3. INTRODUCTION
A pipe rack is the main artery of a process unit. It connects all equipment
with lines that cannot run through adjacent areas. Because it is located in
the middle of the most plants, the pipe rack must be erected first, before it
becomes obstructed by rows of equipment. Pipe racks carry process, utility
piping and also include instrument and electrical cable trays as well as
equipment mounted over all of these.
The primary data required for detailed development of a pipe rack :
Plot Plan
P&ID’s
Client Specification
Construction Materials
Fire proofing requirements
Statutory requirements
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5. PIPE RACK DESIGN CRITERIA
Shapes
Future Space
There are various shapes of pipe rack like L/T/U/H/Z. These shapes
shall be considered based on the area available.
The total width of the pipe rack shall include 25% extra space for
future expansion/modification in unit for rack-width upto 16m and
10% for rack-width above 16m. The future space %age is normally
based on the client requirements.
Width of Pipe rack
The width of the rack shall be 6m, 8m or 10m for single bay and 12m,
16m or 20m for double bay having 4 tiers maximum. The spacing
between pipe rack portals shall be taken as 6m in general. However it
can be increased to 8m depending on the size of the pumps to be
housed below pipe rack.
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7. DIFFERENT SHAPES OF PIPE RACKS
DEAD END YARD LINES ENTER &
LEAVE ONE END OF THE RACK
L-SHAPED YARD LINES CAN
ENTER & LEAVE NORTH & EAST
OF THE RACK
STRAIGHT THROUGH YARD LINES
CAN ENTER & LEAVE BOTH ENDS
OF THE RACK
T-SHAPED RACK PIPING CAN
ENTER & LEAVE THREE SIDES OF
THE RACK
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8. DIFFERENT SHAPES OF PIPE RACKS
COMPBINATION OF I & T SHAPED
RACK
U-SHAPED YARD LINE CAN ENTER
& LEAVE ALL FOUR SIDES OF THE
RACK
COMPLEX RACK PIPING ARRANGEMENT
FOR VERY LARGE CHEMICAL PLANT
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9. PIPE RACK DESIGN CRITERIA
Clearance
For units, clearance beneath pipe rack shall be 4m
minimum both in longitudinal and transverse
directions.
For Offsite, clearance beneath pipe rack shall be 2.2m
minimum both in longitudinal and transverse
directions.
Road clearance shall be 7m for main road and 5m for
secondary road.
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10. PIPE RACK LOADING
Pipe rack loads shall be given by stress group to Civil &
structural discipline for pipe rack design.
Sustain Load (Dead Load)
Thermal Laod
Load by thermal expansion of piping & Reaction force by
internal pressure of expansion bellows
Dynamic Laod
Weight of piping, valve and load insulation
Load by vibration of piping & by wind and earthquake
Sustained Load (Live Load)
Liquid load for hydrostatic pressure test
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11. RACK PIPING
Position of Lines
Predominantly process lines are to be kept at lower
tier and, utility & hot process lines on upper tier.
Hot Lines & Cold Lines
Generally hot lines & cold lines are to kept at
different tiers or at different groups on a tier.
Pipe Spacing
Minimum spacing between adjacent lines shall be decided based
on O.D. of bigger size flange (minimum rating 300# to be
considered), O.D. of the smaller pipe, individual insulation
thickness and additional 25mm clearance. Even if flange is not
appearing the min. spacing shall be based on above basis only.
Actual line spacing, especially at ‘L’ bend and loop locations,
shall take care thermal expansion/thermal contraction/nonexpansion of adjacent line. Non-expansion/thermal contraction
may stop the free expansion of the adjacent line at ‘L’ bend
location.
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12. RACK PIPING
Bigger Size Lines
Anchor Bay
Large size lines (14” and larger) shall be arranged close to the
column in order to decrease the bending moment of beam. Water
lines more than 30” shall not be routed over pipe rack, these shall
be routed underground.
Anchors on the racks are to be provided on the anchor bay if the
concept of anchor bay is adopted. Otherwise anchor shall be
distributed over two to three consecutive bays.
Anchors shall be provided within unit on all hot lines leaving the
unit.
Pipe Route
Racks shall be designed to give the piping shortest possible run
and to provide clear head rooms over main walkways, secondary
walkways and platforms.
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13. RACK PIPING
Trays
Generally top tier is to be kept for Electrical cable trays (if not
provided in underground trench) and Instrument cable ducts/trays.
Cable tray laying to take care of necessary clearances for the fire
proofing of structure.
Battery Limit (ISBL)
Process lines crossing units (within units or from unit to main
pipeway) are normally provided with a block valve, spectacle blind
and drain valve. Block valves are to be grouped and locations of
block valves in vertical run of pipe are preffered. If the block
valves have to be located in an overhead pipe-way, staircase access
to a platform above the lines shall be provided.
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17. EXPANSION LOOPS
Expansion loop is provided on the high temperature
lines. This information shall be given by stress group.
All the loops shall be located around one column only.
MAKE LINES INTO A GROUP AND INSTALL A
LARGE SIZE PIPING AND HIGH TEMPERATURE
PIPING TO THE EDGE OF THE RACK
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18. EXPANSION LOOPS
When necessary to install an expansion loop on the
condensate line, do it horizontally to prevent water
hammering. But do as above if horizontal loop is impossible.
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