A572 Gr.50 + PWHT for Wet H2S Service? 1

[Guest102023]

The application is a refinery pressure vessel in wet H2S service. Thickness is 1.25"; it will be PWHT. Blistering has been found in the shell of the retired vessel of 1970s vintage.

The client was shopping for A516-70N with low S and low CE, but the MTR I'm reviewing is dual certified to A572 Gr.50 & A516-70N. The steel is made by a very reputable mill. S is ultra low and CE = 0.42. The mechanicals are very good, but I am very concerned about the 0.018% Nb in the heat analysis and that PWHT will increase the chance of SSC at the HAZ.

I have serious reservations about approving this material (and in general I take a very dim view of such dual certification practices).

Any thoughts or advice?

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[metengr]

brimstoner;
Have you discussed this issue with the plate mill? They may have test data they are willing to share.

 

[Guest102023]

metengr,

Too late for that - its the usual panic sourcing situation. Anyway the decision has already been made not to use this material per my initial advice.

I would still appreciate comments, as I consider this steel to be A572 Gr.50 ONLY.
How do B&PV Code committees view such practices?
I can think of some other examples: (i) 304/304L, a mongrel non-grade designed by stockists; (ii) sub-arc consumable makers who slip secret sauce (e.g., Ti+B) into the wire and/or flux and then label it under a "carbon steel" designation.
A516-60/70 I have little problem with, and A53/A106 none at all.

"All things are lawful; but not all things edify."


.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[metengr]

The perspective from the Boiler and Pressure Vessel Code committee is that you must use 'buyer beware' as your approach to selection of materials for service. In this instance, I believe the correct decision was made if there was lack of HIC test information, despite the administrative requirements of meeting dual certification.

Dual certifications do indeed serve a useful purpose to provide options. However, as you are aware there are still subtle differences and these determine final use of the material, regardless of dual certification.

 

[Guest102023]

metengr,

That could also be expressed as 'beware of buyers' ;-)




"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[weldstan]

V and Nb additions were commonly used for fine grain melting in SA-516 steels. If aluminum was not used for fine grain melting, the impact toughness properties in the HAZ will decline appreciably after PWHT due to secondary carbonitride precipitation. Hardness in the HAZ will still meet NACE MR-0175 after PWHT.