Hydrotest Pressure for high temp vessel 10

[jmiles]

Hi,

I have a vessel made of SA-516-Gr70N, the vessel max deign temperature is 500°F, the flanges located ont he vessel are ANSI 300.

Now the drawings show a MAWP of 600 PSIG and a test pressure of 780 PSIG.

ASME states that the test presure will be 1.3 times the MAWP times the ratio of the allowable stress at ambient over the stress at max temperature.

For this grade of material that ratio is 1 (20KSI/20KSI)

What has me concerned is the flanges on the vessel, they derate with temperature, but the hydrotest is not going to be completed at temperature.

So this is where i get fuzzy, I believe the flanges and fittings on the vessel would ahve been hydrotested int he factor before they were purchased, but im not

 

[jmiles]

Sorry Jaydee, i misread your initial post, if your testing to the lowest ratio, then i dont believe you are meeting the code, the wording of the code basically says to use the highest ratio unless that results in a test pressure that would overstress other components.

 

[JAYDEE23]

I think the "change" is a clarification of intent. By adding the line "the MAXIMUM calculated value of PT is the minimum test gage pressure" it just leaves no question to what the following paragraph in 2006 implied

(c) if the test pressure as defined above would produce
a nominal pressure stress or longitudinal stress in
excess of the yield strength at test temperature or a
pressure more than 1.5 times the component rating at
test temperature, the test pressure may be reduced to
the maximum pressure that will not exceed the lesser
of the yield strength or 1.5 times the component ratings
at test temperature.

I now see our interpretation of 2006 was not right. I guess thats why they changed it!

 

[moltenmetal]

No, I don't believe that for a moment Jaydee. I think both of us interpreted the 2006 testing requirement (correctly) as similar to the test provisions in ASME VIII div 1, requiring testing at the LOWEST ratio of stresses at temperature for the various materials in a multi-material system.

The B31.3-2008 testing requirements are new, and stricter than those in section VIII.

Paragraph c) from 2006 that you've quoted above is still there in the 2008 version- it's just going to be relied upon a lot more than it once was due to the change in b) noted above. b) will now call for higher test pressures for multi-component hot piping, and c) will now determine the maximum test pressure quite often in our business!

 

[jmiles]

Moltenmetal is completly right, they have made the 2008 code stricter.