Piping Layout Design Introduction The performance requirements of the equipment are developed by design teams which normally include members from the different departments such as process, engineering, maintenance, etc. The equipment can be divided into two groups: standard and custom. Standard equipments can be bought from vendors once their requirements are finalized. Examples are pumps, compressors, fans, etc. Custom equipments are designed and built from performance requirements by vendors or in-house. Vendors provide performance and installation specifications for their products. In piping drawings, equipments need not be drawn in details, often outline drawings with nozzles are adequate. But it is absolutely essential that the volume or space assigned to them is at least equal to the physical volume of the equipments bounding boxes. The bounding box for equipment is defined by the three principal dimensions of the equipment. The principal dimensions of the equipment are the overall sizes in a local 3D rectangular coordinate system for it. In addition to the three principal dimensions, interface feature sizes and location dimensions are also important and required in piping drawings. Interface features contain faces that are attachment points for piping connectors, instruments, and other devices. Others are mounting bases or faces that allow the equipments to be attached to foundations or other surfaces. Both the sizes and location dimensions on these features are required in piping drawings. Fire Safety Concerns Tanks and vessels must be laid out with fire prevention and containment in mind. Accordingly, recommendations of National Fire Protection Association (NFPA) and Occupational Safety and Health Administration (OSHA), and other regulatory bodies must be adhered to. Table 1 gives some guidelines. 1. Flammable liquid facilities should be isolated from important buildings or equipment. 2. Flammable liquids must be confined to closed containers, equipment and piping systems. They should be designed such that (a) uncontrolled escape of vapor from liquid is prevented, (b) accidental discharge of liquid can be shut-up rapidly, and (c) escaping liquid can be confined to the smallest possible area. 3. Tanks containing flammable liquid in open areas must be spaced to meet regulatory requirements. 4. Check insurer requirements 5. Ensure adequate ventilation to keep vapor concentration below the lower flammability limit. 6. Provide explosion panels in buildings to relieve explosion pressure and reduce structural damage. 7. Consider providing water sprays or sprinkler system around flammable liquid tanks 8. Valves for emergency use should be the quick-acting types. CONDITIONS Flammable or combustible liquid storage tanks (greater than 150 in diameter) Crude petroleum 126,000 gal max tank size, Non-congested locale Unstable flammable and unstable combustible liquid storage tanks Liquefied petroleum gas container from flammable or combustible liquid storage tank Liquefied petroleum gas container outside diked area containing flammable or combustible liquid storage tank(s) Tanks surrounded by other tanks Table 1: Tank spacing guidelines MINIMUM TANK GAP Greater of 3 or one-sixth of sum of adjacent tank diameters 3 one-half of sum of adjacent tank diameters 20 10 from center of dike wall. If LPG container is smaller than 125 gal (US) and each liquid storage tank is smaller then 660 gal, exception applies Authority limit 1
Tanks and Vessels 1. Clear space from top to ground is required around tanks and towers for lowering devices by davit or crane. Davits are used to handle removable internals and should be placed on the side away from the pipe rack. 2. Towers should have column davits if top of tower is over 50-0 from grade. Access-ways on towers should be accessible from davits. 3. Vertical tanks and vessels should have access-ways at the top or bottom. Horizontal tanks and vessels should have them at one ends. 4. Largest vertical vessel determines locations of other equipments. 5. The edge of the largest tower should be a minimum of 10-0 from rack column centerline. 6. Towers over 10-0 in diameter need special care when placing access-ways or two davits may be needed. 7. Bottom of tower base ring is 6 above grade. 8. Piping lines should have a minimum of 12 or 3 to 4 times pipe diameter gap from vessel walls. 9. Brace supports for piping line should be about 12 long. Length above 18 needs special design. 10. Piping of tanks and vessels should start from the highest point. Larger pipes should be routed first. 11. Platforms, ladders, and access-ways should be clear of piping areas. 12. Minimum clearance between platform base plate and vessels is 3. 13. Appropriate vents, drains and steam clean-outs are needed on tanks and vessels. 14. Vessels should have relief valves. 15. Nozzle schedule should list and provide dimensions for all attachments on tanks/vessels 16. Nozzle projection on equipment should be the same, except special requirements dictate otherwise. 17. Inlets should be at the top of vertical tanks and vessels and outlets should be at the bottom. 18. Inlets and outlets should be at opposite ends of horizontal tanks and vessels. 19. Horizontal heat exchanger footing should be 13-6 from closet rack centerline. 20. Top grout should be no less than 2-6 for horizontal vessels. 21. Saddle thickness should be about 15% (rounded up to nearest 3 ) of vessel length. Pumps 1. Locate pumps close to access-ways, roads, and driveways for access and maintenance reasons. 