SS Dimpled Jacket Repairs...Any Suggestions?

[RPRad]

Have vessel with an external ASME Section VIII Appendix 17 designed ss dimpled jacket assembly which is showing all the classic signs of age (30 yrs) with fatigue cracks developing at the toe of the condensate outlet nozzle, around some of the plug welds and at the jacket boundary welds. The jacket is operated at 60 psig Sat steam (designed for 100 psig)and very much in cyclic operation (2 hrs on, 1/2 hour off cycle repeated over a 24 hour period. The stainless steel jacket is approximately 0.070" thick, while I suppose there may be an SCC angle to this as well lets assume for the time being we are dealing with primarily a pure fatigue mechanism.

Obviously the end is near for this thing as the leaks will become more frequent, but as is typical the accountants need it to operate for another 2 - 3 years before they can come to terms with replacing the vessel. The standard way to repair is just to grind out the cracks best as possible and weld them up (using good welding practices etc) and hope for the best (which is dicey given the thin wall).

Anybody got any innovative ideas with regard to a longer term "temporary" repair of these types of problems or are we pretty much faced with chasing the cracks in the conventional manner.

That is to say for example: could you first repair a leaking plug weld and then weld a flat plate (2" dia)over the plug weld to act as secondary pressure boundary in the event it leaks again (ie assuming you could even get the regulatory authority to agree to it)? or would this just transfer the cyclic stress to the edge of the plate and then you would have created an even bigger mess.

Please dont tell me to junk it because that conversation has already been had.

 

[rmw]

Well, OK, I am not going to tell you to junk it, but I might ask you where to send flowers for its funeral. Sounds like I need to rush my suit out to the cleaners.

I'm worried about where you do a proper job of grinding, welding, etc., and thereby strengthening a portion of it forcing the stresses over onto adjacent thin metal.

Are you faced with replacing the entire vessel or just the jacket?

Can you "jacket" over the "jacket"? Can you strip the jacket off and add some "clamp-on"?

rmw

 

[RPRad]

We prefer black roses for this occasion..if your asking, but I do agree the patient will likely not recover

I agree any attempt to plate over a plug weld will probably result in the development of cracks at the toe of the plate perimeter welds, and hence a worse future repair. It would be nice to know if anyone out there has attempted this and how long they got out of it.

As to the size of the vessel, 12 - 15 foot diameter with a cone bottom. There are six pie shaped dimpled jackets on the cone and a standard configured dimpled jacket on the shell (about 25 feet high). As with all sad stories access is terrible...and as is typical in these cases the plant was built around the vessel...so there is no way to pull them out the roof or a side wall (or vice versa with new vessels). Were actually talking 4 tanks in total with 2 already developing the symptoms describe above.

Removing the old dimpled jacket would be next to impossible (at least I think it would the plug welds are on a 3" pitch..so there is alot going on). Again if anyone has ever attempted it I be interested in hearing how it went.

As to jacketing over the old jacket well that might be possible...I guess you could look at a strapped on steam coil system or you possibly you might even be able to make a stayed jacket by installing welded studs at the some of the plug weld locations and fashioning the jacket design under Appendix 9. I dont know what the efficiency would be like but I guess in this latter case you could punch/drill lots of holes in the existing jacket to get better heat transfer.

I suppose it might even be possible to install a new jacket on the inside surface of the vessel..although I am not sure what the logistics of this would be.

The only other option in terms of replacement would be to field install a new vessel (using prefabed parts).

Thank you for your input...and sympathies