Causes and Preventive Measures of Local Deformation in Welding of Longitudinal Welded Pipe

Causes and Preventive Measures of Local Deformation in Welding of Longitudinal Welded Pipe

1.Cause

(1) The rigidity of the work piece is uneven or small, and the shrinkage after welding is inconsistent.
(2) Uneven arrangement of welds will lead to uneven shrinkage, and the shrinkage deformation of multiple welds is large.

(3) Improper operation, no symmetrical layering, intermittent welding, inconsistent welding speed, current and direction, resulting in inconsistent deformation of machined parts.

(4) The bite is too large during welding, resulting in stress concentration and large deformation.

(5) Uneven welding results in deformation when stress concentration is released.

2. Preventive measures

(1) The welds and stiffness of each part of the work piece shall be arranged evenly and symmetrically to reduce dense and cross welds.

(2) The welding sequence shall be reasonable to reduce deformation, such as welding the main weld first and then the secondary weld, welding the butt weld first and then the fillet weld, welding the weld with large shrinkage first and then the weld with small shrinkage.

(3) Work pieces with many welds and large size shall be welded in sections and intervals, and the speed, current and direction shall be controlled in the same direction.

(4) When manually welding long welds, the intermittent welding method shall be used in sections, and the back welding shall be carried out from the middle of the work piece to both ends. During welding, personnel shall be symmetrically distributed to avoid deformation caused by heat concentration

(5) The work piece is asymmetric. In order to reduce the overall deformation, assemble and weld the small parts after rectification.

(6) During welding, it shall be turned frequently so that the deformation can offset each other.

(7) For parts prone to angular deformation after welding, pre deformation treatment shall be carried out before welding, such as V-shaped groove of steel plate. The interface shall be padded up before welding to make it flat after welding.

(8) The rigidity of the work piece is increased by external welding reinforcement, the welding deformation is limited, and the reinforcement is set on the opposite side of the shrinkage stress.

3.Treatment method

For the deformed work piece, if the deformation is small, it can be corrected by fire baking. If the deformation is large, it can be corrected by jacking while baking.