Neck w/ seam in seamless head

[JStephen]

Okay, putting a neck with longitudinal weld seam in a seamless head, Section VIII Div 1 . I see that if the allowable stress is lower in the neck, that is taken into account in the design. But if the joint efficiency in the neck is lower than in the head, I don't see anything that accounts for that fact- but seems like it should. Am I missing something?

 

[GenB]

YOU CALC THE NECK/NOZZLE SEPARATE taking into account the head S
somewhere in the formulas you have F=Sv/Sn, the formula takes into account the diff in S and eff. of the smls head.
genb

 

[JStephen]

That's the approach I would have assumed, only the definitions of Sv and Sn refer back to the material stress tables, without any mention of joint efficiency. I would have thought it would be (Sv/SnE) or something of the sort, but it's not.

 

[GenB]

the join eff will be in the seam weld of the nozzle only
and not the connection
genb

 

[deanc]

see UG-45

 

[TomBarsh]

This is an interesting question. I was waiting for discussion on this issue, since I find it unclear myself.

UG-45(a) specifies that the minimum wall thk of the nozzle neck shall not be less than the thickness computed from loadings of UG-22 plus corrosion allowance, etc. Assuming internal pressure only and no longitudinal loadings this requirement means that the nozzle neck should be designed as a cylindrical shell per UG-27(c)(1).

UG-27(c)(1) (thickness for circumferential stress) is based on the joint efficiency E, defined in UG-27(a).

Assume that this neck is made from rolled plate with a welded seam with some specified level of radiography (full, spot, or none). This weld seam is a category A joint (UW-3). The nozzle-to-shell joint is category D. Then refer to UW-12 for corresponding joint efficiency.


Full=>UW-12(a): "A value of E not greater than that given in column (a) of Table UW-12 shall be used in the design calculations...except that when the requirements of UW-11(a)(5) are not met, a value of E not greater than that given in column (b) of Table UW-12 shall be used."


Spot=>UW-12(b): "A value of E not greater than that given in column (b) of Table UW-12 shall be used in the design calculations...."


None=>UW-12(c): "A value of E not greater than that given in column (c) of Table UW-12 shall be used in the design calculations...."


The cases of Spot RT and None are straightforward. Just take the joint efficiency value from the corresponding column of Table UW-12.

But the case of Full RT raises some questions; the joint efficiency can be either 1.0 or 0.85 (for Type 1 joint) from columns (a) and (b). We are directed to UW-11(a)(5) to determine which may govern.



UW-11(a)(5) imposes full RT for "all Category A...butt welds in vessel sections...where the design of the joint or part is based on a joint efficiency permitted by UW-12(a), in which case:"

UW-11(a)(5)(a) addresses category A and B welds, which are not relevant to this matter.

UW-11(a)(5)(b) addresses B and C butt welds and requires that any of these that intersect the category A joint in question must meet the requirements for spot RT per UW-52. But only "butt welds" are specifically mentioned, not "corner welds".


The same question come up if the nozzle neck is seamless because UW-12(d) for seamless sections directs us to UW-11(a)(5)(b).



So I am left perplexed as to how rules of UW-11(a)(5)(b) should be applied to a corner joint (which is not typically radiographable). I can conclude that if these rules are NOT met at the nozzle-shell joint then the joint efficiency of the fully RT'd longitudinal joint in the nozzle neck can only be 0.85, and if the rules ARE met, then the joint efficiency is 1.0. But what constitutes meeting these rules for case of the corner joint???

 

[JStephen]

In this case, the nozzle-to-head weld is per Fig. UW 16.1(i), with nozzle inserted through head and fillet welded on either side. I'm not concerned with the nozzle-head weld itself, but rather the longitudinal weld in the nozzle.

If there was some requirement that the category A weld in the nozzle be fully radiographed, or possibly some exemption from radiography that still allowed 100% joint efficiency, then my original question would be a moot point. But I don't see any such requirement or exemption for this particular case.

So assuming that allowable stress in the neck and the head are the same (ie, same material), with 100% joint efficiency in the head and 70% joint efficiency in the neck, it seems that should make some difference in the reinforcing, only I can't see that it does.

