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Tank shell replacement procedure

Tuesday, May 23, 2017   By: Ali [409] 1 Stars
What is the weld sequence of shell plate replacement? Vertical seams should be welded first or horizontal? When first horizontal seam is welded the second seam should be tack welded or not?

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Wednesday, May 24, 2017   By: ITS [1678] 4 Stars
Your tank shell replacement procedure is too detailed, for the welding firm or repair company knows how to attach a replacement rolled steel shell sheet or plate in an opening for a strong weld and minimum distortions that follow the welding code section 9. The most important initial items is having the correct fit-up that matches the weld specification procedure or WPS that the repair firm will use.

Do you have a photo to look at what is going on?

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Thursday, May 25, 2017   By: Ali [409] 1 Stars
Here is photos. You can see temporary attachment on the fifth and sixth course of 15mm and 10mm respectively applied inside the tank.

Click on picture for full size view or to view PDF!

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Thursday, May 25, 2017   By: Ali [409] 1 Stars
Here is photos. You can see temporary attachment on the fifth and sixth course of 15mm and 10mm respectively applied inside the tank


Click on picture for full size view or to view PDF!

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Thursday, May 25, 2017   By: ITS [1678] 4 Stars
Nice photo!

The shell plates are heavy and positioning those heavy shell plates is difficult. I saw a generous amount of temporary positioning jigs or bars to help in positioning and holding in-place the shell plates during welding and they can assist in the weld joint fit up during positioning by being welded when the fit up is right and in tolerance to the WPS. I would think one of the welders has a thickness gauge for the fit up or can determine it visually by comparison. Tack welds may not be necessary or because of the heavy shell plate they may break causing unwanted problems.

Once in place, the welding of the joints, whether horizontal or vertical is ultimately left to the experience of the repair firm. What is important is controlling heat while making sound weld joints. Those are heavy shell plates and those plates are a large heat sink Here again, experience with the WPS compliment each other.

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Thursday, May 25, 2017   By: Ali [409] 1 Stars
When the Vertical seams of the replacement plates are welded, All parameters such as plumbness, peaking are in the standard range. Then horizontal seams to be welded, the distortion occurs on adjacent plates Both sides of the replacement area.

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Thursday, May 25, 2017   By: ITS [1678] 4 Stars
That is a problem and the additional information is better.

The distortion of the adjacent shell plate and plates seems or gives the impression that uneven control of heat as a result of sequencing or something else. Also, it might need only a simple fix. The condition also give the impression the WPS may need adjustment or work too or at least a review. It may not mean it is an essential variable required by the welding code Section 9.

The distortion give the impression it may simply be a weld joint sequencing issue where a review might be needed. A professional on-site is needed for sure.

Ship builders have in the past had similar problems. Their solution was employing the Egg-Box Method of weld sequencing. Basically, this requires a layout of all weld joints say on paper and then mapping out the sequence and their lengths with starts and stops. You may need significant tack welds to assist to start with. Experience is everything here!

The Egg-Box Method works something like this, but applying it here is not exactly a good fit since you are staggering the plates. In general, do half of the lower horizontal weld joint of one plate starting from the center, then do the next adjoining shell plate horizontal the same way, then repeat this on the top shell plates above them, then weld the vertical completely between them the lower two. Then repeat. But remember you are only doing two shell course between existing shell course.

You may have issues that you have not shared or conditions that are unknown that may contribute to the problem. But, this additional knowledge may help in finding a solution even if the egg box method is not the solution.

It is good to read that the parameters such as plumbness, peaking are in the standard range.

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Friday, May 26, 2017   By: davidr@fast.net [39] 5 Stars
Remember - weld deposits shrink when cooling. The metal has to have somewhere to shrink from. If you lock in both verts and then weld the horizontal, where can the metal come from? If you weld from both sides towards the middle, same question. Either your contractor is inexperienced or your tolerances are too tight.

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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