Welded pipe defect distribution
Posted by zora li on April 3rd, 2023
Welded pipe refers to a steel pipe with seams on the surface that is welded after bending and deforming a steel strip or steel plate into a round, square or other shape. The blanks used for welded steel pipes are steel plates or steel strips. With the rapid development of continuous rolling production of high-quality strip steel and the advancement of welding and inspection technology, the quality of welds has been continuously improved, the varieties and specifications of welded steel pipes have increased day by day, and more and more fields of seamless steel pipes have begun to replace pipes. Welded steel pipes are cheaper than seamless pipes and have higher production efficiency.
The production process of welded steel pipe is to use various forming methods to make straight or spiral coils of steel plates, steel strips, etc. into the required cross-sectional shape. Then, with the help of heat and pressure, different welding methods are used to weld the seams together to obtain steel pipes. Therefore, the defects of welded steel pipes are divided into two parts: steel plate base metal defects and weld defects.
1. Defects of the base metal of the steel plate
After rolling and other processes, most of the defects in the plate are flat and parallel to the surface; the main defects include delamination, inclusions, cracks, folds, etc., among which delamination is the most common internal defect. Delamination produces various cracks. When the sheet is subjected to tensile stress perpendicular to the surface, delamination can seriously affect the strength of the steel pipe. This is an unacceptable defect.
2 weld defects
Welding defects refer to defects generated in the weld during or after welding, and are divided into welding defects such as cracks, pores, slag inclusions, incomplete penetration, incomplete fusion, and undercuts. The dense pores and slag inclusions in the weld are dense three-dimensional defects, and the cracks and lack of fusion are planar defects, which are very harmful. Strip slag inclusions and incomplete penetration are strip defects, which are very harmful. Pores, small slag inclusions, etc. are point defects. Defects in the weld are more likely to cause problems such as strength and plasticity of the steel pipe, seriously affecting the quality of the steel pipe. The quality of welded steel pipe directly affects the safe operation and service life of oil and gas pipelines. Therefore, weld flaw detection is mainly aimed at dangerous defects such as cracks, pores, slag inclusions, incomplete penetration, and incomplete fusion in welds.
