Piping Fundamentals – For Fresher Engineers

Piping System - What is that?

Concept Layout Development

Piping Components & their access requirement.

Straight length requirements.

Orientation of various tapings, components, etc.

Piping Drains & Vents

Insulation.

Material & Sizing

Critical piping system consideration.

Pipe Stress Analysis.

Pipe Supports

Let us first Discuss about WHAT IS PIPE!

It is a Tubular item made of metal, plastic, glass etc.

meant for conveying Liquid, Gas or any thing that

flows.

It is a very important component for any industrial

plant. And it’s engineering plays a major part in overall

engineering of a Plant.

In next few pages we shall try to familiarize about pipe

and it’s components.

Piping Fundamentals – For Fresher Engineers

In any plant various fluids flow through pipes

from one end to other.

Now let us start with a plant where we see three

tanks.

Tank-1, Tank-2 and Tank-3

We have to transfer the content of Tank no. 1 to

the other two tanks.

We will need to connect pipes to transfer the

fluids from Tank-1 to Tank-2 and Tank-3

LET US BRING THE PIPES.

We have just brought the pipes, now we

need to solve some more problems.

Pipes are all straight pieces.

We need some

branch

connections

We need some bend

connections

To solve these

problems we need the

pipe components,

which are called

PIPE FITTINGS

These are the pipe fittings,

There are various types of fittings for various

purposes, some common types are -

Elbows/Bends, Tees/Branches,

Reducers/Expanders, Couplings, Olets, etc.

Anyway, the pipes and

fittings are in place, but the

ends are yet to be joined with

the Tank nozzles.

We now have to complete the

end connections.

These, in piping term, we call

TERMINAL CONNECTIONS.

These are flanged joints

This is a welded joint

So far this is a nice arrangement.

But there is no control over the flow from Tank-1

to other tanks.

We need some arrangement to stop the

flow if needed

To control the flow in a pipe line we

need to fit a special component.

That is called - VALVE

There are many types of valves, categorized

based on their construction and functionality,

Those are - Gate, Globe, Check, Butterfly, etc.

Other than valves another important

line component of pipe line is a filter,

which cleans out derbies from the

flowing fluid. This is called a

STRAINER

Here we see a more or less functional piping

system, with valves and strainer installed.

Let us now investigate some aspects of pipe

flexibility.

If this tank nozzle

expands, when

the tank is hot.

In such case we need to fit a flexible

pipe component at that location,

which is called an EXPANSION

JOINT

When some fluid is flowing in a pipe we may

also like know the parameters like, pressure,

temperature, flow rate etc. of the fluid.

To know these information we need

to install INSTRUMENTS in the

pipeline.

There are various types instruments to measure various

parameters. Also there are specific criteria for installation

of various pipe line instruments. Next we shall look

into how to

SUPPORT the

pipe/and it’s

components.

Here are some of the pipe supporting arrangements.

There can be numerous variants. All depend on

piping designer’s preference and judgement.

Let us see some OTHER types of supports

We have just completed a pipe line design.

We shall rewind and check how it is really done in practice.

First the flow scheme is planned,

1) What, 2) From what point, 3) To which point

Pipe sizes are selected, pipe material and pipe wall thickness are selected.

Types of Valves are planned

Also the types of instruments required are planned

We represent the whole thing in a drawing which is called Piping and

Instrumentation Drawing, in short P&ID. For P&ID generation we use SPP&ID

software.

By this time you have already come to know that while we prepare P&IDs in

SPP&ID, we enter all the pipe lines system information in the drawing.

So the SPP&ID drawing is an Intelligent drawing which under it’s surface carries all

the information about a pipe like, Pipe size, Flowing Fluid, etc.

Let us see a P&ID prepared in SPP&ID

This is screen picture of P&ID made by SPP&ID

If we click on any line it will show the Data embedded.

After the P&ID is ready we start the layout work.

Here we carryout pipe routing / layout in Virtual 3D environment.

Preferable

Not Preferable

We use PDS 3D software to route piping in the Plant virtual 3D space.

We call this as piping modeling or physical design.

While development of piping layout we have to consider the following

Piping from source to destination should be as short as possible with minimum

change in direction.

Should not hinder any normal passage way. Also should not encroach any

equipment maintenance space.

While carrying out pipe routing we also need to consider the following

Valves, strainers, instruments on the pipe should be easily accessible.

