PIPING COURSE MATERIAL

AVENIR ENGINEERING TRAINING ACADEMY

PIPING COURSE MATERIAL

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TABLE OF CONTENTS

1. INTRODUCTION TO PIPING……………………………… 03

2. PIPING SHAPES………………………………………………… 04

3. PIPING MATERIALS………………………………………….. 05

4. SELECTION OF WALL THICKNESS………………………. 08

5. FLUIDS AND PRESSURE DROP…………………………… 09

6. PIPING INSULATION…………………………………………… 10

7. METHODS OF JOINING PIPE……………………………….. 11

8. PIPE FITTINGS…………………………………………………….. 12

9. FLANGES……………………………………………………………. 14

10. VALVES ………………………………………………………………. 20

11. STRESS ANALYSIS FOR PIPING…………………………….. 24

12. SUPPORT & RESTRAINTS…………………………………… 31

13. EXPANSION LOOP……………………………………………. 34

14. EXPANSION JOINTS…………………………………………… 35

15. TEN DOS AND DON’TS………………………………………… 36

16. PIPING AND INSTRUMENT DIAGRAM………………… 37

17. PROCESS AND FLOW DIAGRAM…………………………. 41

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1. INTRODUCTION TO PIPING

Pipe is a pressure tight cylinder used to convey a fluid or to transmit a fluid pressure,

ordinarily designated pipe in applicable material specifications. Materials designated

tube or tubing in the specifications are treated as pipe when intended for pressure

service.

Piping is an assembly of piping components used to convey, distribute, mix, separate,

discharge, meter, control or snub fluid flows. Piping also includes pipe-supporting

elements but does not include support structures, such as building frames, bents,

foundations, or any equipment excluded from Code definitions.

Piping components are mechanical elements suitable for joining or assembly into

pressure-tight fluid containing piping systems. Components include pipe, tubing, fittings,

flanges, gaskets, bolting, valves and devices such as expansion joints, flexible joints,

pressure hoses, traps, strainers, in-line portions of instruments and separators.

Piping is used in industry for conveying fluids and heat transfer. Pipes are generally

hollow cylindrical in shape.

Nominal pipe size (NPS)

The Nominal Pipe Size in an ASME method of indicating the approximate method outside

diameter of the connected pipe in inches.

Pipes

• The nominal dimension of pipe is inside diameter-ID. A 2” pipe has approximately

a 2inches inside diameter.

• Outside diameter depends on the “schedule”, the thickness, of the pipe. The

schedule and actual thickness vary with the size of the pipe.

• Pipe can be defined by Nominal Pipe Size (NPS) under American standards

classifications.

• Nominal bore may be specified under British standards classification along with a

schedule (wall thickness).

• Looser tolerances compared with tubes

• Less expensive to produce than tubes.

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Tubes

• The nominal dimension of pipe is outside diameter-OD. A 2” pipe has

approximately 2 inches outside diameter.

• Inside diameter depends on the thickness of the tube. The thickness is common

described as gauge.

• Higher tolerance compared with pipes

• More expensive to produce than pipes.

The Figure Showing Relation between ID, OD and Wall Thickness

ID = OD – (2 x Wall thickness)

2. PIPING SHAPES

The shape of pipe is hollow-cylindrical. Hollow cylindrical shape leads to economic

design. Hollow square pipes are used in cases where space restriction is predominant.

The pipes used for structural application are usually hollow rectangular. The thickness

required for hollow cylindrical shape is the minimum among various shapes. As per

ASME sec I, thickness of more than one half of the internal radius is considered as a thick

cylinder.

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3. PIPING MATERIALS

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4. SELECTION OF WALL THICKNESS

Minimum wall thickness of pipe is calculated by using this formula:

tm = minimum required wall thickness, inches

P = Design pressure, psi

D = Pipe outside diameter, inches.

A = Corrosion allowance, inches

S = Allowable Stress @ Design Temperature, psi (From ASME B31.3, Table A-1)

E = Longitudinal-joint quality factor (From ASME B31.3, Table A-1B)

Y = Wall thickness correction factor (From ASME B31.3, Table 304.1.1)

Pipe Schedule & Thickness Sample Calculation

Calculate the pipe wall thickness as per ASME B31.3

Design Condition:

Design Pressure (P) = 3000 psig

Design Temp (T) = 85°C = 185 °F

Diameter of Pipe (D) = 12”

Material = API 5L Gr B Seamless

Corrosion Allowance (A) = 3mm = 0.1181099 inch

Mill Tolerance = 12.5 %

= (1- Mill Tolerance)

= (1-0.125)

= 0.875

As per ASME B 31.3,

Tensile Stress = 60Ksi = 60000Psi

Yield Stress = 35Ksi = 35000Psi

Allowable Stress

@ Design Temperature (S) = 20000 Psi

Longitudinal weld joints (E) = 1.0 for Seamless pipe.

