Why hydro multiplier on B31.3 but not B31.1?

[JAYDEE23]

I am curious why B31.3 required a hydrotest increase relative to operating vs test allowable stresses ratio

and B31.1 does not. It uses a straight 1.5x design.

 

[stanweld]

Different strokes for different folks.
B31.1 follows basic tenants of ASME I.

 

[JAYDEE23]

right...but why..

There must be some reason it is implemented in one and not the other. Could it be B31.1 applications tend to be higher temp and therfore result in impractical test pressures at room temp? I just dont know...

 

[rneill]

It likely has something to do with the fact that B31.1 provides more conservative allowable stress values than B31.3. For example, A106-B material has an allowable of 17.1 KSI from -20 to 650 F in B31.1 but has an allowable of 20.0 KSI from -20 to 400 F.

For this reason, Even if B31.1 required the increase, there would be far fewer cases where the calculation actually resulted in an increase above 1.5x.

 

[JAYDEE23]

There we go. I am still new to the code books but am familiar enough with the stress tables that i should have picked up on that....

Thanks for pointing that out...

 

[stanweld]

Another reason could be that B31.1 primarily deals with water and steam as the fluids transported, while B31.3 deals with a multitude of flamable, explosive or toxic fluids to be transported.