Specifications for Welding of Thermal Pipelines

Standard process for welding methods of thermal pipelines:

1. Bottoming: The bottoming for argon arc welding should be welded from bottom to top. For welding joints that require preheating before welding, the heat treatment personnel should be notified in advance to make preparations for preheating the welding joint. Welding can only be performed after the preheating temperature is reached. When welding, canvas should be used around the welding joint to prevent wind from affecting the quality of the weld. The starting and ending points of spot welding can be ground with an angle grinder to create a slope suitable for the joint, so as to facilitate good fusion and transition of the weld. The entire root layer weld must be evenly penetrated, and must not be welded through, causing defects such as weld meat resting on the root and indentation of the top. The quality of the bottom welds should be checked in a timely manner and the secondary welds should be welded at the same time to avoid cracks. For pipes with an outer diameter greater than 194mm, two-person symmetrical welding should be used for pipe butt joints.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. Interlayer filling: After the bottom is welded, if there are no defects, the next layer should be welded immediately. Welding of large-diameter and thick-walled pipes should adopt multi-layer and multi-pass welding. The thickness of a single weld bead shall not be greater than the diameter of the welding rod, and the width of a single welding pass shall not exceed 4 times the diameter of the welding rod. During welding, special attention should be paid to the quality of the joints and the closing arc. When closing the arc, the molten pool should be filled and the joints should be staggered. The quality of welds should be checked layer by layer, and defects found must be dealt with immediately.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3. Cover surface: In order to make the weld look beautiful, welding rods with a diameter of φ3.2 are generally used. The surface of the weld should be complete and even, with a smooth transition to the pipe. The width of the weld should be about 2mm covering both sides of the groove, and the height should be strengthened. The weld surface shall be 1 to 3 mm. There shall be no cracks, pores, slag inclusions, spatter, etc. on the surface of the weld. There shall be no undercut with a depth greater than 0.5 mm and a total length greater than 10% of the total length of the weld.