Piping Design and Pipeline Engineering
Piping Design and Pipeline Engineering
The art of design and construction of piping systems and pipelines dates back to the earliest civilizations. Its progress reflects the steady evolution of cultures around the world e.g., the needs of developing agricultures, the growth of cities, the industrial revolution and the use of steam power, the discovery and use of oil, the improvements in steelmaking and welding technologies, the discovery and use of plastics, the fast growth of the chemical and thermal power industries, and the increasing need for reliable water, oil, and gas pipelines.
Pipelines are used to transport materials between equipment. These can be pipes, tubes, and hoses. Pipes come in different materials and sizes, but steel pipes are the most popular type of pipes. Fittings are components attached to the pipelines and equipments. Pipelines can be of different pipe sizes. They provide means of changing flow directions and allow branches and connections. Fittings include connectors and joints. Instruments are auxiliary equipment and tools used to measure, monitor and control parameters of piping processes. Instruments include meters and gauges, indicators and recorders, valves and actuators, and controllers. Meters and gauges are used to measure process variables like flow, temperature, and pressure etc., indicators and recorders are used to monitor process variables, valves and actuators are used to regulate the variables while controllers are used to make appropriate changes in variables for ensuring proper operating conditions and prevent health hazards.
Piping structures provide support to all the elements in a piping system and help hold them together. These include foundations, racks and sleepers, platforms, and ladders and different types of local supports and locators. Pipes need supports for rigidity, hence, hangers, clamps, saddles, and anchors etc. are used. Equipments are positioned and oriented on suitable supports such as saddles and beds. Pipe runs can be mounted on raised concrete beds on the floor known as sleepers or on pipe racks. Pipe racks are structural steel works constructed to support pipes and conduits. Anchors, roller chairs, and clamps are used to position and secure the pipes on the pipe racks.
Piping design and pipeline engineering refer to the creation and documentation of industry standard layout of pipes, equipment, instruments, and controls. Application areas are plumbing, civil, process, and transportation. Plumbing deals with piping in buildings which carry water, gas, and wastes in the industrial buildings. Here, pipes sizes are normally small and are made from materials such as copper, steel, cast iron, and plastic. Civil piping deals with large diameter underground pipes which carry water, and collect and carry wastes from the treatment plants. Steel, cast iron, and concrete are the materials used for these pipes. Industrial piping involves the transportation of fluids with pipes between containers and equipments in production facilities. Transportation piping deals with the transportation of materials with pipes over long distances. These are frequently called pipelines.
Pipes are used for connecting different processes and utility equipments contained within a production unit as well as for conveying utilities, water and fuel etc within the entire plant. It is necessary to use an assortment of piping components which, when used collectively, are called a piping system. A piping system consists of several components which can be categorized into (i) equipments, (ii) pipelines, (iii) fittings, (iv) instruments, and (v) structures. Equipment is a component which provides power, process, and stores materials. Common equipments includes pumps, tanks, vessels, heat exchangers, and towers etc. The individual components necessary to complete a piping system are (i) pipe, (ii) piping flanges and fittings, (iii) valves, (iv) bolts and gaskets (fasteners and sealing), and (v) piping special items, such as steam traps, pipe supports, and valve interlocking etc.
Applied in a normal sense, the pipe is a term used to designate a hollow, tubular body which is used to transport a commodity possessing flow characteristics such as those found in liquids, gases, vapours, fluidized solids, and fine powders. Pipe is identified by three different size categories namely (i) diameter nominal (DN), (ii) outside diameter (OD), and (iii) inside diameter (ID). It is the main component of a piping system which connects the different pieces of process and utility equipments within a process plant. Although it can be considered to be the least complex component within a piping system, it is not without its peculiarities. Pipe used are designed to one of several national / international standards.
The materials used to manufacture pipes include concrete, glass, lead, brass, copper, plastic, aluminum, cast iron, carbon steel, and alloy and stainless steels. With such a broad range of materials available, selecting one to fit a particular need can be confusing. A thorough understanding of the intended use of the pipes is necessary. Each material has limitations which can make it inappropriate for a given application. However, carbon steel is the most common material used in a piping system.
The piping components have their design function and they are to be specified, manufactured, and installed as per their function. All the piping components have their own characteristics, both positive and negative, and it is necessary to be aware of their strengths and weaknesses. Specifying them can become complex, especially for valves and piping special items. Further, the pressure-containing and non-pressure-containing components combine to form the ingredients of a piping system.
Project personnel, process technologists and engineers, senior-level designers, and the operating personnel provide input into the design of the production units. It is normally accepted that the piping design has a very high influence on the efficient design of the entire plant. Inputs from different design groups such as civil, structural, instrumentation, and electrical are to be incorporated throughout the design process. Coordination is necessary from all design groups and disciplines. Sharing detailed information in a timely manner is imperative for meeting the piping design objectives. Also, pipeline routing is to clear different equipments, obstructions from civil foundations, and structural members.
A good piping configuration is the least expensive over a long-term basis. This needs the consideration of installation cost, pressure loss effect on production, stress level concern, fatigue failure, support and anchor effects, stability, easy maintenance, parallel expansion capacity and others. The expansion loops which are normally used in cross- country pipelines are ‘L’ bends, ‘Z’ bends, conventional 90-degree elbows and ‘V’ bends.
The drawings are always considered as the language of the engineers. The machine drawings and the geometrical drawings are the basic engineering drawings. Piping engineers derive basics from these drawings to represent the pipeline routing on the drawing. There are two types of views used in the piping drawings (i) orthographic views representing plans and elevations, and (ii) perspective views which are isometric views. Fig 1 shows single-line and double-line orthographic pipeline drawings.
Fig 1 Types of pipeline drawings
Piping layout is developed in both plan view and elevation view and section / details are added for clarity wherever necessary. These drawings are called the ‘general arrangement’ (GA) of piping. For representing a three-plane piping in two dimensions of the paper, certain symbols as given in the national and international standards are followed. Orthographic symbols are available in templates which are used for speeding up the manual drafting and also in the symbol library for computer aided design (CAD).
In complex piping systems, especially within the unit / plant building where orthographic views do not show the details of design fully, pictorial view in isometric presentation is drawn for clarity. Specially printed isometric sheets are available with lines drawn vertically and at 30-degree clockwise and 30-degree counter-clockwise respectively from the horizontal axis of the paper, the use of which 3D (three dimensional) representation of the pipelines can be prepared. Fig 2 shows isometric pipeline drawings.