Values of Co-efficient (Y) = 0.4 (Below 900 °F)

Att

APYSE

PDt

m

m

+=

++

=)(2

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Design Formula: tm = [PD / 2 (SE + PY)] + A

t = (3000 x 12) / 2 [(20000 x 1) + (3000 x 0.4)]

= 36000 / 42400

t = 0.849056 inch

t m = t + C

= 0.849056 + 0.1181099

= 0.96716 inch

t nom = 0.96716 / 0.875

= 1.1053 inch

t nom = 28.07462 mm (As per Design)

Minimum Thickness Required = Sch 140 (28.58 mm)

5. PRESSURE DROP

The piping can carry a single phase fluid or two phase fluid or three phase fluid. The

following fluids are conveyed by the piping,

1. Liquid

2. Gas

3. Liquid-Solid slurry

4. Gas-solid mixture

5. Liquid-gas mixture

6. Gas-Liquid-solid mixture

In a maze of piping, flow distribution plays a major role in piping design. The following

formulas are commonly used to calculate the Pressure drop and the pumping power

required for a hollow cylindrical horizontal pipe carrying a liquid.

The following formula we have been used to find out the pressure drop,

Pressure Drop ∆P (Kg/m2) = W ((fxLxV

2/ 2gd) + (Z x V

2/ 2g))

Where,

W - Mean Specific weight of the fluid (Kg/m3)

V - Mean Velocity of the fluid (m/Sec)

g - Gravitational constant (Friction factor)

f - co-efficient of friction

L - Sum of straight pipe Lengths of same size (m)

D - Bore of pipe (m)

Z - Sum of Co-efficient of fluid resistance of each fitting such as bend,

elbow, tee, reducer, valve, etc.

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Reynolds’s number

It is a dimensionless number representing the ration of inertial and viscous forces

governing a flow

Re = (103

x ρ x V x d) / µ

Where,

V - Mean Velocity of the fluid (m/Sec)

D - Bore of pipe (m)

ρ - The density of the fluid, (kg/m3)

µ - Dynamic viscosity (Centipoise)

When the Reynold’s number for a flow through closed conduit is less than 2000 the

flow is said to be LAMINAR. When the Reynold’s number exceeds 4000, the flow is

called TURBULENT. In between the values of 2000 and 4000, the flow could be either

laminar or turbulent depending upon several factors. Such as flows are called

TRANSIENT flows.

6. PIPING INSULATION

Insulation is the material, which resist the heat flow from one medium to other.

List of insulation material:

• Lightly bonded wool mattress

o Rock wool

o Slag wool

o Glass wool

• Pourable insulation

• Calcium silicate

• Insulating Bricks

• Asbestos mill board

• Asbestos rope

• Preformed pipe section

o Calcium silicate pipe section

o Mineral fiber wool pipe section

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7. METHODS OF JOINING PIPE

BUTT WELDED PIPE

Two pipes are joined by butt welding. Ends are beveled (tapered edge).

Ends are having tapered edge.

SCREWED OR THREADED CONNECTION:

Two pipes are joined by using thread. Tapered grooves are also prepared.

SOCKET WELDED CONNECTION:

Two pipes are joined by using SOCKET and then welding.

COLLAR is also used.

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8. PIPE FITTINGS

BENDS

Bends are used to change the direction of flow of fluid in pipes. Bends are usually made,

using a bending machine, from straight pipes.

ELBOWS

Elbows are made using a pressing machine or a forging machine, from a straight pipe.

Elbows are of the following types:

45° elbow, 90° elbow and 180° elbow.

Elbows of the following types are also available:

22.5 °elbow and 11.25° elbow.

REDUCER

The purpose of the reducer is to reduce the diameter of straight run of pipe.

There are about two types of reducers. They are:

• Concentric reducer

• Eccentric reducer.

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CONCENTRIC REDUCER

Concentric reducer will be having common Centre line.

Concentric reducer will be used for vertical and Pump Discharge Piping.

ECCENTRIC REDUCER

Eccentric reducer will be having offset centerline between inlet pipe and exit pipe.

Eccentric reducer will be used for horizontal and Pump Suction Piping.

For horizontal piping, flat on Bottom for maintaining the elevation in the Rack Piping.

For Pump Suction, flat on top to avoid the cavitation.

TEES

Tees are used to distribute to collect flow. Tees are of the following types: formed

tees, forged and machined tees, unequal tees and pregnant tees.

BRANCHES

Branches are similar to tees. Branches are made from straight pipes by machining

and welding.

Y-PIECES

Y-pieces are rarely used. The y are used to collect and distribute flow. The pressure

drop in a y-piece is less than that of a comparable tee.

