3.2　Headroom or Buried Depth of Piping

3.2.1　If the piping crosses over onsite railways and plant roads，it shall comply with the following requirements：

a）When the piping crosses over the railways in plant area and process units，piping for flammable gas，liquefied hydrocarbon and flammable/combustible liquid services shall have a headroom not less than 6.0m above the top of rail，and piping for other services shall have a headroom not less than 5.5m above the top of rail.

b）When the piping crosses over the plant roads in plant area and process units，it shall have a headroom not less than 5m above the road surface.

c）When the piping crosses over maintenance accesses and fire roads in process units，it shall have a headroom not less than 4.5m above the road surface.

3.2.2　If the piping is routed parallel with railways or plant roads，the distance from the protrusions of the piping or the outer edge of the piperacks to the outboard side of rail shall not be less than 3m，and the distance from the protrusions of the piping or the outer edge of the piperacks to the outboard side of road shall not be less than 1m.

3.2.3　If the piping passes railways and plant roads in plant area，it shall comply with the following requirements：

a）The intersection angle between piping and railways or plant roads should not be less than 60°，and the piping crossing section shall be routed in pipe culvert or sleeves.

b）Each end of sleeves shall extend at least 2m beyond the surface of roadbed slope.If drainage ditch is constructed along the road，each end of sleeves shall extend at least 1m beyond the edge of drainage ditch.

c）The distance from the top of sleeves to the bottom of rail shall not be less than 1.2m，and the distance from the top of sleeves to road surface shall not be less than 0.7m，otherwise，strength of sleeves shall be checked.

d）If the piping for liquefied hydrocarbon service passes railways or plant roads，it shall be routed in sleeves.

The minimum buried depth from the top of sleeves to the bottom of rail shall not be less than 1.4m，and the minimum buried depth from the top of sleeves to road surface shall not be less than 1m.

3.2.4　Clearance of plant-wide above ground piping shall comply with the following requirements：

a）The headroom from the piping to the ground shall not be less than 0.4m.

b）If walkway is required under piperacks，the headroom from the piping to the ground shall not be less than 2.2m.

3.2.5　Clearance of the piping routed in ISBL piperacks shall comply with the following provisions in addition to equipment connections and maintenance requirements：

a）If the space under piperacks is used as fire road，the headroom from the piping to the ground shall not be less than 4.5m.

b）If the space under piperacks is used as pump maintenance access，the headroom from the piping to the ground shall not be less than 3.2m.

3.2.6　The headroom from ISBL piping to the surface of walkway shall not be less than 2.2m，and the width of operation access should not be less than 0.8m.

3.2.7　The horizontal distance from the edge of ISBL pipe support to the edge of walkway，the exterior wall of building with doors and windows，and the exterior wall of building without doors or windows shall not be less than 0.5m，3.0m and 1.5m respectively.

3.2.8　For piping routed at ground level，it shall have an erected height enough for valves and pipe fittings.it shall have a headroom not less than 0.15m above ground with consideration a space reserved for pipe draining and strainer screen withdrawal.

3.2.9　The buried depth of ISBL piping shall be determined according to the maximum soil frozen depth，ground water table and avoidance of damage to piping，which should comply with the following requirements：

a）In area not paved with reinforced concrete，the distance from the top of the piping to the ground should not be less than 0.5m.

b）In indoor or outdoor area paved with reinforced concrete，the distance from the top of the piping to the ground should not be less than 0.3m.

c）In vehicle access area，the distance from the top of the piping to pavement should not be less than 0.7m.

3.2.10　If valves are installed in buried piping，valve pit shall be constructed.

Space for operation and maintenance shall be provided in the valve pit，the top surface of valve pit wall shall be 0.1m above ground，and cover shall be installed for valve pit.The headroom from buried piping to pit bottom shall not be less than 0.2m and water drainage facilities shall be provided in valve chamber.

3.2.11　Buried piping for flammable gas and flammable/combustible liquid services should not pass through cable trenches，otherwise，sleeves shall be provided.

If thefluid in piping exceeds 60℃，insulation materials shall be filled in piping sleeves to control the temperature of sleeves exterior wall not higher than 60℃.

Each end of the sleeves shall extend at least 0.5m beyond the exterior wall of cable trenches.

3.2.12　Piping routed in trenches shall comply with the following requirements：

a）Piping，which is neither overhead routed nor buried，may be routed in inaccessible pipe trenches.

b）Accessible pipe trenches include fully enclosed pipe trenches and open pipe trenches.

Fully enclosed pipe trenches are suitable for the piping requiring no frequent inspection and maintenance.

Open pipe trenches are suitable for the piping requiring frequent inspection and maintenance，the top surface of trench wall shall be 0.1m above ground，and cover or steel grating shall be provided.

c）If valves are installed in piping erected in fully enclosed pipe trenches，valve pit shall be constructed in accordance with the requirements the same as those for buried piping.

d）The headroom from piping to trench bottom shall not be less than 0.2m.

e）Pipe trench bottom shall have a slope not less than 0.003，and water drainage devices shall be provided at the lowest point in pipe trenches.

f）If a pipe trench is located within an extent in 30m to process equipment releasing flammable gas heavier than air，provisions shall be made to prevent flammable gas from being dispersed into and accumulated in pipe trenches.

g）Piping for flammable gas，liquefied hydrocarbon and flammable/combustible liquid services should not be routed in pipe trenches.If such piping must be routed in pipe trenches，provisions shall be made to prevent flammable gas，liquefied hydrocarbon and flammable/combustible liquid from being accumulated in pipe trenches，and seal partition shall be constructed at the location where piping is routed to/from process plants and building.Wastewater accumulated in pipe trenches shall be sent to process wastewater piping via water seal pit.