Help: Identifying the cause of equipment corrosion
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There is a leak in the tubes of the boiler feedwater heat exchanger; upon disassembly and inspection, it was found that there was a hole at the bent section of the heat exchange tubes. Please, expert, help analyze the reason. Tube side fluid: H2, CO, CO2, CH4; Shell side fluid: deionized water. Heat exchange tube material: 304. Suspicion turned to a water quality issue; after sampling and analysis, the chloride content in the water was zero, and the conductivity was less than 2 μs/cm.
It is recommended to replace it with a silicon carbide tubular heat exchanger, whose heat exchange efficiency is twice that of stainless steel.
Since the problem occurs only at the bends, stress corrosion must be considered.
The stress at the bend is high; stress corrosion could be a consideration. Although the chloride content in the desalinated water is zero, if the resin is treated with HCL, there is a risk that it may enter the water system without being completely replaced, resulting in an excessive chloride level in the desalinated water; however, this is temporary, and no chloride ions are detected afterward. We encountered a similar situation in a project; it was only by analyzing the causes of failure of the damaged pipes that we discovered the damage was caused by stress corrosion.
It is recommended to cut off the tube and inspect it to determine whether the corrosion occurs on the inside or outside of the heat exchange tube. Based on the photos, the corrosion on the outside of the heat exchange tube is mild.
Is it just this one pipe that is corroded? Since there is no mechanism of chemical corrosion in the medium, let’s consider whether there is something wrong with the quality of this pipe
The exhaust gas recovery heat exchanger may suffer from dew point corrosion; moreover, stainless steel is prone to corrosion after work hardening due to cold bending.
Tube side medium: H2, CO, CO2, CH4 Shell side medium: deionized water? ? Is the shell-side medium H2, CO, CO2, or CH4? Stress corrosion cracking is considered to be the possible mechanism, and CO-CO2-H2O might be involved in this process