Data about heat exchanger tube are listed below.Tube materials: Cu-Ni 90-10 (UNS C70600)Service liquid: sea water (tube) and propane (shell)Sea water cools down propane down to 40 C (104 F)
If Zebra muscles(sp?) get in there, your efficiency goes to hell. Keep your pressures constant or flexures will iniatiate stress cracks. If your propane is from a well, it may have an acid content. Any moisture in the system will generate a mineral acid--death for the cu alloy. Worse case is that thieves will know what the exchangers are worth and steal them before installation! (Sorry, I couldn't resist that.)
You haven't stated what kind of failure. Is it pin hole leaks from come form of corrosion or splits the tubes or even buckling. If there is a lot of debris in the water, it can plug some of the tubes causing them to overheat and split or buckle. If there is mud or silt, it can plate out on the tubes and cause hot spots that lead to failure. There could also be a problem with the actual manufacture of the tubes in terms of the alloy or even the welding of the seams if the tubes are not seamless.
And let's not forget of organic fouling(other than zebra mussels) and galvanic corrosion. Better put some sacrificial anodes in there. Other failures could be over-pressurization, potential brittle fracture if there are large differences in temperatures, pitting corrosion leading to pin-hole leaks. I would say your major failure is going to be related to corrosion though. Maintain good chemistry and they shouldn't fail if they are designed well.
