Impact test exemption for PQR for 304 SS in low temp service

[jtseng123]

Dear all,
We have an existing 304 SS vessel with design temp of -150 F. Recently added a new 304 SS 6" feed nozzle.
However, our client indicated that the inlet temp for this new nozzle is -245F, so the local area on the shell will be colder and raised the question that our PQR does not show impact test.

We are looking into UHA-51, especially UHA-51(g) to see if we can exempt impact test on PQR. Can the very low stress ratio for the nozzle by UHA-51(g) be used to exempt the PQR from impact test for the nozzle to shell weld ?

 

[metengr]

I think this would be a tough sell to the AI given the circumstances. I would just run a weld coupon using the same WPS and have the impact qualification.

 

[Duwe6]

If it was me, I'd have the test lab run the charpys at -300 to -320°F, the boiling point of liquid nitrogen. If your weld is OK at -250, it will be good at -320.

 

[jwhit]

I agree with the others as well, at -320F there should be no problems meeting the impact criteria for this material.

 

[jtseng123]

metengr,

I would like to make sure I understand UHA-519(g) correctly: The primary membrane tensile stress from pressure and from UG-22 for the nozzle 'itself', is below 35% of the allowable tensile stress. From the wording in that clause, does it mean any welding to this nozzle (such as flange to pipe weld and pipe to shell weld), PQR can be exempt from impact test ?

 

[metengr]

The wording as interpret it would apply to the entire vessel and any nozzle or appurtenance welded directly to the vessel.

 

[weldtek]

I would add that each pressure containing component has to evaluated individually. See Interpretation VIII-1-98-50