One-quarter inch diameter 304 stainless steel cooling tower hanger rods failed by chloride-induced stress-corrosion cracking (SCC). The rods were located in an area of the cooling tower where the air contains drop lets of water below the mist eliminators and above the flow of water The most extensive cracking was observed in the rod nuts and in the portions of the rod which were covered by the nuts. Cracking was transgranular with extensive branching, and some corrosion occurred along the crack paths. The clamping force from the nuts used on both sides of the supported member and residual stresses from thread rolling likely contributed to the stresses for the cracking mechanism, along with the stresses induced by the supported load. The external surfaces of the hanger rods were reportedly exposed to a chloride-containing atmosphere, likely due to the biocide. Type 304 stainless steel is not a suitable material for this application, and materials that resist SCC, such as Inconel, should be considered.
Wendy L. Weiss, Chloride-Induced Stress-Corrosion Cracking of Cooling Tower Hanger Rods, Handbook of Case Histories in Failure Analysis, Vol 2, Edited By Khlefa A. Esaklul, ASM International, 1993, p 478–479, https://doi.org/10.31399/asm.fach.v02.c9001273
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