TCE CONSULTING ENGINEERS LIMITED

DESIGN GUIDE FOR

LARGE DIAMETER STEEL PIPING

TCE.M6-ME-590-424

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DESIGN GUIDE FOR

LARGE DIAMETER STEEL PIPING

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REV. NO.

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INITIALS

SIGN.

INITIALS

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INITIALS

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VBS

Sd/-

SMM

Sd/-

PV

CKD. BY

RKC

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VBS

APP. BY

SJB

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DATE

19.04.1991

25.03.2000

29.01.2003
TCE FORM NO. 020R2

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TCE.M6-ME-590-424

SECTION CONTENTS

DESIGN GUIDE FOR

LARGE DIAMETER STEEL PIPING

SHEET (ii) OF (iv)

CONTENTS

SL. NO.

DESCRIPTION

SH. NO.

1.0

INTRODUCTION

2.0

INPUT DATA

3.0

MATERIALS

4.0

HYDRAULICS OF PIPELINES

5.0

DETERMINATION OF PIPE WALL

THICKNESS

6.0

SUPPORTS

7.0

WATER HAMMER

8.0

ANCHORS

9.0

SPECIALS

10

10.0

PIPE JOINTS

12

11.0

TESTING OF PIPE LINES

14

12.0

PROTECTIVE COATING

14

13.0

REFERENCES

15

FIGURES
Fig.1, Fig. 2 a

TYPES OF SUPPORTS

16

Fig. 2 b & Fig.3

TYPES OF SUPPORTS

17

Fig. 4 a TO Fig. 4 c DIRECTION

FITTINGS

OF

FORCES

Fig. 5 a TO Fig. 5 c TYPES OF ANCHORS

IN

VARIOUS

18

19

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DESIGN GUIDE FOR

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SECTION CONTENTS
SHEET (iii) OF (iv)

Fig. 5 d TO Fig. 5 g TYPES OF ANCHORS

20

Fig. 6

TYPES OF FLANGES

21

Fig.7

PAD TYPE REINFORCEMENT

21

Fig. 8

EXPANSION JOINT ASSEMBLY

22

Fig. 9

VARIOUS PIPE JOINTS

23

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DESIGN GUIDE FOR

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SHEET (iv) OF (iv)

TCE.M6-ME-590-424

REVISION STATUS

REV. NO.

DATE

DESCRIPTION

R0

19.04.1991

--

R1

25.03.2000

REVISED TO CONVERT THE

DOCUMENT IN MS-WORD
AND
FEW
TECHNICAL
DETAILS ADDED. TITLE OF
THE GUIDE REVISED.

R2

29.01.2003

MINOR REVISION CARRIED

OUT

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DESIGN GUIDE FOR

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SHEET 1 OF 23

INTRODUCTION
This design guide covers the criteria for design of large diameter steel
pipes > 400 NB for the benefit of practising water works Engineers.

2.0

INPUT DATA
The following input are required for the design of large diameter steel
pipelines for systems like cooling water, water supply etc :

3.0

(a)

Normal and maximum flow and flow for any future expansion
if any.

(b)

Operating and maximum internal pressure envisaged.

(c)

Design pressure

(d)

External pressure.

(e)

Soil conditions and related data.

(f)

Water hammer pressure/Vacuum

(g)

Normal, minimum and maximum temperature of the water.

(h)

Ambient temperature variations.

(i)

Quality of the water in circulation.

(j)

Any additional loading, as applicable.

MATERIALS
Materials depend upon the type of fluid which is being handled.
Normally carbon steel pipes are used with internal lining, if applicable.
The normally used internal lining material is mortar. This is especially
applicable for service like sea water and in case of water supply
system. For details chapter on 'Protective Coating & Lining' in
AWWA Manual-M11 shall be referred.

4.0

HYDRAULICS OF PIPELINES

4.1

SELECTION OF DIAMETER
The criteria for design is that the pipeline should convey the required
quantity of water at the lowest capitalised cost i.e. the cost inclusive of
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initial installation and cost loading for power. For preliminary sizing
of the piping, a velocity of 2 m/sec may be used. The recommended
velocity range is 1.25 m/sec to 3 m/sec. Additional flow requirement
in the line in future, if any, due to plant expansion shall be considered
for pipe sizing in consultation with the client.
4.2

DESIGN PRESSURE
The design pressure to be adopted for designing the pipelines will
depend on the following factors.
(a)

Normal operating pressure

(b)

Maximum pressure encountered in the system that is pump shut

off head plus static head, if any.

