smallest size of shell plate

[ayaan5739]

i want to know what is the smallest size of a shell plate we can use in storage tanks as per api650,we are constructing 96m dia tank in 6th shell course 200mm shortage(gap)coming in circumference so is there any solution for this one according to api.

thanks in advance

 

[VeJi]

In theory, you can make shell plates as small as you wish.
Now, API 653 states that the minimum dimension for a replacement shell plate is 12" or 12 x shell plate thickness, whichever is the greater.
that would mean tat 200 mm would not be allowed.

API 650 does not mention this, but realistically, I'd suggest to have a tank 100mm higher in order to meet the 12" requirement, OR have the lower shell plates realigned, so you don't have the issue at the top plate.

 

[ayaan5739]

thanks for your response,now it is very difficult to realigned the lower shell plate so please if its possible can you give me the clause no.for api653 where it is mention for replacement of shell plate.

 

[VeJi]

Sure, that would be §9.2.2.1.

 

[IFRs]

I believe the OP is short on circumference, not height. API has a minimum width of 72" in 5.6.1.2 unless otherwise agreed to by the Purchaser. I would stick with 12" for appearance, and shell distortion reasons.

 

[JStephen]

If you can weld the short piece on to another plate prior to setting everything in place, it may help on the weld distortion, otherwise, several feet between verts would be preferable, and even then, weld distortion may be an issue if not done correctly.

 

[VeJi]

You are right, I misunderstood the question.
In that case, I agree with the minimum width of 72".

 

[ayaan5739]

thank you very much mr veji but shall we use this one during constructing the tank as api653 is for repair work.

 

[ayaan5739]

yes its short on circumference not height.

 

[IFRs]

My apologies - API 650 5.6.1.2 is referring the the minimum vertical dimension of a shell plate, not the horizontal dimension. This is not truly clear until you see L.3-10 where it says "Plate Widths (Shell Course Heights)". The minimum plate width should be determined to not have overlapping heat affected zones and be wide enough to minimize distortions. 12" may be enough to separate heat affected zones but probably not be enough to minimize distortion, 72" is surely enough for both, some amount in between may be sufficient also.

 

[ayaan5739]

thanks guys for powerfull and supportive reply