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API ALLOWABLE STRESS

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gbratis

Mechanical
Jun 23, 2006
29
Hi to all,
I'm currently working on this project where the following question arised:
I am performing a wall thickness calculation according to B31.3 ASME code. I have to choose between an A106 Gr.B and an API 5L X65 pipe for a 20'' pipeline. Regarding the allowable stress issue it seems that even though the min. yield strength for the API pipe is merely twice as much as the A106 one, the allowable stress values obtained from the relevant ASME 31.3 tables are pretty close (20ksi-23ksi).First of all how can this be explained?Secondly, if this is the case, is it worth buying an API pipe of this strength considering the fact that the wall thickness will be pretty much the same as the A106 Gr.B pipe?
Thanks in advance
George (Mechanical Engineer)
 
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B31.3 allowable stresses are based on minimum specified tensile strength. ASME B31.8 code bases design allowables as a percentage of Specified Minimum Yield Strength.
 
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