circumstances, such as . . .

 Incorrect chemical feedwater treatment and/or TDS control.

 Transient peak loads in other parts of the plant.

. . . can cause priming and carryover of boiler water into the steam mains.

Separators, as shown by the cut section in Figure 10.3.12, may be installed to remove this water.
 Fig. 10.3.12 Cut section
through a separator
As a general rule, providing the velocities in the pipework are within reasonable limits, separators will be line sized.
(Separators are discussed in detail in Tutorial 12.5)

A separator will remove both droplets of water from pipe walls and suspended mist entrained in the steam itself. The
presence and effect of waterhammer can be eradicated by fitting a separator in a steam main, and can often be less
expensive than increasing the pipe size and fabricating drain pockets.

A separator is recommended before control valves and flowmeters. It is also wise to fit a separator where a steam
main enters a building from outside. This will ensure that any condensate produced in the external distribution system
is removed and the building always receives dry steam. This is equally important where steam usage in the building
is monitored and charged for.
Top

Strainers
When new pipework is installed, it is not uncommon for fragments of casting sand, packing, jointing, swarf, welding
rods and even nuts and bolts to be accidentally deposited inside the pipe. In the case of older pipework, there will be
rust, and in hard water districts, a carbonate deposit. Occasionally, pieces will break loose and pass along the
pipework with the steam to rest inside a piece of steam using equipment. This may, for example, prevent a valve from
opening/closing correctly. Steam using equipment may also suffer permanent damage through wiredrawing - the
cutting action of high velocity steam and water passing through a partly open valve. Once wiredrawing has occurred,
the valve will never give a tight shut-off, even if the dirt is removed.

It is therefore wise to fit a line-size strainer in front of every steam trap, flowmeter, reducing valve and regulating
valve. The illustration shown in Figure 10.3.13 shows a cut section through a typical strainer.
 Fig. 10.3.13 Cut section
through a Y-type strainer.
Steam flows from the inlet 'A' through the perforated screen 'B' to the outlet 'C'. While steam and water will pass
readily through the screen, dirt cannot. The cap 'D', can be removed, allowing the screen to be withdrawn and
cleaned at regular intervals. A blowdown valve can also be fitted to cap 'D' to facilitate regular cleaning.

Strainers can however, be a source of wet steam as previously mentioned. To avoid this situation, strainers should
always be installed in steam lines with their baskets to the side.

Strainers and screen details are discussed in Tutorial 12.4.

Top

How to drain steam mains

Steam traps are the most effective and efficient method of draining condensate from a steam distribution system.

The steam traps selected must suit the system in terms of:

 Pressure rating
 Capacity
 Suitability

Pressure rating
Pressure rating is easily dealt with; the maximum possible working pressure at the steam trap will either be known or
should be established.

Capacity
Capacity, that is, the quantity of condensate to be discharged, which needs to be divided into two categories; warm-
up load and running load.

Warm-up load - In the first instance, the pipework needs to be brought up to operating temperature. This can be
determined by calculation, knowing the mass and specific heat of the pipework and fittings. Alternatively, Table 10.3.2
may be used.
  The table shows the amount of condensate generated when bringing 50 m of steam main up to working
temperature; 50 m being the maximum recommended distance between trapping points.
 The values shown are in kilograms. To determine the average condensing rate, the time taken for the
process must be considered. For example, if the warm-up process required 50 kg of steam, and was to take
20 minutes, then the average condensing rate would be:

 When using these capacities to size a steam trap, it is worth remembering that the initial pressure in the
main will be little more than atmospheric when the warm-up process begins. However, the condensate loads
will still generally be well within the capacity of a DN15 'low capacity' steam trap. Only in rare applications at
very high pressures (above 70 bar g), combined with large pipe sizes, will greater trap capacity be needed.

Running load - Once the steam main is up to operating temperature, the rate of condensation is mainly a function of
the pipe size and the quality and thickness of the insulation.

Alternatively, for quick approximations of running load, Table 10.3.3 can be used which shows typical amounts of
steam condensed each hour per 50 m of insulated steam main at various pressures. For accurate means of
calculating running losses from steam mains, refer to Tutorial 2.12 'Steam consumption of pipes and air heaters'.

