Piping Design Specification 

This article provides you with a example piping design specification that is used in the industrial plant engineering and construction work. 

Piping Design Specification

The piping inspection and testing requirements is covered in the I4I Academy API 570 Piping Inspector Training Course


1.1. SCOPE

1.1.1. This specification covers general and detailed design and layout requirements for all process and utility piping systems and supplements the requirements of the codes under which the piping systems are to be designed, for industrial plant engineering and construction work.

No variation from this engineering specification is permitted unless approved in writing by owner.

1.1.2. All process and utility piping shall be designed based on the requirements of this specification.

In the case of a part of this specification is not applicable due to specific requirements of Client, local code, etc., supplementary paragraphs may be added to the end of specification, after OWNER’s approval.

1.1.3. This specification shall be applied to all piping systems indicated on piping & instrument flow diagram (P&ID) and plot plan, except for following:

a) H.V.A.C Design & Plumbing piping systems

b) Piping line running after first block valve (or fitting) of piping system connected to instrumentation, except for control valves, safety valves and orifice flanges.

c) Accessory piping of vendor supplied equipment.

d) Piping line running after first block valve of piping system connected to steam tracing, tracers and instrument air consumers.

1.1.4. Requirement of supporting shall be considered in accordance with “Engineering Specification for Piping Hanging & Support”.

1.1.5. Requirement of stress analysis shall be considered in accordance with “Engineering Specification for Piping Stress Analysis”.

1.1.6. Requirement of piping material and material design shall be considered in accordance with “Engineering Specification for Piping Material”.

1.1.7. Requirement of steam tracing (winterizing / heat conservation) shall be considered in accordance with “Engineering Specification for Steam Tracing”.

1.1.8. Requirement of piping marking and coding shall be considered in accordance with “Engineering Specification for Marking & Coding”.

1.1.9. Requirement of thermal insulation for hot lines shall be considered in accordance with “Engineering Specification for Thermal insulation (Hot)”.

1.1.10.Requirement of thermal insulation for cold lines shall be considered in accordance with “Engineering Specification for Thermal insulation (Cold)”.


The following Codes, Standards and Engineering Specifications are referenced documents to this specification.

In case of conflict between referenced documents and this engineering specification, the most severe requirement shall govern, subject to OWNER’s approval.

Where this engineering specification is in contradiction with Piping and Instrument Diagram (P&ID) and Utility Flow Diagram (UFD), the OWNER’s approval for any decision is necessary.


Design specification and inspection of piping shall be in accordance with the following Codes and Standards. 

  • ASME B31.1 Power Piping
  • ASME B31.3 Process Piping
  • ASME B16.5 Pipe Flanges and Flanged Fittings NPS 1/2" through NPS 24"
  • ASME B16.47 Large Diameter Steel Flanges NPS 26" through NPS 60"

For piping material codes, referred to “Engineering Specification for Piping Material“.


The relevant engineering specifications are as follow and all specification shall be of the latest revision.

1.3. UNITS

Unless otherwise specified, Metric Units (Kg, mm, Kg.m, Kg/cm2) shall be applied as the measurement system for drawings and documents to be submitted.  However, nominal sizes of piping components shall be in accordance with Inch system (NPS).



2.1.1. Piping arrangement drawings shall generally be drawn to a scale of 1/33-1/3 for process areas (1/50 may be used for pipe rack area) and 1/100 and 1/200 for offsite areas.  For clarification purposes offsite drawings may be drawn to a scale of 1/50.

2.1.2. The drawings shall show, but not be limited to:

a) Equipment structures, platforms, ladders, stairs, foundations, ducts, etc.

b) A key plan should appear above the title block to identify the location of the drawing relative to remaining part of the plot.


2.2.1. Fully dimensioned Isometric drawing with bills of material shall be prepared for 2" & larger piping for Carbon Steel and 1-1/2" & larger piping for Stainless Steel lines.

2.2.2. Informational Iso-sketch with approximated  information, will be prepared for Carbon Steel piping below 2”and Stainless Steel piping below 1-1/2”. 

2.2.3. In addition to the physical routing of the line/lines the following information shall be included in the Isometric drawings:

a) Material class.

b) Paint and Insulation specification.

c) Line designation.

d) Hydrostatic test pressure and media.

e) Process design & operating conditions.

2.2.4. Unless otherwise specified, centerline of pipe elevation shall be applied for pipe elevation in the Isometric drawings.


2.3.1. Location of steam and condensate manifolds shall be shown on a reproducible copy of the plot plan or piping arrangements.

2.3.2. Tracer routing shall be shown on the reproducible copy of the piping arrangement drawing, together with the block valve numbers of the tracer feed and return.


2.4.1. Following drawings shall be prepared for pipe supports:

a) Standard Pipe Support Drawings

b) Special Pipe Support Drawings

2.4.2. Location of all supports together with support designation and number shall be indicated on Piping Arrangement Drawings for pipe rack, pipe way and offsite areas.

2.4.3. Location together with support designation and number of all supports shall be indicated on Isometric drawings for areas other than clause 2.4.2 above.

No support indication is to be shown on piping arrangement drawing for such areas.



3.1.1. Piping shall be designed to maintain its lifetime during whole span of life of the plant.

3.1.2. Design pressures and temperatures, allowable stresses, joint efficiencies and other design conditions shall be used as a basis for wall thickness calculation and the material selection.


3.2.1. Pressure Temperature Ratings have been established for certain piping components.

3.2.2. Flange Ratings shall be determined, based on ASME B16.5 or ASME B16.47-B.


Where a line with a lower rating connected to a pipe or equipment with a higher rating, such line shall be rated at the higher rating (and shall be the same material as the line of the higher rating) to and including the first block valve or, when double block valves are used, to and including the second block valve. Block valves on both sides of a control valve and the by pass valve shall be rated at the same specification of the line with the higher rating. The class breaking shall be indicated in the P&IDs and piping Isometric drawings.


