Porosity and Crack of Spiral Welded Pipe

Spiral pipe holes in low height single echo waveform is a single slit, less chaotic. From all directions to detect the reflected waves is substantially the same, but slightly movable probe disappeared a dense cluster of pores arise from the reflected wave, the wave height with different pore size, for the fixed scroll when the probe, a phenomenon will be thrown after another. The main cause of such defects is failure to delineate temperature drying of welding consumables, welding rod coating bad off, welding core corrosion, wire cleanup is not clean, when manual welding current is too large, the arc is too long; while submerged arc voltage is too voltage fluctuation is too high or the network; protective gas purity and low when gas welding. If there is a spiral welded pipe weld porosity, both destroyed the weld metal density, but also makes the effective cross-sectional area of the weld decrease, reducing the mechanical function, especially when kept chained holes, bending and impact toughness will be relatively significantly reduced. Measures to prevent such defects prevention are: do not use drugs skin cracking, spalling, deterioration and corrosion core welding electrodes, welding wire rusty rust necessary before use. Welding materials used in the drying temperature should be delineated, and both sides of the groove clean and to choose suitable welding current, arc voltage and welding speed. Echo height is bigger, wide band, the reflection peak, continuous flush probe when translation reflection wave amplitude is changed, turn probe, crest fluctuation dislocation phenomenon. Crack is the largest risk of a defect, which in addition to reducing the strength of the welded joint, but also because the end of the crack tip of the pin was notched, the pipe load, stress concentration and become the origin of the fracture structure. Crack into hot cracking, cold cracking and reheat cracking three. The reason is that the heat cracks: The weld pool cooling quickly, resulting in segregation; weld heat does not mean tensile stress. So often the hub spiral pipe flaw length, but the most important thing is the best preventive measures well in advance in order to reduce the product has quality problems thrown up, reducing unnecessary losses; preventive measures: Limit the base metal and weld materials easily segregation content of impurities and harmful elements, the main limiting the sulfur content, manganese content progress; progress electrodes or basicity flux to reduce the impurity content to improve the degree of segregation; improved form welded structure using the welding sequence fair, progressive contraction of the weld freedom. Cold crack reasons: the person to be subjected to welding when a large tensile force can be easily torn in the process of cooling the welding material hardenability; welding cooling rate was too late to escape the residual hydrogen in the weld, a hydrogen atom bonded to a hydrogen molecules to a gaseous state into the fine pores of the metal and cause a lot of pressure, so that the local cold-formed metal cracks a lot of pressure; welding stress and tensile stress analysis with a focus on hydrogen embrittlement and hardening occur simultaneously easy to form when cold cracking. Prevention measures: preheat and slow cooling after welding, heat-affected zone austenite decomposition can be a sufficient temperature range, to avoid hardened tissue, while reducing the role of stress in welding; timely hypothermia after welding annealing, dehydroepiandrosterone treatment, eliminate stress generated during welding, and to the diffusion of hydrogen in a timely manner to the outside to go; selection of low hydrogen type electrode and an alkaline flux or austenitic stainless steel welding wire, etc., welding delineated by drying, and strictly Cleanup groove; strengthen the protection of welding and welded at the surface of the clean-up, to avoid intrusion of hydrogen; selection justice welding specifications, using sequence assembly and welding fair in order to improve the stress state of the steel pipe.