An article on pipe support span for beginners. - What is Piping

An article on pipe support span for beginners.

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
Figure showing pipe support span
Fig. 1: Figure showing pipe support span

Span Length Depends On-

  • Bending Stress
  • Deflection
  • Indentation
  • Allowable Loads

BENDING STRESS:

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

Concentrated Load

  • Weight Of Valve, Flanges,
  • Strainer, specialty in line items etc.

DEFLECTION:

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

Natural Frequency

INDENTATION:

Indentation

Where,

t=corroded Thickness of pipe Wall(mm)

S=0.67Sh(N/mm2)

R=Radius of pipe (mm)

d=Bearing Length(mm)

b=Bearing width(mm)

ALLOWABLE LOAD AT SUPPORT:

Allowable Load

Where,

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.

Factor to reduce support span depending on layout.
Fig. 2: Factor to reduce support span depending on layout.
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2 thoughts on “An article on pipe support span for beginners.”

  1. hi all,
    with respect to Pa (allowable load at spport) where Sh is “hot allowable stress” or “Bending stress got from caesar software”

  2. ost but I was wanting to know if you could write a litte more on this subject? I’d be very thankful if you could elaborate a little bit more. Thanks!

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