Analysis of Corrosion Resistance of Heat Exchanger Plates Made of AISI 316L Steel

Abstract

For the corrosion resistance analysis of the heat exchanger plates (made of AISI 316L steel) the samples with visible damage was delivered. The major part of the surface damages was located at the place of "close proximity" (or surface contact) of individual plates. Some of delivered samples showed an unequal layers of sediments, which indicating a different flow velocities of operating fluid through the plates. At locations of the upper part of the plates with no sedimentation (high velocity flow), the most surface damage was detected in "near contact" areas as well as outside. On the other hand, the area of the lower part of the plates, where the sediment deposition was massive (lowest velocity flow), was observed the smallest surface damage. The results of the chemical composition analyses showed a lower amount of molybdenum and a higher amount of phosphorus in case of all samples. The contents of the key elements necessary for the corrosion resistance (chromium and nickel) were only just above the lower limit of the prescribed chemical composition interval. For detailed study of surface damage, selected defects were observed and documented using scanning electron microscopy. Localized damage showed intercrystalline failure of material with typical surface morphology degraded as a result of cavitation damage under hydrodynamic stress.