END COVERS

End covers are of the following types: flat end cover, hemi-spherical end cover,

tori-spherical end cover, semi -ellipsoidal end cover and tori-conical end cover.

SAFETY VALVE STUBS

Safety valve stubs are used to attach safety valves to the pipes. Safety valve stubs are

designed to with stand the bending moments imposed on them by safety valve

blowing jet reaction, over and above the internal pressure load.

RADIOGRAPHIC PLUG

Radiographic plugs are used to facilitate insertion of radioactive substance for doing

radiographic test of butt weld on the pipes.

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END CONNECTIONS

The following end connections are popularly used butt welding, flanged

connection ,screwed connection, screwed and flanged connection ,socket welded

connection, slip-on type of connection, thrust block connection and mechanical type

of connection.

VALVES, FLOW MEASURING DEVICES AND INSTRUMENTS

Valves, flow measuring devices and instruments are used to stop, direct, check,

measure and control flow, temperature, pressure, level and quality of fluid in the

piping.

9. FLANGES:

A flange will be consisting of 2 flanges with gasket in between them.

FLANGE RATING AND CLASS

• Based on ASME B16.5

• Acceptable pressure/temperature combinations

• Seven classes (150, 300, 400, 600, 900,1500,2500)

• Flange strength increases with class number

• Material and design temperature combinations without pressure indicated not

acceptable

TYPES OF FLANGES

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WELD NECK FLANGE

• Weld Neck Flange This flange is designed to be joined to a piping system by butt

welding.

• It is relatively expensive because of its long neck, but is preferred for high stress

applications.

• The neck, or hub, transmits stresses to the pipe, reducing stress concentrations at

the base of the flange.

• The gradual transition of thickness from the base of the hub to the wall thickness

at the butt weld provides important reinforcement of the flange.

SLIP ON FLANGE

Slip on Weld Flange The flange is slipped over the pipe and

• Welded (usually both inside and outside) to provide strength and prevent

leakage.

• These flanges are at the low cost end of the scale, and do not require high

accuracy when cutting the pipe to length.

• They can sometimes have a boss or hub, and can be made with a bore to suit

either pipe or tube.

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LAP JOINT FLANGE

• Lap Joint Flange This is again similar to a slip-on flange, but it has a radius at the

intersection of the bore and the flange face, and no raised face, to accommodate

a lap joint stub end.

• The face on the stub end forms the gasket face of the flange.

• This type of flange is used in applications where sections of piping systems need

to be dismantled quickly and easily for inspection or replacement, because the

stub end is welded to the pipe, not the flange.

THREADED FLANGE

• Threaded Flange this is similar to a slip-on flange in outline, but the bore is

threaded, thus enabling assembly without welding.

• This obviously limits its application to relatively low pressure piping systems.

• The flange may be welded around

• The joint after assembly, but this is not considered a satisfactory method of

increasing its pressure applications.

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SOCKET-WELD FLANGE

• It is used in small diameter high pressure piping systems.

• The pipe is inserted into the socket and then welded.

BLIND FLANGE

• It has a function similar to plug or cap.

• This is used to terminate the end of piping system.

• This flange does not have a bored center or hub.

• This can be used to seal a nozzle opening in pressure vessel.

ORIFICE FLANGE

The function of orifice flange is to measure the rate of flow of commodity through

piping system.

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• They have a hole drilled to the face of flange.

• They have additional set of bolts called as jackscrews. Jack screw is used to

separate the flanges so inspection/replacement of orifice plate can be

performed.

• Orifice flange union is composed of two orifice flanges, an orifice plate, bolts,

nuts, jack screws, and two gaskets. Orifice flange is used to measure the amount

of pressure drop through the orifice plate.

• The length of pipe where orifice flanges are installed and where measurements

are recorded is known as meter run.

• The orifice plate is similar to large ring washer with handle attached.

• Orifice plate is sandwiched between the two orifice flanges.

• Valve taps are inserted into the pressure holes that allow for attachment of field

monitoring equipment so accurate measurements can be recorded.

• Orifice flanges can be either weld-neck, slip-on or threaded.

• Weld neck and threaded - 300# pound and larger ratings

• Slip-on - 300# pound rating.

FLAT FACE FLANGE

Flat face flange has flat, level connecting surface. There will be two flanges with

gasket in between them. The external or mating surface for two flanges will be flat

face.

Using a flat face flange will assure full surface contact, thereby reducing the

possibility of cracking the softer cast iron.

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RAISED FACE FLANGE

This flange face has raised surface. With shallow grooves attached into raised

surface, this flange face assures a positive grip with the gasket.

RING TYPE JOINT FLANGE

It does not use a gasket to form a seal between connecting flanges.

Instead a round metallic ring is used that rests in a deep groove cut into the flange

face.

The donut-shaped ring can be oval or octagonal in design. As the bolts are tightened,

the metal ring is compressed, creating a tight seal.