3.4.1. Allowable stresses which specified in ASME B31.1-1998 edition or ASME B31.3-1999 edition (which ever is applicable), shall be used in design calculations.



4.1.1. Piping shall be designed for the most severe coincidental conditions of pressure and temperature, arrived on the basis of the following considerations:

1)  Design pressure and temperature of the equipment to which is connected.

2)  Set pressure of the safety valve, which protects the system.

4.1.2. All pipelines shall be routed in shortest possible run with minimum number of fittings consistence with provision for expansion and flexibility. The assembly, removal and support of piping and equipment shall also be taken into consideration.

4.1.3. All pipelines shall be routed for the convenience of installation, operation, and maintenance of the pipeline, equipment and instruments.

4.1.4. All lines inside battery limits, except drain lines, sewer lines and other special use lines shall be run side by side on overhead pipe supports or on sleepers. The use of pipe trenches within units shall be avoided as much as possible.

4.1.5. Buried piping shall be kept at a sufficient distance from electrical cables for power and lighting, and from instrument signal cables. They shall also be run in concrete trenches only under the pipe rack. Above ground lines which have to buried partially (passing roads, etc.) shall be run in pipe sleeves, tunnels, culverts or bridges.

4.1.6. Unless otherwise specified, bottom of pipe (BOP) elevation shall be applied for pipe elevation.

4.1.7. Bottoms of hot and cold insulated lines, which are run on overhead supports, shall generally be supported with steel shoes and cradles respectively.

4.1.8. Un-insulated lines shall not be supported on steel shoes and cradles, and shall generally be carried at a common elevation of bottom of piping.  Insulated lines shall be carried at a common elevation of bottom of shoes and cradles. The lines, which are run on overhead supports, shall generally be changed in its elevation when there is a change in direction. Intersecting main pipe runs, shall be routed at different levels to facilitate changing direction and/or crossing of lines.

4.1.9. Large piping (18" and larger) of thin wall shall be supported by adequate methods, to reduce local stresses at the supporting point.

4.1.10. Lines carrying molten solids or service fluids of high viscosity, or those lines so indicated on the applicable P&IDs, shall be designed to have a continuous slope and drain into a vessel. The shortest and most direct layout possible shall be provided for lines in which gravity flow is required, especially, when the line fluid is subject to solidification or when the available differential pressure is small.

4.1.11. Concrete trenches must be adequately drained into a liquid sealed drainage system and must be covered with grating, except near plant access or at road crossing, etc., where the type of covering shall be as per Civil Engineering details.

4.1.12. Minimum elevation for top of foundation shall be as follows:

ItemMin. Elevation (mm)
Column300 * or as required
Drum vertical300 * or as required
Drum horizontal300 * or as required
S/T heat exchanger300 * or as required
Pump300 * or as required
Compressor300 * or as required
Tank300 * or as required
Flare stack300 * or as required
Fired heater300 * or as required
Packaged equipment300 * or as required
Pipe sleeper250 * or as required
Pipe support on independent foundation150 *
Pipe support on paving100 *
Steel pipe rack & structure300 * or as required
Pump station top of dike300 * or as required
Ladder and stairway200 * or as required

Notes : *   Elevations are measured from H.P.P.EL (high point paving elevation EL.= 0 for each terrace) 

4.1.13. In general, all major process lines should be carried on overhead pipe ways or sleeper pipe ways.

All lines in process type areas shall preferably run, side by side on over head pipe rack to common supporting elevations for bottom of pipe. Hot lines on pipe rack shall be grouped and expansion loops shall be nested together, the number of expansion loops shall be kept to a minimum. Lines, handling corrosive fluids shall be run under piping handling non-corrosive fluids, and shall not, where possible, be run overhead across walkways or normal passages for personnel. Piping shall run on sleepers in tank areas.

4.1.14. Overhead pipe ways and sleeper pipe ways shall have one 10% spare space for each layer at middle as one continuous space and also future load shall be considered on 10% spare space.

Consideration shall be given to space allocated for instrument and electrical cable trays in the pipe racks and sleepers. 

4.1.15. All branched piping from utility header (steam, steam cond., water, air, nitrogen, fuel gas, fuel oil and etc.) shall be taken from the top of the header to prevent plugging however, water branch piping of 2” and larger may be taken from the bottom of the header.

4.1.16. All valve pit shall be equipped with non-slip metal plate cover.

4.1.17. Line blinds 10” and larger shall be provided with jack scews.

4.1.18. Access platform with ladder or stairs shall be considered in piping design specification for access to equipment, valves, instruments and etc., for operation and maintenance in accordance with section 8 of this specification.

4.1.19. Vent and drain hookup, sample points with or without sample cooler and pressure instrument points, etc., shall be designed in accordance with the relevant piping standards.

4.1.20. Pockets shall be avoided in lines, particularly those carrying corrosive chemicals, slurries, drains and Blow-down, those which may congeal or freeze, etc.

4.1.21. Material of construction of each piping system with specific operating condition, shall Conform to the service classifications and pipe classes in accordance to “Engineering Specification for Piping Material”.

4.1.22. Cold pulling of pipes for alignment during construction or other purposes is not permitted.

4.1.23. When reducers are used, the maximum reduction shall not be greater than 2 nominal line sizes per reducers.

4.1.24. Change in line sizes, shall be made by Eccentric or Concentric reducers and swages. Bushing and reducing elbows, are not permitted except for instrument piping and sewers.

