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# Code ASME B31.4 - D/t ratio less than 202

## Code ASME B31.4 - D/t ratio less than 20

(OP)
[b]Clause 402.3 Stress From Internal Pressure[/b]
[i]For both restrained and unrestrained pipelines, the circumferential (hoop) stress due to internal pressure is
calculated as (U.S. Customary Units)
SH =PiD/2t
The above equation may not be applicable for pipe D/t less than 20.[/i]

Is there any reference or any code interpretation which formula to be used where D/t ratio is less than 20?

### RE: Code ASME B31.4 - D/t ratio less than 20

Yeh, I've always loved that in a code - xxx may not apply, then doesn't say anything more (!)

The equation below comes from section 6.4.2.1 of PD 8010 from British standards, where it recommends use of equation 4 for Do/tmin <= 20

The thin wall calculation is the same as ASME 31.4 so should be directly comparable.

Basically it looks at the mid wall diameter to take the Stress value as far as I know, but use the formula to be correct.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Code ASME B31.4 - D/t ratio less than 20

Just in case someone asks you, this is usually referred to as the Lame formula.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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