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Pipe Support Design Guidelines

Posted by Antony Thomas at Wednesday, June 08, 2011
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Pipe Support Design Guidelines


A piping system shall be adequately supported and restrained to prevent line overstress, equipment nozzle overload, excessive bending of flange joints, excessive pipe sagging, high vibration, excessive deflection / movement, etc.

Scope:

The purpose of this guideline is to simplify and standardise the approach to pipe support design and selection for common support applications with the aim to improve quality, efficiency and productivity. The document shall be read in conjunction with the office standard pipe support drawings and the office piping stress analysis guide.

Pipe Support Identification Tagging:

Each pipe support standard detail drawing contains a legend for support identification tagging
applicable to the supports in the drawing.

Normally all the supports, covers under Standard Piping supports will be STD Pipe Supports.
If the supports needs modification or above the STD pipe support range (e.g. max length, height, pipe range) then it should be considered as Special Pipe Support (SPS).

All SPS as designed and checked  by Civil discipline.

Pipe Support Register:

Standard pipe supports, project specific pipe supports and temporary pipe supports will be listed in the project pipe support index drawing. Special pipe supports and temporary support frames are part of the Structural design and will be listed in the Structural discipline project deliverables.

Piping Fabrication Isometrics:

The Material section of the piping fabrication isometric will call up all standard pipe supports. The following information will be included:

  • Pipe support identification tag and description / nominal pipe size / quantity
  • Pipe support components that are welded to pipe, such as welded shoes and Trunnions, will be shown under “Fabrication Materials”.
  • Pipe support components that are field fitted, such as U-bolts, guides, line stops, will be shown under “Erection Materials”. 
  • The Drawing section of the fabrication piping isometric will show all the above pipe supports and will also reference structural SPecial Supports (SPS). 
  • Pipe support position will be dimensioned on the isometric drawing. This position corresponds to the location point indicated on the pipe support detail drawing. 

  • Also shown in the Drawing section of the isometric will be clarification notes, such as “no gaps”, nonstandard gaps and support orientation if required. 
Other Supports:

Use of spring hangers, snubbers and other such devices shall be specified by Stress Engineer. The project pipe support register will contain all design information required for procurement of these items.

Supports for extreme conditions, such as for very low operating temperature or acoustic vibration, shall be engineered, designed and procured from a reliable supplier.
These supports shall be designed for and installed in accordance with the Supplier’s instructions.

Small Bore Brace:

Small bore brace is typically used to protect a small size branch from damage.

Branch lines in sizes 2” and below are considered small bore and prone to fatigue failures in vibrating piping systems. They are also prone to mechanical damaged by an external force. The failure is usually at the branch weld to the main line or weldolet. Small bore branches are normally braced for that reason. Bracing shall be to the branch flange in preference to the branch pipe. Nipoflanges shall be used in preference to weldolets.

Small bore brace will not be required on small branches when:
  • The branch is continuous and supported and there is no valve within the first span;
  • Standard tees are used;
  • The piping is used for utility services.

Shoes:

For carbon and stainless steel piping welded shoes shall be used instead of clamped shoes where the temperature limit for clamped shoes has been exceed or where specified / approved by Stress Engineer for strength purposes.

Welded shoes shall not be used on lined piping, piping in expensive material, piping PWHT before shoe installation and piping galvanized before shoe welding.

Long length shoes shall be used where specified by Stress Engineer, a line stop is required or
there is an excessive support movement in longitudinal direction.

On insulated lines the standard shoe height of 100mm can be increased to up to 150mm where the insulation thickness is greater than 75mm. If required, shoes higher than 150mm will be designed by the stress engineer.

Pipe shoes shall be installed centrally on the support steel unless noted otherwise on the piping fabrication isometric.

When the design requires a continuously sloping line, this shall be achieved with the use of variable height shoes in combinations with adjustments of supporting steelwork.
Lines having a design temperature above 120°C shall be supported on shoes because of the
temperature limitations of PTFE isolation pads used with uninsulated lines.

Lines having a design temperature below minus 29°C shall be supported on shoes to avoid cold temperature embritellment of the supporting structural steel.

Trunnions:

Use of trunnion supports will be minimised and approved by Stress Engineer.

Trunnion supports on elbows will be avoided, particularly when a reinforcing pad is required. The use of the trunnion on an elbow with a reinforcing pad shall be approved by the Lead Piping Engineer.

Guides and Line Stops:

Guides  and line stops will be installed with the installation tolerance gap of maximum 3mm
on each side of the support unless noted otherwise on the isometric.

Hold down guides shall only be used when specified by Stress Engineer. Using these guides for guiding vertical pipes is not preferred.
Alternative line stops of high load capacity shall only be used when approved by Stress
Engineer.


U-Bolts:

A U-bolt shall be installed in such a way that the dead weight of the piping is supported by the
structure and not the U-bolt itself.

U-bolts can be used on both horizontal and vertical lines.

Isolation Pads:

Isolation pad (PD-01) made of PTFE is used to support the line and reduce the risk of fretting
corrosion to the underside of the pipe. Isolation pads shall be bonded directly to the structural steel. Bonding / fixing of the isolation pad to the structural steel shall be suitable for the required service life of the support.

Pipe shoes shall be used instead of isolation pads if the temperature limit of the pad bonding
adhesive or material has been exceeded.

Isolation pads are not required under shoes, trunnions, reinforcing pads and on the facings of guides and line stops.

Reinforcing Pads:

Reinforcing pads are typically used to reduce stress level in the pipe wall from welded attachment or high bearing load. They can also be used to protect pipe wall from external corrosion.

Support Span:

Piping will be subject to internal and external loads during topside transportation and installation, environmental loads and operating and transient process loads. Piping movement shall be restrained on all three orthogonal directions allowing sufficient flexibility for thermal expansion and other imposed deflections, such as bridge and wellhead movements.

Small size piping in 2” and below shall be restrained with U-bolts wherever possible. Larger piping shall use guides and line stops with guides installed on every second support on a straight run.

Welded Attachments:

Non-pressure retaining pipe attachments that are enclosed, such as reinforcing pads and trunnions, shall have a vent/test hole to release the gas build up during welding and to provide an inspection point for any pipe leak. The hole shall be tapped with an NPT thread to allow low pressure pneumatic testing after welding.

Special Applications:

Control valve sets will typically be anchored with a line stop and hold-down guide on one side and guided on the other side.

Pig traps will typically be anchored with a line stop and hold-down guide at the pipeline end and guided at the closure end.

Manifolds will typically have guides at each end and a centrally located line stop.
Drain systems with rodding points shall be supported in such a way to withstand rodding loads.
The free pipe ends on Utility Stations shall be securely fixed. That may be accomplished with U-bolts either as guides or anchors.

For piping supported from a pressure vessel the pipe support details and loads will be issued to the Mechanical discipline for incorporation in the pressure vessel design by the vessel supplier.

SUPPORT MATERIAL:

Material for pipe supports can be generally divided into three categories:
1. Welded attachments to piping. The attachments shall be of the same material grade as the
run pipe.

2. Pipe supports or pipe support parts not welded to piping. ASTM A36 or equivalent material can be used unless noted otherwise.

3. Structural pipe supports. Frames fabricated from ASTM A36 or equivalent structural steel
sections and plates.

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