Can a low content of Cl ions in the leak detection steam cause stress corrosion?
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A composition analysis was conducted on the cracks on the back side of the lining in the urea synthesis tower, and it was found that the chloride ion content at those cracks was relatively low, less than 0.1%. Experts, could stress corrosion occur under such conditions? This Cl ion should have been brought in with the leak detection steam; if its concentration is not high, then no accumulation or concentration of Cl ions will occur at the leak detection tank, meaning the likelihood of stress corrosion is lower, right? If not around the leak detection tank, the concentration theory can indeed explain it. Please ask an expert for help.
Strictly speaking, the chloride ion level in the steam used for leak detection in urine towers should be kept below 2 ppm (some sources suggest that it should be below 0.5 ppm); otherwise, corrosion will definitely occur on the back side of the liner of the urine tower. Here, it is recommended that the poster: if steam is still used as the leak detection medium in the urine tower, it should be changed to air or nitrogen as soon as possible; otherwise, it is extremely dangerous in the situation you mentioned.
It was originally common to use steam for leak detection in urine treatment towers; however, there are now many reports of stress corrosion occurring due to metal ions such as chloride ions, potassium, and sodium when using steam for this purpose. As a result, air or nitrogen is now used for leak detection. Nitrogen has stable properties and, as an inert gas, it is currently considered the preferred option from a theoretical standpoint. What about air? If oxygen is also concentrated in a certain area, could that have an adverse effect on the equipment as well? I’m not an expert in this area; it’s better to listen to those who are more knowledgeable
Austenitic stainless steel is very sensitive to chloride ions; it is better not to use steam for leak detection. Many manufacturers have encountered cracks in their linings, so it is recommended to use nitrogen instead for leak detection.
The Cl ion content in the leak detection steam is 2 or below 0.5 ppm. Has anyone conducted similar experiments? At such concentrations, if scale samples are taken, or if cracks occur and the chemical composition of those areas is analyzed, what is approximately the Cl ion content there? What’s needed now is to determine a critical value; if the concentration of Cl ions is very high, it will definitely lead to stress corrosion. This doesn’t have any practical significance for finding a solution to this problem – what’s important is that threshold value. Furthermore, when using other media for leak detection, there is also an issue related to the quality of that medium, such as whether the air is clean and dry. Could some of these also cause the leak-detection steam to not flow properly, or could moisture be present? Additionally, the presence of oxygen, carbon dioxide, and other substances might also lead to some degree of corrosion of carbon steel.
" The requirement for chloride ions in the steam used for leak detection in urine analysis systems is to be kept below 2 ppm (some sources indicate that it should be below 0.5 ppm). May I ask where this specific requirement comes from? I’m not very familiar with this area; thank you~
The equipment maintenance procedures specify that the chloride ion content should be less than 2 ppm; it is safer to keep it below 0.5 ppm. However, steam is considered a utility, and it is difficult to control urea users. To avoid chloride corrosion, many manufacturers no longer use steam for reduction purposes, opting instead for nitrogen or ammonia for infrared leak detection. Some of them are theoretical in nature; some manufacturers use leak-detection steam, and urea synthesis towers can operate for 20 years without any problems.
What is 0.1%? It should be 1000 PPm – what’s the difference from the critical value of 0.5 PPm? Why is it said that \"no accumulation or concentration of Cl ions occurs at the leak detection area\"? Stress corrosion is definitely a possibility; it’s necessary to switch to another nitrogen-based leak detection method right away, etc
It is mainly because the leak detection steam at the leak detection tank is in a flowing state, which reduces the likelihood of Cl ions accumulating and concentrating. At the base material, since the flow of the leak detection medium is not very smooth, it may remain stationary, allowing for concentration to occur. Additionally, when the leak detection steam condenses, concentration of Cl ions can also take place at the bottom of each tube section. My personal assumptions may not reflect the actual situation; I would appreciate some guidance from those who are more knowledgeable.