Fig 2 Isometric pipeline drawings
For presentation of unit piping layout, the scale adopted normally are 1:25 or 1:33.33 and 1:100 for the pipe rack. There are different sizes of drawing sheets available for the preparation of the drawings.
The purpose of drawing is to give detailed information so that the pipelines can be fabricated and erected to satisfy the process needs. Prior to making the piping drawings, the equipment layout drawings and plot plan are prepared and these drawings are used as the basis for developing the piping drawing. Sometimes, preliminary piping study is made to fix the equipment co-ordinates.
In the design and layout of a plant complex, thousands of piping drawings are needed to provide detailed information to the project personnel who carry out the construction of the plant. Piping design and layout are to meet the safety standards and codes, statutory standards, the specifications, budget, and start-up date. There are three categories of piping drawings namely (i) design drawings, (ii) plant site drawings, and (iii) as built drawings.
Design drawings are made during the initial stages of the project and used for all initial activities including contract bidding. These drawings are subject to revision with the progress of the project. Plant site drawings are prepared during the detailed engineering of the project. These drawings take into account on-site issues and are detailed drawings used for ordering the pipeline components and installation of the pipeline. The as-built drawings are made after the pipeline installation is complete. These drawings represent installed pipeline system and is used by the operating personnel as reference drawings.
Piping GA drawing is normally drawn on A0 size sheet. If the area to be covered is small, then A1 size sheet can also be used. A ‘key plan’ is first prepared. The key plan is a plot plan on a small scale (1:500, 1:750 or 1:1000 or smaller), which can be accommodated above the title block, dividing the total area into smaller areas which are covered in all the piping drawings. For identifying the relative location of the area covered in the plan the area covered in that particular drawing is hatched or shaded.
The dimensional details of the title block are developed based on the project requirement. The drawing sheet is divided along the length and the breadth in equal spaces and marked along the boundary. The longitudinal blocks are identified by alphabets and those along the breadth numerically. These co-ordinates are used to locate the area on the drawing which the reviewer or a discussion team wants to draw attention to. The direction of the north is taken either towards the right or left on the top of the drawing sheet. This direction is kept constant in all the areas covered in the plant, so also is the scale of the drawing.
Piping diagrams and drawings – Diagrams and drawings are graphic models of objects. Diagrams are refined sketches which are created without scale. However, good proportion is encouraged in diagrams since it improves aesthetics. Drawings are made to scale and hence bear direct relationship to the physical size and spatial orientation of the object represented. There are five types of piping diagrams which are normally used. These are (i) schematic or block flow diagrams (BFD), (ii) process flow diagrams (PFD), (iii) piping (process) and instrumentation diagram (P&ID), (iv) piping isometric diagram, and (iv) piping spool diagram.
BFDs are simplified models of piping systems created at the initial stages of the design process. PFDs are made with piping symbols which represent main equipment, instruments, and fittings. Lines are used to represent pipes. PFDs are elaborations of schematic diagrams. Both plan and elevation views of the facility can be drawn. They provide non-technical personnel the basic information for understanding complex systems. P&IDs are more detail versions of PFDs and include all equipment, lines, fittings, and instrumentations. Flow parameters like flow rates, pressure, and temperatures are indicated on these diagrams.
Piping isometric is a pseudo-3D diagram of a single pipe run. All fittings and attachments on the pipe are shown. Spool drawings are detail section drawings of pipes and fittings used by pipe fitters and welders during construction. A spool diagram is a sub-section of a piping isometric drawing which can be assembled in a shop and shipped to the plant site. Sometimes piping spool and isometric diagrams are drawn to scale.
Piping drawings are scaled graphic representations of piping systems and devices. They include plans (top views), elevations (frontal or profile views) and sections (internal frontal or profile views). Piping drawings can be very complex sometimes as they show all equipment, fittings, instrumentations, dimensions and notes. Data for piping drawings are derived from PFDs, structural, mechanical, instrumentation drawings, and catalogues / manuals of the suppliers. Piping drawings include (i) plot or site plan, (ii) unit plan, (iii) zone plan, (iv) equipment drawings, (v) equipment layout drawings, (vi) piping plans and elevations, and (vii) 3D (three dimensional) plant model.
3D models are constructed at full-size. 3D plant representations can be a plain model or a rendered model. 3D plain models represent objects, as they appear in reality at full-size but in vector format. They provide accurate locations, dimensions, and elevations for equipment, pipes, and instrumentations etc. They hence provide a data base for all components in the piping system. 3D rendered models are derived from the plain models by applying colours, texture, shading, and special effects. They give more realistic appearances to plain 3D models. Rendered models are normally raster objects. As the power of the computer continues to grow, 3D model modelling is becoming the vogue because of their realism.
Plant utilities – A piping facility is designed for the purpose of making a product or group of related products. The equipment and piping layout is hence unique to each facility. The substance fed into the equipment is called a feed-stock or feed. The piping layout consists of two systems namely (i) the product pipelines, and (ii) the utility pipelines. The product pipelines consist of the piping which convey the feed-stock(s) through the facility to the finished station(s). The utility pipelines consist of the piping which are used to provide utilities for the plant.
Plant utilities provide services which are necessary for the efficient operation of the production units. The requirement of utilities is specific to the process and varies depending on the process. Some important plant utilities are water, gases, steam, condensates, fuel oil, air, drains, and flares. Plant utility piping is designed along with product piping. Colours are used to identify different utilities.
Water utilities include process water, cooling water, demineralized water, soft water, drinking water, fire-fighting water, and emergency water etc. These types of waters have their separate pipelines normally forming a closed circulating system. Process water is used as input to the process. Cooling water is used to cool equipments, heat exchangers, and condenser and passed through a cooling tower for the reuse of the water. Demineralized water is used in all steam producing equipments such as boilers, heaters and reactors. Emergency water is provided for the safety of the employees and made available in eye and shower stations. It can be used for eye wash or emergency shower to treat chemical sprays or hazardous fumes.
Steam is a vapour which is used to heat buildings during cold months, generate electricity, power turbines, clean parts and equipment, and used as feed for tracing. Super-heated steam, also known as stripping steam, is used in fractionating tower for improving the process effectiveness. Steam pipes are insulated.
Condensate is condensed vapour removed from steam by means of traps at low points and dead ends of steam headers. It is piped back and converted into steam for reuse. Heaters and boilers use fuel oil and fuel gas in process plants. Fuel oil pipes are insulated and steam traced to keep the fuel oil warm and flowing in cold climates.
