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Corrosion Cracks in the Tube Sheets of Stainless Steel Shell-and-Tube Heat Exchangers and Corrosion Prevention Measures: After more than a year of operation, two stainless steel shell-and-tube heat exchangers owned by a certain company developed through-going corrosion cracks in their tube sheets. The crack started at the expansion joint between the tube and the tube sheet, gradually extending toward the other tube opening. The junction between the tube and the tube sheet was covered with rust-like corrosion products; after removing these deposits, multiple corrosion cracks were visible around the tube opening. The heat exchanger is an 8-tube-side fixed-plate heat exchanger, with a designed pressure of 0.71 Mpa on the tube side and 0.3 Mpa on the shell side ； The designed temperature is 170°C for the tube side and 100°C for the shell side; the fluid on the tube side is steam, while the fluid on the shell side is No. 190 engine oil. The tube sheet and head are made of 1Cr18Ni9Ti, while the heat exchange tubes are made of 0Cr18Ni9. The steam used in the heat exchanger comes from the plant’s recycled industrial water and is used after being heated; the condensed steam water contains a high amount of Cl-, with a chloride concentration (expressed as Cl-) of 25.5 mg/l in the vapor analysis. The crack characteristics are consistent with those of intergranular corrosion (network-like) and stress corrosion (along grain boundaries); the main components of the corrosion products are Fe and Cr, along with localized enrichment of Cl-. Generally, in water at 200°C, the presence of only 2PMCl- can cause stress corrosion in austenitic stainless steels, with pitting and crevice corrosion being the most common forms. The Cl- content in the steam condensate from this plant is as high as 25.5 mg/l, and this level of Cl- is sufficient to cause intergranular stress corrosion in stainless steel at temperatures between 200 and 300°C. The analysis results also show a significant local enrichment of Cl- within the crack surface. After microcracks form, stress is highly concentrated at the crack tips, causing rapid deformation and yielding in those tips and the surrounding areas. This leads to the formation of slip steps; the recurrence of these slip steps causes the tip surface to be torn open again. Each such tearing of the tip accelerates its further dissolution, and this process repeats itself, allowing the crack to propagate deeper over time. As corrosion progresses and corrosion products accumulate, closed-cell corrosion forms within the cracks; under the combined effect of stress and corrosion, this develops into cracks that extend deeper. Furthermore, the material used in the stainless steel shell-and-tube heat exchangers did not meet the required standards, which resulted in a reduced ability of the matrix and grain boundaries to resist intergranular corrosion and intergranular stress corrosion. The Cl- ions present in the medium, combined with grain boundary sensitization and residual stresses, caused intergranular stress corrosion. Additionally, Cl- ions remained trapped in the gaps between the tubes and the tube sheets, and under the influence of residual stresses and acidic autocatalysis, this led to gap corrosion ； The intergranular non-metallic inclusions cause stress concentration and result in larger grain sizes, which further promotes the occurrence and progression of corrosion. To address these corrosion issues, the following anti-corrosion measures should be taken: 1. Structurally, efforts should be made to avoid the formation of enclosed spaces; sealing welding should be used between the tube sheet and tubes, and stress relief procedures should be carried out after welding. The temperature, duration, and rate of temperature change during heat treatment must meet specified requirements in order to minimize the precipitation of chromium carbides, effectively control grain size, and reduce the likelihood of corrosion. 2. Use chromium-nickel austenitic stainless steels with a lower carbon content, such as 0Cr18Ni10Ti, 0Cr18Ni11Nb, or ultra-low carbon stainless steel 00Cr19Ni10, in order to reduce the risks associated with grain boundary sensitization ； Strictly control the Cl- content to reduce the susceptibility of stainless steel to chloride stress corrosion cracking. After implementing the aforementioned anti-corrosion measures, the corrosion hazards caused by cracks in stainless steel tube sheets were effectively addressed.