Anchor chair gusset welded over the skirt long seam 2

[jtseng123]

Dear all,

Vessel shop asked our approval after the fact that they welded anchor chair gusset over the skirt long seam as shown in the attached sketch. Is it acceptable ?

 

[marty007]

The skirt is not a part of the pressure boundary, so this is outside the scope of any pressure vessel codes.

At this point you're down to good engineering judgment and/or project specifications.

 

[JStephen]

It's undesirable to locate it like that. But it's also undesirable to cut stuff off and re-weld it. That being the case, I'd leave it as is.
The main stress from an anchor chair is in the vertical direction, I believe, as is the stress in the skirt.

 

[KevinNZ]

In this case there very little difference in locating the seam weld way from the HD bolt location. You still have the ring weld crossing the seam. As above this is not part of the pressure containment shell.

 

[r6155]

This is wrong engineering practice. Also two bolts per chair is wrong.

Regards
r6155

 

[Duwe6]

r6155, not 'Wrong' per ASME, but very poor practice. Imagine all the extra problems found when trying to set this vessel onto cast-in-place pairs of anchor bolts, trying to get each pair to slip into their pockets!

 

[r6155]

Minimum spacing betwenn anchor bolts is required. See PIP STE05121 Anchor bolt design guide.

Regards
r6155

 

[JStephen]

Right offhand, I can't think why you'd need a minimum spacing between bolts. You need room to turn the nuts. Bolt spacing enters into the embedment design, see ACI-318 Appendix D, for example, but isn't limited in the design. Threading a vessel onto the bolts is an issue, but I don't see that being any worse with say, 6 pairs of bolts as opposed to 12 equally spaced bolts. And if the tank is leg-supported, you'll generally have bolts in pairs or sets of 4 or whatever anyway.

 

[r6155]

Minimum spacing betwenn anchor bolts is required to avoid overlap of "shear cone" of concrete.

Regards
r6155

 

[jte]

Well, just because one industry document - which is not used by anywhere near "all" industry, not even all of the Process industry - says that this is how an anchor bolt chair is supposed to look does not make anything else inherently "wrong".

Has anybody stopped to wonder whether or not the anchor bolts in question are actually embedded in concrete? Does the possibility exist that they are thru bolted on a steel structure?

Surely, all vessels are alike, none are unique, and the Process Industry Practices (the PIP's) cover every possibility for every vessel ever built for every industry?. Sheesh. My company is a member of the PIP organization, and I can freely use the PIPs for our vessel standard drawings. But most of them we don't use. Does that make our standard drawings "wrong"?

Is welding over a long seam on a skirt ideal? No, I'd say it isn't. But it is not the end of the world either.

 

[JStephen]

r6155, refer to ACI 318 Appendix D. Having bolts close together just means you consider the bolts as a group for that shear cone instead of singly. No problem. Not wrong.

 

[r6155]

Appendix D not exist in ACI 318.
Please see ACI 318 edition 2014 Chapter 17

17.2.1.1 Anchor group effects shall be considered wherever
two or more anchors have spacing less than the critical
spacing as follows:

Regards
r6155

 

[jtseng123]

Thanks for all the comments.
As for anchor bolt spacing, we apply 5 x bolt diameter as the minimum for concrete support. Less than 5D is not desirable, but can be achieved by using isolation sleeve or other means according to our civil engineer. We even have 3 anchor bolts next to each other on a concrete table top in the past. On steel structure support, 2 or 3 through bolting next to each other is not uncommon.

For the welding issue, I accept their ill design since no strong technical reason to reject it from everyone's opinion, but ask UT and MT on the skirt butt weld and let it go.

 

[jte]

jtseng123-

Sounds like a reasonable response to me. Thanks for closing the loop on this discussion with your planned path forward, and also with your points about various methods of anchor bolt installation which you've seen.