4.1.25. Unions shall only be used, when permitted by the particular piping classes.

4.1.26. Supports and/or anchors shall be provided close to changes indirection of lines, branch lines and, close to valves.

4.1.27. In general piping shall be designed for zero expansion at the battery limits. 

4.1.28. In general, all piping leaving the plant battery limits shall be designed for a closed valve at the battery limit when defined in P&IDs.

4.1.29. When discharging to a closed collector system, the discharge line shall be sloped downwards to the header and the header connection shall be made on the topside of the header line, so that the flow direction angle between the axes of the outlet line and the header is 45°. 

When a collector system includes a knockout drum and flare, the headers shall be slopped to the knockout drum with a falling gradient of minimum 2/1000.

4.1.30. Where a common header used to vent lighter than air gases to atmosphere, the header shall slope upwards to the relieving stack or pipe. Discharge lines carrying air and steam slop upwards and discharge in upward direction.


4.2.1. Overhead Clearances

The minimum pass way overhead clearances, shall generally be as follows;

A). Inside Battery Limit of Plant - Piping Design Specification

a) Below structure or platforms ..............…….…...………… 2500 mm

b) Inside buildings ........................................................…….. 2500 mm

c) Main plant road ........................................................…….. 7000 mm

d) Secondary roads and truck area ..................................… 5000 mm

e) Mobile lifting equipment access areas .......................….. 3500 mm

f) Headroom below piping and structures...………………… 2200 mm

B). Outside Battery Limit of Plant - Piping Design Specification

a) Railroads and main roads ......……………………………. 7000 mm

b) Secondary roads ...................................................……… 5000 mm

4.2.2. Horizontal Clearances - Piping Design Specification

The minimum pass way horizontal clearances, shall generally be as follows;

a) Between exchangers (aisles between piping and exchanger)………. 900 mm

b) Around pumps (aisles between piping) ………………….............…… 900 mm

c) Fired heaters to pumps handling in flammable stock ……............... 15000 mm or as required

d) Fired heaters to other equipment containing inflammable

Stock, not closely associated with heaters ……………………..1500 mm or as required

e) At driver and of pumps, where truck access is required.…... 3000 mm

f) At driver end of pumps, where truck access not required ……1800 mm

g) At shell cover end of exchangers at ground, for access way ..1300 mm

h) Furnace to day tanks or towers …………………………......… As required

i) Between shells of adjacent horizontal vessels………......……. 1200 mm

j) From edge of equipment to wall………………………..........…. 750 mm

k) Electrical motors from wall ………………………….........… 750mm or as vendor Recommend

l) Equipment part removal  ……………………………..............  As vendor recommend

4.2.3. Clearances to the Bottoms of Pipe (BOP) - Piping Design Specification

The minimum clearances below the bottoms of pipe (BOP) other than pass ways shall be as follows:

a) At grade.……………………………………………………. 250 mm

b) Buildings floor ……………………………………………… 100 ~ 300 mm

c) At platforms ………………………………………………… 250 mm

d) Sleeper way ………………………………………………… 300 mm

e) Over exchangers at shell cover, channel end………….... 1500 mm

f) Over pumps ………………………………………………… 3500 mm

g) Pit floor…………………………………………….……….. 100 ~ 300 mm

4.2.4. Equipment Spacing - Piping Design Specification

The minimum spacing between equipment shall generally be as follows:

a) Small pumps (3.75 KW and less)………………………… Mounted on common

foundations suitable center to center distance

b) Medium and large pumps (more than 3.75 KW) ………… 900 mm clear aisle

c) Other equipment on structures ………………………….... 900 mm clear aisle

d) Clearance in front of channel or 

Bonnet flange of horizontal exchanger…………………........ 1200 mm

e) Heat exchanger tube bundle removal space……………….. Tube bundle length 

plus 1000 mm

f) Minimum clearance of exchanger shell flanges………….... 450 mm

Note: these requirements are not applied to the inside of packaged equipment assembled on the skid.

4.2.5. Platforms - Piping Design Specification

The minimum platforms clearance and width shall generally be as follows:

a) Towers, vertical and horizontal vessels distance of 

Platform below centerline of manhole……………………    900 - 1050 mm

b) Width of manhole platform from manhole cover 

to edge of platform ……………………………………………. 900 mm

c) Platform extension beyond centerline of manhole

side platform …………………………………………………. 900 mm

d) Distance of platform below under-side of flanged head….… …. 175 mm

e) Width of platform on the sides of manhole head platform …….. 750 mm

f) Width of access platforms (generally) …………………………... 750 mm

g) Over head clearance between equipment platforms structures  2200 mm

4.2.6. Other Clearances - Piping Design Specification

(1) The minimum clearances around control panels shall generally be as follows:

a) Control panels, front ………………………………………      2000 mm

b) Control panels, rear ………………………………………      1500 mm

(2) The minimum operating aisles shall be as follows:

a) At grade ……………………………………………………       750 mm 

b) On structures …………………………………………….        750 mm

c) On vessels ………………………………………..………       750 mm

d) Communicating ……………………………………..……       600 mm

(3) The minimum clearance between the lowest points of all flanges or insulation of lines running in trenches shall be 75 mm above the floor of the trench. 

(4) The minimum free distance above a control valve and minimum clearance under the control     valve, shall be in accordance to ISA PR4.2

(5) Impact wrench clearance shall be provided at any equipment flange.

(6) Underground pipe risers shall be terminated 500 mm aboveground, unless otherwise specified.


4.3.1. To permit ready access for the removal or maintenance of a pipeline, under operating conditions, a minimum side clearance of 25 mm shall be provided between parallel lines outside of insulation or between flange and pipe (insulation). Thermal expansion movements shall be taken into consideration in determining the minimum side clearances.

