Choosing the Right Material Can Extend the Lifetime of Your Heat Exchanger
Heat exchangers are crucial within process industries such as refineries, petrochemical, and chemical plants. They are used to heat and cool process streams by transferring heat between them, thereby conserving the energy within the process plant and minimizing the need to add heat from external sources by burning gas or oil or using electricity. The most common type of industrial heat exchanger is the shell-and-tube type.
The process fluids in the heat exchangers can be highly corrosive and proper material selection is critical to reducing failures, maintenance, and repair costs. A corroding heat exchanger can also cause contamination, leading to expensive purification processes or in the worst case a non-sellable product.
Sandvik Materials Technology is a world leader in the innovation, development, and manufacture of stainless steel and special alloys to meet the corrosion resistance demands of shell and tube heat exchangers. Supported by more than 150 years of research, product development, and expertise, when we see a client’s challenge, we can normally deliver an improved solution.
How to Improve the Life of Your Heat Exchanger
A petrochemical plant in the Nordic region was frequently buying Sandvik 254 SMO* tubes for a shell-and-tube heat exchanger. Sandvik 254 SMO* is a high-alloy austenitic stainless steel developed for use in seawater and other aggressive chloride-bearing media.
We saw that these tubes were experiencing a rather short lifetime for the application. We contacted the customer to investigate if a change in material could lead to a longer lifetime of the tube bundle and reduce their overall costs.
Together with the customer, we analyzed the process conditions for the heat exchanger to determine what could be causing the short tube lifetime.
Hydrochloric acid was condensing in the lower part of the tube bundle, causing rapid corrosion of the tubes in that area. Hydrochloric acid is a strong, inorganic acid that is well known to be very corrosive to stainless steel alloys, even to high-alloyed grades such as Sandvik 254 SMO*.
We set out to identify a replacement grade that would give a better service life for the application.
Sanicro® 28 for Heat Exchanger Tubing
We identified Sanicro® 28, a high-alloyed multi-purpose austenitic stainless steel designed for service in highly corrosive conditions, as a promising solution for the customer.
According to the iso-corrosion diagrams available for the two grades, Sanicro® 28 has better resistance toward hydrochloric acid when compared to Sandvik 254 SMO*. Sanicro® 28 is also alloyed with 27% chromium and 31% nickel, compared to Sandvik 254 SMO’s* 20% chromium and 18% nickel content. In the case of active corrosion, this combination of higher nickel and chromium concentrations for Sanicro® 28 is also expected to give lower corrosion rates than for Sandvik 254 SMO*, which will also enable a longer service life for the tubes even if corrosion still occurs.
Iso-corrosion lines for Sandvik 254 SMO* and Sanicro 28, drawn at 0.1 mm/year corrosion rate.
Avoiding Corrosion in Heat Exchangers
The customer followed our advice, and when the time came for their next replacement of the Sandvik 254 SMO* tubes, they chose Sanicro® 28 instead.
After approximately six months in service, the customer reported that the outgoing process stream from the heat exchanger showed almost negligible levels of metal ions, indicating a very low corrosion rate. After one additional year in service, the tube bundle was inspected and showed no signs of corrosion.
After the inspection, the customer told us: “We’re extremely satisfied with this solution and your guidance during the design.”
How can we help solve your heat exchanger tubing challenges today?
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*Trademark information: 254 SMO is a trademark owned by Outokumpu