If needed separate ACCESS PLATFORMS to be provided to facilitate these.

Desired location and orientation of valves / instruments and other pipe

components are to be checked and maintained, like some valves or strainers

can only be installed in horizontal position.

Specific requirements for instrument installation to be checked, like

temperature gauge can not be installed in pipe which is less than 4 inch in size.

Specific requirements of STRAIGHT LENGTH of pipe for some components to

be maintained, like for flow orifice we need to provide 15 times diameter

straight pipe length at upstream of orifice and 5 times diameter straight at down

stream of orifice.

Example of Straight length requirement for Flow Orifice

Also arrangement is kept in the

pipeline so that liquid can be

drained out if required.

To achieve this a DRAIN

connection with Valve is provided

at the lowest point of the pipeline

Pipes are also slopped towards low

points.

For Pipeline which shall carry liquid, we have to make sure that all air is allowed

to vent out of the line when the line is filled with liquid.

To achieve this a VENT connection with Valve is provided at the top most point

of the pipeline.

Let us look

into typical

Vent and

Drain

arrangement

in a pipeline

Let us have a look into a piping model done by PDS 3D

This is a 3D model

of Feed water line

along with pumps

and other

accessories

INSULATION - When hot fluid flows through pipe then generally pipe is insulated.

There are two primary reasons for insulating the pipe carrying hot fluid.

Containing the heat inside the pipe. Insulation preserves the heat of the fluid. It

is called Hot Insulation

Personnel safety, so that people do not get burn injury by touching hot surface

of pipe. It is called Personnel Protection Insulation

Cold pipes are also insulated

Cold or chilled fluid carrying pipes are insulated to prevent heating of cold fluid

from outside. It is called Cold Insulation.

Some times cold pipes are insulated to prevent condensation of atmospheric

water vapor on pipe surface. It is called Anti-Sweat Insulation.

Other types of Insulation

When gas flows through pipes at high velocity, it creates noise. In such cases

pipes are insulated to reduce noise. It is called Acoustic Insulation.

Some times pipe and it’s content are heated from outside, by heat tracing

element. In that case pipe along with heat tracing element are insulated to

conserve the heat of the tracer. It is called Heat Tracing Insulation.

INSULATION MATERIAL - The insulating material should be bad conductor of heat.

There are two basic categories

1) Fibrous Material, which has large voids full of air between fibers - Cork, Glass Wool,

Mineral Wool, Organic Fibers. Note stagnant air is a bad conductor.

2) Cellular Material, which has closed void cells full or air - Calcium Silicate, Cellular

Glass (Foam Glass), Polyurethane Foam (PUF), Polystyrene (Thermocol), etc.

Some times Cast material like Cement Plaster or Plaster of Paris are also used.

INSULATION CLADDING - Insulation materials are generally soft or fragile. So the

outer surface of insulation are protected with Aluminum sheet or GI sheet

cladding.

Have a look at how

pipes are insulated,

and general

components of

insulation

Pipe Sizing Calculation - to select required pipe diameter based on velocity and pressure drop.

Find out

Flow volume

per second

Check Velocity

Allowable per

second

Calc. flow area

required and

Pipe size

Calc. Press.

Drop for that

Pipe size

Check Press.

Drop meets

Press. Budget

Pipe

Size

OK

YES

Increase

Pipe Size

NO

Pipe Material Selection - to select appropriate pipe material based on flowing fluid property.

Find out type

of Fluid

flowing

Check Pipe

life

Expectancy

Select suitable

Material per

practice (Note-1)

Check Mat.

Listed in

Design Code

Pipe

Material

OK

YES

See Note-

1

NO Note-1 : Material is selected per past experience with cost in

mind and per material listed in design code. If material is

not listed in code we may select next suitable material

listed.

Find out

Fluid Temp.

& Pressure

Pipe Thickness Selection - to select appropriate pipe thickness based on flowing fluid property.

Select Mat.

& Diameter

as above

Decide on

Corrosion

allowance

Calc. Pipe

Thickness per

Code

Find out

Fluid Temp.

& Pressure

In Power plant there are some piping which carries steam at high pressure and

temperature. And also there are piping which carries water at High pressure.

These pipes carries the main cycle steam and water of the steam power plant.

These pipelines are call the CRITICAL PIPING.

Very special care are taken for design of these piping.

First the pipe material selection for such piping is very important as it has to

withstand the high pressure and may be also high temperature.

