ASME Allowable Stress - Safety Factors

[Percy99504]

B31.4 clearly states use of safety factor of .72.
For B31.3, we use .5 and .6, but I cannot locate references to these factors in the code. Do you know where they are referenced and shown?

 

[metengr]

Are you referring to strength reduction factors? If so, please review Table 302.3.4 in the 2004 Edition of ASME B31.3 for longitudinal weld joint Quality factors, which can range from 0.6 up to 1.0.

 

[Percy99504]

Thanks for your reply! I am not talking about strength reduction or joint factors. I am referring to B31.4 402.3 "Allowable Stresses" which is given as .72. We use this for B31.4 MAWP calculations.
For B31.3 we use .5, .6, or can use .72 with engineer approval. But I do not see a similar reference in 31.3 to the 402.3 ref in 31.4 that show where .5 or .6 are stated or how to apply. I would appreciate your thoughts. Thanks!

 

[BigInch]

You are referring to the "Area Class Factors" of B31.3 and B31.8, where the yield stress of a component's material is multiplied by the class factor to arrive at an allowable stress for that component. In B31.3 there arn't any.

B31.3 has no corresponding "Area Class Factor" and allowable stresses are defined for each material. For example, you will find the method for determination of thickness required for designing a pipe component under B31.3 in Par 304.1.1 under the definition of "S", for which you are referred to Table A-1 for specific values for various materials.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[BigInch]

P.S.

"B31.3 we use .5, .6, or can use .72 with engineer approval"

You should not be using Class Factors for B31.3 designs.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Percy99504]

Thanks for your replies BI & Met. Your information was helpful!