The ring and groove design actually uses internal pressures to enhance the sealing

capacity of the connecting flanges.

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GASKETS

Gaskets are used to produce a leak-free environment.

Using a gasket material softer than two adjoining flanges is an excellent way to

eliminate the possibility of a fluid escape.

Gaskets can be made of materials such as asbestos, rubber, neoprene, Teflon, lead,

or copper.

BOLTS & NUTS

Bolts obviously hold mating flanges, nozzles or valves together Pressure rating of

flange will determine the size, spacing and no of bolts required.

Flanges are designed to match the bolt circle and bolt hole dimensions of other

flanges that are of the same and bolt diameter and pressure rating.

Bolts are available in two types, machine or stud.

Machine bolts have a "head" on one end and threads on the other.

Stud bolts have threads throughout their entire length and require the use of two

nuts.

10. VALVES

A Valve is a device that controls flow of a fluid.

Valves can Control not Only the flow but also the rate, the Volume, the Pressure and the

direction of a fluid within a pipe.

STEM

Stem can be moved manually (or) to be driven hydraulically, pneumatically (or)

electrically under remote or) Automatic control (or) mechanically by weighted lever,

Spring etc.

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Valve Action Explanation

ON / OFF - Starting Flow / Stopping Flow

Regulating - Varying the rate of Flow

Checking - Permitting Flow in one direction only

Switching - Switching Flow Along different Router

Discharging - Discharging fluid from a system.

SELECTION OF VALVE

• Fluid properties

• Service

• Valve size – design

• Pressure losses/friction losses

• Temperature and pressure

• End connection Flanged Medium pressure

Butt High pressure

Socket

Threaded Commercial

END CONNECTIONS

FUNCTION OF VALVE

FLANGED WELDED SCREWED

• Low and medium

Pressure valve <500°c

• Easily dismantling repair

and replacement of parts at

site with least possible delay

• High pressure & temperature

• long service

• Dismantling then for maintenance

Purpose is frequent

• Low pressure system

for gas and water

service

ISOLATION REGULATING NON-RETURN SPECIAL PUROSE VALVE

• Gate valve

• Ball valve

• Plug valve

• Piston valve

• Butterfly valve

• Globe valve

• Needle valve

• Butterfly valve

• Piston valve

• Lift check valve

• Swing check valve

• Multi-port valve

• Float valve

• Line blind valve

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SPECIAL PURPOSE VALVE

Valves that perform duties other than the two - way isolation control and check are

called special purpose valve.

SAFETY VALVE

Automatic in action and having released the undue pressure should close down and

remain closed until such time as it is again required to perform its design function.

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VALVE SYMBOLS

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11. STRESS ANALYSIS FOR PIPING

INTRODUCTION TO STRESS - STRAIN RELATIONSHIP

STRESS: Stress of a material is the internal resistance per unit area to the

deformation caused by applied load.

STRAIN: Strain is unit deformation under applied load.

STRESS –STRAIN CURVE: It is a curve in which unit load or stress is plotted against

unit elongation, technically known as strain.

• O– A represents the stress is directly proportional to strain, and point A is known

proportional limit.

• Point B represents elastic limit beyond which the material will not return to its

original shape when unloaded but will retain a permanent deformation called

permanent set.

• Point C is called yield point and is the point at which there is an appreciable

elongation or yielding of the material without any corresponding increases of

load.

• Point D is ultimate stress or ultimate strength of material.

• Point E is the stress at failure known as rupture strength.

WHAT IS STRESS ANALYSIS?

Piping Stress analysis is a term applied to calculations, which address the static and

dynamic loading resulting from the effects of gravity, temperature changes, internal

and external pressures, changes in fluid flow rate and seismic activity. Codes and

standards establish the minimum requirements of stress analysis.

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PURPOSE OF PIPING STRESS ANALYSIS

Purpose of piping stress analysis is to ensure:

• Safety of piping and piping components

• Safety of connected equipment and supporting structure

• Piping deflections are within the limits.

ASME B31 PIPING CODES

Piping codes developed by the American Society of Mechanical Engineers:

• B31.1 Power Piping

Piping typically found in electric power generating stations, in industrial and

Institutional plants, geothermal heating systems and central and district heating

and cooling plants.

• B31.3 Process Piping

Piping typically found in petroleum refineries, chemical, pharmaceutical, textile,

semiconductor and cryogenic plants and related processing plants and terminals.

