Questions on Joint Efficiencies 9

[Needmetal]

Hi

1. I can’t understand why a the joint efficiency for a longitudinal joint for a seamless shell is not automatically 1.

It use to be like this decades ago and without any actual joint there is no weld metal to consider to reduce the joint efficiency

2. How come stress reliving is no longer taken into consideration for joint efficiencies? This seemed to have changed back in the 70s

Thanks in advance for any info

 

[TGS4]

For starters, I'd like to suggest that you make reference to a specific Code/Standard. That way we can have a common frame of reference for this discussion.

Specific to you comments/questions:
1. Can you provide a specific reference for this?
2. Why would you think that stress relieving would make any difference to weld joint efficiency?

General comments regarding weld joint efficiency:
- The purpose of the weld joint efficiency in the pressure vessel code is to penalize the manufacturer for not doing enough NDE to ensure that the weld is "as-good-as" base metal. The values in the ASME Section VIII, Division 1 and Division 2 Codes are entirely empirically-determined (meaning that the Code Committee members decided by consensus, and not by some mathematical formula, what the values should be). Do not look for any deterministic rationale for these values - there is none.
- The way that I like to think about weld joint efficiency is this: what's an appropriate factor to de-rate the weld-metal (for tensile stresses) on the basis of embedded flaws of unknown size, location, and frequency - solely on the basis that no NDE was done on those regions? The manufacturer never looks for the flaws, so doesn't know what they are, where they are, or how big they are, yet we need to provide an appropriate factor solely on the basis of what NDE was done (or not done). Seems like coming up with a deterministic value would be a Sisyphean task...
- Weld joint efficiency is only applicable in tension, and not compression. It's partially applicable in bending (on the tensile side).

 

[Christine74]

I can confirm that older editions of ASME Section VIII from the 1940s used E = 1.0 for seamless components regardless of the degree of radiography, and that certain editions of the API/ASME Code for Pressure Vessels from the 1940s/50s allowed you to increase the joint efficiency by 5% if PWHT was performed.


-Christine

 

[Needmetal]

@TGS4

Sorry about that

ASME VIII div 1, 2021

Table UW-12 and UW-12d (this is where seamless components are discussed)

I hear you but that still doesn’t explain why joint efficiency for a seamless shell doesn’t equal 1 for the longitudinal weld. There is no weld in that case

Regarding your second question I don’t think SR should be used to increase the joint efficiency. But why was credit given for SR back in the days? Did they have a reason ?

@Christine74

Thanks for that info

 

[BJI]

As far as I can tell there is no sound basis for this change to the code, except to add an additional layer of conservatism where inspection is not performed on the circumferential weld seam. However, IMO this would already be suitably covered by the circumferential weld joint efficiency.

Following on from the below thread, I can confirm this requirement was also not in the 1968 edition.

https://www.eng-tips.com/viewthread.cfm?qid=503176

 

[DriveMeNuts]

1. It is UW-11(a)(5)(-b) which requires that circ seams of a seamless shell need to be spot radiographed, to give the seamless Longitudinal stress an E=1.0. If you don't do these spot tests, then you have to use E=0.85.

It seems irrational to X-Ray the circ seams to give a seamless shell E=1.0. I 'guess' that this requirement is for empirical reasons explained by TGS4.
The best I can come up with is that the committee feel that spot checks on the all circ seams are desirable for peace of mind. The only way that they can coercively force the fabricator into spot X-Raying the circ seam, is to irrationally penalise them on the Longitudinal stress (and therefore shell thickness). If you don't do a few circ Spot radiographs to confirm general adequacy of the welds, then you have to accept a thickness penalty. Sarcasm intended.

There must be a couple of hundred vessels fabricators in the US. If is this rule didn't exist, then a small number of these fabricators would be welding dangerous circ seams, and not knowing it. This rule forces them to learn and become aware of their weld quality.

 

[TGS4]

@Needmetal - thank you for the clarification.

It appears that the current wording has been the same since it was changed in the 1987 Addenda. Nevertheless, I agree with you that because there is weld joint, there is no need for a weld joint efficiency. There is a current item in front of the Code Committee to re-write UW-12 as part of the Code's Clarity Rewrite project. That item is 20-2417. I recommend that you send an email to the ASME staff secretary for Section VIII, requesting that a clarification on this particular item be added to that item.

Thanks @Christine74 for the info regarding the API/ASME Code. Do you have a paragraph reference for that?

 

[Christine74]

TGS4,

Yes see Table W-318.2.1 here from the 1951 edition:

https://babel.hathitrust.org/cgi/pt?id=osu.32435052091030&seq=68

-Christine

 

[Needmetal]

@BJl

Thanks for the info

@drivenenuts

That’s a very good theory

@TGS4

I shall email the committee. Hope they can clear this up

@christine74

Wow I been looking all over for that. Do you have a free version of the API-ASME from the early to mid 30s?

 

[Christine74]

Needmetal,

Here's a link to the 1938 edition:

https://babel.hathitrust.org/cgi/pt?id=uva.x002223060&seq=1

-Christine

 

[Needmetal]

Great thanks!

 

[TGS4]

@DriveMeNuts - I think that your assessment is, for the most part, spot-on.

@Christine74 - thank you for the reference. I had not seen that Table before - it is rather enlightening.

 

[r6155]

Example: PV NPS 24 sch 80 (31 mm) SA-106 B with seamless semi-elliptical heads.
Does anyone think that these two girth welds don't need to be RT and E=1 for the shell?
Required amount of this PV: 100
383 m of 31 mm thick welds without any RT !!
This doesn't sound good.

I AGREE with ASME VIII Div.1

Regards

 

[DriveMeNuts]

A vessel made up of a seamless cylinder and heads welded together with circ weld seams, which has its circ seams spot radiographed in accordance with UW-12(b), will have circ seam longitudinal stress with E=0.85. What doesn't make sense, is that the seamless shell circ stress still has an E=0.85.

You still have to do additional and separate UW-11(a)(5)(-b) radiographs of the circ seam to upgrade the seamless shell circ stress to E=1.0.

This doesn't align with my theory above. UW-12(b) should be enough to prove the general adequacy of the circ seam weld, negating a need to do the extra UW-11(a)(5)(-b) spot requirement.

On my first post, excuse the errors with getting circ and long stress around the wrong way.

Some interesting parts of UW-52: