Design of Piping System

Piping System Design - What is that?Concept Layout DevelopmentPiping Components & their access requirement.Straight length requirements.Orientation of various tapings, components, etc.Piping Drains & VentsInsulation.Material & Sizing Critical piping system consideration. Pipe Stress Analysis.Pipe SupportsPipe Fabrication

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 Fundamentals

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-3We 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-3LET US BRING THE PIPES.

We have just brought the pipes, now we need to solve some more problems.Pipes are all straight pieces. 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.We now have to complete the end connections. These, in piping term, we call TERMINAL CONNECTIONS.

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 neededTo 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.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 its components.

Here are some of the pipe supporting arrangements. There can be numerous variants. All depend on piping designers 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 plannedWe 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 its 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&IDIf 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. 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 followingPiping 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 followingValves, 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 pipelinePipes 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 3DThis is a 3D model of Feed water line along with pumps and other accessories

INSULATION - When hot or Cold fluid flows through pipe then generally pipe is insulated Hot or Cold insulation respectively.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 InsulationPersonnel safety, so that people do not get burn injury by touching hot surface of pipe. It is called Personnel Protection InsulationCold pipes are also insulatedCold 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 InsulationWhen 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 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 categories1) 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, Stainless Steel or GI sheet cladding.Have a look at how pipes are insulated, and general components of insulation

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 PumpsThere 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 AnalysisWe 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 ANALYSISInputsGeometric layout of PipePipe supporting configurationPipe Diameter and ThicknessPressure inside PipeCold and Hot temperatures of PipeWeight of Pipe and insulationWeight of carrying FluidPipe material Property (Youngs Modulus, Thermal Expansion Coefficient) Thrust on pipe due to blowing wind.Thrust on pipe due to earthquakeLoad of Snow on pipeAny transient loading like Steam Hammer loadAny other load on the piping

Tools we usePIPSYS - is an integrated pipe stress analysis module of PLADES 2000CEASER - Commercial Piping analysis softwareThere are many other commercial software availableOutputsStress of the pipe at various loading conditionsLoad at various supports and restrains.Movement of pipe at support locationsPipe terminal point loading.

Codes and StandardsIn general Power Plant Piping have to comply stipulations of ASME ANSI B31.1In India Power cycle Piping to comply IBR code requirements.

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 typesRigid 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 supportVariable load type, here support load changes as the pipe moves.Constant load support, the load remains constant within some range of movement.

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 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.

An assembly of fittings, flanges and pipe that may be pre-fabricated. It does not include: Bolts Gaskets Valves InstrumentsSpool size is limited by transportationSPOOL

Piping Fabrication

Drawing/Documents for Pipe Work

THE MAIN PURPOSE OF A DRAWING IS TO COMMUNICATE INFORMATION IN A SIMPLE AND EXPLICIT WAYPURPOSE

STAGES OF DRAWINGS

Issued for informationIFI Issued for reviewIFR Issued for approvalIFA Issued for constructionIFC Issued for as builtIFAB

DRAWINGS/DOCUMENTS FOR PIPE WORK

Overall Plot Plan Key Plan Schematic diagrams Flow diagrams (Process or service) Isometric drawings Line identification Process and Instrumentation Diagrams (PID)

Isometric sketches (ISOS)/spool drawings Cutting Plan Field routing drawings for small bore piping General Arrangement drawings Test Packs As built drawings Process Flow Diagram (Optional)

.contd

Pipe Supports Schedule Project Specifications for Fabrication, Welding and Erection Project Quality Plan (PQP)/Quality Inspection Plans (QIPs) Material Specifications Stress Relieving Standards

OVERALL PLOT PLAN

INFORMATION ON AN OVERALL PLOT PLAN Battery limit of overall Plot of the Project Location of Project Site with reference to any other known/established facilities Plant North, actual north, wind direction. This information help in erecting the plant equipment General grade level with reference to a known level for example mean sea level

INFORMATION ON AN OVERALL PLOT PLAN Layout of various units/sections of a project indicating roads and other facilities within the site It also gives the layout of plant equipment within various units/section of Plant It also gives equipment list in various units of the Project, their elevation

KEY PLAN

INFORMATION ON A KEY PLANIn addition to the information given in Plot Plan, Key Plan gives: Plant area/classification Drawings classification for each area/block

SCHEMATIC DIAGRAM

Shows Path of flow by single lines Process equipment shown by simple figures (rectangle, circle. square etc.) Process notes includedDiagram is not to scale butRelationships between equipment, piping, process is shown

FLOW DIAGRAM

Un scaled drawing Describing the process (flow sheet) State materials to be conveyed Specify their flow rates and information like temperature, pressure etc.