4.3.2. The minimum center to center distance between hand wheels of valves shall be determined take operability of the valve into consideration. 

4.3.3. To determine the distance between pipe and others such as wall of the trench, edge of pipe rack and etc., access for removal or maintenance for the pipe shall be considered.


4.4.1. General

(a)  Valves shall preferably be installed so that the centerline of the hand wheel shall not be more  than 1800mm above the pavement or platform levels.

(b)  In case of the centerline of the hand wheel is more than 1800mm above the pavement or platform levels, the valve accessibility shall be provided in accordance with section 8, of this specification.

(c)  Frequently operated valves, which can not be operate from grade or platform levels, shall be equipped with remote operation device such as chain wheel or extension stem to permit ease of operation.

(d)  For valves, which operated with remote operating chain device, Chains shall hang to within 900mm of the operating level and Spark proof chain shall be used. 

(e)  Valves in trenches, pit, etc., which can not be operate from a platform, shall be provided with a stem extension, if required.

(f)  Valves requiring extension stem or chain operate device, shall be noted in piping drawings, such valves shall be specified on Isometric drawings for decision.

(g) Valves in piping arrangements shall be designed so that they do not obstruct walkways, platforms, pass ways, etc., and yet accessible for operation.

(h) Valves at towers shall be located directly against or close to the tower nozzles unless physical interference would prevent proper operation of the valves. Valves shall preferably not be located inside vessel skirts.

(i)  All valve outlet ends, in process services, which do not connect to a piping system, shall be provided with a blind flange or a screwed cap/plug assembly, unless otherwise indicated on the P&IDs.

(j) Manually operated valves, which are used in conjunction with locally mounted flow indicators, etc., shall be placed at the same operating level and located where the instrument can be readily observed.

(k) Valves, whose type and number are shown on the applicable P&IDs, shall be installed on the suitable places to permit proper and safe operation of the unit. 

(l)  Under any condition, Valves shall not be installed with their stems below horizontal. 

(m) Hand wheels of valves shall never be made of a light alloy that could melt in case of fire.

(n) Double block and bleed valve system shall be provided only where necessary to avoid product contamination or hazardous condition, as shown on the P&IDs.

(o) Valves in overhead pipe rack, shall be kept to minimum.

(p) Check valves shall be suitable for installation in vertical lines with flow upward as well as for installation in horizontal lines. They shall be used in cases where reversal of flow may occur.

(q) All ball and plug valves shall have the ball or plug stem and lever electro statically grounded to valve body.

(r)  All gate and globe valves shall have back seat, except for 2” and smaller, inside screw rising stem (ISRS) type valves such as bronze valves.

(s)  For check, globe and any directional valves, which are insulated or coated, the direction of flow through the valves shall be suitably marked on insulation.

4.4.2. Control valve system - Piping Design Specification

a) Control valve shall be installed over 600 mm from floor or platform.

b) Control valve shall be designed to facilitate its operation and maintenance.

c) Drain shall be installed before or behind the control valve as shown on P&IDs.

d) By pass valve and block valve shall be installed within 1800mm from floor or platform.

e) In control valve manifold piping arrangement, reducers type shall be so selected to prevent non- drainable pocket.

f) Control valves and safety relief valves and relevant isolating valve and bypass valve, if any, shall be located close to the platform, or on the grade for maintenance.

4.4.3. Safety relief valve - Piping Design Specification

a) Safety relief valves shall be provided to the extent shown on P&IDs and UFDs.

b) Safety relief valves on process systems shall be connected to a flare or other disposal system only when indicated on P&IDs.

c) Safety relief valves, which are not connected to flare or other disposal systems, shall have the pipe extending at least 3000 mm above any platform or working area within a 12M radius of the point of gas discharge.

d) Steam relief valves shall discharge to atmosphere through discharge piping extending at least  3000 mm above any platform or working area within 8000 mm radius of the point of discharge.

e) A 10 mm minimum weep hole shall be provided at the low point of the discharge piping when discharging to atmosphere.  Drain piping shall be provided in discharge piping when necessary.

f) Safety relief valves shall generally have a minimum length of piping between the protected line or equipment and the valve inlet.

g) Discharge lines from relief valves shall have a minimum use of elbows and shall be supported and braced to prevent movement of the line due to reaction forces of the discharge flow.

h) Safety and relief valves shall be installed with their springs in a vertical position. Any thermal relief valves shall also be installed only with their springs in a vertical position.

I) Relief valve inlet and discharge piping shall be designed to avoid moments and forces on the valve body.

j) Outlet piping of safety and relief valves (including flare lines) shall be designed to prevent excessive stresses in the line resulting from larger rapid temperature changes or from uneven temperature distribution.


4.5.1. Piping joint types shall generally be as follows:

a) Flanged joints.

b) Butt welded joints.

c) Socket welded joints.

d) Threaded joints.

4.5.2. The joint type shall be selected according to reliability, maintainability and economy, except when limited by specific note.

4.5.3. Bolts with nut and gasket shall be used for all flanged joints, in accordance with related pipe class of “Engineering Specification for piping Material”.

4.5.4. For piping components, joint type shall be considered in accordance with “Engineering Specification for Piping Material”.

4.5.5. Field weld joints in alloy steel piping, shall be avoided as far as practicable, where heat treatment is required after welding.

4.5.6. Welded carbon and alloy steel pipe shall be stress relieved when required by ANSI B.31.3.

Welding on of attachments such as clips, brackets, etc. after stress relieving is not permitted.

4.5.7. Threaded joints shall be used only in moderate service conditions, and connection to instrumentation and shall not be used in corrosive, flammable and toxic services. Unless otherwise specified, pipe thread shall be in accordance with NPT as per “Engineering Specification for Piping Material”.

