Hi everyone,

I am collecting information regarding pipe support span.

found- two ways to design

Based on pipe deflection

Based on stress

I came across that in B31.1
it is decided based on allowable stress -15 Mpa at 400 C.

whated to know why such a low value of allowable taken for pipe support span?

Dear shamaliabhavin

You can refer the book INTODUCTION TO PIPE STRESS ANALYSIS by SAM KANNAPAN for the information regarding pipe support span Based on limitation of pipe deflection and Based on limitation of stresswhich is given in this book,chapter 2 "pipe span calculation".

Reagards

Tanmay

Old BS 3974 (now discontinued) used to use 25MPa due to self weight and I think that is conservative enough. The balance of the strength is left for all other types of stresses: thermal, pressure, local, etc.

Dear tanmay/RS

Thank you for your response.

But that is not what i want.

My question is why B31.1 used allowable bending stress value as 15.86 MPa for calculated pipe support span at 400 C.

If you can refer, For CS material as per B31.1 allowable value is much much more than 15.86 Mpa.

Also why as per B31.1 sag limit is 2.5mm.
I want to know the basis.


Mr Dave Diehl / Mr. Richard Ay, Plz give your opinion on this.

Thanks .

Dear tanmay
Thank you for your response.

But that is not what i want.

My question is why B31.1 used allowable bending stress value as 15.86 MPa for calculated pipe support span at 400 C.

If you can refer, For CS material as per B31.1 allowable value is much much more than 15.86 Mpa.

Also why as per B31.1 sag limit is 2.5mm.
I want to know the basis.


Mr Dave Diehl / Mr. Richard Ay, Plz give your opinion on this.

Thanks .

Rule of thumb for manual span calculation is usually Sh/4 as a stress level due to weight / bending (in addition to other criteria for deflection, local stresses, natural frequency, etc.).

B31.1 may give a deflection limit as for steam piping you wouldn't want a lot of potential condensate collection points in excessively sagging lines.

I agree with Dclarkfive's figure of Sh/4, the basis of most company span charts. Remember that up to Sh/2 must be assigned to axial pressure stress according to B31 codes.

Also, in addition to mid-span bending and deflection criteria, in larger and thin wall pipe, local stress at the support attachment / rest point may be a limiting factor

In common with shamaliabhavin,

1. I'm wondering why B31.1 used allowable bending stress value as 15.86 MPa for calculated pipe support span at 400 C. I don't know exactly where this value(15.86Mpa)is derived from. Is it just Sh/4 ??

2. whenever we calculate bending stress, It is affected by pipe material, pipe size, section modulus and so on. I think that allowable bending stress is variable factor(ASME B31.1 has only one value in considering maximum pipe span). So How do we get the allowable bending stress for pipe support span?