Plate Heat Exchanger Gasket Failure Signs

Gaskets are the wearing part of a gasketed plate heat exchanger. The plates can run for decades; the gaskets cannot. They age with temperature, with the chemistry of the media and with every opening and closing of the pack. Each kind of failure leaves a different mark, and reading it correctly decides whether you need new gaskets, a different compound, or a look at how the unit is being run.

1. Weeping along the edge of the plate pack

Small drips or a wet film along the outside of the pack mean a field gasket is no longer sealing against the next plate. It usually starts at one or two plates and spreads. Tightening the pack may stop it for a while, but if the pack is already near its minimum tightening dimension, the gaskets have lost their elasticity and further tightening will damage the plates rather than seal them.

A leak that shows only after a shutdown, or after a sudden change in temperature, and stops once the unit is back at running temperature, is cold leakage. It often seals again by itself, but it is an early sign that the gaskets are ageing. Note where and when it appears.

2. Liquid coming out of the leakage vents near the ports

Around each port the gasket has a double seal with a small vent between the two barriers, open to the atmosphere. If liquid appears there, one of the port seals has failed. The vent is doing its job: the leak goes outside where you can see it, instead of into the other medium. Treat it as a warning to regasket soon, not as a reason to plug the vent.

If one medium is turning up in the other, the gasket is rarely the cause, because the vents send gasket leaks outside. Suspect a cracked or pinholed plate instead, and have the plates inspected.

3. Gaskets that are hard, flat and shiny

When a pack is opened, a healthy gasket springs back and still has a rounded profile. A gasket that stays flat, feels hard and has a glazed surface has taken a permanent compression set, usually from age and temperature. It will not seal again however hard the pack is tightened. This is normal end of life: plan a regasket of the whole pack.

4. Gaskets that are swollen, soft or sticky

Swelling, softening or a tacky surface is not age. Most often it is the wrong compound for the medium, but cleaning chemicals that are too strong, and temperatures above what the compound is made for, do the same. The usual pairings are:

• EPDM for water, steam and many dilute chemicals. It swells in oils.
• Nitrile (NBR) for oils and fats at moderate temperature.
• Viton (FKM) for hot oils, many acids and solvents, where nitrile hardens or swells. This is why edible oil refining duties specify it.

Replacing a swollen gasket with the same compound only repeats the failure. Check the media, the temperature and the cleaning chemicals and their strength, then choose the compound against all three.

5. Gaskets out of their groove

A gasket that has crept out of its groove, or is pinched between plates, points to how the pack is being handled or run: overtightening, tightening unevenly, a pack left loose, pressure surges or water hammer, a groove that has been bent, a gasket that was sitting on the edge of the groove instead of in it, or glue that has failed on a glued gasket. Fitting new gaskets without fixing the cause will see them displaced again.

Before you open the pack

• Mark where the leak is while the unit is still closed. Once the pack is open, the trace is lost.
• Draw a diagonal line across the side of the pack and number the plates, so every plate goes back in its place and the right way round.
• To tell a plate leak from a gasket leak, pressure test one side at a time with the other side open. Liquid on the open side means a plate is leaking.

What to do when you see these signs

1. Regasket the whole pack, not single plates. New gaskets beside old ones compress differently and the pack will not close evenly. Once a pack has been opened, fit new gaskets rather than refitting the old ones.
2. Clean the grooves fully before fitting new gaskets. On a glued gasket, remove every trace of the old glue and let the new glue cure fully before closing. On a clip-on (glue-free) gasket, check that every clip is seated.
3. Close the pack evenly: tighten the bolts diagonally and in steps, keep the frame plate and pressure plate parallel, and stop at the tightening dimension on the nameplate. Go further towards the minimum only if it still leaks, and never below it.
4. Inspect the plates while the pack is open. Backlighting in a dark room is a quick check: a crack right through the plate shows as a line of light. Finer cracks need a dye penetrant test.
5. Store spare gaskets cool, dry and in the dark, away from electric motors and welding, which give off ozone that ages rubber.
6. Record the date and the compound, so the next regasket is planned rather than forced.

We supply replacement gaskets and plates for most major makes, with every gasket checked for fit against the plate and every plate backlit before despatch. Find your model in the plates and gaskets catalogue, or go straight to Alfa Laval, APV, Kelvion, Danfoss or API Schmidt-Bretten. If you are not sure which compound your duty needs, send us the media and temperatures and we will advise.