Welding, water wall tubes

The water wall tubes need to be replaced when defects exceeding the specified limits occur due to creep, wear, corrosion, or external damage of the water wall, or when leaks occur during operation. The tube replacement steps are as follows: (1) Identify the location of leakage or defects exceeding acceptable limits in the boiler’s water wall tubes, and check whether there are any other tubes in the vicinity that have been damaged due to the leakage. (2) Remove the external insulation of the furnace wall according to the location of the leak, and set up scaffolding or maintenance hoists as needed. (3) Mark and cut the tube, being careful not to damage the tube itself when cutting the fin tubes. (4) Receive pipes that meet quality standards, cut them to the measured dimensions, prepare grooves at both ends, and leave a 2mm gap at each end. (5) For butt welds, full TIG welding should be used, or TIG welding can be employed for the root pass with welding done by MIG welding for the cover pass. When sealing between welded fins, use welding rods that are compatible with the base material. During welding, single-sided welding is not allowed; gaps or serrations must not remain after welding, and the base material of the pipe must not be damaged, to avoid affecting its lifespan. (6) Inspect the weld quality; once it passes, fill it with water for a hydrostatic test. After the hydrostatic test is successful, restore the external insulation of the furnace wall. During the tube replacement process of the boiler’s water wall, it is essential to be very careful to prevent iron slag or tools from falling into the water wall tubes; it is best to seal them immediately after cutting them out. Once something falls in, it should be reported promptly and measures taken to remove it, in order to prevent the pipes from overheating and bursting during operation.