A-105 Flange MDMT

[Mike1704]

The 2019 B&PV Sect VIII code changed the UCS-66 curve for as forged A-105 flanges from the b curve to the a curve which has the result of increasing the MDMT of those flanges from -20 to +18 deg F. I have a client with C3 refrigeration vessels with MDMT of -20 deg F that have as forged A-105 nozzles. These vessels operate at about 0 deg F. How is the vessel MDMT affected in this case by the code change. Thanks for your comments

 

[Some Curious Guy]

I am answering this assuming that this vessel is not manufactured yet.

I do not know the the Code edition applicable in your case. Please read Appendix 43 of ASME Sec VIII Div 1. The applicable edition of the code is that edition which is mandatory at the time the Purchase order / Contract. So if a manufacturer got the purchase order before Jan 2020 then 2017 would be applicable edition of the code and you do not have to bother about 2019 edition. Please also get the opinion of the AI in this case. This is a little touchy issue and interpretation may vary.

If 2019 is the applicable edition then you have to evaluate as forged SA-105 flange per Curve A. You can use concession given UCS-66(b) and UCS-68 . That's the best you can do. The Vessel MDMT would be the warmest MDMT of all its components including the standard flanges. So the vessel MDMT would increase in this case.

Have you already ordered the flanges. If not consider shifting to Low temperature LTCS flanges. SA-350 costs almost same as SA-105. Considering cases of poor performances of as forged SA-105 flanges in low temperature application SA-350 would also be safe.

Codeware has a very good article on their website. Consider reading that before making an informed decision. The link is here.

https://www.codeware.com/all-material-is-created-the-sameright/

 

[Mike1704]

Vessels are already built and in operation (20 years).

 

[Morcuse]

Vessels are not affected because Code changes are not retroactive, unless you are doing an API 579 evaluation and/or planning a modification.

 

[Mike1704]

For me, there are 2 concerns. First is "code compliance" and second is "are these flanges safe?" In my previous life (30+ years with "Big Oil"), it was recognized almost 40 years ago, A105 flanges were a problem in low temperature service and most bigger companies with lots of tech resources and $$ moved to A333 piping and A350 flanges. My current company does PHAs and in my experience, lots of smaller companies are still using A105 flanges in new construction in spite of the knowledge that A350 would be better and not much more $$. ASME didn't change the MDMT curve for A105 flanges for no reason which raises the question "are these A105 flanges safe at 0 deg F". I can deal with the "built to an older code" problem, but I don't know how to give assurance that the existing A105s are safe. The link that "Some Curious Guy" sent above wrt Mn content may be useful. If the flanges in question are "as forged" not A105N, can I give some assurance they are safe with PMI testing assuming a certain Mn content? Thanks for all the comments... greatly appreciated.

 

[Morcuse]

Check Fluor's paper on this topic:

https://asmedigitalcollection.asme.org/PVP/proceedings-abstract/PVP2017/57991/V06AT06A053/286065

ABSA has interesting information bulletins as well.

What to do with existing equipment (and lets not forget about piping!) that was constructed prior to ASME VIII-1 2019 Edition, is something to consider on a company by company basis.

 

[SnTMan]

... but I don't know how to give assurance that the existing A105s are safe.

20 years successful experience maybe? I'd maybe add, not just your successful experience, but many others as well.

Regards,

Mike

PS: Mike1704, please consider editing your post of 14 Sep 20 10:47. Formatting is awful

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

Given the vintage, the flanges are likely just fine. It's the later vintages that had issues with brittle fracture.

 

[Mike1704]

SnTMan,

All the formatting in italics was apparently added by the system, not me. Looked better when I posted it. Yes, I agree that 20 years of successful experience has value,
but no promise it won't break next week.
See attached pic of vessel that was in service +/- 20 years but failed dramatically under hydrotest at about 35deg F. Old picture...

 

[SnTMan]

Yeah I get it, but it doesn't seem as though the flanges were involved...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[weldstan]

Mike1704, I believe that you are over analyzing a theoretical problem that does not really exist.
SA-105 flanges have successfully been used for decades in vessel with MDMT at -20F and operating at 0F and that includes the earlier 4:1 and the current
3.5:1 allowable stress ratios. I do believe and have always required in the past that all A-105 flanges be normalized.

 

[TGS4]

weldstan - the problem is real and does exist, and has so since about 2012. Even normalizing does not seem to"fix" the problem. The link to the Fluor paper earlier, plus the bulletins put out by ABSA do detail the technical issues well.

Prior to ~2012, I would have agreed with you that there was not a problem. But raw material supplies changed and forging practices around the world changed in about that time, and the experimental evidence is rather compelling about how brittle these flanges can be.

 

[Mike1704]

The Flour paper is very informative and paints a somewhat disturbing picture.

 

[weldstan]

I've read the Fluor paper some years ago shortly after its publication and commented on it at that time on these forums. I've known of the lack of toughness at -20F of the majority of steels used in vessel construction.
steels that were used with that MDMT. This is largely due to my testing of them long before the Fluor paper. If the vessel discussed by the OP was to change operating conditions to include high cyclic loading, I would agree with his concerns. If not, he is making a mountain out of a mole hill.