Joint Efficiency for single side weld. 2

[SJEC]

I am working on a mercaptan tank.
As per our client direction, the vessel should not have any manway and inspection hole due to the smelly mercaptan.
The vessel will be replaced every inspection period.

In general, the vessel will be designed per RT-2. JE=1.
The question is what joint efficiency shall be used for close weld. It should be circ weld between head and cylinder.

As per UW-12, Circ weld shall meet spot RT requirement and double side weld. We already add 100% RT on this weld seam. In addition, we can use GTAW for root pass. However per UW-35, it sounds like unless people can inspect both side. the weld can not be recognized as double weld.

See following link Page 5. It may give you more details.

http://www.nationalboard.org/SiteDocuments/Bulletins/SU06.pdf

Thanks

 

[vesselfab]

First off, how do you get by with meeting code requirements for inspection openings?

what size is this vessel?

 

[CodeRef]

FYI...This is your second posting of the same question...? didn't like the first answer I guess...
Your interpretation of the National Board article implies that the examination can only be a visual examination. This is not what the article is stating. It can be any method of examination acceptable to the requirements of the Code. Here is the words from that article.....I have underlined and bolded the word examined for your convenience.
...Paragraph UW-35(a) states: “Butt-welded joints shall have complete penetration and full fusion.” The paragraph then goes on to describe the as-welded condition required on both sides of the weld. The determination as to the weld type becomes a question of proving the condition of the as-welded joint on both the inside and outside weld faces. A type 1 weld must be examined over its full length on both surfaces to ensure requirements of UW-35 have been met. Failing to provide this examination will result in the weld joint defaulting to type 3.

FAQ731-376 A question properly stated is a question half solved.

 

[MrBTU]

Also, Table UW-12 type 1 weld is double welded or by other means (single sided weld) which will obtain the same quality of deposited weld metal....
I would think you would want to TIG the root then MIG.

 

[trottiey]

SJEC's stated question was "what joint efficiency shall be used for close weld?" Well if your vessel is really RT-2, then the "equivalent longitudinal efficiency" (as the NBIC calls it) of that closure joint is 2.

What really seems to trouble SJEC is how to examine the closure weld. I think what you're looking for is UW-11(a)(7), which says that "ultrasonic examination in accordance with UW-53 may be substituted for radiography for the final
closure seam of a pressure vessel if the construction of the vessel does not permit interpretable radiographs in accordance with Code requirements." Basically what metengr suggested in the other thread.

If SJEC applies neither UT nor any surface inspection of the ID, then the closure joint defaults to type 3,
UW-11(a)(5)(a) is not met, and UG-116 RT-2 is not met. The closure joint efficiency might still be greater than 1, but it doesn't matter since the longitudinal joint efficiency of the vessel section can be no higher than 0.85, even if it is seamless, per UW-12(d).

 

[CodeRef]

then the "equivalent longitudinal efficiency" (as the NBIC calls it) of that closure joint is 2.

?? 2 ??
There are too many variables in this discussion, lots of unknowns, vessel diameter limitations for opening exemptions, vessel diameter limitations for Type 3 circumfirential joints.
Apply Table UW-12 as you would for any other vessel design.

FAQ731-376 A question properly stated is a question half solved.

 

[trottiey]

The joint efficiency of the closure would be 1; the "equivalent longitudinal efficiency" would be 2X that. See the NBBI bulletin that SJEC linked to for an explanation.

And yes, practically every answer about the code would ideally need to be followed by the statement "provided that all other code rules are met."

 

[CodeRef]

Thanks trottiey, I thought that was what you meant, I only needed clarification.

FAQ731-376 A question properly stated is a question half solved.

 

[SJEC]

I am sorry, CodeRef, I post the question again here, because I hope more people will notice it. It does not mean I do not like your answer.

The vessel is about 1.2 meter diameter and 6.9 meter long.

Yes, Vesselfab, it is another challenge for me to obtain approval from local authority. However, It sounds like our client have the same experience, So it is not a concern now.

In general , the vessel will be designed as per JE=1.

The key point of my question is that in what condition ( UT,RT TIG Root?) the single side weld can be treated as “same quality of deposited weld meta" as double side weld.

The same NB artical also indicate that UT and RT can not be lieu of visual examination in this case.

 

[CodeRef]

SJEC,
Yes, I agree RT provides only a two dimensional image as stated in the article. However, the article did not exclude UT. Is it possible to utilize the openings to perform a full visual in addition to UT in lieu of RT for the closing seam per UW-11(a)(7) as suggested by trottiey?


FAQ731-376 A question properly stated is a question half solved.

 

[SJEC]

the largest nozzle is 3" only.
the only way to inspect it is to insert a camera inside the vessel. I know somebody use it to inspect internals (nonpressure parts) and never saw anybody to use it inspect weld seam.

Is here somebody have the experience?

THX

 

[r6155]

This nozzle can be used to radiographic inspection of the close weld, where a panoramic type source of radiation is placed in the center of the cylinder (see ASME V).
A leak test should be made after pressure test.

My opinion only

Regards
r6155

 

[GenB]

if you are allowed mirrors to do internals, yes you can use cameras as well. and I think real time video will be perfect to get the AI involvement.

 

[SJEC]

Since I start this question, I report what happen at the end.
As per the local jurisdiction, A new handhole is added at the center of the head and the inside surface of the close weld will be inspect by a camera.

thanks guys

 

[vpl]

SJEC

Thanks for providing a "how it all turned out" end of the story.

Patricia Lougheed

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