• B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other

Liquids

Piping transporting products which are predominately quid between plants and

terminals and within terminals, pumping, regulating, and metering stations

• B31.5 Refrigeration Piping

Piping for refrigerants and secondary coolants

• B31.8 Gas Transportation and Distribution Piping Systems

Piping transporting products which are predominately gas between sources and

terminals including compressor, regulating and metering stations, gas gathering

pipelines

• B31.9 Building Services Piping

Piping typically found in industrial, institutional, commercial and public buildings

and in multi-unit residences which does not require the range of sizes, pressures

and temperatures covered in B311.1

• B31.11 Slurry Transportation Piping Systems

Piping transporting aqueous slurries between plants and terminals within

terminals, pumping and regulating stations

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HOW PIPING AND COMPONENTS FAIL (MODES OF FAILURES)

There are various failure modes, which could affect a piping system. The piping

engineers can provide protection against some of these failure modes by performing

stress analysis according to piping codes.

• FAILURE BY GERNRAL YIELDING: Failure is due to excessive plastic deformation.

o Yielding at Sub Elevated temperature: Body undergoes plastic deformation

under slip action of grains

o Yielding at Elevated temperature: After slippage, material re-crystallizes and

hence yielding continues without increasing load. This phenomenon is known

as creep.

• FAILURE BY FRACTURE: Body fails without undergoing yielding.

o Brittle fracture: Occurs in brittle materials.

o Fatigue: Due to cyclic loading initially a small crack is developed which grows

after each cycle and results in sudden failure.

WHEN PIPING AND COMPONENTS FAIL (THEORIES OF FAILURE)

Various theories of failure have been proposed, their purpose being to establish the

point at which failure will occur under any type of combined loading.

The failure theories most commonly used in describing the strength of piping

systems are:

• Maximum principal stress theory

This theory states that yielding in a piping component occurs when the

magnitude of any of the three mutually perpendicular principle stresses exceeds

the yield point strength of the material.

• Maximum shear stress theory

This theory states that failure of a piping component occurs when the maximum

shear stress exceeds the shear stress at the yield point in a tensile test.

In the tensile test, at yield, S1=Sy (yield stress), S2=S3=0.So yielding in the

components occurs When,

Maximum Shear stress =τmax=S1-S2 / 2=Sy / 2

The maximum principal stress theory forms the basis for piping systems governed by

ASME B31.3.

Note: maximum or minimum normal stress is called principal stress.

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STRESS CATEGORIES

The major stress categories are primary, Secondary and peak.

• PRIMARY STRESSES:

These are developed by the imposed loading and are necessary to satisfy the

equilibrium between external and internal forces and moments of the piping

system. Primary stresses are not self-limiting.

• SECONDARY STRESSES:

These are developed by the constraint of displacements of a structure. These

displacements can be caused either by thermal expansion or by outwardly

imposed restraint and anchor point movements. Secondary stresses are

self-limiting.

• PEAK STRESSES:

Unlike loading condition of secondary stress which causes distortion, peak

stresses cause no significant distortion. Peak stresses are the highest stresses in

the region under consideration and are responsible for causing fatigue failure.

BASIC STRESSES IN PIPING:

• LONGITUDINAL STRESS

Longitudinal stress or axial stress is the normal stress acting parallel to the

longitudinal axis of the pipe.

SL = (Fa / A) + (P A i / A) + (M b C / I)

There are a total of three components that make up the longitudinal stress:

I. The stress caused by an internal force axially within the pipe

SL = Fa / A

Where:

SL = longitudinal stress (Pa)

Fa= internal axial force (N)

A = metal cross sectional area of pipe (m2)

II. The longitudinal stress due to internal pressure.

SL = P A i / A

Where:

P = design pressure (Pa)

A i = internal area of pipe (m2)

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• BENDING STRESS

Bending stress is the third component of the axial stress. Bending stress is zero at

the neutral axis of the pipe.

SL = M b C / I

Where:

M b = Bending moment (N-m)

C = distance of point of interest from neutral axis of cross section (m)

I = moment of inertia of cross section (m4)

• HOOP STRESS

This stress is mainly caused by internal pressure, the hoop stress acts in a

direction parallel to the pipe circumference – in a way such that the pipe is split

into two halves. The hoop stress varies throughout the pipe wall.

SH = P do / 2 t

Where:

SH = hoop stress due to pressure (Pa)

P = pressure force (Pa)

do = pipe outer diameter (m)

t = pipe wall thickness (m)

• RADIAL STRESS

Radial stresses which are caused by internal pressure at the pipe’s inner surface.

SR = P (ri2 – ri

2 ro

2 / r

2 ) / ( ro

2 - ri

2 )

Where:

SR = radial stress due to pressure (Pa)

ri = inner radius of pipe (m)

ro = outer radius of pipe (m)

• SHEAR STRESS

Shear stresses are applied in a direction parallel to the face of the plane of the

pipe. Shear Stresses tend to cause adjacent planes of the pipe slip against each

other.