 

[deanc]

I think that you are making this more complicated then need be. Do not try and determine E for a corner joint(no way to xray).

If you notice UG-45 sends you to Appendix L,take a look at L-1 and L-7.

 

[JoeTank]

deanc is right. You guys are getting wrapped around the axle by over thinking this one.

TomBarsh... I have never thought of a nozzle neck as a "vessel section". So, I'm not sure that the dreaded UW-11(a)5(b0 could even apply here.

JStephen... remember, the area replacement method is just a very good method for reinforcing connections. It's not meant to be a precise procedure, so committees do what committees do. They make rules and compromise.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[TomBarsh]

In my experience (having taken literally hundreds of calls from engineers regarding this issue) determining the joint efficiency for sections with full RT or seamless sections is the single most misunderstood issue in the ASME Code (followed by impact test exemption). People consistently believe that they are entitled to JE=1.0 if they apply full RT or have a seamless head. I think this results from a desire to simply look things up in Table UW-12 and not to be bothered reading paragraphs UW-11 and UW-12.

The Code doesn't seem to treat "sumps" or "boots" any differently from nozzles...they are all openings in the shell. Should a large sump NOT be treated as a vessel section? Perhaps a literal reading of the Code might justify this but I think that engineering judgement requires otherwise.

Anyway, my concern is that the Code is not clear on what to do in the situation I described, where the weld intersecting the weld (with full RT) or seamless vessel section in question is a corner weld. Although I do see that example L-1.5.1(e) applies E=1 for the seamless sump; I will hang my hat on this.

 

[JoeTank]

TomBarch,
The UW-11(a)5(b) related problem had its origins back in the late 1950s. What we have now might be marginally better, but it still causes much grief to Code users.

I try to address the E issue for nozzles by remindiung folks that joint efficenciy rules are for butt joints only. Since the nozzle-to-shell connections are not butt joints, the E values are not applied to the area replacement rules.

I treach an exam prep course for API-510 inspectors. The issue of E for a seamless head is always the hardest to get them to accept. No matter how many times I read UW-11(a)5(b) and UW-12(d) to them, it just doesn't sink in. So I keep reading it to them, but just raise the volume each time. Sometimes it works.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JStephen]

Back to the original question, the joint to which the joint efficiency would be applied is a Category A weld in the nozzle neck, not category B or C, so UW-11(a)5(b) is not applicable there. It's not lethal service or an unfired boiler, so UW-11(a)(4) doesn't apply. The design of the "part", ie, the nozzle neck, is not based on UW-12(a), so UW-11(a)(5)(a) doesn't apply.

What I'm left with is the assumption that I can roll a plate into a cylinder, weld it with no xray, use it as a nozzle neck in a seamless head, and get the same reinforcing strength in the calculations as I would if it were xrayed 100% (with a minor variation due to the "required thickness" of the nozzle neck being slightly different). If that's what the code says, I'm fine with that- it simplifies life. I wanted to make sure I wasn't overlooking some obscure requirement here.

 

[JoeTank]

JStephen's summary looks right to me.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[deanc]

Agreed

Take advantage of the appendices in cases such as this. Also consult with your AIA and their Eng. Dept.

 

[AK8824]

I reached this page hoping to get some answers to the questions that arose in my mind regarding clause UW-11(a)(5)(b), but I realised the same questions were raised by other members too.

 

[TomBarsh]

And what would your questions be?

 

[AK8824]

I have a Deaerator that I will design to meet HEI specification. This specification states - "Longitudinal and circumferential head and shell weld seams are to be radiographed per ASME Sec. VIII, Div. 1 in order to obtain a 1.0 joint efficiency." The qusetion is - do I get weld joint efficiency 1.0 if I specify ASME - RT 2? This lead me to the section UW-11(a)(5)(b). As I delved a little more I realised there was an interpretation in the code in this context - interpretation no. VIII-104-14. It says the weld joint efficiency for a Category B joint shall be as per column 'C' of the table UW-12. I would think this to be 1.0.

Am I making some mistake in my interpretation?