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TOPIC: Blanks calculation according to ASME B31.3

5 years 9 months ago #8565

  • gianmt
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Dear pipers,

I have a question related on how the thickness of blanks is calculated in ASME B16.48, more precisely which material has been used in the calculation, I've been reading the complete standard but I could not find any reference to it.

The formula used is according to ASME B31.3 para 304.5.3 or:

THK = dg * sqrt (3P / 16 * SEW) + c

dg is the inside diameter of the gasket (spiral wound) or the pitch of the ring joint

P is the max pressure at 100 °F according to ASME B16.5 or B16.47

S is the stress value according to Table A-1 of ASME B31.3

E is always 1 for plate and forgings

W is always 1 because I never go above 800 °F for the creep welding reduction factor.

There is a big difference in calculating the thickness using a forging material such as A105 (23.3 KSI at 100 °F) or a plate A283 Gr.C (18.3 KSI at 100 °F)

I'm asking because I need to calculate the thickness of 900# spacers above 26", as a test for my calculation against the ASME B16.48 I try to calculate a 24" 900#-RJ (female), if I use A105 I get a thickness of 92.55mm but if I check on the ASME B16.48 the thickness of a 24" 900# is 133mm, that's a huge difference.

I just wonder if it's a matter of material selection (I don't think it is) or if I'm doing something wrong in the calculation.

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