(c)

Water hammer pressure.

It is uneconomical to design the pipelines for water hammer pressure.

Suitable means should be provided to reduce the water hammer effect
to the minimum. The design pressure shall correspond to (b) above
since the water hammer pressure is a transient phenomenon. The stress
in the pipe should be checked to ensure that stresses under water
hammer pressure are within 75% of minimum yield strength.
Depending on the hydraulic gradient of the system, if any portion is
subjected to vacuum during operation, corresponding portion shall be
designed for the maximum envisaged vacuum. However it is normal
practice to provide double acting air release valve which prevents
vacuum formation and also release air while filling the line. Vacuum
could also be due to water hammer phenomena.
4.3

FRICTION LOSS IN PIPE LINES

The most popular formula for computation of friction loss in the
pipelines is Hazen-Williams formula which is given below :
F

V
C

1.852

1
D

1.167

6.815 x

Total friction loss in pipe in MWC

Flow velocity in metre/sec

Internal pipe diameter in metres

x L

where -

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TCE.M6-ME-590-424

Hazen-Williams coefficient (For C values refer

document No. TCE.M6-ME-613-212).

Length of the pipe in metres

Bends, fittings and valves also constitute a major part of the friction
loss in the system. The loss in the system shall be calculated on the
following basis :
Friction loss =

k V2
2g

where k

is the friction factor depending on the type of fitting.

is the velocity in m/sec through the fitting

is the accleration due to gravity in m/sec2

The k value for different fittings shall be taken from the design guide
TCE-M6-ME-613-212 for "Calculation of Hydraulic Losses for Water
in Pipes, Fittings and Valves."
5.0

DETERMINATION OF PIPE WALL THICKNESS

The wall thickness of steel pipe is governed by the following design
criteria :

5.1

UNDERGROUND PIPING

5.1.1

Wall thickness shall be such that under worst combination of external

loads, where internal pressure is atmospheric or sub-atmospheric, the
radial deflection of the pipe shell with or without support of
surrounding soil, is within safe prescribed limits.

5.1.2

Wall thickness shall be such that the compressive stress in the pipe
shell under external loads with the negative internal pressure is within
prescribed limit of allowable stress.Allowable deflection for various
lining and coating system that are often accepted as:
Mortar lined & coated
2% of pipe diameter
Mortar lined & flexible coated 3% of pipe diameter
Flexible lined & coated
5% of pipe diameter

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Wall thickness shall be such that the tensile stress in the pipe shell
under external loads with the internal pressure, is within prescribed
limit of allowable stress.
The allowable stress in the pipe shell shall be related to yield stress (fy)
of pipe material making due allowance for weld efficiency of the joint.
(a)

Working stress for combined bending and direct tensile stress

shall not exceed 60% of yield stress of the material making due
allowance for efficiency of welded joints.
(b)
Working stress for combined bending and direct compressive
stress shall not exceed 50% of yield stress making due
allowance for efficiency of welded joints.
The joint efficiency factor shall be selected based on the following:
Degree of Radiographic Inspection

Joint Efficiency %

Single and double welded butt joints

completely radiographed

100

Single Welded butt joints with backing

strips completely radiographed

90

Double welded butt joints without any

radiography examination.

80

Single or double butt welded joints with

spot radiography

85

For detail design engineering for underground piping, AWWA

publication No. M11 may be referred.
5.2

ABOVE GROUND PIPE LINES

The wall thickness of steel pipe is governed by the internal pressure
and external pressure.

5.2.1

Internal Pressure
The wall thickness of straight pipelines for internal pressure is found
using the following formula:
t

pd
2f

where t
=

minimum wall thickness in mm

design pressure in kg/cm2 (g) (Refer para 4.2)

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TCE.M6-ME-590-424

allowable design stress in kg/cm2

internal pipe diameter in cm

A design stress equal to 50% of the specified minimum yield strength

is adopted. Also refer para 4.2 if water hammer phenomena is
applicable.
5.2.2

External Pressure
Procedure outlined in paras UG-28, UG-29 and UG-30 of ASME
Section VIII Division 1 may be adopted for determining the wall
thickness and stiffening requirements for straight pipe under external
pressure.