4.5.8. Threaded joints shall be made with 1” width ”PTFE” jointing tape for design temperatures 200°C and below, and for Above 200°C, threaded joints shall be seal welded with a full strength fillet weld.

4.5.9. All threaded joints except for instrument connection, irrespective of pressure and temperature on lines carrying corrosive flameable and toxic fluid shall be seal welded with a full strength fillet weld.

4.5.10.End connections for fittings shall be as indicated on the particular pipe classes in accordance with “Engineering Specification for Piping Material”.

4.5.11. For Butt Welded joints, Pipe wall thickness shall be as indicated in the individual pipe classes. Where a heavier pipe wall thickness is used than required by the individual line classes, the inside of the end connection of heavier pipe or fitting shall be machined to an inside diameter equal to the end connection of the lighter pipe or fitting with a taper 1:4.

When in a piping class, a minimum wall thickness is indicated the wall thickness shall be checked for the actual design conditions of the line. 

When a line is subjected to full vacuum, care shall be taken that the correct wall thickness is noted on the P&IDs or line list, If the wall deviated from the one, in the pipe class. 

Beveling to be accordance with ANSI B.16.25.


4.6.1. Branch connections type shall be as follows:

a) Stub - in:  Direct welding.

b) Coupling or Boss: Threaded or Socket welded.

c) Olet:  Weldolet, Threadolet or Sockolet, Latrolet, Elbowlet, etc.

d) Straight or Reducing Tee.

e) Welding Saddle or Reinforced branch outlets.

4.6.2. The type of branch connections used in all piping systems shall match the rest of the system in pressure temperature rating. Design pressure and temperature limits shall not be down graded because of branch connection.

4.6.3. Type of branch connections shall be selected in accordance with related pipe class branch table, in “Engineering Specification for Piping Material”.

4.6.4. The required reinforcement shall be designed in accordance with the ANSI B31.3 

4.6.5. If the wall thickness of the pipe is insufficient to sustain the pressure and thermal stress, branch connection shall be provided with reinforcement according to “Engineering Specification for Piping Material.”

4.6.6. Stub in connections shall be designed so that the angle of intersection between the branch and the run is 90° unless required for process or flow reasons, and shall not be less than 45°.


4.7.1. Vent other than indicated in P&IDs shall be provided at high points of piping of 2” and larger in accordance with the following:

a) ¾” blank off for alloy and stainless steel piping required for hydrostatic testing purposes.

b) ¾” threaded plugged for carbon steel piping required for hydrostatic testing purposes. (To be seal welded after testing).

4.7.2. Drains other than indicated in P&IDs shall be provided at low points of all piping in accordance with the following:

a) ¾” gate valve with blind flange for flanged type valve.

b) ¾” gate valve with threaded plug or screwed cap for threaded/socket welded type valve.

4.7.3. Vent and drain arrangement in accordance with working pressure of the line shall be mentioned and showed on the piping standard drawing.

4.7.4. Where lines are heavily insulated, vents and drains shall be provided with sufficiently long nipple that they will project outside the insulation.

4.7.5. Vents and drains shall be 3/4" NPS, unless otherwise specified in P&IDs.

4.7.6. Vents and drains shall be readily accessible. The discharge end of all drain and vent lines shall be so located and directed so as not to be a hazard to personnel.


4.8.1. Sample points shall not be located in dead ends of piping. They shall be easily accessible, preferably at ground level if a part of the piping is at ground level.  Sample lines shall be as short as possible and shall not exceed 8 m in length.

4.8.2. Sample connections shall be grouped together as far as practicable.

4.8.3. Connections for sampling shall generally be of 3/4" couplings, unless otherwise specified in P&IDs.

4.8.4. The sample connection shall generally be located in vertical line. When pipe is in a horizontal or inclined plane, the sample connection shall generally be located at the side of the pipe unless otherwise indicated on the P&IDs.

4.8.5. Type of sample connection, necessity of cooler, type of block valve and etc., shall be in accordance with the P&IDs requirement.



5.1.1. This piping shall be arranged so that full access is provided for maintenance, e.g. by cranes and trucks, and that removal or replacement of equipment can be done with a minimum dismantling of piping.

5.1.2. Special notes for piping shown on P&IDs shall be considered as mandatory requirements, and it shall be reflected in piping design specification.

5.1.3. Piping for pumping out equipment is a part of the process piping and shall be provided as indicated on the P&IDs.

Pump-out piping shall be designed with a minimum possible additional piping, not regularly required for normal start-up or operation of the process units and utilizing process pumps.

5.1.4. Where equipment may be removed for maintenance, piping shall be supported so that temporary supports are not required upon such removal.

5.1.5. The piping should be supported in a manner to keep forces and moments on equipment within allowable amounts.

5.1.6. Spring hangers may be used on piping subject to thermal expansion, or contraction. In cases where the movement is very large, or the limitations of reactions and stresses are very severe, constant hangers shall be used.

5.1.7. Suction and discharge lines on rotating equipment shall be supported as close as possible to the equipment nozzles and shall be relieved of excessive piping strain by the use of proper pipe supports.


5.2.1. Suction lines to pumps shall generally be designed to avoid pockets.  Horizontal suction lines from towers shall generally be designed to avoid pockets caused by thermal expansion of vertical lines. Pump-suction Lines shall be as direct as possible to avoid collection of vapor or gas when pocket is anticipated due to piping elongation in critical services.

5.2.2. The discharge line from centrifugal pumps shall be provided with a check valve between the pump and the block valve. For vertical discharge pumps, the check valve shall be located in the vertical line whenever practical. Discharge valves shall have the size as indicated on the P&IDs. Reducer shall be provided, if the pump nozzle is not the same size as the discharge valves.

