Brazed Aluminum plate HE inservice inspection

[robsalv]

Folks,

I have a question regarding fully brazed Aluminium plate finned heat exchangers, such as cold boxes (ethylene production plants), that have been in service for many years.

Is there any need (indeed and any way) to inservice inspect a fully brazed APFHE if they are fully insulated/fireproofed, have non degrading fluid services on all sides (e.g. ethylene, propylene, ethane), are not exposed to any mercury, have no indication of leaks, experience an average of one cyclic load per year, have piping arranged in such a way that referred forces are minimal but that have been in service for up to 40years???

API RP-572 and API510 and even our own inservice inspection code, AS3788 is fairly silent on the issue.

I'm struggling to come up with any justification to drive any kind of inspection, but that doesn't "feel" right.

Any thoughts?

 

[dcasto]

There are no test I'm aware of for mechanical integrety as it pertains to gases escaping to the outside. The good news is that these type exchanges would not have a catastrophic release and monitoring for leaks via gas detection or IR would give enough warning of a problem. A leak between streams would be the most common problem. A leak of this type would be picked up as offspec product or low yield. SF8 could be used to trace such an internal leak.

 

[robsalv]

Thanks dcasto.

The thermal imaging/IR sounds like a good idea.

There's no suggestion of a leak or offspec product.

I have half a mind to write a inspection quality document/procedure stating that there are no degradation mechanisms and that disturbing the hX could create a defect so best to leave well enough alone.

I think I might employ external techniques to ensure that there are no cracks in flanges or nozzle welds.


Cheers

 

[timbones]

Have you looked through the ALPEMA standard? If you haven't, it is well worth it (go to

http://www.alpema.org).

The only maintenance procedure they have is for leak detection. Other than that, no specific maintenance is required.

Isolating leaks can be done with dry air or nitrogen or helium leak test.

For detecting leaks, I'll quote right from the standard:

"External leaks will be evident by the appearance of localised freeze spots or vapour cloud on the outer casing of the insulation. In the case of heat exchangers installed in a cold box, an increase in or contamination of the purge gas flowing out of the cold box purge valve will be evident. The smell or sound of the escaping fluid may also be discernible."

"Internal leaks can manifest themselves in the reduction of product purity and, if the leak is of sufficient magnitude, a redistribution of flow levels will occur between affected
streams."


cheers,
tim

 

[dcasto]

Sorry about not getting this point down. There is one degredation mechanism, mercury. You should have at least one data point taken annually to look for it. If you have Hg, then use an carbon based removal system.