Corrosion Test on Heating Tubes by Model Heat Exchanger in Salt-Making Plants
Studies on the Corrosion of Metals in a Salt-Making Apparatus and Its Protection (XII)
1974 Volume 27 Issue 5 Pages 272-284
Details
1974 Volume 27 Issue 5 Pages 272-284
A corrosion test on heating tubes made of various types of stainless steel was conducted by using a model heat exchanger in two actual salt-making plants. The results obtained were as follows:
1. In a 7, 100 hour test conducted in a refined-salt making plant, no stress corrosion cracking was observed to take place on AISI type 304, 316, and 316L heating tubes. However, some pitting corrosion and deposit attacks were found to occur at the inlet or outlet of those heating tubes other than type 316L.
2. In a 5,700 hour test conducted in a common-salt making plant, stress corrosion cracking was observed to occur on types 304, 304L, and 316L with the exception of type 329. These cracks were found to take place near the welded parts on the outlet side of type 304 and 304L, respectively. Also, some cracks were seen on the outside of the tube plate. The cracking on the outside of the tube plate seemed to be caused by the tensil residual stress due to plastic deformation. In the middle part of each tube was also observed some pitting corrosion similar to deposit attack. The test showed that there took place more corrosion on the heating tubes in the common-salt making plant than in the refined-salt making plant. This was considered to be due to the fact that the concentration of MgCl2 in the salt used in the common-salt making plant was greater than the one used in the refined-salt making plant.
3. As the result of the two tests, type 329 proved to be the most suitable stainless steel for a heating tube in a common-salt making plant. This steel seemed to be a most promising one especially for a crystalizer used in high-temperature zones in a common-salt making plant. Types 316 and 316L were considered usable for a crystalizer in a refined-salt making plant, and also for a crystalizer in low-temperature zones or for a concentraing evaporator in a common-salt making plant. Types 304 and 304L were not suitable.
