Pipe Rack and Pipe Track

This weblog provides you brief information about pipe rack and pipe track design, basic differences, width calculation for pipe racks, civil loading for pipe rack, different types, shapes of pipe racks and including basic key points for design and review of any pipe rack or pipe track design.

Introduction

A pipe rack is the main artery of a process unit. It connects all equipment with lines that cannot run through adjacent areas. Pipe racks carry process, utility piping and also include, instrument and electrical cable trays as well as equipment mounted over all of these.

Since pipe rack is located in the middle of the most plants, the pipe rack must be erected first, before it becomes obstructed by rows of equipment.

Basic difference between pipe rack and pipe track:-

Pipe Rack consists of overhead piping supported on structural steel or on concrete bents.
Pipe track consists of above ground piping supported on concrete sleeper at grade level.

The primary data required for detailed development of a pipe rack and pipe track:-

• Plot Plan
• P&ID’s
• Utility distribution diagram
• Line list (Insulation thickness, operating temp. etc)
• Client Specification
• Construction Materials (Concrete or Steel)
• Fire proofing requirements

PIPE RACK and PIPE TRACK DESIGN

We will see below, how to start pipe rack design and what are the basics,

• First and topmost step in the development of any pipe rack is the generation or development of line–routing diagram.
• What is line routine diagram? A line–routing diagram is a schematic representation of all process and utility piping or systems drawn on a draft of plot plan or it is also called as planometric drawing or representation of the process as well as utility lines drawn as diagrams.
• Since this is just a schematic representation, it doesn’t cover any exact location or or any interfaces. It is just used to see the most congested area.
• Subsequent second step is to find out the most congested area, based on schematic line-routing diagram and arrange all process piping as well as utility piping to finalize width of pipe rack, including no of tiers or racks required.
• Third step is to make sure about client requirements, stated in their specifications or feed documents provided, and same shall be checked and taken care in pipe rack design, while deciding width of pipe rack as well as tiers etc.
• Every pipe rack shall have some future space requirements. Hence total width of the any pipe rack shall include 20% additional space for future expansion or modification in unit for rack-width upto 16m and 10% for rack-width above 16m. Client requirement is governing the future space requirements, as stated in feed or specification documents.
• 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. In general spacing between pipe rack portals or bays shall be taken as 6m. However pump sizes and installation of pumps below pipe rack, may need more increased to 8m.

Width of Pipe rack

The width of the pipe rack is estimated as per below equation,

W = (f x n x s) + A + B

f = Safety factor
= 1.5 if pipes are counted from the PFD
= 1.2 if pipes are counted from P & ID.
n = Number of lines in the densest area upto the size of 18 Inch
s  = 300mm (estimated average spacing)
= 225mm (if lines are smaller than 10 Inch)
A = Additional width for
(1) Lines larger than 18 Inch
(2) For instrument cable tray/duct
(3) For electrical cable tray
B = Future provision
= 20% of (f x n x s) + A

Different Shapes of Pipe Racks

• All plants are segregated or split into convenient parts based on pipe rack design.  There are various shapes of pipe racks, which are indicated as ‘straight’, ‘L’, ‘T’, ‘U’, ‘H’ and ‘C’ or ‘Z’.
• These shapes of pipe racks or configuration is based on the overall facility layout and arrangement of equipment’s as well as site physical conditions. Pipe rack is designed with location based on the incoming and outgoing piping lines.

After finalizing width of Pipe Rack, clearance below pipe rack or clearance beneath pipe rack is important and shall be maintained as below,

• 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.
• All these are general requirements, which needs to be maintained based on the client requirements.

RACK PIPING

Most important key points to be taken in account for any pipe rack design are indicated as below,

Position of Lines

• Mainly process lines are to be kept at lower tier and utility & hot process lines on upper tier.
• Hot Lines & Cold Lines are generally located at edge of rack for expansion loops feasibilities.
• Flare lines are kept at top tier.
• Lines with Orifice plates.
• Big Size pipes

Future Space

• Every pipe rack shall have some future space requirements. Hence total width of the any pipe rack shall include 20% additional space for future expansion or modification in unit for rack-width upto 16m and 10% for rack-width above 16m. Client requirement is governing the future space requirements, as stated in feed or specification documents.

Pipe Spacing

• Pipe Spacing charts, standards or table shall be followed for pipe spacing on pipe rack.
• High temperature lines spacing shall be as per thermal expansion.
• Fire proof thickness to be considered while deciding pipe spacing.

Bigger Size Lines

• Large size lines (14” and larger) shall be arranged close to the column in order to decrease the bending moment of beam.

Anchor Bay

• 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.
• Bracing locations shall be at anchor bays.

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.

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.

Expansion Loops required on Pipe Rack and Pipe Track

• 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

• 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.

PIPE RACK and PIPE TRACK LOADING

Pipe rack loads shall be given by stress group to Civil & structural discipline for pipe rack design, which contains below cases and relevant loads to be taken care in civil design.

• Sustain Load (Dead Load)
• Weight of piping, valve and load insulation
• Thermal Load
• Load by thermal expansion of piping & Reaction force by internal pressure of expansion bellows
• Dynamic Load
• Load by vibration of piping & by wind and earthquake
• Sustained Load (Live Load)
• Liquid load for hydrostatic pressure test

KEY POINTS for any PIPE RACK and PIPE TRACK

• Construction priority.
• Drip legs Location
• Expansion loops & Drop out location for relief valves or big sized valves.
• Bracings at anchor bay locations.
• U/G Lines crossing at Anchor bay location.
• Plan bracing locations
• Flat turns on pipe rack.
• Small Bore Piping with below 2”.
• Slope lines.
• Pipe rack concrete or steel.
• If concrete check for Insert plate requirements.
• Monorail requirements
• Platform requirements for C&A condensate pot access for orifice.
• Pipe rack Interface between two units or between two contractors.
• Pipe rack loading for future space.
• Escape ladders and proper access requirements.
• Relief Headers
• Check for Fire water lines requirements. (Since these are not coming under utility)
• Where possible interconnect adjacent platforms with pipe rack platforms for better access and better escape routes in case of any accidents. Since both the structures are having difference expansion rates, keep gap of 50mm between interconnection.
• Utility stations.
• Electrical & instrument junction box locations check.
• Davit requirements with drop out area.
• Control valve station assembly, Heat tracing steam trap assemblies.
• Check for construction sequence for hydro test on pipe rack pipes. i.e. no of lines at once for hydro test for economic design of pipe rack.