There is leakage at the welds of the reactor with a semi-tube structure; some of the base material also shows leakage
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The reaction vessel has a capacity of 30,000 liters. Its heat exchange structure features outer half-tubes that are welded to the outside of the cylinder; both the cylinder and these half-tubes are made of S30408 material. The diameter of the half-tubes is 108 mm, and their thickness is 4 mm; they are formed by steel pressing. The working temperature inside the cylinder is -15°C, with atmospheric pressure applied; inside the half-tubes, there is frozen calcium chloride solution at a temperature of -25 to -20°C, under a pressure of 0.2–0.3 MPa； It has been in operation for over a year; recently it was shut down. The material inside the cylinder was emptied, as well as the brine in the semi-pipe. Clean water was added to the inner cylinder, and steam was used to raise the temperature in order to clean the reactor. The cleaning temperature was around 100°C. After cleaning, the temperature was lowered and the water was drained. The jacket was tested under a water pressure of 0.4 MPa, and no significant leaks were detected ； Another 3 months passed, and the device was put back into use. A pressure test was conducted using compressed air at a pressure of 0.4 MPa; it was found that there were numerous leakage points in the fillet welds, as well as some leakage points in the base material ； Please analyze it again – what is the reason? Please discuss. Thank you!
First, it is necessary to determine the type of leakage – what form it takes – and then analyze the causes of the leakage based on that information in order to assess the nature of the leak. Only by identifying the causes can the problem be resolved properly
1. Chloride corrosion: 304 material is not resistant to chloride ions. In our company, we used 304-coiled tubes filled with saline at -5°C in the synthesis reactors; intergranular corrosion and leaks occurred in both the welds and the pipes. 2. It is possible to use alternative coolants, such as ethylene glycol, which are non-corrosive.
1. Chloride corrosion: 304 material is not resistant to chloride ions. In our company, we used 304-coiled tubes filled with saline at -5°C in the synthesis reactors; intergranular corrosion and leaks occurred in both the welds and the pipes. 2. It is possible to use alternative coolants, such as ethylene glycol, which are non-corrosive.
1. Chloride corrosion: 304 material is not resistant to chloride ions. In our company, we used 304-coiled tubes filled with saline at -5°C in the synthesis reactors; intergranular corrosion and leaks occurred in both the welds and the pipes. 2. It is possible to use alternative coolants, such as ethylene glycol, which are non-corrosive.
Alternating stress plus corrosion. Does it need repair? Professional pressure vessel maintenance personnel. If needed, add v18516058918
For chloride ion corrosion, polyaniline coatings are recommended as a corrosion protection solution – they offer good cost-effectiveness and effective performance. There are many application cases to draw from.
Was the brine in the jacket flushed clean before heating with steam?
Both the cylinder and the semi-tubes are made of S30408 material; the semi-tubes with a diameter of 108 mm are formed by steel pressing. The operating temperature on the inside of the cylinder is -15°C, and the pressure is at atmospheric level. Inside the semi-tubes, there is frozen calcium chloride solution at a temperature of -25 to -20°C, with a pressure of 0.2–0.3 MPa； Recently, the reactor was parked; the material inside the cylinder was emptied, as well as the brine in the semi-pipe. Clean water was added to the inner cylinder, and steam was used to raise the temperature in order to clean the reactor. The cleaning temperature was around 100°C. After cleaning, the temperature was lowered and the water was drained. The jacket was tested under a water pressure of 0.4 MPa, and no significant leaks were detected ； Another 3 months passed, and the device was put back into use. A pressure test was conducted using compressed air at a pressure of 0.4 MPa; it was found that there were numerous leakage points in the fillet welds, as well as some leakage points in the base metal. Problem analysis: 1. Stress exists due to the pressing formation of the semi-tube steel strip with a diameter of 108 ； If heat treatment is not carried out, stress will exist. 2. The fact that there are no problems during operation indicates that stainless steel can be used under low-temperature conditions; the issue lies in the cleaning and pressure testing that need to be carried out during shutdown. The saline water in the half-tube has not been completely drained, and the amount of chloride ions inside the inner tube is unknown. Therefore, cleaning at 100°C under such conditions meant that although no issues were detected during the pressure test at that time, obvious leaks were found upon inspection after some time. 3. The main problem here is that we ignored the fact that high-temperature cleaning was carried out without first draining the saltwater, which leads to significant stress corrosion cracking and typical chloride-induced electrocorrosion. Therefore, the next time the equipment is shut down for cleaning, it is essential to drain all the existing medium and clean it thoroughly to avoid high concentrations of chloride ions.