5.3

GENERAL

5.3.1

AWWA C-208, Dimensions for Fabricated Steel Water Pipe Fittings

may be referred for dimensions of fabricated pipe fittings.However
adequacy of thickness of fittings like mitre shall be checked based on
the guidelines given in ANSI B 31.1-Code for Power Piping.

5.3.2

Corrosion Allowance
Internal corrosion of unlined pipes depends upon the nature of water
carried. It is preferable to design the required wall thickness of pipe as
determined by above considerations, then select linings, coatings and
cathodic protection as necessary to provide the required level of
corrosion protection. However, if measures are not made to combat
the corrosion, a minimum corrosion allowance of 1.5 mm shall be
added to the net wall thickness found as per above paras 5.1 and 5.2.

5.3.3

Minimum Wall Thickness

From handling point of view, minimum plate thickness is based on
following formula :
t

_D_ for pipe size upto 1350 mm ID

288

D+508 for pipe sizes greater than 1350 mm ID

400

wheret = Minimum plate thickness in mm

D = Internal diameter in mm
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However the requirements of minimum thickness with relevant

standards like API 5L / IS:1916 shall be checked.
6.0

SUPPORTS

6.1

UNDERGROUND PIPE LINE

Underground pipe line is laid either in trench or under embankment.
Underground pipe is generally subjected to any one or all of the
following external loads.

6.2

(a)

Fill load

(b)

Surcharged load due to concentrated wheel load or sur charged

uniform load

(c)

Load due to water in the pipe

(d)

Self load due to weight of pipe and its lining and coating.

ABOVE GROUND PIPE

Pipes are supported in various ways, depending on size, circumstances,
and economics. Pipes are normally supported on suitable concrete
saddles or RCC sleeper with insert plate or by means of ring girders.

6.2.1

Saddle Supports
The pipe shell carried on saddles can be divided into two classes :

6.2.2

(a)

Unstiffened pipe shell as shown in Fig. 1

(b)

Stiffened pipe with stiffener rings as shown in Fig. 2 a. In

water supply installations, both these methods of construction
are used, though unstiffened pipes are more common.

Unstiffened Pipe Shell

Saddle supports cause high local stresses both longitudinally and
circumferentially in unstiffened, comparatively thin-wall pipes at the
tips and edges of the supports. Stresses are dependent on the
magnitude of load or reaction at the support and the subtended angle in
degrees (B), being small for larger value of (B). The width of the
saddle does not, however, influence these stresses. In practice, the
subtended angle varies from 90 to 120.
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The pipe should be held in each saddle by a steel hold-down strap

bolted to the concrete. Secure anchorages must be provided at
intervals in multiple-span installations.
The maximum value of the localised stresses in a pipe that fits the
saddle well is given by the following formula :
fL

P loge
t2

R
t

where fL
=

the localised stress in kg/cm2

the total saddle reaction in kg.

the pipe outer radius in mm

the pipe thickness in mm

factor = 0.02 - 0.00012 (B - 90)

where B is in degrees
In addition to the above stress, pipe shell also develops flexural stress
(fb) due to beam action while spanning across saddle supports, as also
ring stress fr due to internal pressure. Thus the total stress ft in the
pipe shell will be ft = fL + fr + fb where fr represents 25% of
maximum hoop stress.
fb = bending stress = Bending moment
Section modulus
Maximum stress will, therefore, occur at the support where localised
stress and bending stress are maximum.
The stresses in the shell in the region of support can be further reduced
by welding a reinforcing pad to pipe shell, at the support as shown in
Fig. 2 b.
6.2.3

Stiffened Pipe Shell

Pipeline laid on saddles can be strengthened to span across supports
placed at greater interval than those adopted for unstiffened pipe line,
by providing stiffener rings centrally or on either side of the supports.
For configuration in Fig.2a, minimum two rings are provided, one on
each side of saddle at spacing not exceeding radius nor closer than
1.285 rt.
Where r = Internal radius of pipe & t = Thickness of pipe

