pitting on SS304 shell 2

[mehdiza]

Hello friends,

We have an SS304 shell. there are tubes in it (like shell & tube heat exchangers). in the shell we have cooling water. We found pitting on bottom welds of the shell and the leakage of water. perhaps it was because of chloride content of water. we test the water and it has more than 800 ppm chloride.

We used belzona but the leakage continued (maybe because of wrong usage)

What is your suggestion for repair of the shell and stopping the pitting?
Do you know when the base material may affect by pitting seriously?

Consider that there are some problems :
1- We dont have access to inside of the shell.
2- re-welding may be harmfull because there is gasket behind the weld. and also removing the shell is impossible.

Your help is appreciated.

 

[stanweld]

Pitting is resulting from high Chloride content. You need examine the ID surface to determine full extent of corrosion and whether the shell is salvageable through welding repair. If you cannot examine from the ID, UT examine for pitting. After repairs are made, treat the water to greatly reduce chloride. If chloride content cannot be controlled, you will need to change metallurgy.

 

[mehdiza]

Thanks.

The problem is we dont have access inside because there is a bundle of tube then repair of inside is difficult. Also the shell is flanged to a bottom channel (equipment is vertical) and welding outside may harm gasket.

about the water also it maybe impossible to treat and reduce chloride.

Is a solution possible for this problem?

 

[stanweld]

Why do you think that the gasket would be harmed? Are the repair areas immediately adjacent? That would seem to be the least of your problems.

Welding repairs could be effected from the OD surface; however, the metallurgy is insufficient to protect from continued corrosion. Such repairs would only be temporary.

Any non welding repair would also only be temporary.

 

[mehdiza]

the tubesheet thk. is 10 mm. it means that when we re-weld it may burn the gasket because of the heat. also we cant replace the gasket cause the equipment is installed and removing the shell is very difficult.

however it maybe the last choice to re-weld it and we hope that the gasket could be safe. but it maybe 50-50.

 

[EdStainless]

This shell is scrap.
Your fix is to order a new one with a 2205 shell.
Any attempt to reweld or coat will only result in the problem cropping up in a new location.

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Plymouth Tube

 

[mehdiza]

Thanks anyway.

You are right. Although we reweld or coat again we will face with new leakages.

But I dont agree with your solution because of the cost. it is the last solution. if we could stop a plant and remove the shell there are lots of ways to solve the problem. e.g. cutting the shell and repair of inside and coat the base metal. (the base metal is now safe).

 

[EdStainless]

If you coat 304 in this application, and there is one microscopic defect in the coating then the 304 will fail by pitting there. And it will happen faster because it will act like crevice corrosion under the edges of the coating.
Your only solutions are to either remove the chlorides or select the correct metallurgy.

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Plymouth Tube