ISOMETRIC DRAWINGS

The purpose of an isometric drawing is to show a three-dimensional picture in one drawing It resembles a picture without the artistic details The isometric drawing combines the floor plan and the elevation It clearly shows the details and the relationship of the pipes in a piping installation The isometric drawing follows certain rules or conventions to show three dimensions on a flat surface ISOMETRIC DRAWINGS

ORTHOGRAPHIC AND ISOMETRIC DRAWINGS

ISO Number & Revision Orientation Reference to Project Site (North). Coordinates of Key Reference Items Elevation of Piping Sections and their angle with reference to horizontal (H) and vertical (V). Pipe Supports No., type, elevation (T.O.S). Reference to other ISOs and GA drawing.INFORMATION ON AN ISOMETRIC DRAWING..contd.

MTOs Piping class and line number Test pressure Test media Line to be heat traced or not P&ID referenceINFORMATION ON AN ISOMETRIC DRAWING..contd.

Insulation requirement In line instruments & valve numbers, size, type Painting requirement Weld positions (spool b/d to mark FW&SW) Welding specifications Operating & design temperature & pressure

INFORMATION ON AN ISOMETRIC DRAWING

ISOMETRIC DRAWINGS

LINE IDENTIFICATION

Size Plant number/area Fluid piping service Material class Coating/Insulation category Line sequence number

INFORMATION ON A LINE IDENTIFICATION DIAGRAM

EXAMPLE OF AN ISOMETRIC DRAWING NUMBER74 /BZ /6 /412 /23-2Plant/AreaFluidNominal Pipe SizeISO NumberMaterial SpecificationLine Number-ASpoolNumber

PROCESS AND

INSTRUMENT DIAGRAM(P&ID)

Process diagrams can be broken down into two major categories:

process flow diagrams (PFDs) and

2. process and instrument drawings (P&IDs)sometimes called piping and instrumentation drawings.

Types of Process Diagrams

A flow diagram is a simple illustration to describe the primary flow path through a unit.

A process flow diagram provides a quick snapshot of the operating unit. Process Flow Diagrams (PFDs)

Process Flow Diagram (PFD)

Interpretation of Process Flow DiagramPrevious Figure is a PFD that shows the basic relationships and flow paths found in a process unit. It is easier to understand a simple flow diagram if it is broken down into sections: feed, preheating, the process, and the final products. This simple left-to-right approach identifywhere the process starts and where it will eventually end. The feed section includes the feed tanks, mixers, piping, and valves. Contd

In the second step, the process flow is gradually heated for processing. This section includes heat exchangers and furnaces. In the third section, the process is included.Typical examples found in the process section could include distillation columns or reactors. The process area is a complex collection of equipment that works together to produce products that will be sent to the final section.

A process and instrument drawing is more complex. The P&ID includes a graphic representation of the equipment, piping, and instrumentation. Modern process control can be clearly inserted into the drawing to provide a process technician with a complete picture of electronic and instrument systems. Process operators can look at their process and see how the engineering department has automated the unit. Pressure, temperature, flow, and level control loops are all included on the unit P&ID.

Process And Instrument Drawings (P&IDs)

Process and Instrument Diagram (P&ID)

Interpretation of P&IDsIn order to read a P&ID, one needs an understanding of the equipment, instrumentation, and technology. The next step in using a P&ID is to memorize your plants process symbol list. This information can be found on the process legend. Process and instrument drawings have a variety of elements, including flow diagrams, equipment locations, elevation plans, electrical layouts, loop diagrams, title blocks and legends, and foundation drawings. The entire P&ID provides a three-dimensional look at the various operating units in a plant.

Process Legends

INFORMATION ON P&ID Process flow direction of flow Line numbers, Their terminal points including equipment connections Identification of Field Instruments In line instruments/vendor items Simple Depiction of Control Strategy

Design/Operating parameters

SYMBOLS

For example, when two steel plates are joined together into a T shape, welding may be done on either side of the stem of the T.

The weld symbol distinguishes between the two sides of a joint by usingthe arrow and the spaces above and below the reference line. The side of the joint to which the arrow points is known as the arrow side, and its weld is made according to the instructions given below the reference line.The other side of the joint is known as the other side, and its weld is made according to the instructions given above the reference line. The below=arrow and above=other rules apply regardless of the arrow's direction.