Shell plate replacement.

[Syahar1975]

Dear experts,

During construction a new tank, by mistake my subcontractor install the wrong shell plate (1 plate only) in the first course. All verticals have been completely welded.

We are not allowing them to erect the 2nd shell course till the wrong plate is replaced.

The correct plate is available. We have to cut the 2 verticals (V3 and V4), remove the wrong plate and insert the correct one. There would be 2- verticals welding on the same location (V3 and V4). The width of the shell is 2100 mm.

My concern is this V3 and V4 have been welded, flame cut and again re-weld.

Is there any restriction in API 650 or 653 in regards to the above issue

Syah

 

[IFRs]

What size tank ( diameter and height ), what thickness and grade is the first ring, is the tank heated or cooled, what is the design metal temperature?

 

[Syahar1975]

IFRs,

Tank : 56 M dia. x 15 M Ht.

Material A516-Gr. 70(N). Thickness 8 mm.

The plate size is 2100 mm (W) x 11000 (L).

Design metal temp. 95 deg. C.

We just erected 1st shell course only. We could not erect 2nd course till this plate is replaced.

Syah

 

[IFRs]

Hmmm - Over 93 DegC so it is an Annex M tank, using API Group V steel. Based on the 8mm thickness, this can't be the bottom ring, perhaps it is the top ring and you are going to use the jacking method of erecting the tank? If this is true, I would not feel badly about cutting the verts and re-welding in another plate because the thickness is more than the hydrostatic pressure would require so the actual stresses would be quite low and the risk of failure low. If it were however closer to 25mm or 26mm thick plate and used for the bottom ring, I would be conservative and cut out the heat affected zones and add a small plate, say 300mm wide on one end. An alternative might be to hardness test the heat affected zones on both sides of both new welds to see if were embrittled but if that resulted in replacement plates that would be much more expensive than just doing it from the beginning. My opinion only and I would not be surprised to see or hear different from experts here.

 

[Syahar1975]

IFR,

Yes, you are right. We are using jacking method. The first course here meaning top shell course.

The maximum liquid level by the design is not reaching this top shell course.

Thanks for your opinion.

 

[JStephen]

I don't think there's a limit on that kind of re-work, although it is undesirable.
If the plate is thicker than it needs to be, I'd leave it in.
If cutting on the seams is a concern, cut a section out just a little wider than the plate that was welded in.

 

[Duwe6]

Is it permissible to flame-cut new material? Yes
Does flame-cut material require any special restrictions that mechanically sheared material does not? Not really; just grid to shiny metal prior to welding.
If you trim off the weld plus the HAZ [HAZ will be < 0.1mm], do you think that the remaining material 'remembers' being welded on? Not possible.

Thee is no 'problem', except in some folks minds; they are thinking 'Repair'. JStephen got it right - this is Rework. The problem is completely removed & the area will be returned to its original condition. Rework, not Repair.

 

[Syahar1975]

Dear all,

Thanks for all your opinions.

The PMC welding inspector is concerning about the vertical joint of existing plates on the tank. The vertical on this plate had been welded then flame cut then weld again. So many heat input will be received by this plate on the vertical joint area.

This is really unfortunate situation. Because if we cut let say 100 mm beyond (both side) the existing verticals, we do not have extra length 200 mm on the correct shell plate.

If we are taking the risk by putting the correct plate, welded then client will request hardness test on HAZ area. If the hardness is not acceptable we have to cut again and buy a new material from overseas.

The PMC welding engineer shows me API 653 (we know this is not relevant since we are building new tank per API 650) that cut and re-weld on horizontal joint is acceptable.

This issue still being discussed. I will suggest to the management to take the risk maybe we are lucky I mean the hardness still acceptable.

Syah