Table
10.3.2 Amount of steam condensed to warm-up 50 m of schedule 40 pipe (kg)
Note: Figures are based on an ambient temperature of 20°C, and an insulation efficiency of 80%
 Table
10.3.3 Condensing rate of steam in 50 m of schedule 40 pipe - at working temperature (kg/h)
Note: Figures are based on an ambient temperature of 20°C, and an insulation efficiency of 80%

Suitability
A mains drain trap should consider the following constraints:

 Discharge temperature - The steam trap should discharge at, or very close to saturation temperature,
unless cooling legs are used between the drain point and the trap. This means that the choice is a
mechanical type trap (such as a float, inverted bucket type, or thermodynamic traps).
 Frost damage - Where the steam main is located outside a building and there is a possibility of sub-zero
ambient temperature, the thermodynamic steam trap is ideal, as it is not damaged by frost. Even if the
installation causes water to be left in the trap at shutdown and freezing occurs, the thermodynamic trap may
be thawed out without suffering damage when brought back into use.
 Waterhammer - In the past, on poorly laid out installations where waterhammer was a common occurrence,
float traps were not always ideal due to their susceptibility to float damage. Contemporary design and
manufacturing techniques now produce extremely robust units for mains drainage purposes. Float traps are
certainly the first choice for proprietary separators as high capacities are readily achieved, and they are able
to respond quickly to rapid load increases.

Steam traps used to drain condensate from steam mains, are shown in Figure 10.3.14. The thermostatic trap is
included because it is ideal where there is no choice but to discharge condensate into a flooded return pipe.

The subject of steam trapping is dealt with in detail in the Block 11, 'Steam Trapping'.
 Fig.
10.3.14 Steam traps suitable for steam mains drainage
Top

Steam leaks
Steam leaking from pipework is often ignored. Leaks can be costly in both the economic and environmental sense
and therefore need prompt attention to ensure the steam system is working at its optimum efficiency with a minimum
impact on the environment.

Figure 10.3.15 illustrates the steam loss for various sizes of hole at various pressures. This loss can be readily
translated into a fuel saving based on the annual hours of operation.

Fig. 10.3.15 Steam leakage rate

through holes
Top

Summary
Proper pipe alignment and drainage means observing a few simple rules:

 Steam lines should be arranged to fall in the direction of flow, at not less than 100 mm per 10 metres of pipe
(1:100). Steam lines rising in the direction of flow should slope at not less than 250 mm per 10 metres of
pipe (1:40).
 Steam lines should be drained at regular intervals of 30-50 m and at any low points in the system.
 lWhere drainage has to be provided in straight lengths of pipe, then a large bore pocket should be used to
collect condensate.
 If strainers are to be fitted, then they should be fitted on their sides.
 Branch connections should always be taken from the top of the main from where the driest steam is taken.
 Separators should be considered before any piece of steam using equipment ensuring that dry steam is
used.
 Traps selected should be robust enough to avoid waterhammer damage and frost damage.
Allowance for expansion
All pipes will be installed at ambient temperature. Pipes carrying hot fluids such as water or steam operate at higher
temperatures.

It follows that they expand, especially in length, with an increase from ambient to working temperatures. This will
create stress upon certain areas within the distribution system, such as pipe joints, which, in the extreme, could
fracture. The amount of the expansion is readily calculated using Equation 10.4.1, or read from an appropriate chart
such as Figure 10.4.1.

Equation 10.4.1
Where:

L = Length of pipe between anchors (m)

ΔT = Temperature difference between ambient temperature and operating temperatures (°C)
α = Expansion coefficient (mm/m °C) x 10-3

Table
10.4.1 Expansion coefficients (a) (mm/m °C x 10-3)
Example 10.4.1
A 30 m length of carbon steel pipe is to be used to transport steam at 4 bar g (152°C). If the pipe is installed at 10°C,
determine the expansion using Equation 10.4.1.
Alternatively, the chart in Figure 10.4.1 can be used for finding the approximate expansion of a variety of steel pipe
lengths - see Example 10.4.2 for explanation of use.

Example 10.4.2
Using Figure 10.4.1. Find the approximate expansion from 15°C, of 100 metres of carbon steel pipework used to
distribute steam at 265°C.

Temperature difference is 265 - 15°C = 250°C.

Where the diagonal temperature difference line of 250°C cuts the horizontal pipe length line at 100 m, drop a vertical
line down. For this example an approximate expansion of 330 mm is indicated.