6.2.4

Ring-Girder Construction
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When large diameter steel pipe is laid above ground or across ravines
or streams, rigid ring girders spaced at relatively long intervals, have
been found to be very effective supports. Typical ring girder support
detail is given in Fig. 3. The stresses developed in shell as a result of
internal pressure and gravity load due to weight of shell and water are
as follows :
(a)

Hoop stress

(b)

Stress due to beam action

(a)

Rim bending stress

For detail calculations for supports refer design guide no. TCE.M6CV-HS-G-010 - Design Guide For High Pressure Exposed Steel
Conduits.
7.0

WATER HAMMER
The problem of water hammer in a pipeline consists of containing the
pressure and dissipating the water flow energy. When the waterhammer wave loads the pipe wall, the strain in the wall increases
slightly faster than in strict proportion to stress within the elastic region
and on release of the loading, the reverse occurs. If the pressure rise in
the pipe is sufficient, the walls may be stressed into the plastic region
and experience a permanent set. The water hammer of the system shall
be worked out considering the characteristics of pumps, types and
valves used, distribution system details ,duration of valve closure etc.
The phenomenon of water hammer is extremely complex. Suitable
means like surge tank, surge damper or hydropneumatic chamber,
spring loaded check valve / zero velocity valve should be provided to
reduce the water hammer effect, if required. For further details refer
design guide for Water Hammer Analysis for Pumping Mains
TCE.M6-CV-HS-G-019.

8.0

ANCHORS
The necessity for anchors or thrust blocks arise at angle points, side
outlets, and valves and on steep slopes. When water transmission is
under internal pressure, unbalanced forces develop at these points.
These forces act in the direction bisecting the angle of bend, outwardly
causing development of stresses in pipe shell. The magnitude of the
thrust force for tees and bulk head is equal to the product of the
internal pressure and the cross sectional area of the pipe. At elbows or
bends, the resultant force is given by
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2 PA sin
2

where T

the thrust force in kg.

internal pressure kg/cm2 (g)

cross sectional areas of the pipe in sq.cm.

Angle of deflection in degrees.

The above forces are shown in Fig. 4. In addition there are also small
unbalanced forces at bends caused by the velocity of water flow within
the pipeline. In general this velocity is so low in transmission or
distribution system that its effect is negligible and the thrust force
caused by velocity is not considered.
The anchorages commonly used on pipelines are classified under
following four categories, viz.
(a)

Solid or gravity type anchor block (refer Fig 5 a).

(b)

Solid type of thrust block for above ground

pipe line(refer Fig.5b)

(b)

Open type anchor blocks (refer Fig 5c).

(c)

Frame anchors (refer Fig 5 d).

(c)

Ground anchors (refer Fig 5e).

(d)

Gravity block(full block) (refer Fig.5f)

(e)

Gravity block(half block)(refer Fig.5g)

Frame anchors are generally adopted for ring girder pipelines for
resisting unbalanced forces due to friction in expansion joints and at
supports. Anchor indicated in Fig. 5 g is used where the soil is hard or
the terrain is rocky.
Pipelines laid on slopes, particularly above ground, always have a
tendency to creep downhill. It is necessary to provide anchor blocks
placed against undisturbed earth at sufficiently frequent intervals on a
long, steep slope to reduce the weight of pipe supported at each
anchorage to a safe figure.
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SPECIALS
Various types of fixtures adopted in pipeline for ensuring proper
functioning, such as, flanges, branches, expansion joints etc. The
design aspects of some of these fixtures are given in the ensuring
paragraphs.

9.1

FLANGES
Flanges commonly used on pipelines for fixing appurtenances, such as
valves, are of slip ring type or loose rings. These flange rings are
either of unsupported construction or of supported type as illustrated in
the Figs. 6 .
The standard flanges used for fixing appurtenances are of unsupported
type, generally conforming to the requirements of IS 6392 or BS 4504
(Part I), in regard to drilling pattern, number of bolts, diameter of bolts,
thickness, PCD etc. for different pressure ratings.

