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Tmin for elbows for B31.3

Tmin for elbows for B31.3

B31.3 has the formulas for determining tmin for straight pipe and elbows based on internal pressure.

From some of my calculations based on the code, the tmin for bends will be thicker than straight pipe. Does that mean when creating a material specification, one would select a pipe schedule based on the elbow thickness selection ?

Some of my plant's material specifications seem to be based on the tmin for straight pipe under internal pressure.

So tmin for straight pipe may be 4 NPS sch. 40 but an elbow may call for something thicker and the specification would state 4 NPS sch. 40 components.

RE: Tmin for elbows for B31.3

Noted that the SIF (stress intensification factor)of the "bend" is different from the "elbow" per B31.3. So, the actual tmin of the bend could be thicker than the nominal pipe schedule of elbow. And, the bend should use the thicker (actual) tmin instead of the pipe schedule of the elbow.

RE: Tmin for elbows for B31.3

For wrought fittings in general design to ASME B16.9 which under 2.1 Pressure Ratings states that you design as for straight seamless pipe of equivalent material. Usually in Piping Class it will state wall thickness to match pipe.

RE: Tmin for elbows for B31.3

Quote (NovaStark)

Does that mean when creating a material specification, one would select a pipe schedule based on the elbow thickness selection ?
No, see B31.3 para 302.2.2(a). Unless you are using pipe bends to make 'elbows'; in that case, you are using para 304.2 and it's formulae.

RE: Tmin for elbows for B31.3

It seems I had my definitions interchanged.

Thanks for the clarification!

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