Care must be taken when changing the cooling water in stainless steel coolers

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Care must be taken when changing the cooling water in stainless steel coolers. Example: A factory had a series of stainless steel coolers that used circulating cooling water, and no corrosion problems occurred over ten years. During an accident, when circulating cooling water could not be supplied, untreated river water was used as a substitute for 48 hours. A few weeks later, five water coolers developed extensive chloride stress corrosion cracks. Analysis: This reflects another not-uncommon misconception: “It won’t be a problem if it’s used for only a short time,” or “It’s fine to use it just once.” Austenitic stainless steels are prone to pitting and crevice corrosion in chloride-containing solutions ； When residual stress exists in the equipment, stress corrosion cracking (abbreviated as SCC) is also likely to occur. Chloride SCC is the most harmful form of local corrosion for austenitic stainless steels. The chloride content in the river water is not specified in this case. However, untreated river water inevitably presents two problems. First, it contains chlorides; second, it contains sediment. In shell-and-tube heat exchangers, there are gaps at the junctions where the tubes meet the tube sheet. Gaps formed by sediment deposition can lead to local concentration of chlorides, reaching very high levels. The residual stresses generated during assembly, and the thermal stresses resulting from uneven local temperatures due to sediment deposition – these factors combined lead to localized corrosion at the gaps, forming pitting. SCC cracks originate from the bottom of these pits, and ultimately the water cooler is damaged as a result of SCC.