Air utilities are of two types namely (i) plant air, and (ii) instrument air. Plant air is compressed air used to power pneumatic tools and equipment. It is also used for cleaning. Instrument air is dried compressed air used to operate pneumatic instruments. Instrument air pipes are galvanized to keep rust particles from reaching instruments.
Drain utility is an underground non-pressurized system. It collects drains from funnels and catch basins and transports them to a disposal point. The pipes normally have a slope of 1 metre per 100 metres. There can be more than one drain system in a plant. Separate drains can be provided for oily water sewer, acid sewer, and storm water sewer etc.
Flare utility is used to burn off waste gases and vapours at flare stacks. It collects gas fumes at start-ups and those released from pressure safety valves and pipes them to the flare stacks, placed at least 60 metres from the nearest process equipment.
Pressure classes – Pipe class is a document which specifies the type of the components such as a type of pipe, schedule, material, flange ratings, branch types, valve types and valve trim material, gasket, and all the other components specific requirements to be used for different fluids under different operating conditions in a plant. Pipe class is developed considering operating pressure, operating temperature, and corrosive environment. Piping specifications are technical documents which are generated by organizations for addressing additional requirements applicable to a specific product or application. These specifications provide specific / additional requirements for the materials, components, or services which are beyond requirements specified in standards and codes.
Piping systems, devices, and components are designed for specific pressure classes. Pipes, fittings, and valves are designed or selected to meet certain pressure loads. A pressure class indicates approximately the pressure resisting capacity of a component or device. Operating conditions (pressure, temperature, flow rate, etc) influence ratings. Normally, the mechanical strength of materials decreases with increasing temperature, so the operating pressures are determined by the operating temperatures. Hence devices and components of high-pressure rating at ambient temperature can be used for lower pressures at higher temperatures. When pressure load is specified on the basis of operating temperature, it is called pressure rating. In metric system, ‘pressure number’ or ‘PN’ is used to identify pressure classes which are expressed in bar (1 bar = 0.1 MPa). The ‘PN’ is equivalent to the working pressure (WP) for the class at ambient temperature. Pressure classes allow for the standardization of equipment, valves, flanges, and component dimensions etc.
Design and layout – The design of all systems is to be as per the latest edition of the applicable standards and codes. Design conditions are to be as per applicable standards except where the requirements are more stringent than specified in the standards. The numbering systems for piping, piping items and valves are to be as per the specification of the organization.
Ergonomic consideration which are to be taken in design are (i) tools, valves and control devices, including emergency controls devices are accessible, and (ii) there is provision for cleaning, maintenance, and repair. Requirements related to safety and working environment are to conform to the norm as per the specification of the organization. Potential source of hazard (e.g., flange joints) are located inside hazardous areas as defined in the ‘area classification’ of the standards. Where applicable, provision is to be made to protect pipes and equipment from falling objects.
All pipes are arranged to provide specified headroom and clearances for technical safety, easy operation, inspection, maintenance, and dismantling. Particular attention is addressed to clearances needed for the removal of pump, compressor, and turbine casings and shafts, drives for pumps and fans, exchanger bundles, pistons for compressors and engines etc. Piping is kept clear of manholes, access openings, inspection points, hatches, davits, overhead cranes, runway beams, clearance areas for instrument removal, tower dropout areas, access ways and emergency escape routes. A vertical clearance of 40 mm is desired between bottom of skid and deck / floor to facilitate cleaning / maintenance. Pipe, fittings, valve controls, access panels or other equipment are not to extend into the escape areas.
All pipes are routed so as to provide a simple, neat, and economical layout, allowing for easy support and adequate flexibility. Pipes are arranged on horizontal racks at specific elevations. When changing direction (from longitudinal to transverse or vice versa) the pipes are to change elevation, but care is to be taken to avoid pockets. No pipes are to be located inside instrument, electrical or tele-communication control / switchgear rooms, except fire-fighting pipes serving these rooms. Bridge pipes are to be designed with expansion loops capable of handling relative movement of platforms in design storm conditions.
Cold pipes and hot pipes are grouped separately with hot, non-insulated, pipelines at a higher elevation than cold pipelines. Uninsulated pipelines with possibility for ice build-up, are not to run above walk ways. When expansion loops are needed, pipelines are grouped together and located on the outside of the rack. Small pipes are grouped together to simplify support design.
Locating small pipes between large pipes is to be avoided especially when the large pipelines are hot. Heaviest pipelines are located furthest from the centre of the rack.
Sloping pipes, such as flare headers and drain lines, are located together and the routing is established at an early stage in the design period to prevent difficulties which can occur if other process and utility pipelines are routed first. Utility headers for water, steam, and air etc. are to be arranged on the top of multi-tiered pipe racks.
Valves – All valves needing operation during normal or emergency conditions are to be accessible from a deck or platform. Isolation valves are preferably to be accessible from deck or platform. However, if this is not possible, valves are to be positioned such that access from temporary facilities is achieved. Fire-fighting water ring main isolation valves always are to be accessible from deck or platform.
Pressure relief devices (relief valves, and rupture discs etc.) are to be accessible and installed for easy removal from deck or permanent platform. Relief valves are installed with the stem in the vertical position. Other valves can be tilted, as long as the stem is above horizontal position. When emergency shut down (ESD) valves are installed as isolation valves, they are located as close as possible to the fire-fighting / blast partition.
Check valves are installed in vertical lines provided the flow is upwards, with the exception of some type of lift checks. Draining of the down-stream side is to be provided.
Control valves are located as near as possible to the relevant equipment to which they apply and where possible along stanchions, columns, bulk heads, or tower skirts. Suitable areas where control valves are also to be located are alongside walkways, working areas, and other aisles providing no obstructions such as valve stems extended into the walkways do not occurs. Control valves operated by a local controller are located within the visual range of the controller to enable the operation of the valve to be observed while adjustments are being made on the controller. Where an increase in pipeline size is needed down-stream, the control valve is located as close to the reducer as possible.
Where size of the control valves is less than pipeline size, the reducers are placed adjacent to the valve. Spools or reducers between flanged block and control valves are made long enough to permit bolt removal. In screwed pipelines with a screwed control valve, unions are installed on each side of the control valve.
Where high pressure drop conditions exists across control valves, sonic harmonics together with extreme noise levels can be expected. Pipelines subjected to these conditions are to be carefully evaluated and designed for ensuring that its size and configuration down-stream of the valve prevents transmission of excessive vibration and noise.
