piping basics 1

8/2/2019 Piping Basics 1

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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 its engineering plays a major part in overall

engineering of a Plant.

In next few pages we shall try to familiarize about pipe

and its components.

Piping FundamentalsFor Fresher Engineers


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In any plant various fluids flow through pipesfrom one end to other.

Now let us start with a plant where we see threetanks.

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

LET US BRING THE PIPES.


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We have just brought the pipes, now weneed to solve some more problems.

Pipes are all straight pieces.

We need somebranch

connections

We need some bendconnections

To solve theseproblems we need thepipe components,which are called

PIPE FITTINGS


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These are the pipe fittings,

There are various types of fittings for variouspurposes, some common types are -

Elbows/Bends, Tees/Branches,Reducers/Expanders, Couplings, Olets, etc.

Anyway, the pipes andfittings are in place, but the

ends are yet to be joined withthe Tank nozzles.

We now have to complete theend connections.

These, in piping term, we call

TERMINAL CONNECTIONS.


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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-1to other tanks.

We need some arrangement to stop theflow if needed

To control the flow in a pipe line weneed to fit a special component.

That is called - VALVE


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There are many types of valves, categorizedbased on their construction and functionality,

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

Other than valves another importantline component of pipe line is a filter,

which cleans out derbies from theflowing fluid. This is called a

STRAINER


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Here we see a more or less functional pipingsystem, with valves and strainer installed.

Let us now investigate some aspects of pipeflexibility.

If this tank nozzleexpands, whenthe tank is hot.

In such case we need to fit a flexiblepipe component at that location,

which is called an EXPANSIONJOINT


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When some fluid is flowing in a pipe we mayalso like know the parameters like, pressure,temperature, flow rate etc. of the fluid.

To know these information we need

to install INSTRUMENTS in thepipeline.


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There are various types instruments to measure variousparameters. Also there are specific criteria for installationof various pipe line instruments.

Next we shall lookinto how to

SUPPORT thepipe/and its

components.


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Here are some of the pipe supporting arrangements.There can be numerous variants. All depend onpiping designers preference and judgement.

Let us see some OTHER types of supports


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

By this time you have already come to know that while we prepare P&IDs inSPP&ID, we enter all the pipe lines system information in the drawing.

So the SPP&ID drawing is an Intelligent drawing which under its surface carries allthe information about a pipe like, Pipe size, Flowing Fluid, etc.

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


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

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


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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 minimumchange in direction.

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

equipment maintenance space.


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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 pipecomponents are to be checked and maintained, like some valves or strainerscan only be installed in horizontal position.

Specific requirements for instrument installation to be checked, liketemperature 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 tobe maintained, like for flow orifice we need to provide 15 times diameterstraight pipe length at upstream of orifice and 5 times diameter straight at downstream of orifice.

Example of Straight length requirement for Flow Orifice


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Also arrangement is kept in thepipeline so that liquid can bedrained out if required.

To achieve this a DRAINconnection 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 allowedto 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 pointof the pipeline.

Let us look

into typicalVent andDrainarrangementin a pipeline


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

This is a 3D model

of Feed water linealong with pumps

and otheraccessories


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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 its content are heated from outside, by heat tracing

element. In that case pipe along with heat tracing element are insulated toconserve the heat of the tracer. It is called Heat Tracing Insulation.


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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, CellularGlass (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 theouter surface of insulation are protected with Aluminum sheet or GI sheetcladding.

Have a look at howpipes are insulated,and general

components ofinsulation

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


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

Find outFlow volumeper second

Check VelocityAllowable per

second

Calc. flow arearequired and

Pipe size

Calc. Press.Drop for that

Pipe size

Check Press.Drop meets

Press. Budget

PipeSizeOK

YES

IncreasePipe Size

NO

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

Find out typeof Fluidflowing

Check Pipelife

Expectancy

Select suitableMaterial per

practice (Note-1)

Check Mat.Listed in

Design Code

PipeMaterial

OK

YES

See Note-1

NONote-1 : Material is selected per past experience with cost in

mind and per material listed in design code. If material isnot listed in code we may select next suitable materiallisted.

Find outFluid Temp.& Pressure

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

Select Mat.

& Diameteras above

Decide on

Corrosionallowance

Calc. Pipe

Thickness perCode

Find out

Fluid Temp.& Pressure


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In Power plant there are some piping which carries steam at high pressure andtemperature. 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 towithstand the high pressure and may be also high temperature.

As these pipes carry the main system fluid of the power plant, they are giventhe 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 tobuilt in flexibility in the high temperature pipe routing so that the expansionforce is absorbed within the piping.

Also there should be enough flexibility in these pipe routing so that high loadsare not transferred to the nozzles of Turbine or Pumps

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


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Pipe Stress Analysis

We have already seen that some of the pipes are subjected to high pressureand 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 variousloading is called Pipe Stress Analysis/Flexibility analysis.

In the process of Analysis we apply various postulated loading on the pipe andfind 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 theequipment connected to the pipe. This loading are to be within acceptablelimits of the equipment suggested by the vendors.

We also find out the pipe growth due to change in temperature and need tokeep the movement of pipe within acceptable limits.

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

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

PIPE STRESS ANALYSIS


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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 (Youngs 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 Hammerload

Any other load on the piping

Tools we use

PIPSYS - is an integrated pipe stressanalysis module of PLADES 2000

CEASER - Commercial Piping analysissoftware

There are many other commercial softwareavailable

Outputs

Stress of the pipe at various loadingconditions

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


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Types of Pipe Supports

In the beginning of this discussion wetalked about various types of pipe

supports. Here is some elaboration

There are three general types

Rigid type (no flexibility in thedirection of restrain)

Spring type (Allows pipemovement in direction ofloading)

Dynamic Support (Degree ofrestrain depends on accelerationof load)

There are two types of springsupport

Variable load type, here support

load changes as the pipe moves.

Constant load support, the loadremains constant within somerange of movement.

Constant Load Spring

Variable Spring

Rigid

Hanger

Rigid

Support

Dynamic Support,Snubber

Rigid Support

Some Special Considerations for Piping


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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 pipecarrying 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 thatthe 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 belowfreezing.

Electric Heat tracing is done by wrapping electric coil around pipe, which turns on as theambient temperature goes down. Pipes are insulated over the heat tracing coils.

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


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We have come to the End of Session.

Hope you have gathered the fundamentals

on the subject of Piping

piping basics 1

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