B31.3 calculation for unlisted materials

[Silje]

Hey engineers,

My company has only unlisted components for tubing. We follow 304 of B31.3 and because there are too many parts, I asked an engineering office to do the calculations for us to prove that the thickness is over the calculated minimum thickness for tubes.
I think, the calculation 3a under 304.1 is easy to use, but this office used a different calculation. They used t= ch+(P/10* D)/2(SEW+(P/10)*Y)) whereas ch is 12,5% additional thickness.
Is it from an ASME calculating program? Can we really use this calculation ?
Is somebody in this community familiar with these unlisted materials. I searched the internet but nobody seams to use ch.

Greetings Silje

 

[ijzer]

The formula used by the eng. office is the same as mentioned under B31.3 par 304.1.2.
Because they prabably use metric system the pressure is in Bar and the allowable stress in N/mm2 (same as MPa) so they need to devide the pressure by 10 to get N/mm2

 

[Silje]

Thank you Ijzer, absolutely right. Now I have the same result.
But there is still the question about the ch-value. I see, it is the c from calculation 2. It is the sum of mechanical allowances.
An Idea why they used 12.5% and not 0,5 mm at it is described in the explanation for c? With 12,5% the additional thickness for my tube is 0,25mm

 

[XL83NL]

12.5% is the mill or manufacturer undertolerance, wheras c is the sum of mechanical, plus corrosion,plus erosion allowances.
To me it seems your mixing things up. Review B31.3 304.1.1 eq (2) and (3a) again.