Use of ‘combination’ valves are to be evaluated instead of a double block and single blinded bleed valve arrangement. Evaluation includes space requirement, risks for vibration, leak risk and life cycle cost.
Vents, drains and sample connections – Vents and drains exclusively used for hydrostatic pressure testing are to be provided if these shown on the P&IDs are not sufficient / suitable. Operational vents and drains are to be designed as per the specification of the organization. Sloped drain lines are to run to the nearest deck drain, avoiding walking areas. Open drains are to be valved and located such that discharge can be observed. Open pipe ends extend well into tundishes to avoid spillage. Supports from any fixed structure components are to be avoided. High point vents and low point drains are designed as per the specification of the organization.
Sample points – All sample point connections are to be designed as per the specification of the organization with capability to flush through test lines and containers before samples are taken. Sample points for gas are to be connected to the flare system for ensuring satisfactory flushing in advance of samples being taken. The sample connection is to be located as close as possible to the separator / scrubber outlet, and preferably directly after the first elbow on the vertical line. Points for oil samples are to be located on vertical part of pipe. Sample station is designed to minimize oil spillage.
Equipment piping – Pipes connected to equipment are designed so that any forces or moments caused by thermal expansion, dead and operating loads, do not exceed the limits specified by the specification or the manufacturer. Piping configurations at equipment are designed and supported so that equipment can be dismantled or removed without adding temporary supports or dismantling valves and piping other than removing spool pieces or reducers adjacent to equipment. Clearances are to permit installing blind flanges, or reversible spades on block valves on hazardous fluids, or high-pressure lines. Break out spools are to be as short as possible.
In the design of piping for rotating equipment provision is to be made for sufficient flexibility without the use of flexible couplings and expansion bellows. Cold springing of piping at rotating equipment is not used. Where deck level pipe supports are needed at pumps, compressors, or turbines, they are to be supported on integral extensions of the equipment support structure, and are not anchored to the equipment base-plate. This requirement applies to resilient as well as fixed supports, guides, and anchors. Provision is made for the isolation of equipment with blinds or the removal of spool pieces for pressure testing and maintenance.
Suitable supports and anchors are provided so that excessive weight and thermal stresses are not imposed on the casing of rotating equipment. Piping is to be balanced through the use of spring supports and other supports to minimize the load exerted on the main compressor gas nozzles. The same is applicable for nozzles of large centrifugal pumps.
In case of pumps, suction lines are as short as possible and designed without pockets where vapour or gas can collect. Where possible the piping is to be self-venting to the suction source. The suction line is checked for ensuring e that the ‘net positive suction head’ (NPSH) fulfils relevant pump requirements.
Eccentric reducers are used in horizontal runs. If there is a possibility for air or gas pockets, the flat side is mounted up. If this is not the case, the flat side is mounted down, in order to avoid debris and to simplify drainage. Concentric reducers are used in vertical piping.
For minimizing the unbalancing effect of liquid flow entering double suction centrifugal pumps, vertical elbows are preferred adjacent to suction flanges. If this requirement cannot be met, the elbows in piping are to be at least 5 pipe diameters upstream of the pump suction flanges with such qualifications as (i) where no reducer is used between the pump flange and the elbow, a straight run at least 5 pipe diameters long is to be provided, and (ii) where a reducer is located between the pump flange and the elbow, a straight run of at least 3 pipe diameters long, based on the larger pipe diameter, is to be provided. A reducer next to the pump flange is considered to be equivalent to 3 large diameters.
Valves in pump discharge pipelines are located as close to the pump nozzles as possible. All valves adjacent to pumps are to be accessible for hand operation without the use of chains or extension-stems. Hand-wheels and stems are not to interfere with the operational passage-ways or the removal of pumps. Suction pipes are designed to enable strainers to be easily installed or removed without springing the pipe.
In case of gas compressors, in order to get a neat layout, top and bottom entry compressors are evaluated. All gas compressors suction piping between the knock-out vessel and the compressor are arranged for preventing the possibility of trapping or collecting liquid. Pipes are to slope continuously downwards from the suction cooler to the knock-out vessel connection. Piping is to be routed so that any condensate drains back from the compressor suction to the knock-out vessel.
All compressors are provided with a temporary strainer in the suction line unless a permanent strainer is called for on the P&IDs. The strainer is to be located as close to the compressor as possible, unless the P&IDs indicate otherwise. Compressor discharge lines are to be equipped with check valves installed as close as possible to the compressor discharge nozzle.
In case of air compressors, for parallel compressor trains, with a parallel layout within the same area, utility pipe nozzles for two trains can be mirror imaged in order to get easy access to common maintenance areas. Suction line silencers, where needed, are located as close to the compressor suction connection as possible as per the instructions of the compressor manufacturer.
In case of turbines, in hazardous areas the fuel gas pipes are designed as per the specification of the organization. In non-hazardous area all connections are butt-welded except that valves and turbine connection are to be flanged inside turbine enclosure. Turbine fuel control and fuel filters are to be easily accessible. All inlet and exhaust piping / ducting for turbines are adequately supported to the approval of the equipment manufacturer. Exhausts are routed into a non-hazardous area so that they are not proved hazardous to personnel or foul air inlet.
In case of diesel engine, pipes are not run directly over diesel engines, exhaust piping, or any position where leaking fuel oil can impinge onto hot parts. The pipes are not supported by hanger type supports. The fuel oil header is not to be ‘dead ended’, for simplify cleaning / purging. Where a positive static head is needed from the day tank, the minimum operating level is to be 300 mm above inlet of the fuel injection pump. The drain pipeline from the day tank is positioned so that the outlet of the drain pipeline into the main drain is visible from the drain valve position.
In case of vessels and towers, where possible, blinds, spacers, and block valves are located directly on the vessel nozzles. Check valves are installed on the block valve at the vessel nozzle where they are not in conflict with providing the flow upwards, and draining in the down-stream side.
In case of heat transfer equipment, valves are not located directly on top of channel nozzles, to avoid obstructing the removal of channel ends. Spool pieces are provided to facilitate the pipe pulling and maintenance. Pipes are arranged to permit cooling fluid to remain in all units on loss of cooling fluid supply. Thermo-wells for inlet and outlet temperatures for each fluid service are provided and are to be located in adjacent piping when the exchanger nozzles do not permit a 90 mm immersion for the thermo-well.