Fig. 10.4.1 A chart

showing the expansion in various steel pipe lengths at various temperature differences

Table
10.4.2 Temperature of saturated steam
Top

Pipework flexibility
The pipework system must be sufficiently flexible to accommodate the movements of the components as they
expand. In many cases the flexibility of the pipework system, due to the length of the pipe and number of bends and
supports, means that no undue stresses are imposed. In other installations, however, it will be necessary to
incorporate some means of achieving this required flexibility.

An example on a typical steam system is the discharge of condensate from a steam mains drain trap into the
condensate return line that runs along the steam line (Figure 10.4.2). Here, the difference between the expansions of
the two pipework systems must be taken into account. The steam main will be operating at a higher temperature than
that of the condensate main, and the two connection points will move relative to each other during system warm-up.
 Fig. 10.4.2 Flexibility in connection to
condensate return line
The amount of movement to be taken up by the piping and any device incorporated in it can be reduced by 'cold
draw'. The total amount of expansion is first calculated for each section between fixed anchor points. The pipes are
left short by half of this amount, and stretched cold by pulling up bolts at a flanged joint, so that at ambient
temperature, the system is stressed in one direction. When warmed through half of the total temperature rise, the
piping is unstressed. At working temperature and having fully expanded, the piping is stressed in the opposite
direction. The effect is that instead of being stressed from 0 F to +1 F units of force, the piping is stressed from -½ F
to + ½ F units of force.

In practical terms, the pipework is assembled cold with a spacer piece, of length equal to half the expansion, between
two flanges. When the pipework is fully installed and anchored at both ends, the spacer is removed and the joint
pulled up tight (see Figure 10.4.3).

Fig. 10.4.3 Use of spacer

for expansion when pipework is installed
The remaining part of the expansion, if not accepted by the natural flexibility of the pipework will call for the use of an
expansion fitting.

In practice, pipework expansion and support can be classified into three areas as shown in Figure 10.4.4.

Fig. 10.4.4
Diagram of pipeline with fixed point, variable anchor point and expansion fitting
The fixed or 'anchor' points 'A' provide a datum position from which expansion takes place.

The sliding support points 'B' allow free movement for expansion of the pipework, while keeping the pipeline in
alignment.

The expansion device at point 'C' is to accommodate the expansion and contraction of the pipe.

Fig. 10.4.5 Chair and roller

Fig. 10.4.6 Chair roller and saddle

Roller supports (Figure 10.4.5 and 10.4.6) are ideal methods for supporting pipes, at the same time allowing them to
move in two directions. For steel pipework, the rollers should be manufactured from ferrous material. For copper
pipework, they should be manufactured from non-ferrous material. It is good practice for pipework supported on
rollers to be fitted with a pipe saddle bolted to a support bracket at not more than distances of 6 metres to keep the
pipework in alignment during any expansion and contraction.

Where two pipes are to be supported one below the other, it is poor practice to carry the bottom pipe from the top
pipe using a pipe clip. This will cause extra stress to be added to the top pipe whose thickness has been sized to take
only the stress of its working pressure.

All pipe supports should be specifically designed to suit the outside diameter of the pipe concerned.
Top

Expansion fittings
The expansion fitting ('C' Figure 10.4.4) is one method of accommodating expansion. These fittings are placed within
a line, and are designed to accommodate the expansion, without the total length of the line changing. They are
commonly called expansion bellows, due to the bellows construction of the expansion sleeve.

Other expansion fittings can be made from the pipework itself. This can be a cheaper way to solve the problem, but
more space is needed to accommodate the pipe.

Full loop
This is simply one complete turn of the pipe and, on steam pipework, should preferably be fitted in a horizontal rather
than a vertical position to prevent condensate accumulating on the upstream side.

The downstream side passes below the upstream side and great care must be taken that it is not fitted the wrong way
round, as condensate can accumulate in the bottom. When full loops are to be fitted in a confined space, care must
be taken to specify that wrong-handed loops are not supplied.

The full loop does not produce a force in opposition to the expanding pipework as in some other types, but with steam
pressure inside the loop, there is a slight tendency to unwind, which puts an additional stress on the flanges.

Fig. 10.4.7 Full loop

This design is used rarely today due to the space taken up by the pipework, and proprietary expansion bellows are
now more readily available. However large steam users such as power stations or establishments with large outside
distribution systems still tend to use full loop type expansion devices, as space is usually available and the cost is
relatively low.

