Hello ,

I'm performing a stress analysis of piping connected to four pumps in according to the criteria of the standard B31.4 . In this analysis there is a case with consideration of forces caused by a transient .

With the action of these forces ,in point of junction with reinforcement, the stresses acting are above the permissible values ​​in the occasional case .

Changing the parameter " B31.3 Sustained SIF Multiplier " to 0.75 , the stresses are below the allowable value . In the report " Stresses Extended Report" , all values ​​(Axial Stress, Bending Stress, Torsion Stress, Hoop Stress, Max Stress Intensity, SIF In Plane, SIF Out Plane and Allowable Stress) remain unchanged , except that the Code Stress decreases .

Three questions :

Why a parameter that explicitly references the B31.3 changes the result in a calculation based on B31.4 ?

Is it right to make this consideration in a calculation based on B31.4 ?

Can I use, in this case, the value 0.0001 for this parameter ?

Thanks for any help sent.

It was an "interpretation" to B31.3 that introduced this idea, bringing B31.3 in-line with B31.1.

Can you apply this to B31.4 - if you agree with the interpretation and it is acceptable to the client/inspector.

Can you use a value of 0.00001 - that will effectively remove the SIF from the equation. One can argue that the SIF is for cyclic loads, and the Sustained case isn't cyclic. However, the Codes are introducing "stress index values" in place of SIFs. I would not use the 0.00001.

Thank you.

I use 0.75.

Hi Richard,

Will you throw some light regarding the SIF multiplier for PPH(Polypropelene) Pipes.I did analysis with 0.75 but ASME B 31.3 is not applicable here.The client is asking to provide SIF Multiplier as 1.

Regards

Sayed

The best thing you can do is ask your pipe vendor for this information. The SIFs in the B31 codes are for steel pipe, based on the testing that Markl performed in the late 1940s and early 1950s.

Even the recent B31J is focused on steel pipe.