Pipe Support Span (Fig. 1) is defined as the optimum distance between two supports so as to avoid excessive sagging. Pipe span varies with changes in
- Pipe Material
- Nominal Diameter Of pipe & Schedule
- Type of service
- Type and Thickness Insulation
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 in line items etc.
Deflection (Δ) is defined as relative displacement of 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)
ALLOWABLE LOAD AT SUPPORT:
Pa=Allowable Load at 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. 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 a specific pipe diameter and thickness are available in MSS code. For Shell group of companies support span is provided in DEP.