Corrosion of heat exchanger tube sheets

Thread Content

Corrosion, scaling, thinning, and leakage of heat exchanger tube sheets are common problems in industrial enterprises. Many solutions such as changing the material used, installing sacrificial anodes, and applying coatings have been tried, but with little success. Firstly, regarding the issue of repairing corrosion defects, some people believe in welding, thinking that arc welding is the safest method. What they don’t realize is that if not handled properly, the stress defects resulting from this process can accelerate the corrosion of the tube sheet, causing the equipment to corrode and leak again very quickly. It is highly necessary to adopt a safe repair method. Then, there is the anti-corrosion protection. Methods such as material selection and zinc block protection may delay corrosion to a certain extent, but corrosion occurs due to a wide range of complex factors including the medium, electrochemistry, and material defects; it is therefore not advisable to try to solve the problem by focusing solely on one aspect. As for coatings, due to frequent temperature changes and impurity ions in water quality, ordinary coatings simply cannot withstand such a changing environment, resulting in peeling and failure. Finally, the problem of corrosion caused by direct contact between the insulating material and metal can be addressed by using special coatings. Good materials do exist, but there are too few specialized construction techniques available. Most cases involve sandblasting, but problems arise after this process: first, the sandblasting is not thorough enough, and the existing rust layer is not completely removed; cleaning with cleaning agents is also inadequate. Coupled with poor-quality circulating water, scaling occurs. This leads to corrosion beneath the scale, and the coating, once intact, is corroded from within and ends up falling off. Second, sandblasting was done properly and cleaning was adequate as well, but due to various ions in the circulating water, they had already penetrated into the tube sheet matrix (in older equipment). The desalination cleaning of the matrix was not carried out properly, which led to corrosion beneath the coating, resulting in flaky peeling. The above overview is not entirely comprehensive; every manufacturer and every piece of equipment comes with complex operating conditions. When choosing anti-corrosion methods, manufacturers should consider not only the materials but also factors such as the manufacturing process, service quality, and level of expertise – all of which represent added value.