In case of launcher and receiver traps, consideration is given for mechanical handling facilities for pigs and line logging devices. The facilities include (i) overhead hoists or access for fork lift truck, (ii) winching points for logging device withdrawal, (iii) storage and inflation facilities for pigs and logging devices, and (iv) cradle for inserting the pig. Vertical launchers are to be placed on the outside area on the platform and are to be open to air. Provision is made within the closure for hydraulic connections to allow the operation of a hydraulic equipment, such as maintenance pigs and hydro-plugs.
Elevation of traps are kept to a minimum. Where a sight glass is specified on the drain line, sufficient space is to be provided for observation of flow. The traps have a pressure indicator positioned so that it is visible to personnel operating the trap closures. Piping between risers and launchers and / or receivers have a bend radius as per the specifications from intelligent pig supplier. The junction between the production line and the inlet / outlet to the launcher / receiver is designed to prevent pigs from entering the production line. The launcher / receiver is sloped towards the trap closure, and a spillage retention tray provided with drain, is to be installed. The retention tray for the receiver is sized as per the length and volume.
A minimum of 2 metre straight run is arranged between the sphere or bar tee and the pipeline ESD valve in order to accommodate for installation of an inflatable welding sphere. This is to provide double isolation against the pipeline if repair of the isolation valves to the pig trap or isolation valves to the process area is necessary. This is applicable to piping, where non flexible risers are used.
In case of well-head area piping and valves, preference is given to the use of extruded branches in the design of piping manifolds. On fabricated manifolds the terminus of the manifold runs is to be blind flanged or hubbed for simplifying cleaning and inspection.
Production manifolds are designed for solid (scale) removal where this can be a problem. Consideration is given to any change of direction in the flow-lines where the product contains particles at high velocities which erodes the fittings, e.g., target, tees, and bends. An erosion pipe spool around 2 metres in length is considered for installation immediately down-stream of each choke valve for corrosion / erosion monitoring. If the spool length between the choke valve and the shut off valve on the manifold is sufficiently short, it can be considered as an erosion spool.
Additional requirements related to piping systems – Air piping have self-draining provision at all low points for the collection of condensates. Air traps are provided with isolation valves, balance lines and drains to local collection points. Instrument air headers and manifolds are not to be dead ended but supplied with blind flanges for cleaning and maintenance. All branches and take-offs are to be from the top of the headers.
Steam piping are to run to prevent pockets. Condensate is collected at low points by using a standard steam trapping system. Drain points are from the bottom of the header and steam take-offs from the top.
Utility stations are provided as needed for air, water, steam / hot water, oxygen, and nitrogen. Each station is numbered and located in the general working areas at deck level. Fresh water, sea water and plant air systems are to be equipped with hose reels. Oxygen and nitrogen stations are not located inside enclosed areas. Nitrogen hoses are installed if needed. Different types of couplings are used for air, oxygen, and nitrogen.
Piping to pressure relief valve inlet is to be as short as possible. Where relief valves discharge to atmosphere, the elevation at the top of the discharge pipeline is typically 3 metres above all adjacent equipment. This is to keep adjacent equipment outside the plume area. Discharge tail pipes have a drain hole at the low point of the pipeline. Relief valves discharging to a flare system is to be installed so as to prevent liquid being trapped on the outlet side of the valve. All relief pipelines and headers are designed to eliminate pockets, but if a relief valve is to be located at a lower elevation than the header, an automatically operated drain valve is installed at the valve outlet and piped to a collecting vessel or closed drain.
Relief valve headers slope towards the knock-out drum, taking into account anticipated deck deflection and platform tilt during operation. Pockets are to be avoided, but where a pocket is unavoidable, some approved means of continuous draining for the header is incorporated. Unless specifically noted on the P&ID, all branch connections on relief and blow-down systems are at 90-degree to the pipe run. In case, there is a special requirement for a particular branch to enter a header at 45-degree, this is to be highlighted by process engineer on P&ID.
Drains have slope as specified on the P&IDs. All the open drain branch connections are at 45-degree. Rodding points are preferably be through drain boxes and change of direction is evaluated against flushing requirements, where the total change of direction is higher than 135-degree.
Pneumatic conveying piping is designed as per the specification of the pneumatic conveying system manufacturer. Purge connections are to be easily accessible to avoid waste of time when plugs occur.
For fire / explosion protection, all project accidental load requirements are to be met. The layout of the fire-fighting water distribution system is to be carefully designed with respect to hydraulic pressure drop. Deluge nozzles branch off is located away from the bottom of the header to avoid plugging of nozzles. Location of nozzles are as specified by the safety personnel. Necessary deviations to avoid obstructions etc. are to be approved by the safety personnel. Dead end headers are avoided. Lube, seal, and hydraulic oil systems have flanges and blind flanges on header ends for pickling and hot oil flushing.
Fittings – All piping fittings are to conform to the relevant standards and codes. Branch connections to conform to the applicable ESD valve. Short radius elbows and reducing elbows are not used. Expansion bellows and flexible couplings are not used, without written approval. Where entrained sand is expected within the fluid flow, target tees or long radius bends are considered in place of elbows for changes of direction to minimize the effect of erosion, provided the total pressure loss for the system is acceptable. Where pipeline clean out facilities are needed on headers, a blind flange is provided to close the end. Where no clean out facility is needed and no future extension is expected, the pipeline is closed with a welding cap.
Line blinds – Location of line blinds are indicated on P&IDs. The provision for blinding consists of a pair of flanges, one of which can be a flanged valve (except wafer type valves) or equipment nozzle. Spectacle blinds, blinds, and spacers are used as per the specification of the organization. Provision is made for using mechanical means of lifting either by davits or block and tackle lifting points, where the weight exceeds the standards. Wherever possible, blind / spacer are located in horizontal runs.
Where pipeline blinds are installed, the piping is designed to allow enough flexibility to spring the pipeline by means of either jack screws or other jacking arrangements. On ring joint flanges, the flexibility allowance is to be sufficient to allow for the removal of the ring without overstressing the piping. If needed, a break out spool is provided for dismantling. For preventing galvanic corrosion, rubber or plastic lined insulation spools are used.
Strainers – The P&IDs indicate whether a permanent or a temporary strainer is to be used to protect equipment. The mesh size of the strainer has a free area of 250 % of the cross-sectional flow area of the pipeline in which it is installed. Easy removal and cleaning of filters is to be possible. The strainer housing is to conform to the appropriate material classification for the service in which it is installed. The housing of permanent strainers has either flanged ends or butt-welded ends. Butt-welded ends are preferred because of the weight saving, especially for the larger sizes. The installation of permanent strainers permits cleaning without dismantling the strainer housing or piping. Break out spool are to be installed in conjunction with temporary strainers.
