the measures to prevent welded pipe cold crack

Usually, the pipe welded joints are rigid, multi-layered welding and welding metal bulky. In the high stress state such as the weld metal has a higher yield point; plastic deformation is difficult to relax by the welded joints of high stress. So welded joints are easy to weld cracks in the heat and affect zone of white areas or areas produce martensite to form the cold cracking. It is the most effective way to butt up to 550 ~ 700 ℃ pieces of the overall warm-up for the high pressure pipe to prevent cold cracking followed by the use of heterogeneous welding materials. Brittle fracture is caused by different reasons. For example, grain boundary precipitates, whatever the strength is stronger or weaker than matrix strength, are causes cracks; grain boundary segregation of inclusions is also the reasons for the fracture. In addition, the yield limit in the cross variable load can also cause fatigue fracture.



Generally, hydraulic components is used in the design of mechanical properties, it is assumed that the material is uniform, continuous and isotropic depending on the method of analysis of design that is safe, sometimes accidents breakage. The study found that the organization of materials is far from uniform and isotropic in high-strength metals that occurs in low stress brittle fracture process. The organization of materials will have cracks, inclusions, porosity and other defects, which can be seen as material in the micro-cracks. Furthermore, the brittle fracture is related with the use of component temperature.

People found that when the temperature is below a certain temperature, the material will be changed into brittle state, the impact absorbed energy decreased, this is known as cold brittle by the study. So the design must work under the component temperature select a suitable cold-brittle transition temperature of the material. Cold drawn seamless steel pipe is too small to achieve the surface finish and dimensional accuracy requirements. They can’t achieve the strength index components; Deformation is too large, high pressure plastic pipe reduces too much toughness and grain is pulled excessively slender forming a fibrous tissue. The metal will have obvious anisotropy. For steel and fibrous tissue appear dislocations, vacancies and other crystal defects, generally taken to annealing or normalizing heat treatment methods to eliminate them. The purpose of annealing is grain refinement, elimination of tissue defects reduce the hardness and improve ductility.