Non standard flanges, where adapted, are designed for specific

pressure operating in the pipeline, meeting the requirements of
allowable stresses in the flange, bolt and gasket material, as per
relevant codes.
9.2

BRANCHES
For the purpose of dividing or combining flow in pressure pipelines,
branch assembly, such as, tees, wyes and headers are used. These
branches are often reinforced to take care of unbalanced forces
developed in the shell, due to removal of pipe shell portion at the
junction of the arms of the branch.
These branches are usually fabricated from thicker plates than those
required from hoop stress consideration. They are generally reinforced,
where required, with saddle type reinforcement.
In saddle type reinforcement, steel is added, if necessary, to make up
for the area lost in the cutting within the prescribed zone, equal to half
the diameter of opening on either side of main pipe, such that, the hoop
tension that would be taken by the metal lost in cutting would now be
taken by this reinforcement along with the spare thickness available in
the main pipe and the branch pipe, as shown in the Fig. 7.
Referring to Fig. 7, the area remo ved by the opening of the branch is
compensated by the spare area available in pipe shell and branch wall
in the figure as well as by saddle reinforcement and the welds. If
required, reinforcement pad calculation shall be carried out as per
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ASME Section-VIII, Div.1. Complicated branch-off especially on high

pressure lines require finite element analysis.
9.3

EXPANSION JOINTS
Steel pipelines when laid above ground require expansion joints at
specified intervals to absorb the effect of expansion and contraction
taking place in the metal particularly when the pipeline is empty.
Expansion joints may be located midway between the anchors if the
pipeline is laid level. On slope, the joint is usually best placed adjacent
to or on the downhill side of the anchor point. If such expansion joints
are not provided, the pipeline when it expands is likely to shift away
from its alignment and if such lateral movement is prevented by
providing anchorages, the pipe shell is likely to be subjected to heavy
stresses necessitating the thickness of pipes being considerably
increased. Cost of pipes with thick shells and bulky anchorages would
be high as compared to installation of expansion joints at required
intervals. The most common type of expansion joint used in water
mains of telescopic construction, which accommodate the expansion
and contraction movement of the pipe by suitable displacement of
inner stake, Fig. 8 gives the details of telescopic expansion joints. It is
also recommended to provide guide support after the expansion joint
with the first guide at a distance not exceeding 4 times outside
diameter of pipe.

9.4

MANHOLES
For inspection and maintenance of the pipelines sufficient number of
manholes are to be provided. The most common type in water work is
circular, having a short, flanged neck and a flat, bolted cover.
Manholes will be most useful if located close to valves in the line and
sometimes close to the low points that might need to be pumped out
for inspection or repair. Manholes shall preferably be located at a
spacing of 300 to 500 m.

10.0

PIPE JOINTS
Steel pipe lengths can be joined together in the field by many different
methods to effect rigid or flexible connections, though this type of
joints are not normally used in our office, details are enclosed for
information only:.
Bell & Spigot Lap Welded Joint
Bell & Spigot rubber Gasket Joint
Butt Welded Joints
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Butt strap joint for welding

Mechanically Coupled Joints
Flanged joint for Bolting
For details of each joint indicated above refer Fig 9
10.1

BELL & SPIGOT LAP WELDED JOINTS

The Bell and Spigot lap welded joint is widely used because of its
flexibility, ease in forming and joining, water-tightness and simplicity,
small angle changes can be made in this joint. The joint is welded on
either the inside, or outside with properly sized weld.

10.2

BELL & SPIGOT RUBBER GASKET JOINT

(a)

Formed rubber gasket joint, usually applied to large diameter

water pipe

(b)

Rolled-groove rubber gasket joint, usually applied to small

diameter water pipe

Bell and Spigot Rubber Gasket Joints simplify laying the pipe and
require no field welding. They permit flexibility, water-tightness,
lower installation costs, elimination of bell-holes, etc. Gaskets
conform to AWWA Standards. But these require anchors to prevent
opening out due to internal pressure.
10.3

BUTT-WELDED JOINTS
Butt-welded joints will develop full strength, but will require more
care in cutting and fitting up in the field if changes in alignment or
profile occur frequently. Where welded joints are used, the pipe should
be left bare a sufficient distance back from the ends to avoid damaging
the protective coating by the heat produced during welding. These
joints should be field coated after welding.

10.4

BUTT STRAP JOINT FOR WELDING

The butt strap is closure-joint used for joining ends of pipe when
adjustments are required in the field. This is used for cement lined
piping.