Ssh = MT C / R

Where:

Ssh = maximum shear stress (Pa)

MR = torsion resistance of cross section (m4)

R = torsion resistance of cross section (m4)

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CLASSCIFICATION OF LOADS

• PRIMARY LOADS: These can be divided into two categories based on the

duration of loading.

o Sustained loads: These loads are expected to be present throughout the

plant operation. E.g. pressure and weight.

o Occasional loads: These loads are present at infrequent intervals during plant

operation. E.g. earthquake, wind, etc.

• EXPANSION LOADS: These are loads due to displacements of piping. e,g .thermal

expansion, seismic anchor movements, and building settlement.

REQUIRMENTS OF ASME B31.3 (PROCESS PIPING CODE)

This code governs all piping within the property limits of facilities engaged in the

processing or handling of chemical, petroleum or related products. Examples are a

chemical plant, petroleum refinery, loading terminal, natural gas processing plant,

bulk plant, compounding plant and tank farm.

The loadings required to be considered are pressure, weight (live and dead loads),

impact, wind, earthquake-induced horizontal forces, vibration discharge reactions,

thermal expansion and contraction, temperature gradients, anchor movements.

The governing equations are as follows:

• STRESSES DUE TO SUSTAINED LOADS.

SL < Sh

SL = (PD/4t) + Sb

Sh = Basic allowable stress at maximum metal temperature.

The thickness of the pipe used in calculating SL shall be the nominal thickness

minus mechanical, corrosion, and erosion allowance.

• STRESSES DUE TO OCCASIONAL LOADS.

The sum of the longitudinal loads due pressure, weight and other sustained

loads and of stresses produced by occasional loads such as earthquake or wind

shall not exceed 1.33Sh.

• STRESS RANGE DUE TO EXPANSION LOADS.

The displacement stress range SE shall not exceed SA:

SE < SA

Where,

SE = (Sb2 + 4St

2)

½

Sb = resultant bending stress, psi

= [(IiMi) 2 + (IoMo) 2] / Z

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Mi = in-plane bending moment, in.lb

Mo = out-plane bending moment, in.lb

Ii = in- plane stress intensification factor obtained from appendix of B31.3

Io = out- plane stress intensification factor obtained from appendix of B31.3

St = Torsional stress, psi

= Mt / (2Z)

Mt = Torsional moment, in.lb

SA = Allowable displacement stress range:

(Allowable stress) cold = Sc = (2 / 3) Syc ⇒ Syc = (3/2) Sc

(Allowable stress) hot = Sh = (2 / 3) Syh ⇒ Syh = (3/2) Sh

Where,

Syc = yield point stress at cold temperature

Syh = yield point stress at hot temperature

Allowable stress =Syc + Syh

=3/2 (Sc + Sh)

= 1.5 (Sc + Sh)

= 1.25(Sc + Sh) after dividing with F.O.S

Final allowable stress = [(1.25(Sc + Sh) – SL]

SA = f [(1.25(Sc + Sh) – SL]

Sc = basic allowable stress at minimum metal temperature

f = stress range reduction factor from table 302.2.5 of B31.3

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12. SUPPORTS & RESTRAINTS

SUPPORTS

Supports are provided to the piping to resist various loads. The loads can be

classified into three categories.

They are primary loads, secondary loads and occasional loads. The response of the

piping to various loads is different. The primary load is also known as sustained load.

The primary loads are due to self-weight of the piping, its contents, insulation,

refractory, inner casing, outer casing, internal pressure and external pressure. The

secondary loads are due to temperature change and relative settlement of

foundations. The occasional loads are due to wind, earth quake, water hammer,

steam hammer, safety valves blowing jet reactions, surge load, blast load and

accidental loads.

If the piping is not provided with adequate supports, it will be over-stressed and

excessively deform. Over-stressing will cause premature failure. Excessive

deformation will impair the performance of piping.

RESTRAINTS

A device which prevents resists or limits the free thermal movement of pipe

restraints can be either directional, rotational or a combination of both.

SUPPORT AND RESTRAINT SELECTION FACTORS

• Weight load

• Available attachment clearance

• Availability of structural steel

• Direction of loads and/or movement

• Design temperature

• Vertical thermal movement at supports

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ANCHOR

This is an anchor type support; it restricts the pipe’s movements in all six degrees of

freedom.

GUIDE

This is a guide type support. Even though, it allows the horizontally mounted pipe to

move vertically, it prevents the vertically and horizontally mounted pipe from any side

movements.

REST

This is a support in the vertical direction only (upwards), it represents the support

under the Flanges and valves.

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SPRING HANGERS

These are used to support a piping system that is subjected to vertical thermal

movements. Variable effort spring hangers are usually incorporated for vertical

thermal movements up to approximately 50 mm, the variation between the preset

and operating loads should be no more than 25% of the operating load. Constant

effort spring hangers are usually incorporated for vertical thermal movements in

excess of 50mm.