5.2.3. Suction and discharge lines of pumps shall be drained through drains located at the low point of the pump casing whenever possible. Provisions shall be made for draining suction and discharge lines. Suction lines may be drained through pump casing.

5.2.4. Sealing oil systems and cooling water piping for gland, shall be furnished in accordance with the pump vendor's recommendations. All fluids from pump drain shall be drained in accordance with P&IDs requirement. Gland and seal oil pumping shall be designed in accordance with relevant standard.

5.2.5. Reducers, when required in the horizontal run of a pump suction line, shall be eccentric type and installed with the flat portion on top (top flat).

5.2.6. To avoid Cavitation in horizontal centrifugal pumps of the double suction type, the suction line shall be arranged so that equal flow distribution to both impeller entrances, is warranted.

5.2.7. Break flanges shall be provided, when necessary, for pumps, in order to install temporary strainers.

5.2.8. Where necessary, provisions as spool pieces shall be made in order to facilitate removal of internal elements, housing sections and strainers.

5.2.9. Piping shall be arranged to provide full access to all pumps, and to permit pump removal or replacement with the minimum dismantling of the piping.

Piping shall be arranged so they do not hamper removal of pumps (especially barrel type).

5.2.10. Thermal expansion, vibration, fabrication and erection tolerance shall be taken into consideration, so that excessive forces and moments are not developed at the pump casing and nozzles.


5.3.1. Generally, piping at columns should drop or rise immediately upon leaving the nozzle and run parallel and as close as practicable to the column itself.  However, for ease of supports a number of lines can be grouped together and run parallel in one plane.

5.3.2. For ease of operation and maintenance, columns and vessels, which are grouped together, should have their platforms at the same elevation with interconnecting walkways.  

5.3.3. Vessel connections, carrying inlet stream, shall be arranged to avoid impingement on the vessel wall or against liquid level and gauge glass connections.

The nozzle for level controlling instruments shall be oriented within an angle not exceeding 60° against the fluid inlet nozzle.

5.3.4. Drain valves on tanks and towers are to be located close to the equipment nozzle in order to avoid water pockets, which would freeze during the winter.

5.3.5. Davit or trolly beam shall be provided on vessel over 9m high where the weight of removable internals and/or external equipment, such as relief valves, is greater than 50Kg.


5.4.1. Piping shall be arranged so that they do not hamper removal of shell and channel covers and the withdrawal of the tube bundle.   It may be necessary to provide for a pipe spool, elbow or other removable pipe piece, other than the block valve, adjacent to the channel cover. Piping shall be so arranged as to permit removal of shell cover, channel and channel cover with minimum dismantling of piping.

5.4.2. For inlet piping to Air Fin Cooler, symmetrical piping arrangement consisting of multiple cascading headers shall be taken to equalize the flow to each bundle, in accordance with the requirement of P&IDs.

5.4.3. Pockets in exchanger piping shall be provided with low point drains to avoid freezing.

5.4.4. Enough clearance shall be provided around channel and shell flanges to permit tightening of studs with, impact wrench during maintenance.

5.4.5. In general, piping shall not be supported on exchangers.


5.5.1. Pulsation dampers, snubbers suction stabilizer or volume bottles shall be provided on reciprocating mechinery suction and discharge piping, in accordance with the requirements of P&IDs.

5.5.2. Compressor headers shall be suitably anchored and guided to eliminate excessive vibrations in piping or building structures, making at the same time adequate provision for thermal expansion.

5.5.3. The piping shall be so designed as to permit maintenance and dismantling of the machine with the minimum interference with piping.

5.5.4. Strainers shall be provided in accordance with P&IDs requirement.

5.5.5. Discharge check valve on compressors shall be installed as near to the compressor as possible.

5.5.6. Suction lines to gas compressors shall be designed to prevent entrained liquid from getting into the compressors.

5.5.7. Pipe supports shall not be combined with the compressor and other foundation. The compressor foundation shall not be combined with the compressor house foundation. Pipe racks shall not be connected to the compressor house.

5.5.8. Requirements for removal of mill scale, etc., by chemical cleaning for compressor piping, shall be reviewed for each individual case and indicated on the P&IDs. Where chemical cleaning is specified, the piping design specification shall be such that this is feasible.


5.6.1. Piping for this type of equipment shall be flexible. Refer to related specification for piping stress analysis.

5.6.2. Design shall allow for sufficient space below turbine inlets to permit the use of a blow down.


5.7.1. Piping at the burners, etc., shall be arranged so that it does not hamper insertion/removal of lighting torches and burner guns. Furthermore, piping shall not obstruct observation windows, access doors, header box covers, etc.

5.7.2. Main fuel gas block valves for each furnace shall be located 15 meters away from the furnace it services.

5.7.3. Smothering steam lines, shall be grouped and manifold in a remote location at least 9m from the heater and accessible from grade.


5.8.1. All piping in the system supplying sealing fluid to equipment mechanical seals shall be furnished in accordance with the equipment vendor's recommendations.


5.9.1. Local pressure gages and pressure transmitters shall be rigidly supported on the lines to which they are connected.

5.9.2. Except as specifically shown in project specification, orifice flanges may be located in horizontal or vertical lines. In a horizontal line, the orifice taps shall be in the vertical on the top for gas lines and in the 45° down for oil and liquid lines.


5.10.1. Sufficient distance shall be kept from tank nozzle to the first pipe support to prevent damaging of the pipe by tank settling.

5.10.2. In general, piping within tank dikes shall be routed in the shortest possible distance to the pipe-ways with adequate allowance for expansion and settling of tank without crossing trough other dike-in areas. 

