Opening in skirt through skirt weld 1

[sixeightnick]

Good morning,

I found out this morning that the shop people made an error by not following the shop prints and subsequently put a skirt opening through both a longitudinal weld and a circumferential weld on the skirt.
I've always been told that basically you can do whatever you want on any non-pressure retaining item provided it remains a sound mechanical design.
However I was trying to find something in section VIII Div.1 to back this up that I could show to my salesman and he in turn to the customer, but I cannot find anything on that specific item.

Where can I find any pertinent information?

Thanks

 

[MJCronin]

6-8

There is a book called "The Pressure Vessel Handbook" that may give you some help.

IMHO, skirts are kind of a a "funny" area where the purchaser must state specifically what he wants in terms of fabrication practices.

I do not believe that ASME VIII will help you with this issue

What does the purchaser's specification state about the skirt design?

-MJC

 

[JoeTank]

This is related to your situtaion... ASME permits an opening in a longitudinal seam of a vessel if RT is performed adjacent to it. So, openings in vessel seams are not prophibited in long seams. ASME is silent on opening in circ seams, so they are not prohibited either. This is about one half of your answer.

Stress-wise, the opening must be properly reinforced for the loads.

Joe Tank

 

[bhushan76]

Skirt Opening in weld should not be a problem as skirt is a non-pressure part.
You can have loook at UW-14 "Openings in or Adjacent to welds" which talks about openings in weld for pressure part.

 

[jte]

Skirts are not directly addressed within (warning: assumption follows) VIII Div. 1 (Nick - just for completeness, what code is the vessel built to and where will it be installed?).

Having said that, what is the concern? Overstressing the longitudinal seam in tension? Overstressing the circ seam in tension? Not likely.

If the concern is for reinforcing the opening, then it should be reinforced whether or not it happens to pass through one or more weld seams. Your shop did put a collar on the opening, right?

jt

 

[sixeightnick]

jte,

Absolutely they put a collar on the opening.
It's a VIII Div.1 going to Louisiana.

The concern is that the contact at the customer is not really very experienced in code and in their opinion any opening through a weld is a problem. They haven't said anything about it yet, but I know from past experience with this client that they ask the strangest questions.

I was just wondering if there is anything I could show them in the code that referenced this directly.

 

[vesselfab]

Just right a Request for Clarification letter.

state that you have an opening going through skirt seam
list the specification that says no openings in seams.

the, say

we feel that the specification listed refers to pressure contain seams and not structual support seams and feel that the vessel support will not be compromised in any way.

please confirm.

 

[jte]

sixeight-

Well, we can't prove a negative. Section VIII-1 says nothing about this. Thus, it is up to the folks involved to interpret the situation. If your client made no written demands (i.e. PO, specs, std dwgs) explicitly about openings in skirts, then you have the upper hand. Lacking written requirements, I'd say that whether or not you take vesselfab's approach depends on your relationship with your client. They may not ever realize that there is a problem, so... no problem. On the other hand, if you relate well with them (i.e. they're willing to learn), then being up front about it may be the way to go.

Guess its not always dealing with an under-(experienced, educated, informed...) client. Not always easy dealing with experienced, educated, and well informed clients either, but those issues tend to be different!

jt

 

[mrpsi]

Sometimes these difficult customers are placated by a colorful yet simple FEA, showing that there is no cause for concern. The results would be interpreted per ASME VIII-2. The allowable strengths would correspond to VIII-1 (IID-Table 1A), imposing the applicable weld efficiency. The applied loads come straight from VIII-1 calculations.

 

[jte]

Mr. psi-

Good point about the FEA. I'll admit to sometimes overkilling an analysis just to get some "pretty pictures" which will resolve the problem. Sometimes it is a quicker approach. In this case, though, if a fabricator came to me with their crayons and showed me an FEA using the Div. 1 allowable tensile stress and a Div. 2 acceptnce criteria (S, 1.5*S, 3*S) I would not accept the analysis. I'll send 'em home to run a buckling analysis unless the d/D for the opening is relatively small. 'Course I would moan and groan a bit and then accept the situation rather than requireing an FEA to begin with...

jt

p.s. Welcome to the forum; I like the handle! Please consider telling us a bit about your background in the "personal profile" button on the top left. You can see mine by clicking on the "jte" at the top of this post.