Horseshoe or lyre loop

When space is available this type is sometimes used. It is best fitted horizontally so that the loop and the main are on
the same plane. Pressure does not tend to blow the ends of the loop apart, but there is a very slight straightening out
effect. This is due to the design but causes no misalignment of the flanges.

If any of these arrangements are fitted with the loop vertically above the pipe then a drain point must be provided on
the upstream side as depicted in Figure 10.4.8.

Fig. 10.4.8 Horseshoe or lyre loop

Expansion loops
 Fig. 10.4.9
Expansion loop
The expansion loop can be fabricated from lengths of straight pipes and elbows welded at the joints (Figure 10.4.9).
An indication of the expansion of pipe that can be accommodated by these assemblies is shown in Figure 10.4.10.

It can be seen from Figure 10.4.9 that the depth of the loop should be twice the width, and the width is determined
from Figure 10.4.10, knowing the total amount of expansion expected from the pipes either side of the loop.
 Fig. 10.4.10
Expansion loop capacity for carbon steel pipes
Sliding joint
These are sometimes used because they take up little room, but it is essential that the pipeline is rigidly anchored
and guided in strict accordance with the manufacturers' instructions; otherwise steam pressure acting on the cross
sectional area of the sleeve part of the joint tends to blow the joint apart in opposition to the forces produced by the
expanding pipework (see Figure 10.4.11). Misalignment will cause the sliding sleeve to bend, while regular
maintenance of the gland packing may also be needed.
 Fig. 10.4.11 Sliding joint
Expansion bellows
An expansion bellows, Figures 10.4.12, has the advantage that it requires no packing (as does the sliding joint type).
But it does have the same disadvantages as the sliding joint in that pressure inside tends to extend the fitting,
consequently, anchors and guides must be able to withstand this force.

Fig. 10.4.12 Simple expansion bellows

Bellows may incorporate limit rods, which limit over-compression and over-extension of the element. These may have
little function under normal operating conditions, as most simple bellows assemblies are able to withstand small
lateral and angular movement. However, in the event of anchor failure, they behave as tie rods and contain the
pressure thrust forces, preventing damage to the unit whilst reducing the possibility of further damage to piping,
equipment and personnel (Figure 10.4.13 (b)).

Where larger forces are expected, some form of additional mechanical reinforcement should be built into the device,
such as hinged stay bars (Figure 10.4.13 (c)).

There is invariably more than one way to accommodate the relative movement between two laterally displaced pipes
depending upon the relative positions of bellows anchors and guides. In terms of preference, axial displacement is
better than angular, which in turn, is better than lateral. Angular and lateral movement should be avoided wherever
possible.

Figure 10.4.13 (a), (b), and (c) give a rough indication of the effects of these movements, but, under all
circumstances, it is highly recommended that expert advice is sought from the bellows' manufacturer regarding any
installation of expansion bellows.
 Fig.
10.4.13 (a) Axial movement of bellows

Fig.
10.4.13 (b) Lateral and angular movement of bellows
 Fig. 10.4.13 (c) Angular
and axial movement of bellows
Top

Pipe support spacing

The frequency of pipe supports will vary according to the bore of the pipe; the actual pipe material (i.e. steel or
copper); and whether the pipe is horizontal or vertical.

Some practical points worthy of consideration are as follows:

 Pipe supports should be provided at intervals not greater than shown in Table 10.4.3, and run along those
parts of buildings and structures where appropriate supports may be mounted.
 Where two or more pipes are supported on a common bracket, the spacing between the supports should be
that for the smallest pipe.
 When an appreciable movement will occur, i.e. where straight pipes are greater than 15 metres in length,
the supports should be of the roller type as outlined previously.
 Vertical pipes should be adequately supported at the base, to withstand the total weight of the vertical pipe
and the fluid within it. Branches from vertical pipes must not be used as a means of support for the pipe,
because this will place undue strain upon the tee joint.
 All pipe supports should be specifically designed to suit the outside diameter of the pipe concerned. The use
of oversized pipe brackets is not good practice.

Table 10.4.3 can be used as a guide when calculating the distance between pipe supports for steel and copper
pipework.
 Table
10.4.3 Recommended support for pipework
The subject of pipe supports is covered comprehensively in the European standard EN 13480, Part3.