Seeking help online regarding the welding areas of the boiler’s heat exchange tubes and headers; cracks have appeared in the welds during boiler operation.
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Question: In the first image, cracks have appeared at the joint where the boiler’s heat exchange tubes meet the header; these cracks are located right above the weld seam, adjacent to it. (The boiler has not been in operation for long.) The second diagram shows the detailed drawings of the heat exchange tubes and headers in our company. The welds between this heat exchange tube and the header have experienced multiple leaks, all caused by cracks. Could the cracks in this area be caused by too high a welding current, leading to overheating? It’s because the welding current is too high, causing overburning. Change the material properties of the heat exchange tubes? I hope experts can give some advice.
Welding cracks may be caused by overheating resulting from excessive welding current, which alters the material properties of the heat exchange tubes. It is recommended to check the welding process parameters to avoid excessive current, and also to examine the preheating and post-heating procedures during welding in order to ensure welding quality. It may also be necessary to consider whether the welding materials or the material of the heat exchange tubes are suitable, and whether a change in material is required to improve the performance of the welded joints. .
1. What is the height between the upper and lower box frames? 2. What are the operating pressure and temperature of the header, as well as the flue gas temperature? 3. Do the cracks appear in a single row in large numbers, or in multiple rows with one crack each? 4. Do the cracks concentrate in the lower header, or do they appear in both the upper and lower headers? 5. Are the cracks concentrated in the middle or are there also ones at the inlet and outlet? 5. What is the pipe end welding type?
The distance between the upper and lower collectors is 6 meters; the operating pressure is 0.8 Mpa, the maximum flue gas temperature is 300 degrees. Cracks appear in a single row and are mainly located in the lower collector area. Cracks are not concentrated; they are present in various locations. At the pipe ends, insertion welding of heat exchange tubes is primarily used.
Give it a push. Dear experts, please help.
Give it a push. Dear experts, please help.
Cracks occur at the weld line and heat-affected zone, which are areas with the weakest mechanical properties. It is essential to control the heat input during welding; corner welds should be formed in a concave shape rather than convex, in order to reduce stress concentration. If process requirements dictate it, post-weld heat treatment should be carried out. I’ve never worked on boilers, but I guess a large temperature difference might also be related to it?
Occasional issues with one or two pipes can be attributed to welding quality problems, while problems with multiple pipes are most likely related to welding and installation techniques. I remember that when welding boiler tubes, it’s necessary to specify the grade of the welding rod as well as to ensure proper heating and insulation ； Workers need a pressure vessel welding certification and relevant work experience ； After completion, it is necessary to commission a special inspection agency to conduct random inspections of the welds and issue a report. It is recommended that the poster check whether there are any missing documents related to the boiler’s acceptance, and if there are quality issues, contact the boiler manufacturer to send someone to make repairs (they are still obligated to provide technical support even outside the warranty period).