As these pipes carry the main system fluid of the power plant, they are given

the right of way, and routed at beginning of the overall plant layout.

Steam pipes run at very high temperature and the hot pipes expand. We have to

built in flexibility in the high temperature pipe routing so that the expansion

force is absorbed within the piping.

Also there should be enough flexibility in these pipe routing so that high loads

are not transferred to the nozzles of Turbine or Pumps

There are many recognized international codes which lay down guide lines and

mandatory requirements for design of such piping.

The most important codes used by power plant piping engineers are

ASME ANSI B31.1- Power Piping Code & IBR - the Indian Boiler Regulation

Pipe Stress Analysis

We have already seen that some of the pipes are subjected to high pressure

and high temperature. Also pipes carry the load of the flowing fluid.

We need to check and confirm the pipe is not going to fail with these loading.

This process of checking the stress developed in the piping due to various

loading is called Pipe Stress Analysis/Flexibility analysis.

In the process of Analysis we apply various postulated loading on the pipe and

find out the stress resulted from these loading.

Then we check with governing codes if those stresses generated are

acceptable or not.

We check support load & movement for various loading condition.

We also check out the terminal point loading generated from pipe to the

equipment connected to the pipe. This loading are to be within acceptable

limits of the equipment suggested by the vendors.

We also find out the pipe growth due to change in temperature and need to

keep the movement of pipe within acceptable limits.

Pipe Stress Analysis is an Interactive and Iterative process. Each step is

checked

If a check fails we have to go back, modify the layout and restart the analysis.

PIPE STRESS ANALYSIS

Inputs

Geometric layout of Pipe

Pipe supporting configuration

Pipe Diameter and Thickness

Pressure inside Pipe

Cold and Hot temperatures of Pipe

Weight of Pipe and insulation

Weight of carrying Fluid

Pipe material Property (Young’s Modulus,

Thermal Expansion Coefficient)

Thrust on pipe due to blowing wind.

Thrust on pipe due to earthquake

Load of Snow on pipe

Any transient loading like Steam Hammer

load

Any other load on the piping

Tools we use

PIPSYS - is an integrated pipe stress

analysis module of PLADES 2000

CEASER - Commercial Piping analysis

software

There are many other commercial software

available

Outputs

Stress of the pipe at various loading

conditions

Load at various supports and restrains.

Movement of pipe at support locations

Pipe terminal point loading.

Codes and Standards

In general Power Plant Piping have to

comply stipulations of ASME ANSI B31.1

In India Power cycle Piping to comply IBR

code requirements.

Types of Pipe Supports

In the beginning of this discussion we

talked about various types of pipe

supports. Here is some elaboration

There are three general types

Rigid type (no flexibility in the

direction of restrain)

Spring type (Allows pipe

movement in direction of

loading)

Dynamic Support (Degree of

restrain depends on acceleration

of load)

There are two types of spring

support

Variable load type, here support

load changes as the pipe moves.

Constant load support, the load

remains constant within some

range of movement.

Constant Load Spring

Variable Spring

Rig

id H

an

ge

r

Rig

id S

up

po

rt

Dynamic Support,

Snubber

Rigid Support

Some Special Considerations for Piping

When pipes are routed UNDER GROUND (Buried) following points to be kept in mind:

Minimum pipe size to be routed under ground shall be not less than1 inch.

Avoid flange joint in U/G piping.

Keep in mind if pipe leaks U/G, it will be difficult to detect, so avoid U/G routing of pipe

carrying hazardous fluid.

Pipe to be laid below Frost Zone at areas where ambient temperature goes below freezing.

U/G, Buried piping should be properly protected from corrosion.

Pipe may be properly wrapped and coated to prevent corrosion.

Or U/G piping be protected by using Cathodic protection.

Freeze Protection of outdoor Piping:

In the areas where the ambient temperature goes below freezing there is a possibility that

the liquid content of pipe may freeze while the plant is under shut down.

For similar case pipes are wrapped with heat tracing elements to maintain the content

temperature above freezing (around 4 deg. C) even when the ambient temp. is below

freezing.

Electric Heat tracing is done by wrapping electric coil around pipe, which turns on as the

ambient temperature goes down. Pipes are insulated over the heat tracing coils.

Heat tracing can also be done by winding Steam tubes around main pipes.

We have come to the End of Session.

Hope you have gathered the fundamentals

on the subject of Piping