Basic Requirements for Welding of Steel Truss Branch Pipe

The steel truss branch pipe is usually welded by a single arc welding and double sided forming method. This welding method inevitably brings the weld in the tube inner wall concave, or in the weld root part of the local area that does not produce (1-2 mm). And there is no weld allowed to exist according to GB11345 requirements. The defect must be repaired. The defect must be removed by air gouging or grinding wheel and then repaired. And the same defect may still exist after repairing. Moreover, the welding seam is concentrated in one part. After repeated heating, the hot expansion and contraction produces a great stress, which will cause the lamellar tearing of the matrix of the mother tube ( the rolling direction of the matrix is perpendicular to the direction of welding stress), or the residual shrinkage stress in the welding head, and it may result in the tendency of delay cold cracking and therefore the tendencies of the delay cold cracking. So there will be a serious hidden danger in the toughened.

Through analyzing the welding of steel truss branch pipe and truss girder welding machine and considering the safety and maneuverability of the welded joint, it is considered that the strength of welding joint and the strength of the parent material are the basic requirements which should be in accordance with the design specification. And the strength of welded joints depends on the effective area of weld.

1. The effective area of the welded pipe for the joint is 4 5m liner for the inner wall of the butt pipe. It can reach the same area as the base material, and it can reach the standard of UT by the nondestructive testing standard, and the design requirements can be met.

2. The welded joint is intersected with the parent tube, and the strength of the welded joint is hard to reach the strength of the welded joint because of the 1 - 2m non penetration phenomenon in the inner surface of the weld and its local area. We believe that the method of reinforcing fillet welds is an effective way to make the weld and base metal equal. The diameter of steel truss branch pipe used in current design is generally less than 159 mm, but the normal coverage can not be achieved by adopting GB-11345 standard. Therefore, the non-destructive testing standard for the welded joint can be tested by the industry standard, JG/T30342-1996, the method of super Lu Bo flaw detection and quality classification for the welded joint of bolt ball joints.

3. The welding seam and base metal of supporting pipe are mainly depended on the effective area of weld and welder qualification and welding specification.