Re: Pipe Support Span Distances

From: <hasan>
Date: Mon Jun 23 2008 - 09:16:00 EDT

Dear Paul
In general Pipe span is limited by pipe material (allowable stress), sectional modulus (nominal size and Sch. of pipe) and weight of its content and insulation and design temperature of the pipe system which affects allowable stress in calculation of pipe span. In general pipe span is limited by allowable deflection and allowable bending and shear stress. To simplify pipe support spacing calculation MSS- SP69 has provided recommended practice for support spacing which has been accepted by ASME. These spans are limited to max. combined stress(bending and shear) to 1500 PSI and max. pipe sag of 0.1 inch we use allowable pipe span as a general and primary solution for supporting but some points should be considered in supporting: 1- All span should be adjusted based on available structure for supporting. 2- In case of change of direction in horizontal pipes you should reduce pipe span. as a good practice you can use 0.75 of span. 3- Span should be decreased based on concentrated weight and load in piping system such as valve and flange. As a good practice you can use 0.75 of span for one element and 0.6 of span for two elements in piping system. 4- finally you should consider maintenance requirement(for example for valve maintenance and removal) you should consider supports as possible as near to valves).
Also I should note hear that occasional loads such as wind and earthquake do not concern span of weight support because using span is used for dead loads. For this loads stress analyzer engineer should use proper guide and other dynamic supports such as rigid strut and shock absorber with careful attention to thermal expansion and load.
When you see various recommended span for a same size it may means using of various safety factor, various fluid content, various design temp. Various pipe materials and other design objects in calculation of max. allowable span.

In general we have:

L < (10 * Z* F * S/W)^0.5
In which

L= Max. allowable span(mm)
Z= Pipe sectional modulus(mm3)
F= Safety factor
S=Allowable stress in design temp(N/mm2).
W=Weight per linear unit of pipe(N/mm)

I hope these all are useful for you.

Best Regards
Hassan Hajitabar

Piping Engineer
Engineering Department
Iranian Offshore Engineering & Construction Company (IOEC) E-mail: Hajitabar@Ioec.com Received on Mon Jun 23 09:16:00 2008