Piping Introduction
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Transcript of Piping Introduction
Power Plant FundamentalPiping System
Piping System - What is that?Concept - Layout DevelopmentPiping Components & their access requirement.Straight length requirements.Orientation of various tapings, components, etc.Piping Drains & VentsInsulation.Material & Sizing, PDT/VDT selection.Critical piping system consideration. Pipe Stress Analysis. Pipe Supports Special Considerations Piping Designer’s Input & Output GET-DET Training Prog.,2003-Somnath Kundu
1
Let us first Discuss about WHAT IS PIPE!
PIPING SYSTEMIt 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 SYSTEM
Now we will try to understand step by step how a piping system is
formed based on the requirements
We shall start with a plane white sheet
This is the plane white sheet we start with
Let us start drawing a simple piping system
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
Even some pipes are
of different sizes!
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 CADME software.
By this time you have already come to know that while we prepare P&IDs in CADME, we enter all the pipe lines system information in the drawing.
So the CADME 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 CADME
This is screen picture of P&ID made by CADME
If we click on any line it will show the Data embedded.
Let us look in to a simple P&ID for understanding of P&IDs.
This is part P&ID for DM water transfer system Click to see Iso
After the P&ID is ready we start the layout work.
Preferable
Not Preferable
We use PDWB 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.
Here we carryout pipe routing / layout in Virtual 3D environment.
While carrying out pipe routing we also need to consider the following
Example of Straight length requirement for Flow Orifice
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.
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
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
Pipes are also slopped towards low points.
Pipe line Vents and Drains
Let us have a look into a piping model done by PDWB
The Term PDWB stands for Piping Design Work Bench
Let us look in to a Piping Isometric Drawing
From the Piping 3D Model we create the Piping Isometric drawings.
These piping isometric drawings are used to fabricate and erect the piping at job site.
Let us look in to a PipingIsometric Drawing
From the Piping 3D Model we create the Piping Isometric drawings.
These isometric drawings are used to fabricate and erect the piping at job site.
This is part Isometric for DM water transfer system
Click to see P&ID
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 InsulationCold 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
NONote-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 (Note-2)
Check if S&L PDT matches requirement
Selected S&L PDT for Project
YES
Create new PDT for Project
NONote-2 : S&L has a standardized sets of piping materials suitable for various fluids and various service conditions, These are call - Piping Design Table (PDT). If calculated pipe thickness do not match with standard PDT, Project Specific PDT are created with PDTS software.
Find out Fluid Temp. & Pressure
Created new PDT for Project
Piping Design Table and Valve Design TableS&L has standardized sets of pipe and valves grouped based of various application.
These sets are call Piping Design Table (PDT) for pipes and fittings, and Valve Design Table (VDT) for valves.
These Tables with all their physical data are consolidated in the PLADES 2000 Database.
When we create piping 3D model by using PDWB software all Pipe and Valve data are fetched from Database and automatically inserted in the piping model based on the PDT selected.
While we select pipe or valve material for any intended service we try to select the best suited S&L PDT already available in the Database.
If in any case we can not find a suitable match we have to create a new project specific PDT or VDT.
This creation of PDT and VDT is done through PDTS software.
The created design table is reviewed and approved by authorized person.
As it is approved PLADES Database is updated, and the NEW PDT can be used in generation of piping model.
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.
PIPSYS - the analysis module of PLADES 2000
It is a very powerful and flexible, integrated stress analysis module of PLADES 2000.
We work in PIPSYS in close interaction with PDWB piping Models.
Here are some of the Screen views
Opening screen - It has a Nick name - The Blue Screen
Geometry Plot screen - It shows the model geometry
Types of Pipe SupportsIn 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
ange
r
Rig
id S
uppo
rtDynamic Support, Snubber
Rigid Support
Some Typical Pipe Support DrawingsHere is some typical Pipe support drawings showing some typical vendor supplied component numbers. (See Support Catalogues in G drive g:\snl\techdocs)
Some Special Considerations for PipingWhen 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 than 1 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.
Piping Designer’s Input & OutputINPUTS TO PIPING DESIGNER
From ProcessWhat FluidFrom Where to Where.Pressure, Temp. and Flow rate. Type of Flow control.
From ProjectWhat Project Specific
Requirements.Any existing facility or U/G work
From MechanicalEquipment Locations and terminal
parametersFrom CivilLocations of foundations and
structuresFrom C&ITypes of control and instrument
installation, tapping requirementsFrom ElectricalLocations of electrical equipment,
cable tray and bus ducts
OUTPUT OF PIPING DESIGNER
To ProcessFinal Pipe Size and Pressure classPiping system Material
To ProjectPlant Interface drawingInterface with existing facility
To MechanicalPipe layout both A/G and U/GEquipment terminal Loading
To CivilLocations of Pipe supportsPipe support loading to
foundations and structuresWall Penetrations
To C&ILocations instruments, control
valves on piping isometricsTo ElectricalPipe layouts both A/G and U/G to
match cable, duct bank routingMotor operated valve locations