5.10.3. Process operational valve manifold shall be located outside dike area, as much as possible.

5.10.4. Tank farm piping shall be routed outside dike area as much as possible.



6.1.1. The steam supply for space and protective heating shall be connected to a source that will not be shut off during unit or equipment shutdown.

6.1.2. In steam piping a steam trap shall be installed at each expansion loop, low points, the upstream side of venturi meters, and any place condensate can accumulate and for NPS 3” & larger, a condensate pot or drip leg (NPS 3”) shall be installed together with a steam trap.

6.1.3. When locating steam traps upstream of venturi meters or any instrument where the upstream or downstream piping is critical, the instrument engineer shall be contacted to indicate the minimum distance the drain valve can be located.

6.1.4. Steam piping systems shall be supplied to the extent shown on the steam flow diagrams and normally shall include systems for the distribution of steam required for process operations, steam turbines, service steam and for steam tracing. 

6.1.5. Steam trap hookup will be indicated in the piping design standard drawings. Traps inside unit battery limit shall generally discharge to a condensate return system or sewer.

Outside battery limit the traps shall discharge to a suitable location, such as ditch, or as defined on the P&IDs.

6.1.6. All branch connections from steam and condensate headers shall be taken off the top of the header with suitable valve.

6.1.7. In general steam exhaust line from reciprocating and centrifugal equipment, connected to a header, shall have a single block valve as per P&IDs.

6.1.8. Single block and check valves shall be provided adjacent to the point of injection of steam into any process stream as shown by flow diagrams.

6.1.9. All steam lines shall be designed to avoid unnecessary traps. Where traps can not be avoided, steam traps with drains shall be designed into the piping to remove condensate.

6.1.10. Block valves shall be provided near the header of each branch to all steam and steam condensate Consumers.

6.1.11. Condensate lines from different coils or system shall not collect in the same trap, but each system shall have its own trap(s).

6.1.12. All clean condensate shall run to a knockout drum, oil contaminated condensate shall be piped up to oily water sewerage system. 


6.2.1. Water lines connected to process lines or equipment where back flow may occur shall be fitted with a check valve as shown on P&IDs.

6.2.2. Potable water shall be used for safety showers and eye bath. Safety showers and eye bath shall be provided in accordance with P&IDs and shall be in accessible location. 

They shall also be in accordance to relevant NFPA code and related Engineering Specification.

6.2.3. Cooling water piping shall preferably be designed to prevent draining exchangers if water failure occurs.  All exchangers shall remain full of water.

6.2.4. Main lines for drinking water, cooling water, fire water and sewer should be underground piping.


6.3.1. All air and nitrogen lines should be installed overhead and shall be designed to avoid condensate pockets. If such low points cannot be avoided, drains shall be installed.

6.3.2. All air and nitrogen branch lines shall take off from the top of horizontal mains. 

Every take-off point from headers to instruments shall be furnished with a block valve, close to the header.

6.3.3. Instrument air sub-header shall have shutoff valve closed to the main air header.

6.3.4. Size of tapping branch from instrument air header for instrument air consumers shall conform to the following:

a) ½” tapping for 1 to 5 consumers.

b) ¾” tapping for 6 to 10 consumers.

c) 1” tapping for 11 to 15 consumers.

d) 1 ½” tapping for 16 to 20 consumers.

6.3.5 Instrument air shall not be used for any other purpose.



1)  In addition of hose stations which specified by process, hose station shall be provided at the following locations:

a) Hose station shall be provided at ground level so that all equipment can be covered within the redius of 15m by using 20 m hose.

b)  Hose station shall be provided at each equipment manhole platform so that equipment manhole can be covered within the redius of 15m by using 20 m hose.

c) Hose station shall be provided at each equipment structure platform so that equipment can be covered within the redius of 15m by using 20 m hose.

d) Hose station shall be provided at each Tie-in valves platform so that all valves can be covered within the redius of 15m by using 20 m hose.

e) Hose station shall be provided at reactor top and bottom platforms so that top and bottom nozzles can be covered within the redius of 15m by using 20 m hose.

2)  The hose connections shall generally be provided with 3/4" valves and hose connectors unless otherwise specified on P&IDs.

3)  Supplied utilities shall be arranged in the order of N2 (if required), air, water and steam from the left in operation side.

4)  Steam trap shall not be required at dead end of steam connection, unless otherwise specified by P&IDs.

5)  Utilities for hose stations could be taken from any header of related area.Block valve at take-off point from utility header shall not be provided unless otherwise specified by P&IDs.

6)  All nitrogen supply lines at utility stations shall be provided with special and different design to prevent the accidental connection to a nitrogen line when compressed air is required.The elevation of hose coupling and valve for nitrogen service shall be located lower than that for other services.

7)  All ground level hose station shall be provided with a steam and water mixing line to make hot water as specified by UDDs.

8)  Unless otherwise specified, general concept for hose station supplied service shall be as follows:

piping design spec


Emergency showers with eye wash fountains shall be provided in areas where operating personnel are subject to hazardous sprays or spills such as acid, caustic, etc. in accordance with P&IDs.


6.5.1. Drainage and sewerage systems shall be supplied to the extent shown on the P&IDs.

6.5.2. Equipment drains shall be collected to drain system in accordance with P&IDs.

6.5.3. Oily sewer systems shall be properly trapped and sealed at manholes and sumps.

6.5.4. Oily sewer shall be drained separate from rainwater and non oily sewer.

6.5.5. All sewer branches shall be connected to main at an angle of 60° or less.

Pressure RatingRun Pipe SizeBy-Pass Size
150 lbAllnot required
300 lbUp to 14”not required
300 lb16” & above¾”
600 lb and higherUp to 4”not required
600 lb and higher6” to 8”¾”
600 lb and higher10” and larger1”


All Piping material and components shall be selected based on items specified on Engineering Specification for Piping Materials.