• Variable Load Hanger is special type of hanger, which accommodate the vertical

thermal movements, while carrying the vertical load. Usually variable load

hangers are made of helical springs. The load varies from cold condition to hot

condition.

• Constant Load Hanger is a special type of hanger, similar to the variable load

hanger. There are several types of constant load hangers. The load variation in

the constant load hanger from cold to hot is limited to 0 %.

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13. EXPANSION LOOPS

Loops provide the necessary leg op piping in a perpendicular direction to absorb the

thermal expansion. They are safer when compare with expansion joints but take

more space. Expansion loops may be symmetrical or non-symmetrical. Symmetrical

loops are advantageous to use because leg is used efficiently to absorb an equal

amount of expansion from both directions.

GUIDELINES FOR LOOP SIZING

1. The Expansion loop is usually located on the side of the hottest line.

2. The Expansion loop, as a rule, should be located in the center of the distance

between two anchors.

3. The height of the expansion loop is normally twice the width.

The formula for calculating thermal expansion:

ΔL = C x L x (Tf - Tg) x 12in./ ft.

Where,

Coefficient of thermal expansion (C):

Steel (C) = 6.5 x 10-6 in./ in.°F

Copper (C) = 9.2 x 10-6 in./ in.°F

Distance between fixed points (L) in feet.

Temperature of fluid (Tf)

Temperature of ground (Tg)

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14. EXPANSION JOINTS:

This is used to control thermal expansion of a pipeline. Bellow joints are tubular

metal conduits with thin walled toriodal convolutes, which greatly reduce the axial

stiffness of the conduit.

Bellows are intended to control the pipe stresses and strains caused by the natural

thermal expansion of material as it changes from ambient temperature to steady

state temperature during start up and in reverse direction during shut down. Pipe

axial stresses and strains are controlled by bellows. The change in bellow length is

met with relatively little existing force because of the inherent flexibility of toroidal

convolutes. The flexibility is expressed as a spring constant over the applicable range

of axial compression for the specific bellow configuration.

Bellows can absorb very limited amount of lateral bending. A Bellow joint does not

have the capability to absorb torsional strains, rotations about the pipe axis in the

plane of pipe cross section.

Types of bellow type expansion joints:

• Simple Expansion Joint.

• Universal Expansion Joint.

• Pressure Balanced Expansion Joint.

• Hinged Expansion Joint.

• Gimbal Expansion Joint.

FLANGE LEAKAGE TEST

The flange leakage test is conducted in piping stress analysis. The flange leakage test

is performed by using various parameters

• Inadequate pressure rating

• Poor gasket selection

• Insufficient bolt loading

• Temperature gradient

• Bolt stress relaxation

• Piping forces and moments.

Equivalent pressure can be calculated using this formula:

Peq = (4Fx/ΠG2) + (192Mz/ΠG

3)

P eq = Equivalent pressure due to pipe loading,

F x = Axial force acting on flange

Mz = bending moment acting at flange

G = Diameter of gasket load reaction

Peq + PDesign = PTOTAL

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15. TEN DOS

The following leads to a good engineering practice.

• Use minimum number of supports.

• Limit the use of flexible supports.

• Provide supports near the already provided columns and beams.

• Provide necessary clearance for thermal movement.

• Consider all the primary, secondary and occasional loads in the design.

• Provide access for valves and fittings.

• Provide additional loops to satisfy flexible requirements.

• Provide guides to resist occasional loads like wind and earth quake.

• Provide an ergonomically acceptable design.

• Provide supports for vents, drains, start up vents and silencers.

TEN DON'TS

• Avoid the following in design.

• Avoid too many anchors

• Avoid too long a span

• Avoid too thin a pipe

• Avoid large local stresses

• Avoid too many fittings

• Avoid too many flexible supports

• Avoid supports on horizontal bends

• Avoid supports on pipes inclined to vertical

• Avoid bunching of too many pipes

• Avoid large vertical or horizontal loops.

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16. PIPING AND INSTRUMENT DIAGRAM

The design of piping involves preparation of the Piping and Instrumentation Diagram (P

& ID). The P & ID is prepared by the process designer, in consultation with Controls and

Instrumentation engineer. For a given process two different designers can prepare two

different P & ID. The P & ID is a single line diagram.

The P & ID indicates the following

• Location of equipment

• Tag numbers of equipment

• Tag number of lines

• Tag number of valves

• Tag number of instruments

• Tag number of motors

• Location of vents and drains

• Type of valves

• Type of Instruments

• Purpose of Instruments

• Output signal from instruments

• Flow measuring devices

• Level Indicating devices

• Equipment interfaces

• Scope of suppliers

The intelligent P & ID used in process industry indicates the complete particulars of

different components and piping. A Piping and Instrumentation Diagram – P & ID, is a

schematic illustration of functional relationship of piping, instrumentation and system

equipment components P & ID shows all of piping including the physical sequence of

branches, reducers, valves, equipment, instrumentation and control interlocks.