2. Locate pumps under pipe racks where ever possible. 3. Place pumps on the same side as vessels and tanks of pipe rack. 4. Pumps should be placed close to hot or cold liquid sources to minimize pipe insulation. 5. Maintenance clear space is 3 for pumps and other equipment. 6. Drive end of pumps should have 5-6 clearance space. 7. Bottom of base plate is at 6 above grade. 8. Pump discharge centerline should be 2 min. (4 preferred) from pipe rack column centerline and a minimum of 1 above grade highest point. 9. Arrange multiple pumps parallel with discharge centerlines aligned. This allows more efficient location of auxiliary piping and drainage. 10. Relieve pumps of loads and stresses by providing supports for all piping, e.g pipe racks. 11. Consider locating pumps at vessel base if operating temperature is 204 o C (400 o F) or more. 12. Pipe suction line of carbon steel is 12 or more above grade but 8 or more for alloy steel. 13. Suction lines should be as short as possible. Use large radius bends if bends are unavoidable. 14. Straight portion of suction line before nozzle should be at least three times line diameter. This tends to prevent turbulence at pump suction. 15. Elbows on pump suction side should be placed in a vertical plane instead of the horizontal to minimize turbulence at pump suction. 16. If vertical suction pipe is required, use eccentric reducers with the flat side at the bottom to avoid air pockets at pump suction. For horizontal suction line, the flat side of eccentric reducers should be on top when placed. 17. Vents must be provided on the suction side to relieve lines of gases and air if eccentric reducers cannot be used. 18. Minimize pipe runs on pump suction side. 2
19. Suction line should slope slightly downwards toward the pump suction. 20. Gate and check valves are required at pump discharge line. 21. Horizontal valve handwheel should point towards maintenance or access area. 22. Ensure adequate NPSH (Net Positive Suction Head) for pump. NPSH is the dimension from bottom of vessel to pump centerline. Add 2 for suction line loss. Heat exchangers 1. Top of foundation s grout should be the same for all exchangers and 2-6 above highest point of grade. This may go up to 3-0 or more for tube-shell exchangers with large nuzzles. 2. A minimum clearance of 1-0 is needed between line insulation and grade. 3. Adequate tube removal space is needed for maintenance. Back head line of exchangers should be 8-0 from rack column centerline. 4. Back concrete footings or saddles of exchangers should line up. 5. Back saddle bolt holes centerlines should be 5-6 from the back head line as a rule. Reactors and Furnaces 1. Reactors should be at least 25 from other equipment, however 50 is preferred. 2. Furnaces should place 50 from hydrocarbon holding equipment. 3. Pulling area space for furnaces with tubes should be tube length plus 5. 4. Snuffing steam manifold should be at least 50 from a heater or furnace 5. Manual fuel shut off valves should be 50 away. 6. Control valves can be at the base of the furnace or near the rack. 7. Floor of vertical furnaces should be 7 from grade. 8. Flare stacks located 200 from nearest equipment. Platforms, Ladders and Stairways 1. Vessel platforms, secondary service levels in structures, furnaces and storage tanks may need ladders. 2. Vertical vessels need circular or hexagonal platforms supported by brackets from the side of the vessels. 3. Ladders, platforms, access-ways, etc should be located on the same side of tanks and vessels. 4. Platforms are needed for all elevated equipment, controls beyond reach from grade, and should have rails on all open sides. 5. Platforms should be about 2-6 to 3-0 below manhole center. 6. Platforms are usually 3 wide with 3-6 high handrails. 7. Platforms are spaced such that ladders are not more than 30 in vertical run 8. Ladder has 7 to 8 headroom clearance from ground. 9. Locate ladder and platform positions. Indicate if fabricator will provide platform and ladder. 10. Escape ladders are needed from service levels or platforms. 11. Exit spacing on service levels should be at most 75 (22.5 m) from main or secondary exit. 12. Side exit ladders are preferred for platforms. 13. Flare stacks need ladders for inspection and top maintenance. 14. Self-closing gates needed at ladder openings on all platforms. 15. Ladders 15 or more above grade need cages. 16. Stacks should be at least 70 (21 m) away from closest equipment. 17. Stacks and vents discharging hazardous vapor continuously should be 10 (3 m) high above platform. 18. Stacks and vents discharging hazardous vapor intermittently should be 10 (3 m) high above platform if within 35 (10.5 m) of closest equipment. 19. Non-hazardous vapors (air, steam) should be directed away from personnel. 20. Stairways required to service levels in structures, buildings, compressor houses, furnace decks requiring frequent access. 21. Storage tanks with diameter of 15 (4.5 m) and higher than 20 (6 m) require stairways for access. 3
