3　General Requirements

3.1　General Requirements for Piping Layout

3.1.1　Piping layout shall be designed in accordance with the requirements of process，piping and instrument diagrams（including P&ID and U&ID）.

3.1.2　An overall consideration shall be given to piping layout for safe and reliable operation，economy，nice appearance，and easy construction，operation and maintenance.

3.1.3　If a project is proposed for construction in phases，an overall consideration shall be given to piping layout for eliminating any interference with construction，operation and maintenance activities.

3.1.4　Permanent above ground（A/G）and under ground（U/G）piping shall not pass or cross over any unrelated process plants，units or tank farms，Valves and piping components susceptible to leak shall not be installed in the piping for flammable gas，liquefied hydrocarbon and flammable/combustible liquid services which crosses over pump rooms in tank farms.

3.1.5　Orientation and routing for the piping to/from process plants or units shall be well coordinated between battery limits.

3.1.6　Plant-wide piping shall be routed to coordinate with process plants，units，roads，buildings and structures in plant area.Piping shall not encompass process plants or units，and shall avoid cross-over with railways and plant roads whenever possible.

3.1.7　Piping should be routed in groups，and A/G piping shall be routed on piperacks or pipe sleepers.

For piping routed at ground level，walk-over stiles shall be provided at location where piping crosses walkway.

If required，piping may be buried or routed in pipe trenches.

3.1.8　Plant-wide piping should be routed above ground.Piping routed at ground level or on piperacks shall not encompass process plants，units and tank farms，and shall not obstruct fire engine accesses.

3.1.9　Plant-wide piping shall be routed in slope which should not be less than 0.002 and should be the same as that of the ground.

Slope transitions for plant-wide piping should be located at changes in direction or near anchors.

3.1.10　Piping on piperacks or pipe sleepers should have the vertical load and horizontal load from piping uniformly distributing on piperacks or pipe sleepers.

3.1.11　Piping layout shall be designed not to interfere with installation and maintenance of equipment and internals.

3.1.12　Piping layout should be designed to avoid high point gas pocket or low point liquid pocket.

Otherwise，vents or drains shall be provided according to operation and maintenance requirements.Piping layout shall be designed to avoid dead end.

3.1.13　Branch pipe for gas service should be taken off the top of the main pipe.

3.1.14　Where piping for liquid-vapor phase flow service is diverted into two or more branchs，the branch pipes should be symmetrically arranged.

3.1.15　Horizontal piping for gravity flow service shall have a slope not less than 0.003 along flow direction.

3.1.16　Layout of piping for solid or solid-bearing fluid service shall be routed for the shortest practical run，minimum number of elbows，and avoiding any dead end.

3.1.17　Branch pipe for solid service shall be laterally connected to the main pipe along flow direction，and the angel of intersection should not be larger than 45°.

3.1.18　Layout of piping for solid-bearing slurry and highly viscous liquid services shall be designed in slope.

3.1.19　Layout of piping in fluid service with special requirements for run distance，angle and delta height，and piping for high temperature service or with large diameter shall be designed to meet the requirements of equipment layout.

3.1.20　Piping for flammable gas，liquefied hydrocarbon and flammable/combustible liquid services shall have isolation valves and blinds provided at battery limit of process plants，and platforms shall be provided at locations where isolation valves are installed.Platforms with a length equal to or larger than 8m shall be provided with ladders at both ends.

3.1.21　Piping for flammable gas，liquefied hydrocarbon and flammable/combustible liquid services shall not pass unrelated buildings.

3.1.22　Layout of the piping for corrosive，toxic and high pressure fluid services shall be designed to avoid any risk of injury to personnel and equipment damage due to the potential leak from valves and piping components.

Any parts or connections susceptible to leak shall not be located above walkways，compressors and pumps；otherwise，safety shields shall be provided.

3.1.23　If the piping crosses over or passes onsite railways and plant roads，valves and piping components susceptible to leak shall not be installed on cross-over or crossing sections.

3.1.24　Plant-wide piping shall not be routed under roadway，above or under road shoulder along the road.

3.1.25　Piping layout shall be designed to have sufficient flexibility，and the forces and moments imposed on equipment nozzles shall be within the allowable value，and shall be routed with the shortest practical run and minimum number of elbows.

3.1.26　Layout of the piping connected to rotating machine shall be designed to have sufficient flexibility，and the forces and moments imposed on equipment nozzles shall be within the allowable value.

Otherwise，the following provisions may betaken，such as：

a）Changing the pipe routing to increase natural compensation.

b）Erecting restraint supports and hangers.

c）Using spring support and hanger.

d）Using metal bellows expansion joint.

3.1.27　Elbow with bending radius not less than 1.5 times the nominal diameter shall be used at changes of reciprocating compressor and reciprocating pump discharge piping susceptible to vibration.

3.1.28　Branches from the main pipe subject to vibration shall not be taken off the section with large bending moment.

3.1.29　If branch pipe with nominal diameter equal to or less than 40mm is taken off the main pipe susceptible to vibration，connections shall be reinforced regardless of the branch pipe installed with or without valves.

3.1.30　Seismic design for metallic piping shall comply with current relevant standard of the nation SH/T 3039.

3.1.31　Piping layout should be designed to provide natural compensation by pipe routing.

3.1.32　Consideration shall be given to the arrangement of supports while pipe routing.

Supports shall befirmly erected to avoid being detached from the piping，or causing piping distortion，sag or the vertical piping out of plumb.

3.1.33　Where piping passes through building floor，roof or wall，sleeves should be provided，and the gap between sleeves and piping should be sealed.

Sleeves shall have a diameter larger than the outside diameter of the piping insulation，and shall not restrain pipe movement.

Welds in piping shall not be located in sleeves，and shall have a distance not less than 150mm to sleeves end.

Sleeves end shall be installed 50mm higher above building floor or roof.

Rain protection hood shall be provided on the roof where piping passes through.

Piping shall not pass through the fireproof wall.

3.1.34　Safety shower and eye washer shall be provided according to the properties of corrosive or toxic fluid，operating conditions and protection requirements，and its service radius shall not be larger than 15m.

3.1.35　Hose station shall be provided，which may include steam，fresh water，plant air and nitrogen as required，and its service radius should be within 15m-20m.

3.1.36　Piping shall be weld joined except that it is required to be flange or thread joined to valves，instruments and equipment.

However，flanged，threaded or other removable joint should be used for the following cases：

a）Any joint required to be removed for maintenance，flushing or purging.

b）Non-metallic lined piping or jacketed piping.

c）Pipe made of different materials，for which welded joint should not be used.

d）Galvanized piping with nominal diameter less than or equal to 80mm.

e）Location where blind is installed（including spectacle blind，spade and spacer）.

3.1.37　For pipe bending at site，bending radius shall comply with Table 1.

3.1.38　Pipe welds shall be arranged according to the following requirements：

a）Except for manufactured bends，the distance between circumferential welds and bending point of bends shall not be less than the outside diameter of pipe and shall not be less than 100mm.

b）Except for manufactured fittings，the distance between two circumferential welds shall not be less than 3 times weldment thickness.When post weld heat treatment（PWHT）is required，it shall not be less than 6 times weldment thickness and shall comply with the following requirements：

1）If the nominal diameter of the piping is less than 150mm，the distance between two circumferential welds shall not be less than the outside diameter of the pipe and shall not be less than 50mm.

2）If the nominal diameter of the piping is larger than or equal to 150mm，the distance between two circumferential welds should not be less than 150mm.