UG-37h split re-pads.

[RonJeremy]

I see some nit-wit has effectively added the ABSA IB05-004 joint efficiencies into the A5 calc in Division 1. Thankfully, this has not been done in Division 2 (AFAIK): probably because those Div2 people understand PV engineering - and know that the old rules (no JE) worked. Hopefully UG-37h will be found out and consined to the bin in a future revision!

Comments?

PE

 

[Duwe6]

I feel sorry for everybody selling vessels into Alberta. Guess there will be a 'tempest in a teapot' over this latest ruling.

It is always 'fun' to watch some entity try to reinvent the wheel. It never ends very well.

Sect VIII Div-1 has too much 'experience' in it, and there are hundreds of thousands of excellent vessels designed and built to VIII-1 that have been in service for over a half a century, to think that making VIII-1 more conservative is a 'Good Idea'. The proof exists that VIII-1 is sufficiently conservative as it stands. Period.

 

[TGS4]

I say this to just about anyone who has a problem with rules in the ASME Code: get involved or "quit yer belly-achin'". Seriously, if you have a problem with a rule, old or new, GO to the committee(s) meeting(s). Every discussion is open to the public, and public comment and discussion is very welcome.

On a related note, the rules in VIII-2 are managed by the same people writing the rules for VIII-1. If course, it you had put any effort into researching the Code Committees, you would already know that.

I guess it's easier to complain than to do something about it. So, come up with a credible rebuttal to the new rules. Write a paper about that rebuttal at the ASME PVP Conference, or in he ASME Journal of Pressure Vessel Technology. Get your rebuttal to the rule peer reviewed and then bring that to the Code Committees as new research that demonstrates that a rule is inappropriate. (How do you think that the new nozzle reinforcement rules in VIII-2 came about? They didn't magically appear all by themselves, and the Code Committee VOLUNTEERS certainly didn't have the time in their regular everyday jobs to go our and develop such rules...)

And Duwe6, that's quite the leap in logic. The design margin in the allowable stresses in VIII-1 have not changed since the 1998 Edition. Sorry, but you can't take credit for the non-failure of older vessels as "proof" that the current design margins and rules are adequate. Furthermore, all that non-failure indicates is that a design margin greater than one has been achieved, not that the poorly-named "safety factors" mandated in the Code have been positively achieved. And I also take issue with your suggestion that the mere existence of such long-lived vessels is proof of anything. I do enough failure investigations of pressure vessels to know that failures indeed happen. And I know from talking with regulators who are advised of all failures in their jurisdiction, that pressure vessel failures are an not-uncommon event - unfortunately.

 

[RonJeremy]

Know what you mean TGS4. That's why I asked for comments: - before I go back to ASME and ask for a ruling.

 

[TGS4]

What's your technical basis for opposing the new rule? Glad to provide some feedback on it.

 

[Duwe6]

"What's your technical basis for opposing the new rule?"

Is there any objective evidence that there is a need to change the split-repad joint efficiency? I used to think that my 'bright ideas' were a good enough reason to add small additional requirements to weldments & vessels. Guess what? I was wrong. Sect VIII - 1 is 'Rules Driven' and those rules work. Which probably means that a substantial number of those rules are excessively conservative; So what? If you feel the need to design with a minimum of metal, use Div-2. And/or propose a relaxation, like the above-cited 1999 design margin change.

But please don't think that your engineering pipe-dreams and whims are a valid and sufficient reason to make the Section VIII Div-1 rules more stringent. If you can show experimental evidence that a split repads have a lower failure stress than solid ones, then you are justified in tightening up the rules. Experimentation, testing, and forensic analysis built the Div-1 rules; the guys who established the rules were conservative - wanted to stop the explosions and deaths. Adding further stringency, without evidence, in 2014 looks like trying to "gild a lilly" from where I am standing.

 

[TGS4]

Sect VIII - 1 is 'Rules Driven' and those rules work.

No, they don't, otherwise we wouldn't be seeing failure after failure. There are an unbelievably large number of failure modes that the rules of VIII-1 don't even address, and yet cause real problems in real facilities. And despite all of our collective efforts, there are still failures in pressure vessels. Thankfully, we've managed to slowly creep away from many catastrophic failures, but there is typically 1-2 PV-related fatality every year in North America.

Indeed - ABSA was foremost in pushing for the new UG-37(h) rules. Do you think that they like to make up rules to make things difficult, or do you think that they saw some things that made them question the lack of a rule.

Experimentation, testing, and forensic analysis built the Div-1 rules[/i]If that's what you think, then I have some ocean-front property in Alberta to sell you. I can't tell you how many times I have sat in committee meetings, when discussing an old rule in the Code, and the members are trying to find out the rationale behind an existing rule. For many of these rules, they were based on old (and possibly shoddy) research, or they were pulled out of someone's posterior. Either way, there is no documentation about the rationale for many of these rules.

I'm personally not a fan of these new split repad rules. When these were being pushed through, I did some analysis demonstrating that whether or not that repad butt-weld was there OR NOT did not affect the burst pressure of the reinforced nozzle. Unfortunately, I wasn't able to present my findings to the appropriate people, mostly because I hadn't had it reviewed and peer reviewed and published.

You want to know what rules don't work: 1-10. The new rules in Div 2 are much better, and have been acknowledged as such since the mid-2000's. And yet, 1-10 is still there...

 

[jclsws]

TGS4 does have a point. The instructor for the Section VIII Div. 1 course sits on the committee. There were many times during the course where he said that a particular rule was devised long ago out of thin air. When asked why those rules have not been changed, his response was that they worked i.e., there have not been any failures directly attributable to that particular rule.

 

[RonJeremy]

TGS4: this is just the sort of debate I wanted to provoke. Thanks for your reply. Personally, I do feel that there are some things that are creeping into Code that are unnecessary, and this is one. Pads are not connected to shell except at the edge and at the nozzle throat, so ASME never gave them a category, and therefore no JE. But it does now (but only in Div 1, not Div 2)!
Thoughts appreciated...

 

[RonJeremy]

Jciws.
... But that is the whole point to DBR isn't it? ASME can' t just build cost in on a whim, without some concrete justification, otherwise it will lose credibility. Mind you, I consider new div 2 to be the new go to code in the coming years.

 

[jclsws]

RonJeremy,

Being on the manufacturing end of things, I understand your point. I am not disagreeing with you, I am just pointing out that even the current committee does not know the origins of all of the rules. As far as Division 2, I would have to agree. I can see a lot of manufacturers moving to Div. 2 as a material cost saving measure. I would like our company to move in that direction eventually as well.

 

[SnTMan]

Not to hijack, but....

You want to know what rules don't work: 1-10.

I am now running some software, which shall remain nameless, that as far as I can tell will ONLY run reinforcemnent per Apx 1-10. Not too familiar with it. Naturally I don't wish to swallow it whole.

TGS4, care to elaborate?

Regards,

Mike

 

[TGS4]

SnTMan - the rules are non-conservative. I'll see if I can track down any papers demonstrating that. Use the large opening rules in Div 2, which you can get from CC2695 from Div 1.

The killing off of 1-10 is awaiting a larger initiative called "common rules". In that initiative, all rules common to Divs 1, 2, and 3 will be contained in Div 2 and referenced in the other Divisions of Section VIII. Of course, that's a precursor to the Class 1 and Class 2 initiative in Division 2, which will (hopefully) eventually leave Division 1 to being only UM vessels.

 

[SnTMan]

TGS4, thanks, meantime I'm going to figure out what my software is doing

Regards,

Mike