Do not use the stainless steel heat exchanger at temperatures above its limit
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Stainless steel heat exchangers should not be used at temperatures above their limits. Example: To test the efficiency and performance of a shell-and-tube heat exchanger made of 304 stainless steel, a company’s technician filled the shell side with lake water and then introduced steam into the tube side; the water boiled away in a short time. Unfortunately, this test caused cracks in almost every tube at the junction with the tube sheet. It was used only once here as well, resulting in serious consequences. Analysis: When it comes to dealing with equipment corrosion, there is no room for luck or short-term approaches. Of course, the examples above may be individual cases. For most production units, during normal operation, the operators in charge know how to keep the process parameters within the range that meets the corrosion resistance requirements of the equipment materials. The start-up and shutdown processes often create harsh environmental conditions that are highly detrimental to the corrosion of equipment materials, such as excessive temperature and pressure, high flow rates, and the concentration of harmful substances. For example, for a new unit in a factory, after testing at the normal operating temperature, 316 stainless steel was chosen as the construction material. However, at startup, the temperature was increased by 33°C to get the system running. Just ten days after being put into operation, the 316 stainless steel was damaged due to pitting. Therefore, the start-up and shutdown of the plant are crucial aspects for corrosion control. By ensuring that these processes proceed smoothly and minimizing fluctuations in temperature, pressure, and flow rates – especially by avoiding excessive temperatures, pressures, and flow rates – corrosion damage to the equipment can be reduced, thereby ensuring a longer operational lifespan.
When using stainless steel heat exchangers, it is indeed necessary not to exceed their temperature tolerance range. Due to the certain temperature tolerance limits of 304 stainless steel, exceeding these limits can lead to a decline in the material’s properties and even the formation of cracks. Operators need to adhere to the process parameters, paying special attention to controlling temperature, pressure, and flow rate when starting up and shutting down the equipment, in order to avoid damaging the materials. Proper operation and maintenance can extend the equipment's service life. .
In my humble opinion, stress corrosion cracking in austenitic stainless steels is primarily related to the compatibility with the surrounding medium. In this case, the main cause was stress corrosion cracking due to chlorides or pitting, resulting from an inappropriate medium. Of course, temperature is directly proportional to all forms of electrochemical corrosion and stress corrosion cracking. However, a temperature difference of twenty to thirty degrees generally does not result in any significant difference in corrosion resistance.