Parent metal corrosion defects

LSAW pipe in the performance of metallurgical testing process for weld defects in the edge of the residual oxide scale during the welding process is the drift of the deposited metal cover caused by the fundamental causes that severely corroded steel.

According to metallographic examination, the specimen was found defective weld reinforcement is high, the presence of bad weld edges and weld deposited metal drift caused. Both inner and outer surfaces of the base material with the same dark gray impurity defects that caused the base metal surface corrosion due to the presence of oxide scale. In observation of the surface of the base material was found, in addition to more than a small dot corrosion products, but also found a flaky rust, close to the surface of the base material in the sample preparation process has yet to fall off, indicating that this type of corrosion and mother there is a certain degree of adhesion between the material more difficult to remove, the danger is greater. Meanwhile, not only the existence of surface rust on the steel surface, and has entered the interior steel sample surface after grinding, rust visible part of the pits.

The presence of base metal surface corrosion pits have formed part of the base metal surface, and deposited weld metal more, and the process flow coverage in the local corrosion surface, this time between the edges of the weld and base metal separated by a layer of scale in metallurgical testing of sample preparation process, the force or friction oxide skin off, similar to the formation of the macroscopic crack separation. This phenomenon produces poor weld, the weld edges and base metal transition is not smooth a great relationship. Corrosion of steel has been an important factor affecting the quality of welding, must be completely removed before welding to create a good welding conditions to ensure weld quality and performance. After determining the mechanism of defects in the subsequent production focuses on strengthening the board edge corrosion cleanup, make sure the groove before welding and bevel edge cleaning. By measuring the external weld reinforcement found in particular weld pipe end weld reinforcement is too large, the process is adjusted by reducing the weld reinforcement, significantly reduces the weld deposited metal edge bias phenomenon.