Hoses and flexible pipes – If hoses are used, it is to be documented that they are suitable for the medium and the required pressure and temperature. Hoses with associated couplings are to be marked as per the applicable standards. Components are designed so as to avoid them being wrongly connected. Hoses are to be protected against damage from crushing / compression if their design does not withstand such loads. Flexible pipes are designed as per a recognized standard such as ISO 10420.
Instrumentation – Materials and rating for instrument connections conform to the relevant material rating classification of the parent pipeline.
Accessibility, location and orientation – Special attention is to be given, with respect to accessibility, location and orientation of valves, vents, and drains as well as block and by pass valves. Control cabinets (accumulator packages) are to be located as close as practically possible to the respective valves. Location of flow orifices is to be as per ISO 5167. For liquid services, flow orifices are not to be put on vertical pipe runs. Tapping points are to be as per the specification of the organization.
Stress analysis – Stress analysis is performed as per standards. As a general guidance, a pipeline is subject to comprehensive stress analysis if it falls into any of these categories namely (i) all pipelines with design temperature of above 180 deg C, (ii) DN 100 mm and larger at design temperature above 130 deg C, (iii) DN 400 mm and higher at design temperature above 105 deg C, (iv) all pipelines which have a design temperature below -30 deg C provided that the difference between the maximum and minimum design temperatures is above -190 deg C for all piping, -140 deg C for piping DN 100 mm and high, and -115 deg C for piping DN 400 mm and higher (these temperatures above are based on a design temperature 30 deg C above maximum operating temperature. Where this is not the case, 30 deg C is to be subtracted from values above), (v) pipelines DN 75 mm and higher with wall thickness in excess of 10 % of the OD, (vi) thin-walled pipeline of DN 500 mm and higher with wall thickness less than 1 % of the OD, (vii) all pipelines DN 75 mm and higher connected to sensitive equipment such as rotating equipment (however, lubrication oil pipelines, and cooling medium pipelines etc. for such equipment are not to be selected because of this item), (viii) all pipelines subject to vibration because of internal forces such as flow pulsation and / or slugging or external mechanical forces, (ix) all relief pipelines connected to pressure relief valves and rupture discs, (x) all blow-down pipelines DN 50 mm and higher excluding drains, (xi) all pipelines along the derrick and the flare tower, (xii) all pipelines above DN 75 mm likely to be affected by movement of connecting equipment or by structural deflection, (xiii) glass-fibre reinforced epoxy (GRE) pipelines DN 75 mm and higher, (xiv) all pipelines DN 75 mm and higher subject to steam out, (xv) long vertical pipelines (typical 20 meter and higher), (xv) other pipelines as per the decision of the stress engineer, (xvi) all production and injection manifolds with connecting piping, and (xvii) pipelines subject to external movements, such as abnormal platform deflections, bridge movements, and platform settlements etc.
The design temperature for the selection of pipelines subject to stress analysis is as stated on the P&IDs / pipe lists. Calculation of expansion stress is based on the algebraic difference between the minimum and maximum design temperature. The maximum design temperature is not to be lower than the maximum ambient temperature.
Reaction forces on supports and connected equipment can be based on the maximum algebraic difference between the installation temperature and the maximum or minimum design temperature. For uninsulated lines subject to heat of sun radiation, 60 deg C is to be used in the calculations, where this is higher than the relevant maximum design temperature.
The minimum / maximum environmental temperature is as specified by the project. Unless otherwise specified, the environmental temperatures which apply are (i) installation temperature of – 4 deg C, (ii) minimum ambient temperature of -7 deg C, and (iii) maximum ambient temperature of 25 deg C.
The design pressure for the piping system is to be as stated on the P&IDs / pipe lists. Where internal pressure below atmospheric pressure can exist, full vacuum is to be assumed for stress calculations. The effects of vibration imposed on piping systems are to be evaluated and vibration sources which can be realistically determined are to be accounted for. This also includes acoustic induced vibration.
Environmental loads such as wind, snow, and ice acting on exposed piping are to be evaluated. When affecting the integrity of the piping system, the imposed deflections or movements from the main structure is to be accounted for.
Process conditions which can result in impulse loadings, such as surge, slugging, water hammering, reaction forces from safety valves and two-phase flow, are to be included in the calculations. The effect of blast loads is to be evaluated, for piping which is needed to maintain the integrity in an explosion event.
In order to minimize the risk of leakage at valves, flanges and mechanical joints, the bending moment on these is to be evaluated. Special attention is to be given to bolt tensioning values for ensuring that sufficient gasket surface pressure is maintained at all conditions. Expansion bellows, sliding joints, ball joint and similar flexible joints are normally not to be permitted.
Cold springing of piping is normally not permitted. Where all other methods have been explored and found unacceptable, cold springing can be applied provided the location of application and the installation procedure gives a reasonable assurance that the cold springing requirements have been achieved during installation. Credit for cold springing to reduce reaction forces can only be given if it can be shown that stress relaxation or yielding do not occur in the pipeline system.
In general, the use of spring supports is to be kept to a minimum by careful consideration of support location and alternative pipe routing.
When analyzing piping connected to parallel located equipment, the relevant worst temperature combination case is to be used. Calculation of thermal nozzle loads is to be based on the maximum or minimum design temperature.
Piping connected to compressor and pump suction and discharge nozzles is to be fully force balanced through its supports in the liquid filled condition and shall exert only minimal loads on the nozzles in order to minimize equipment mis-alignment caused by external loads. Allowable loads on equipment are to be calculated as per standards. When calculating loads on compressor nozzles, the point for resolvement of forces and moments are to be agreed with the compressor supplier.
Preparation of piping GA drawing – The important points during the preparation of piping GA drawing are described here. The north arrow is placed at the top left / right hand corner of the sheet to indicate plant north. The drawing is not planned in the area above the title block of drawing, as this is allotted for general notes, number and title of reference drawings, brief description of changes during revision and the BOMs (bill of material) wherever applicable. Process equipment and piping have priority on the piping GA drawing. The piping drawing is started after fixing positions of the equipments.
In-plant piping drawings are drawn 1:25 or to 1:33.33 scale and pipe rack piping plan to 1:100 scale with junction details enlarged if necessary. Equipment layout is reproduced on the piping GA drawing to its scale and drawn on the reverse side in case of manual drafting. In case of CAD, separate layer is used for equipment layout. The major primary beams and secondary beams are also shown if area covered is indoors. Pertinent background details which govern piping routing, such as floor drains, HVAC (heating, ventilation and air conditioning) ducting, electrical and instrument cable trays, etc. are also drawn in faint on the reverse. Utility stations are also established so that the most convenient utility header routing can be carried out.
