Welding quality of welded steel pipe refers to the degree to which the welding product meets the design technical requirements. Welding quality not only affects the use performance and life of welding products, more importantly, affects personal and property safety. Welding quality is usually ensured by design quality, processing quality, quality inspection and post-weld treatment and other links of the product.
The type of joint used in the welding product and its calculated strength should meet the actual carrying capacity. Welding method should be suitable for the characteristics of components, and its economical efficiency should be good. The welding process should be able to minimize stress, deformation and stress concentration. Production labor and material consumption should be as small as possible, the convenience of flaw detection should also be taken into consideration when design the joint.
The performance of adopted the base metal, wire, flux or welding electrodes and other welding materials should meet the design requirements. The performance of welder, auxiliary equipment and testing equipment should be good. Before welding, the welding material should be dried according to the provisions, the welding groove of workpiece should meet the requirements and remove the cutting residue, cracks and dirt.
Quality inspection runs through the whole production process from design to finished product, we must ensure that the test method used in the quality inspection process is rationality, the reliability of the testing instrument and inspection staff technical level. The properties of the joints, physical properties, mechanical properties, microstructure, chemical composition, corrosion resistance, appearance dimensions and welding defects of products after welding should be checked by means of various inspection methods.
Welding defects can be divided into external defects and internal defects. External defects include: excess height does not meet the requirements, welding tumor, undercut, crater, arc burns, surface pores, surface cracks, welding deformation and warping. Internal defects include: cracks, not penetration, not fused, slag and porosity. The most harmful in welding defects is the crack, the followed is lack of penetration, incomplete fusion and slag inclusion, pores and structure defect. Individual flaws are allowed to exist. The number and the nature of allowed defects are determined by the using conditions and the quality assessment criteria of the product. If the surplus height of welding line is too high, it is allowed for those products by the static load, but it is not allowed for those products by cyclic fatigue loading in high frequency, even the normal excess weld metal also has to be cut off. The presence of welding defects is related to the groove processing and assembly accuracy, the rigor degree of the welding process, the technology of the welder and other factors.