Hydrostatic test for high temperature

[fateton]

Hello:

I need help.

I have a piping system to 520 ºC and 126 bara for steam.

For determined the hydrostatic test pressure in accordance wiht ASME B31.3, I need apply the next :

Pressure test= Pressure design* 1,5* stress(38ºC)/stress(520º)= 126*1,5*24300/15076= 304 bar

I think that is too much big? It´s correct?

Why ASME 31.1 don´t consider the effect of temperature? in this case for the same piping:

Pressure test= 1,5 *pressure design= 189, very much lower

 

[rneill]

I take it this is superheated steam since the saturated steam pressure at 126 bar would be 328 C ?

Anyway, you didn't mention specifically what material (grade, diameter, wall thickness) you were using but in principle, the calculation you have shown is correct and if those are the correct allowable stress values then that is the correct test pressure. Assuming the pipe is correctly designed for the conditions you list then there is no problem testing it to the calculated pressure.

I can not comment on why there is not a similar requirement in B31.1 but concur that B31.1 does not have this same requirement. Technically, the requirement in B31.3 does make sense as you are testing at a temperature where the material is much stronger so if you do not increase the test pressure correspondingly, you will not stress the material to the same percent of yield during test that it will see during operation and it is possible for critical defects to remain undetected.

 

[vpl]

I think the question has been asked before about the differences between B31.1 and B31.3. If I remember correctly, the reason is the difference in allowable materials.

Patricia Lougheed

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[vpl]

Here's a couple threads to review.

thread292-246566
thread794-253472
thread292-220808

Patricia Lougheed

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[ColonelSanders83]

Hello all,

The major differance in the codes on this specific requirement is that B31.1 is concerened with leak testing, and finding leaks. Although the test is 1.5 times design pressure it neglects temperature effects. All the tests is B31.1 are geared to fineing leaks in the system, any gross fabrication errors will also be discovered.

B31.3 gets far closer to an an actual strength test of the piping system by correcting the test pressure for temperature.

Another driver is the differances in inspection requirements of the two codes at your operating temperature. B31.3 only requires 5% radiography for butt joints in normal fluid service. B31.1 at temperatures above 400C requires full RT or UT of all butt joints.

The tighter NDE in B31.1 has given them confidence to use a less stringent test requirement.

Just my two cents worth.



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