Instruments 1. Special consideration to be given to configuration, location and orientation. 2. Important valves must be easily accessible for operation and maintenance (servicing, repair, and replacement). 3. Locate hand-operated valves so that they can be operated from access-ways and maintenance area. Allow a minimum of 2-6 for operating space. 4. Locate automatic after locating hand-operated valves. 5. Avoid use of manual actuators like chain operator except when absolutely necessary. 6. Operating valves at elevation 7-6 and higher above grade or platform need chain operator 7. Locate valves on horizontal runs of pipes. Fluids can become trapped above valves on vertical runs if they are closed. Provide drainage for valves on vertical runs of pipes. 8. Locate valves outside of pipe racks 9. Glass level vials should be located where they can be seen easily. 10. Locally mounted instrument (directly attached to equipment) must be easy to reach, clearly visible and readable, preferably when operating associated valves. 11. Instrument loops should be properly labeled and numbered. 12. Always check with instrumentation and electrical department for loop information. 13. Pressure connections are best located above liquid level in the vessel. 14. Liquid level controller should be located clear of any turbulence from nozzles. 15. Orifice flow meter needs operating space of 2-6 x 6 in plan view. The meter is assumed located midway in zone. Height clearance of 2 is recommended. 16. Level controls, control valves, motor-operated valves, battery limit valves, relief valves, valves 3 and larger, and observation doors should be accessible from grade or platform. 17. Valves 3 and smaller, level gages, pressure and temperature instruments, and hand holes may be accessed from fixed ladders. 18. A minimum clearance of 4 above hand-wheels maximum height is necessary. 19. Control station should be placed close to the equipment it serves. 20. Control station should be located at or near grade or platform. Above Grade Piping 1. Not for pipeline pumping stations, sewers and most water-cooling systems. 2. Long run pipes are routed overhead. 3. Short run pipes (e,g. suction lines) may run on grade but must clear access ways. 4. Piping should allow equipment removal without removing associated controls and their piping. 5. Piping line spacing should be based on regular operating conditions. 6. Piping layout should be flexible so as to accommodate expansions in pipes and hence reduce thermal stresses. 7. Piping layout should avoid using expansion bellows if possible. 8. Un-insulated pipes through dikes, under roads or railways should be coated and wrapped. 9. Insulated pipes through dikes, under roads or railways should be enclosed in metal pipe sleeves. 10. Off-site area piping may run about 18 (450 mm) above grade with adequate maintenance access. 11. Off-site pipe racks should be adjacent to storage tanks. Piping within dikes should be routed directly except for flexibility and tank settlement. Pipe Racks 1. Provide 20% extra space in rack 2. Use single level rack for height requirement of 24 or less. Space column at 20. 3. Consider two level designs with 4 gap for height requirement more than 24. 4. For two level designs, main pipe way is strutted and runs midway between the two levels. 5. Maximum center distance between supports is 25-0. 6. Pipe sizes of 4 or smaller need supplementary supports (pick-ups). 7. If fireproof is required, consider cast-in place concrete as alternative for economy. 8. Keep cooling water lines out of rack if possible as they make rack larger. 9. If lines are 10 or more, they should be underground. In freezing climates, locate all lines underground. 10. Overhang should be about 2 to minimize column size. 4
Summary Reciprocating compressors should be at least 6 from pipe rack column center line. Back head line of heat exchangers should be 8 from rack column center line. Reactors should be at least 25 from other equipment. Manual fuel shut off valves should be 50 away. Floor of vertical furnaces should be 7 from grade. A minimum of 2-6 clear space should be provided for valve operation. A clear space of 3 should be provided around equipment. Motor drive ends should have 5-6 clear space. The bounding box is used to determine the basic space requirement for a device. Valves for emergency use on flammable fluid containers should be of the quickacting type. Pump should be located close to access-ways. Pumps should be placed close to hot or cooled liquid sources to minimize pipe insulation. A minimum of 2 should be added to pump head losses for suction line losses. The largest vertical vessel determines the locations of others in the same unit. Rack column centerline should be 10 from the edge of the largest tower in a unit. All nozzles on equipment should have the same projection, except special requirements dictate otherwise. Saddle thickness should be 15% of vessel length. Tube removal area minimum length for centrifugal compressors should be the tube length plus 12. Tanks, vessels, and pumps should be placed on the same side of a pipe rack. The minimum space gap between combustible or flammable liquid containers is the greater of 3 ft. or one-sixth the sum of adjacent tank diameters. The minimum space gap between liquefied petroleum gas container and combustible or flammable liquid containers is 20. Flammable facilities should be isolated from important buildings and equipment. Pump piping should be properly supported to relieve the pumps of load or stress. NPSH stands for Net Positive Suction Head. The discharge center lines of parallel pumps should be aligned. Bibliography 1. Shumaker, T. M., Process Pipe Drafting, Goodheart-Willcox, Illinois, 1999. 2. Parisher, R. A. and Rhea, R. A., Pipe Drafting and Design, 3 rd Edition, GPD Elsevier, 2012. 3. Bausbacher, E. and Hunt, R., Process Plant Layout and Piping Design, PTR Prentice Hall, New Jersey, 1993. 4. Sherwood, D. R. and Whistance, D. J, The Piping Guide: For the Design and Drafting of Industrial Piping Systems, 5