The P&ID are used to operate the process system.

A P & ID should include: Instrumentation and designations

• Mechanical equipment with names and numbers

• All valves and their identifications

• Process piping, sizes and identification

• Miscellaneous – vents, drains, special fittings, sampling lines,

reducers, increasers and swages

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• Permanent start-up and flush lines

• Flow directions

• Interconnections references

• Control inputs and outputs, interlocks

• Interfaces for class changes

• Seismic category

• Quality level

• Annunciation inputs

• Computer control system input

• Vendor and contractor interfaces

• Identification of components and subsystems delivered by others

• Intended physical sequence of the equipment

A P&ID should not include:

• Instrument root valves

• Control relays

• Manual switches

• Equipment rating or capacity

• Primary instrument tubing and valves

• Pressure temperature and flow data

• Elbow, tees and similar standard fittings

• Extensive explanatory notes

The P & I diagram (Engineering Line Diagram) allows the design to progress from the

“Process Flow Sheet / System and Piping diagram” to the final system design and

installation stage. The P & ID are definitive and comprehensive diagrams showing all of

the equipment, piping, valves and instrumentation. All items to be identified using

standard numbering systems. This normally entails having a unique plant item number

for each item of equipment, valve, instrument and line. Ideally the line number should

include a size, material and fluid contents identifier to enable the anyone reading the

drawing to obtain this information without having to refer to other documents.

An Engineering line should include

• Mechanical equipment with names and numbers

• Instruments with identification and necessary interfaces with

control loops

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• Interconnecting piping, sizes and identification

• Valves with identifications

• Vents, drains, special fittings, sampling lines, reducers and

increasers

• Flow directions

• Interface tags to other ELD’s

• Control interfaces, inputs and outputs.

• Main plant interlocks.

• Identification of symbols used

• Reference list including identification of relevant PFD’s

The symbols used to be in accordance with identified standards and should clearly

indicate the type of component, the method of connection (screwed, flanged etc.) and

the status (Valves – Normally Closed, Normally Open). The method of operating

equipment items should be clearly identified (electric motor, pneumatic actuator). It is

not generally necessary to identify services and electrical supplies to the operators.

A ‘piping and instrumentation diagram / drawing (P & ID)’ is defined by the Institute of

Instrumentation and Control as follows:

A diagram which shows the interconnection of process equipment and the

instrumentation used to control the process. In the process industry, a standard set of

symbols is used to prepare drawings of processes.

The primary schematic drawing used for laying out a process control installation

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P & ID SAMPLE DRAWING

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17. PROCESS FLOW DIAGRAM

Piping design involves preparation of process flow diagram (PFD). The process flow

diagram indicates the following parameters in a single line diagram:

• Flowing fluid

• Fluid temperature

• Fluid pressure

• Fluid mass flow rate

• Direction of fluid flow

The following additional data can also be shown in the PFD:

• Pipe diameter

• Pipe thickness

• Pipe material

• Pipe design code

• Pipe material specification

• Fluid flow velocity

• Fluid properties

The PFD gives the particulars of the processes. The PFD is prepared by the process

designer. Preparation of PFD requires thorough understanding of the process. The

PFD usually indicates the Maximum Continuous Rating parameters (MCR).

The process flow diagram- PFD, a schematic illustration of the system

A Process Flow Diagram- PFD - shows the relationships between the major

components in the system. PFD also tabulate process design values for components

in different operating modes, typical minimum, normal and maximum. A PFD does

not show minor components, piping systems, piping ratings and designations.

A PFD should include

• Process piping

• Major equipment symbols, names and identification numbers

• Control, valves and valves that affect operation of the system

• Interconnection with other systems

• Major bypass and recirculation lines

• System ratings and operational values as minimum, normal and

maximum flow, temperature and pressure

• Composition of fluids

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System flow diagrams should not include

• Pipe class

• Pipe line numbers

• Minor bypass lines

• Isolation and shut off valves

• Maintenance vents and drains

• Relief and safety valve

• Code class information

• Seismic class information

The flow diagram shows all the essential parts pf the process and items of equipment in

sufficient detail to enable the analysis and calculation of the physical characteristics of

the system to be undertaken.

A process flow diagram is a diagram of a fluid flow system showing the equipment items

connected by the major process pipes and containing data on the essential process

control circuits or major process requirements. The drawing is not to scale and the

equipment items are represented by symbols. The main equipment items and flow

streams should be identified and included in tables which identify process requirements

in sufficient detail to enable production of Piping and Instrumentation Diagrams

(Engineering Line Drawings)

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PFD SAMPLE DRAWING

PIPING COURSE MATERIAL

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