All piping items which are not coverd by Engineering Specification for Piping Material shall be considered as Piping Special Item.

All piping special items shall be defined by tag number and  listed in Piping Special Item List.


7.1.1. The minimum pipe size shall generally be 1/2".

7.1.2. The minimum pipe size shall be 4" for the buried main sewer lines, and 2" for other buried lines.

7.1.3. Pipe size 1 ¼”, 2 ½”, 3 ½”, 5”, 7”, 9”, 22” and 26” shall not be used, except for connection to the equipment.

7.1.4. Nipple specification shall be in accordant with” Engineering Specification for Piping Material.”


7.2.1. Welding Fittings

a) Butt welding fittings shall be used in accordance to “Engineering Specification for Piping Material”.

Reducing elbows, straight crosses, reducing outlet tees, reducing outlet crosses and short radius 45 or 90 elbows shall be considered as special fittings. Such specials shall be used only to suit process or piping requirements if no other design is feasible.

b) Socket welding fittings shall be used in accordance to “Engineering Specification for Piping Material”.

7.2.2. Flanged fittings - Piping Design Specification 

In general, flanged fittings shall not be used.  However, when required, it shall be in accordance with ASME /ANSI B16.5 & ASME/ANSI B 16.47-B.

7.2.3. Threaded fittings

Threaded fittings shall be used in accordance to “Engineering Specification for Piping Material”.


7.3.1. Elbows shall generally be used to change the direction of piping, however factory bends and miters may be used in place of elbows.

7.3.2. In general, directional changes in piping arrangements shall be 45°, 90° and 180° turns, other turns are subject to OWNER’s approval.

7.3.3. Miter may be used, only when specified in relavant piping class in accordant with “Engineering Specification for Piping Material.”

7.3.4. The radius of bend shall be generally be 5 time the nominal outside diameter, unless otherwise indicated on the P&IDs.

7.3.5. Welding elbows shall be of the long radius type(R=1.5 OD). 

Short radius welding elbows  (R=OD) shall be used where required for clearance purpose and shall be indicated on piping drawings as SR.

7.3.6. Pipes indicated below may cold bent at site.

a) Carbon Steel pipe: 1" and smaller.

b) Ferrous Alloy and Non Ferrous Alloy pipe: 3/4" and smaller.


7.4.1. Flanges of 24" and smaller shall be consistent with ASME B16.5, and flanges of 26" through 60" shall be in accordance with ASME B16.47 series B.

7.4.2. The use of flanges in piping shall be limited to connections at flanged equipment (instrument equipment) and valves.

Flanges shall also be provided in special cases such as:

a) Where frequent dismantling of piping is required.

b) Where plastics, non metallic, cast iron or lining piping systems cannot be welded or otherwise joined except by flanges.

7.4.3. Welding neck type flanges shall be used for 2” and larger piping.

7.4.4. Flange faces shall be serrated finish in accordance with ASME B16.5.

7.4.5. Threaded flanges shall be kept to a minimum, with OWNER’s approval.

7.4.6. In general, the bolt holes of all flanges shall be straddled in vertical centerline for horizontal piping and shall be straddled in plant north-south line for vertical piping. 


7.5.1. Temporary conical strainers or wire nets for the purpose of flushing shall be provided in suction lines of pumps and compressors, if it has no permanent strainers.

7.5.2. Any other type of strainer or filter requirement shall be in accordance with the relevant P&IDs.

7.5.3. The type of strainers shall be specified in P&IDs.

7.5.4. Duplex type basket strainers shall be used where shut down is not permitted, and specified in the P&IDs.

7.5.5. The strainers shall be provided with connections for easy removal and servicing.


7.6.1. If required by their applicable design code, drain connections shall be provided for valves.

7.6.2. The valves for which by-pass are to be furnished, shall be indicated on the P&IDs.

7.6.3. If the P&IDs require a valve body by-pass, the by-pass size shall be as follows:

a) Material specification of the by-pass line shall be same as the material specification of the run pipe line  unless otherwise specified.

b) The by-pass line shall be provided with globe valve.



8.1.1. Stair Access to Platforms

The stair access shall be provided for following cases.

1) The top platforms of the structure is located 10 m and over above the ground and also the floor, has an area of 50 m2 and larger.

2) The platforms on which equipment or instrument requiring operation at emergency.

3) Platforms for equipment, which require frequent opening and/or closing of some part once or more per day.

4) The elevated platforms more than 1.5 m height on which a sample nozzle requiring sampling once or more per day.

8.1.2. Ladder Access to Platforms - Piping Design Specification

Maximum length of ladder between landing platforms shall be 9 m. 

Ladder access shall be provided for following cases.

1) Platforms other than Par. 8.1.1.

2) The platform with stair, which requires one escape way.

3) Platform height is 1.5 m and lower even though frequent operation is required.

4) Platforms attached directly to equipment.

5) Platforms not attached directly to equipment for access to manhole or instrumentation.

8.1.3. Dual Access Requirements

For following cases, two ways of access shall be provided.

1) When the platform has more than 20 m traveling from a main access ladder or stair, an escape ladder shall be provided. Dead end way shall also be restricted within 20 m.

2) Access ladders for walkway on the pipe rack shall be required at intervals of a maximum of 60m in process plant area (on-site) and a maximum of 100 m in off-site.

For each of the above, a crossover access way to another platform or floor may be planned in place of a ladder or stair.

Piping Design Specification - Minimum Access Requirements Table (1)

Piping Design Specification - Minimum Access Requirements Table (2)


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