UCS 67 Exemptions

[Cluain]

A pressure vessel MDMT is -50 degrees F . I am using curve (B) material and I am able to exempt charpy impacts by utilizing UCS 66 (b) (coincident Ratio) for head, shell, and nozzles.

Reading UCS 67 (a) (1), it appears I do not have to qualify a WPS since the base metal is not required to be impact tested. Also, the HAZ is exempt by UCS 67 (c ) and no production impacts are required per UCS 67 (d) (3) because of the base metal exemption.

Can some clarify UCS 67 (a) (2). Why is it limiting materials to curve C and D and stipulating the use of a weld consumable which has been classified by impact tests at a temp not warmer than the MDMT when the MDMT is colder than -20F and no colder than -55F.

My concern is this. If the base metal is not required to be impact tested then UCS 67 (a) (1) applys but, UCS 67(a) (2) requires one to use a consumable rated for the MDMT if it falls between -20F thru -55F and limits it to UCS 66(g) or Fig UCS- 66 C&D materials.

What am I missing here? My gut is telling me that I should use a weld consumable rated for the MDMT of -50F but UCS 67(a) (1) has me really confused when I try to reconcile the (a) (2) requirement. Note: I realize there’s an OR between UCS 67 (a) (1) & (a) (2) but something does not make sense here.

Regards.

Cluain

 

[DVWE]

If UCS-67 (a)(2) does not mention curves A and B, then they do not apply. Also, if UCS-66(g) does not apply to you, then I don't think you are missing anything.

If you can procure and use filler metal(s) that are classified with impact testing at the required temperature, then you should do it (ie E7018-1). I don't know what Curve B material you're using, but if welding consumables are not available which are classified with impact testing, and all else is true about your coincidence ratio, then you do not need to perform impact testing as part of the WPS qualification.

 

[Cluain]

Many thanks again DVWE!

The base metal is SA 516-70 and I am planning to use ER80S-ni1 (GMAW) and a neutral flux 882 for the SAW process, regardless if UCS 67 (a) (1) applies in this particular case. I just think it makes sense to use a consumable rated for the MDMT stamped on the nameplate. E7018-1 works great, but the process is slow.
It sounds like you have been round this stuff a great deal.
Best regards,
Cluain.

 

[DVWE]

Good choice. You will have a whole array of filler metals to chose from for SAW.

Is the vessel being PWHT?

 

[Cluain]

No PWHT required but, while on that subject. Don’t you think it strange that one has to qualify a procedure for PWHT when one already has an existing procedure in the un-PWHT condition for the same P number?( see QW 407.1)

It appears to me that the physical properties would be more likely to fail in the un-PWHT condition; therefore, by default, the pwht condition only enhances the probability of a procedure passing. Obviously I understand that it doesn’t work vis-versa, nor am I a metallurgist. Just think it’s strange!

 

[DVWE]

PWHT, especially at higher temperatures and longer hold times will definitely degrade the tensile properties of the weld and base metal. Depending on the time and temperature, PWHT has shown to be beneficial to impact properties. Therefore, that's why the code requires it, I think its a good requirement.