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MECHANICAL COUPLINGS
Mechanical couplings provide ease of installation and flexibility and
are represented by the sleeve and clamp type of coupling.

10.6

FLANGED JOINTS
Flanged joints are not generally used for field joints on large diameter
steel pipe because of their high cost and lack of flexibility. They are
advantageous, however, for special conditions, such as connections to
flanged valves, bridge crossings walls etc.

10.7

Besides above mentioned joints, Harness joints and Carnagie Shape

rubber gasket joints are also used.

11.0

TESTING OF PIPE LINES

Factory and field testing requirements of pipe lines shall be as per
AWWA M11.

12.0

PROTECTIVE COATINGS
Interior and exterior surfaces of both above ground and underground
pipes may get corroded depending on several factors. It is the duty of
the design engineer to know the principles and causes of corrosion and
adopt sufficient protective measures to combat the same.

12.1

PROTECTIVE COATINGS FOR EXTERNAL SURFACE

12.1.1

Above Ground Piping

The exterior surface of the above ground pipes is generally protected
from atmospheric corrosion by paints. Two coats of red lead primer
and one coat of an approved paint is generally suitable for average
water works conditions .However based on the site conditions like
proximity to sea etc. the application may vary and suitable protection
methods shall be adopted based on the same.

12.1.2.

Buried Piping
Many factors influence underground soil corrosion. The single most
important factor, however, which is readily measured is the resistivity
of the soil.
Coatings have long been used to inhibit the corrosion process. The
American Water Works Association presently recognises two coatings
materials - coal tar enamel and cement mortar - for steel water pipes.
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Coal tar enamel has a long and successful record of performance. It

provides high electrical resistivity, is impervious to water, is stable and
chemically inert, has good electrical strength, is easy to install, and is
reasonable in cost. Coal tar enamel is an insulating type coating that
bonds tightly to the pipe surface, depending upon its excellent physical
and chemical characteristics for its insulative protective action.
Cement mortar coatings provide protection by shielding steel from the
soil and providing a highly alkaline environment at the steel mortar
interface which tends to passivate the steel. This passivation reduces
the corrosion current flow by polarisation.
Coatings cannot usually be depended upon to provide perfect coverage
of the exterior metal surface, and therefore, corrosion can continue on
a coated pipeline at the voids or holidays on the coating. While these
coatings will always reduce the overall corrosion problem, they can
actually increase the intensity of the pitting attack at their holidays.
Cathodic protection is used to complete the corrosion protection.
Cathodic protection is the physical act of reversing the electromechanical corrosive force and stopping the destructive process which
attacks the ferrous metal at the coating holidays. Normally Cathodic
protection is recommended when the soil resistance is 2000 ohm/cc or
less, For further details refer IS:10221. In case of pipes where
Cathodic protection is provided, insulating joints are provide at the
junction where the pipe becomes above ground.
12.2

PROTECTIVE COATINGS FOR INNER SURFACE

The effectiveness of internal corrosion control provided for steel water
pipes is well established. AWWA has approved two materials - Coal
Tar Enamel (generally 500NB & above) and Cement Mortar - for
lining steel water pipe. The prime function of this lining in a pipeline
is to provide and sustain a high hydraulic flow capacity. The flow
capacity is maintained by preventing a build up of tubercles, and
providing a smooth surface inside the pipe. Lining materials applied in
accordance with AWWA standards provide a minimum HazenWilliams flow coefficient (C) of 140.

13.0

REFERENCES
The following literature can be referred if further details are require
with respect to large diameter piping:
(a)

American Society of Civil Engineers - ASCE Manuals and

Reports on engineering practice no. 79 - steel penstock.

(b)

AWWA - M11
ISSUE
R2

TCE.M6-ME-590-424

TCE CONSULTING ENGINEERS LIMITED

SECTION: WRITE-UP

DESIGN GUIDE FOR

LARGE DIAMETER STEEL PIPING

SHEET 15 OF 23

(c)

AWWA C208

(d)

TCE Design Guides:

TCE.M6-ME-613-212
TCE.M6-CV-HS-G-010
TCE.M6-CV-HS-G-019

ISSUE
R2