In pipeline installation and construction, weld cracks are often encountered. If not detected and repaired in time, there are serious dangers, especially in pipelines transporting flammable, explosive and toxic media, the danger is very serious. This requires construction units, in the construction of steel saw pipe, welding quality can not be ignored.


There are many kinds of cracks in welding operation. Sometimes the cracks in the weld are distributed, sometimes in the heat-affected zone; sometimes on the surface of the weld, the weld may appear in the interior; sometimes you can see macroscopically, sometimes you need to see under the microscope; transverse cracks, longitudinal cracks; sometimes the arc is broken to a so-called crater crack; immediately after the occurrence of welding, it will take some time to appear (so-called delayed opening). There is a sudden cooling crack in winter, called embrittlement. Despite various types of cracks, the nature of cracks is often encountered as follows: hot cracking occurs at high temperatures and cracks along austenite grain boundaries, the main form of which is crystal cracks. That is to say, during the crystallization process of the weld, due to the solidification shrinkage of the metal near the solid phase, the liquid film between the particles is not subject to tensile stress, which causes cracking along the grain boundary. Cold crack: That is, near the martensite transformation temperature, at a relatively low temperature of about 200 e~300 degrees Celsius, due to stress, hardening structure and hydrogen bonded crack welded joints produce cold cracks.