Development of piping GA drawing – The piping drawings is to be developed in such a way that all the process requirements are met with. It is not always possible for the piping drawing to follow exactly the logical arrangement of the P&IDs. Sometimes, pipes are to be routed with different junction sequence and line numbers and subsequently the list can be changed. Performance and economics have to be considered in parallel while deciding the routing.
Piping is represented by single lines up to a size of 150 mm DN and double lines for sizes 200 mm DN and above. This is to save the time of drafting and to avoid confusion. In single line representation, only the centre line of the pipeline is drawn using solid line and in the double line representation, the actual size to scale is drawn with centre line marked in chain-dotted lines.
Line numbers are shown against each line exactly in the same way as represented in the P&IDs. The change in specification is shown in line with P&ID. This change is normally indicated immediately to the downstream of the valve, flange or equipment. Valves are drawn to scale with identification number from the P&ID marked thereon. Valve hand wheels is drawn to scale with stem fully extended. If it is lever operated, then the movement of handle position is marked. If a valve is chain operated, the distance of the chain is noted from the operating floor.
The location of each instrument connection is shown with encircled instrument number taken from P&ID. Similar arrangements is shown as typical detail or covered in a separate organizational standard as ‘instrument hook-up’ drawings.
The plan view of each floor of the plant is drawn and these views are to indicate how the layout look like between floors as seen from top. Each line is identified by line number and it also shows the insulation, and tracing requirements etc. Lines, if needed, is to be broken to show the needed details of hidden lines without drawing other views. Those details which can be covered by a note are not drawn.
The plan is drawn to a larger scale for any part needing more details and is identified as ‘detail A’. The part isometric sketches or part elevations are drawn to clarify complex piping or piping hidden in the plan view. Full sections through the plant can be avoided if isometric drawings are drawn for the lines. Part sections, where needed, are shown to clear the hidden details in plan. Sections in the plan views are identified by numbers, e.g., 1-1, and 2-2, etc. and details by alphabets, e.g., ‘detail A’.
Isometric drawings – Piping isometric drawings are 3D representations of piping on two dimensions of the drawing sheet. An isometric drawing covers a complete line as per the line list connecting one piece of equipment to another. It shows all information necessary for the fabrication and erection.
Isometric drawings are not drawn to scale but are to be proportional for easy understanding. Dimensions are given relative to centre-line of piping.
Isometric drawings also include (i) plant North with the direction (Fig 3) so selected as to facilitate easy checking of GA drawing with isometric drawing, (ii) dimensions and angles, (iii) reference number of P&IDs, GA drawings, line numbers, direction of flow, insulation and tracing, (iv) equipment location and equipment identification, (v) nozzle identification on the connected equipment, (vi) details of flange on the equipment if the specification is different from the connecting piping, (vii) size and type of every valve and direction of operation, (viii) size and number of control valve, (ix) location, orientation and number of each equipment, (x) field weld, preferred in all directions to take care of site variations (it can also be covered with a general note), (xi) location of high point vents and low point drains, which is preferably covered with a standard arrangement note, (xii) any special requirement such as line to be tested prior to installation etc., (xiii) BOMs, and (xiv) requirements of stress relieving, seal welding, pickling, and coating etc.
Fig 3 Plant north with direction
Spools – When the piping is shop fabricated, the isometric drawings are developed further to create spool drawings. A spool is an assembly of fittings, flanges, and pipes which can be pre-fabricated. It does not include bolts, gaskets, valves, or instruments. A spool sheet is an orthographic drawing of a spool drawn either from piping GA drawing or from an isometric drawing sheet.
Each spool sheet shows only one type of spool and carries out four details namely (i) instructions for welder to fabricate the spool, (ii) list of the cut lengths of pipe, fittings, and flanges etc. needed to make the spool, (iii) material of construction and any special treatment of finished piping, and (iv) number of same type of spools needed.
Spool numbers are given to make the identification easy. Each isometric drawing sheet is identified with the line number it represents. Both the spool and the spool sheet can be identified by a number or letter using the isometric drawing sheet number as prefix. Straight run pipes over 6 metres are normally not included in a spool, as such lengths can be welded in the system during erection in the field. The size of a spool is limited by the available means of transport.
As a general practice, carbon steel piping 40 mm DN and below are ‘field fabricated’. All alloy steel and carbon steel spools 50 mm DN and above are normally ‘shop fabricated’. Large diameter piping, being more difficult to handle, is more economically produced in a workshop.
Dimensioning of piping drawings – Fig 4 shows dimensioning of drawings. Sufficient dimensions are given for positioning equipment and for erecting piping. Duplicating dimensions in different views are avoided, as this can lead to errors if changes are made. Horizontal dimensions are reserved for the plan view. If single pipe is to be positioned or a pipe connected to nozzle is to be indicated, then the centre line elevation is shown and is marked as ‘C’. If several pipes are sharing a common support, the elevation of the ‘bottom of pipes’ is shown and is marked as ‘BOP EL’. This is more applicable to non-insulated pipe lines. In case of several pipes on a pipe rack, the ‘top of support’ elevation is shown and is marked as ‘TOS EL’.
Fig 4 Dimensioning of piping drawings
In case of buried pipelines in a trench, the elevation of bottom of pipes is shown. In case of drains and sewers, the ‘invert elevation’ of the inside of the pipe is marked as ‘IE’. Centre lines of the equipment and pipelines are located with reference to the building column centre lines or the co-ordinates which can be considered as a reference base. The distance between the lines is dimensioned centre line to centre line. The horizontal nozzles on the equipment are located from centre to flange face in plan. For vertical nozzles ‘face of flange’ (FOF) elevation is shown.
For valves, instruments and non-standard equipment (Fig 4a), the dimensions from flange face to flange face are shown. Flanged valves are located with dimension to flange faces. Non-flanged valves are dimensioned to their centres or stems. In case of flanged joints, a small gap is shown between dimension lines to indicate gasket (Fig 4b). Flanged joints can also be shown without gasket but the same is covered with a general note and gasket thickness in the valve or equipment dimensions is included.
