pipe wall thickness

[quiinces]

In pipe wall thickness calculation , as per B31.3 , S is the stress value for material from Table A-1, which says Basic Allowable Stresses in Tension.
Firstly my question is that is the Basic Allowable Stresses in Tension the YIELD STRENGTH of the material..
And secondly why dont we use Tensile strength in the calculation formula rather than yield strength ...

 

[LittleInch]

I'm sure this has been answered before, but to be clear,
1) NO. the value in Table A-1 is the value that is used in the equations for wall thickness etc in B 31.3 and is a factor of yield or UTS, it is NOT the yield stress of the material. It is essentially the lower of one third UTS or two thirds SMYS. Hence high yield strength steels ( X60/X 70) only have a marginally higher S value than grade B (X35) in B 31.3 as the UTS doesn't increase in proportion to SMYS.

2) to a certain extent B 31.3 does as the factors behind the calculation of S take account of UTS.

Why don't we use it in pipeline codes? - Yield is the limit state we want to design to and is able to be increased more easily than UTS.

If you allow a material to yield on a number of occasions, it gets harder and can only do this on a few occasions before it breaks. The aim is always to keep the fluid inside the pipe...

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