bonzoboy
Some operating experience from a user of several PCHE's
If you use them in a service where there are lots of pressure or temperature fluctuations on one side, they are prone to fail on the corners, the problem with them in this type of service is they are so compact that if they do fail regularly its difficult to get anything else in their.
We ended up in one location carrying out weld repairs with the manufacturer to get over this. But make sure you dont use them on recycle loops or services where you expect large flow changes.
Another problem in another part of the world was fouling of these exchangers, they easily fould up, if you have a closed loop on one side be it cooling medium or heating medium, make sure you get it adequately filtered and cleaned up in commissioning and ensure that the tank is blanketed. If you have produced gas through one side (as in our worst case of fouling) watch out for carried over lube oils esopecially non synthetics. For waxing problems its a good idea to fit a back flush or ppd injection point and monitor for loss of performance then clean before it fails.
Cheers
Jeremy