For ‘finished floor’ (FF), the elevation is to be the high point of the floor. For paved areas, it is to be the high point of paving (HPP). For foundation, the ‘top of grout’ (TOG) elevation is shown. The dimensions outside the drawn view are shown and the pictures are not cut. The dimension line is drawn unbroken with fine line (Fig 4c). The dimension is written just above the horizontal line. For vertical lines it is written sideways. The dimension lines can be terminated with arrow heads or oblique dashes. If series of dimensions are to be shown, they are string together (Fig 4d). The overall dimension of the string of dimensions is shown. One of the break-up dimensions is avoided to omit repetition and error during changes.
The significant dimension is not to be omitted other than fitting make up (Fig 4e). For field run piping, only those dimensions are given which are necessary to route piping clear of equipments and other obstructions. Only those items are located which are important to the process. The out of scale dimensions are underlined a or marked as ‘not to scale’ (NTS). Also, the dimensions are not to terminate at screwed or welded joints.
Checking of piping drawings – Checking of the piping drawing is done only on the print of the drawings by coloured pencils / pens. Corrected areas and dimensions are marked yellow, areas and dimensions which are to be deleted are marked green, and areas which are to be corrected / incorporated on the drawing are marked in red. The new print after correction is ‘back checked’ for incorporation.
Points to be checked on the piping drawing includes (i) title of the drawing, (ii) orientation i.e., North arrow against plot plan, (iii) inclusion of graphic scale (if drawing is to be reduced), (iv) co-ordinates of equipments against equipment layout, (v) equipment numbers and their appearance on the piping drawing, (vi) correct identification on all lines in all views, (vii) line specification changes, (viii) reference drawing numbers and files, (ix) correctness of all dimensions, (x) whether representation is correctly made in line with the standard symbols or not, (xi) location and identification of all instruments and requirements of upstream / downstream straight lengths, (xii) insulation requirements as per P&IDs, (xiii) piping arrangement against P&ID requirements such as gravity flow, and seals, etc., (xiv) possible interference, (xv) correctness of scale in case of GA drawings, (xvi) whether all stress analysis requirements are met or not, (xvii) adequacy of clearance from civil structures, electrical apparatus, and instrument consoles, (xviii) floor and wall openings, (xix) accessibility of operation and maintenance space and provision of drop out and handling areas, (xx) foundation drawings and supplier equipment requirements, (xxi) details and section identification match, (xxii) ‘match-line’ provision and accuracy, (xxiii) presence of signatures and dates, (xxiv) accuracy of BOMs in Isometrics drawings, and (xxv) number of the issue and the revision.
Piping design process – Technical design normally starts with a sketch. Sketches are quick means of capturing design ideals and or having a visual record of new ideas. They can be used to communicate design intent and also provide opportunity to understand the way people internalize visual signals. Sketches can be refined and developed into drawings. A paper and a pencil are the tools needed for sketching. Thin lines can be sketched with 0.2 mm pencil and thick lines with 0.5 mm to 0.7 mm pencils. Grid (graph) papers help to maintain good proportions when sketching, and hence good quality sketches. The grid lines guide in drawing long lines and help in maintaining parallelism and perpendicularity. A diagram is sketch not drawn to scale.
A design project normally starts with a sketch. The sketch is refined into a drawing as the design project progresses. A drawing is drawn to scale. Preliminary drawings are the products of refined sketches. Preliminary drawings are drawings not the approved drawings. They can be changed without recording changes. Further refinement transforms preliminary drawings into prototype drawings which are the approved drawings, so it is mandatory to record changes, normally in the revision block. Prototype drawings are used to build the first full-size physical model of the design model.
Piping design frequently starts with a schematic diagram which is gradually refined into piping drawings as shown in Fig 5. Design function is an iterative process, needing revisions and optimizations. As the project develops, new information and decisions are to be incorporated. This leads to changes as the best solution is rigorously pursued within budget and time limits. The feedback lines in Fig 5 indicate the iterative nature of the design process.
Fig 5 Design phases in a piping system
The design project is done on a teamwork basis involving several disciplines. Some of these disciplines are piping, architecture, civil, structural, heating, HVAC, electrical, mechanical, instrumentation, and suppliers.
Civil provides site plan, foundations, underground piping, and drains etc. Architecture provides outlines of walls or sidings, indicating thickness, floor penetrations for stairways, lifts, elevators, ducts, and drains etc, and positions of doors and windows. Structural discipline provides positions of steel columns supporting the next higher floor, supporting structures like monorails, platforms, overhead cranes or beams, and wall bracing when pipes are to pass through walls. HVAC provides paths of ducting and rising ducts, space heaters, fan room, and plenums etc. Electrical provides major conduit or wiring runs (surface and buried), positions of lights, motor control centres, (MCCs)
switchgears, junction boxes and control panel. Instrumentation provides instrument panels and console locations. Suppliers provide dimensions of equipment and instruments, positions of nozzles, flange types, and pressure rating. Mechanical provide information on positions and dimensions of mechanical equipment like conveyors, and chutes etc. and piping services for equipment.
Drawings needed for design – Piping system design is based on information from several sources. The site plan is a large-scale map of the plant site and reveals boundaries, roads, railroad, pavement, building outlines, large structures, production shop area, major pipe racks, storage areas, waste effluent ponds, large underground pipes, and disposal, shipping and loading areas. True north and assumed plant north is shown on the site plan. The plant personnel use this plan to decide where the production shops are to be located. The site plan is frequently divided into smaller units which are numbered. These are sometimes called key or index plans and are defined by match (boundary) lines. The unit plot plan is developed from the site plan. It reveals the equipment foundation outlines, structural foundation outlines, and structural members in a unit. Coordinates for centre-lines of equipment are indicated, except for pumps where the pump shaft centre-line is used as reference.
The coordinates of steel column centre-lines and extremities of buildings are to be shown on the unit plot plan. The equipment arrangement drawing is an updated unit plot plan where equipment outlines are added to the unit plan drawing. It shows the positions of equipment with outlines drawn to scale. Several viable drawings are normally made in order to optimize and meet process needs. Some preliminary piping studies are frequently be necessary to achieve the best result for equipment arrangement drawing.
The inputs for piping layout design are (i) process and instrumentation diagram, (ii) equipment layout, (ii) piping specifications, (iv) pipe list, and (v) any special project requirement. The design parameters are pressure higher of 10 % or 0.17 MPa above maximum operating pressure, and temperature higher of 10 deg C above normal or maximum operating temperature
Piping designers are experienced persons who have knowledge and skills in the organizational specifications, layout procedures, and equipment requirements. They prepare piping layout drawings with simplicity in mind, considers equipment access and maintenance, consider construction and space constraints, and consider personnel safety aspects.