A surprise leak in a shell and tube heat exchanger is never a good thing. At best, it will cause down time, resulting in lost revenue. At worst, it could lead to cross-contamination, fouled product, damaged equipment or even a product recall.
However, leaks are bound to happen sooner or later as a piece of equipment ages. There are ways to slow down the aging process. For example, investing in a stainless steel shell and tube heat exchanger will typically result in a much longer lifespan of the equipment than a cheaper material. But the best way to avoid leaks is to be ready for them.
Conducting regular tests on a shell and tube heat exchanger can help you detect small leaks before they become big problems. There are many ways to check out the integrity of your tubes, including:
1. Helium testing
Helium gas can be very useful to hunt down a leak while a heat exchanger is offline. The gas is pumped into the shell side of the exchanger and overpressurized, according to Plant Services. The helium is forced through the vessel and seeps through any holes, welding flaws or cracks in the tubes.
A helium mass spectrometer is attached to each tube to detect the presence of helium. According to the International Atomic Energy Agency, this method is effective due to the mass spectrometer's high sensitivity.
2. Acoustical testing
As anyone who has ever slowly let air out of a balloon knows, leaks tend to have a unique sound. This is the idea behind acoustical testing. A microphone is required, as an air leak in a heat exchanger usually isn't noticed by the average ear. The pitch of the sound gives the inspector clues as to the size, shape and location of the flaw, the IAEA explained.
Plant Services noted that this method can also be used to identify other imperfections as well, including fouling, wall loss and corrosion. Another benefit to acoustical testing is that it can be done quickly; tubes can be tested in as little as 9 seconds. Additionally, it doesn't require a trained expert to perform these tests. However, a drawback of this method is that it isn't as sensitive as other types of tests, such as helium testing or dye penetration. Additionally, this should be performed while the equipment is offline, as sounds from normal processing could interfere with the microphone's ability to pick up sounds of leakage.
3. Dye penetration
Dyes can highlight seams, slight cracks and other imperfections that are difficult to see with the naked eye. This fact is what makes the dye penetration method so intuitively effective. When a leak is suspected, the location is painted with a low viscosity fluid with a tendency to quickly migrate along surfaces. If a leak is present, the fluid will make its way to the other side of the painted wall. This test is simple, inexpensive and sensitive to smaller leaks.
4. Chemical reactions
Some basic chemistry knowledge can go a long way when a simple solution to a complex problem is needed. Some gases commonly used in heat exchangers, such as ammonia, will produce a chemical reaction upon coming in contact with a particular element. In the case of ammonia, pumping hydrochloric acid into the exchanger will result in the formation of ammonium chloride gas. This is identified by white plumes resembling smoke or fog.
When introducing new chemicals to a shell and tube heat exchanger, it's important to be sure that they won't react badly with any substances that are in the tubes or the exchanger itself.
If you find that you need to replace or repair your shell and tube heat exchanger because of small leaks that could become bigger and more problematic, contact the experts at Enerquip. Our team of in-house engineers will work with you and your team to determine the best solution for your operation.