Heat exchanger corrosion: how to prevent an everyday risk becoming a problem

1. Secondary side filled with gas 2. Problem location with H₂ molecules inducting 3. Circulation of the primary side 4. HLD automatic leak detection system

Corrosion is a well-known risk when operating heat exchangers, especially when the foods and fluids inside have a high chloride or salt content. Thin sheets of metal separate pasteurized and unpasteurized product inside a heat exchanger. If they corrode and a hole forms, cross-contamination can occur and compromise product safety and quality. As with the old proverb “a stitch in time saves nine”, the trick is to detect the first signs of corrosion at an early stage – before they have caused a perforation or crack.

A number of integrity testing technologies are available to detect metal thinning in heat exchangers. The traditional solution involves using water pressure to increase the pressure load in a system using a pump and closed valves. Instruments then measure any changes in pressure to determine if there is any corrosion in progress. But as with various other detection applications, this can be a time-consuming process. It is also imprecise in pinpointing the exact position of the leak.

Alternative techniques like conductometry, ultrasonic testing and ultraviolet tracing offer different benefits, but generally also take time.

Another issue is the potential risk, in some cases, of tracing media residues remaining inside the heat exchanger after testing.

Gas is faster, cleaner and more precise

A benign and time-efficient route is to use tracer gas – a mix of hydrogen and nitrogen or helium. Tetra Pak offers advanced testing services based on a mix of hydrogen and nitrogen gas. The mix of hydrogen and nitrogen is non-toxic, eco-friendly and non-corrosive. And unlike helium, it does not stick to equipment surfaces and porous materials, and is therefore residue-free.

Integrity testing with tracer gas works faster than alternative technologies. Downtime is minimal – at just 3-10 minutes per tested section. The level of precision is so high that engineers can pinpoint the exact section of the heat exchanger where corrosion has occurred.

Tetra Pak’s hydrogen gas integrity testing equipment is so sensitive that when customers in Australia first started using it, they discovered multiple small leakages caused by corrosion before they became a problem. “The leakages were tiny and had not yet compromised product quality. They were a surprise for our customers, but we were able to fix them quickly before they caused any damage,” says Martin Eliasson, Tetra Pak Marketing Manager. “After seeing the results, our customers decided to sign up for regular integrity testing. If you want to sleep well at night and be sure your heat exchanger is corrosion-free, it can be a good idea to order an integrity testing plan.”