Cross contamination in a Plate & Frame Exchanger

[mahans]

A concerned customer called with a question about cross contamination in a plate & frame heat exchanger (PHE). This particular heat exchanger was being used as an oil cooler. During regularly scheduled maintenance the customer found water in his oil filter. We have not fully investigated the problem but several things come to mind.

First I would look for evidence of condensation in the oil reservoir, most have some type of ventilation and moisture from the atmosphere can be drawn in with the ambient air. As the reservoir heats up and cools down this moisture can condense in quantities significant enough to cause problems.

If large “slugs” of water are found I would look for other sources. The most logical place is the heat exchanger because that is a location of direct interface between the fluids. This customer originally called because he thought he needed new gaskets but was not seeing any leakage to the floor. By design, PHE’s will leak to atmosphere in the event of a gasket failure, so if the PHE is the source of the water contamination we will need to look at the plates. A cracked plate or one that has failed due to corrosion will cause cross contamination.

The customer has installed a spare plate pack and is sending the old one to us for inspection when we discover the problem we will finish this post.

What is your problem?

[mahans]

Sorry for the delay in answering the “Cross contamination" problem.

It appears the problem was condensation in the oil reservoir. When the PHE was received we hydro tested it to 150PSI, no leak was found, neither to atmosphere nor to the other side of the plate pack. We disassembled the PHE cleaned the plates and visually inspected the gaskets, gasket grooves and the plates. Evidence of overheating was found due to a severe flattening of the gaskets and “heat bluing” of the stainless steel plates. We then preformed a dye-penetrate test on the plates and found no leaks. We installed new gaskets, reassembled the unit and pressure tested the unit again.

Upon reporting our findings to the customer he installed a descant filled vent cap to the reservoir. With the warm days and cool nights we will get this time of year we should know soon if that was the problem.

What is your problem?