out of tolerance peaking and banding

[mechfabricator]

We have a 20m diameter fixed roof supported roof storage tank as per API650, the roundness, plumbness and levelness are ok, but peaking and banding in 4 points are 40mm,
is that possible to accept or it needs repair, the erector said that repair is possible by tearing the seams and re-welding, but it is not necessary,
can anybody tell us what shall we do?
thanks.

 

[Syahar1975]

40 mm is more than 3 times from the tolerance in API 650.

In my previous experiences we have to repaired by removing the existing weld, fit up and re welding.

During this process the fitter must always check with his sweep board.

This can be prevented if during fit up and weld our fitters always control the peaking / banding.

More than tolerance in peaking and banding in tank construction is not unusual. But I have never seen in my past experience out of tolerance till 40 mm.

 

[mechfabricator]

please refer to recently posted thread:

http://www.eng-tips.com/viewthread.cfm?qid=381537

it seems that our inspector has measured and reported both peaking and banding twice.(as per method b in the attached picture).
so if the maximum is 20 what is your opinion?

 

[Syahar1975]

By the code yes it is not acceptable.

I have experiences argue with the QC inspector because 15 mm not 13 mm.

Even 12 mm but visually looks no good then QC is still not accepting.

We have to repair these out of tolerance area.

Off course there were also some cases that we "skip" the bad area and check the good area only.

 

[Duwe6]

You may be getting 'overprecise'. API 650 specifies " 1/2-inch ", not 0.50", for peaking and banding. Also, the measurement area is limited to 36-inches 910mm radius or sweep board. Is the tank closer to 13mm [1/2-inch] or to 19mm [3/4-inch]? If the tank is significantly out-of-tolerance, does the client want it repaired, or is it acceptable to them?

These are tanks, not swiss watches; the tolerances are fairly generous.

 

[Syahar1975]

I agree with Duwe6, it is not watch.

But this excessive peaking or banding could be seen clearly after the tank completely painted.

Especially the new comer QC inspector which is totally text book. They just follow whatever the code said.

Many times the client's construction supervisor said OK but the QC inspector NO for this subject.

Also many cases the client QC inspector asked to check the area 1 M or 2 M behind this bad area. If that area is OK then they will close their eyes.