Pipe Support Span is defined as the optimum distance between two supports so as to avoid excessive stress, sagging or failure of the piping system in extreme cases. We all know that while routing aboveground piping or pipeline from one part or equipment to other we have to support the pipe at some places. Properly designed pipe support span helps the piping personnel to support pipes at regular intervals, thus reducing his work for unnecessary calculations. Refer to Fig. 1.
Factors on Which Pipe Support Span Depends
There are various factors which influences the pipe support span. Pipe support span varies with changes in
- Pipe Material
- Nominal Diameter Of Pipe & Schedule
- Type of service
- Type and Thickness of Insulation Material
Deciding Pipe Support Span
Pipe Support Span Length Depends On-
- Bending Stress
- Allowable Loads
Bending is caused mainly due to two reasons:
- Uniform Weight Load
- Concentrated Weight Load
Uniform Weight Load
- Own Weight Of Pipe
- Insulation Weight
- Weight of Fluid During operation
- Weight of hydrostatic fluid During Hydro Test
- Weight Of Valve, Flanges,
- Strainer, specialty items, inline items, etc.
Deflection (Δ) is defined as a relative displacement of the point from its original position.
- The basic piping practice to limit pipe deflection between supports to 1” or 1/2 the nominal pipe diameter, whichever is the smaller.
- The most important reason for limiting deflection is to make the pipe stiff enough, that is , of high enough natural frequency, to avoid large amplitude response under any slight perturbing force. As a rough rule, for average piping, a natural frequency of 4 cycles per second will be found satisfactory. The natural frequency can be calculated by
- t=corroded Thickness of pipe Wall(mm)
- R=Radius of pipe (mm)
- d=Bearing Length(mm)
- b=Bearing width(mm)
Allowable Load at Support
- Pa=Allowable Load at the Support point
- t=effective local thickness (pipe wall +Reinforced Pad If Any)
- R=outer radius of Pipe
- b=Bearing length of pipe (along the axis) on the support structure
IF ACTUAL LOAD AT SUPPORT IS GREATER THAN ALLOWABLE LOAD GIVEN BY ABOVE FORMULA, REINFORCEMENT PAD WILL BE REQUIRED.
Normally project-specific Support Span is provided in tabular format for straight pipes that is known as “Pipe Support Span Chart”. But for elbows or turns the span to be reduced by a factor as shown in the below-attached figure (Fig. 2). Readymade support spans for specific pipe diameter and thickness are available in MSS code. For Shell group of companies’ support span is provided in DEP in tabular format.
Pipe Support Span Chart
Pipe support span chart is a tabular chart giving a rough idea of supporting distance. These charts are normally mentioned in piping stress analysis project specifications. In the following image (Fig. 3) pipe support span chart from MSS SP-69 is reproduced as a sample.
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