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Annex A API 650 Thickness formula

Annex A API 650 Thickness formula

Annex A API 650 Thickness formula

(OP)
Hello everyone,

I have a question regarding the value of 145 used in thickness formula in Annex A of API 650.
In the thickness formula of annex-A of API 650, a constant value, of 145 mPa, is used instead of allowable stress of a particular material. For material, like A-36, which has allowable stress more than 145 mPa, this approach is understandable, but what about material like 283 Gr C, because allowable stress of 283 gr C is 137 mPa, WHICH IS LESS THAN 145.My question is should I use 137 instead of 145 in the Annex-A thickness formula or not?

Regards,
Inam

RE: Annex A API 650 Thickness formula

I believe the same allowable stress is to be used with all materials.

RE: Annex A API 650 Thickness formula

JStephen is correct

A.1.3 This Annex is applicable to any of the Section 4 materials, although the single allowable stress does not provide any advantage to higher strength steels.

However, that does not address the OP's question - why is the Annex A allowable stress greater than the tabulated product allowable stress for A283 material? Is it just that Annex A is so conservative that the 137 vs 145 is essentially rounding error?

RE: Annex A API 650 Thickness formula

I assume the actual stress level would be lower, since you'd still have an 85% maximum joint efficiency.
Otherwise, just a quirk in the code generation process.

RE: Annex A API 650 Thickness formula

(OP)
But what if Joint efficiency used is 1. In that case required thickness will come out to less by using 145 instead of 137 mpa

RE: Annex A API 650 Thickness formula

But Annex A uses a joint efficiency of either 0.70 or 0.85, not 1.

RE: Annex A API 650 Thickness formula

(OP)
OH Yes my mistake. :)

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