Help broken spiral exchanger - advice

[mrtangent]

Dear All,

I'm curious has anyone performed a fix to a stress crossion cracked spiral. We opened up a unit recently and found severe cracking. We are buying a new duplex stainless replacement but in the mean while, we've only found a few people who repair fixes but they seem only good upto 160 degC.

We need a fix which can ideally with stand 240deg C. Has anyone performed such a fix ? I would imagine some kind of plastic adesive would be required but we have not found one.

We have looked for suitable spare exchangers for the duty but our HTA is large (150 m2+) and we need a pressure rating of 16 barg or 240 psig so we dont expect any spares or second hand units to be available soon. We cannot tollerate carbon steel due to product discolouration so we must have a clean surface.

At the moment we are planning to rapidally install a precooler to maintain 150deg C inlet and fix with the best fix material but I am keen to see if anyone else has any contacts for a better repair

 

[Montemayor]

james1030bruce:

I can't give you a "fix" for such a serious problem on a relatively large Spiral exchanger. But I can offer some experience. Because of the nature of the problem, I would immediately contact the original supplier - something I assume you've already done. I also presume that because of the pressure and temperatures involved, this is a "tubular" spiral (Archimedes shape, rather than helix) and not a flat plate spiral type. Either way, the tooling and fabrication procedures are special and usually limited to the fabricator. It is cumbersome -if not impossible to get into some of the welding sites within each of these models. That is why it is so vitally important to specify a Spiral exchanger with detailed accuracy. When they are specified and applied correctly, they work forever and ever without any problems.

With any luck, your fabricator is well-established and has acknowledged customer service - such as Alfa Laval. Alfa is expensive. But I have, in the past, air-freighted one spiral unit to them for emergency repairs with top-notch help and support from them. This was the reason we selected Alfa Laval - and it paid off in that instance. I believe you will find it troublesome and very difficult to effect repairs in the field - although we don't know the specifics of the damage and where/how it is located. I do know that some metal will have to be sacrificed in stress corrosion cases, and this will be difficult to cure. Are you using 347 SS or similar (Columbium-added) alloy for stress corrosion? This may make the repairs more difficult. Is your stress corrosion due to chloride ions? Has it undergone sensitization?

I hope this experience is of some help. You have a serious and rather large problem; I hope you are able to obtain direct assistance and help locally or from your fabricator.


Art Montemayor
Spring, TX

 

[mrtangent]

Montemayor (Chemical)

Thankyour for your information. We have contacted Vaahto. Basically we cannot repair the exchanger. We had un expected higher than normal HCl (1 ppm) dry conditions but still higher than expected in service.

We are going to purchase a spare in duplex stainless in the meanwhile we are going to install a smaller unit in the same service in series with the exsiting one. We think the failure is manifests itself worst at higher temps and we are going to comprimise on temps as wait for a new one.

Thanks for confirming that there is not an obvious solution that we've not looked over.

James