Concrete Pump Elbow Welding method
What are the welding methods for welding elbows?
The butt welding elbow includes two cases, one is welded pipe welded pipe elbow, the butt welding manufacturer, the use of welded pipe forming process and the use of seamless pipe forming process is basically the same , The butt welding process does not include the welding process; the other is by the welding elbow factory to complete the butt welding of the welding process required for welding, such as single-chip suppression and then assembled welding forming elbow Steel plate reel after welding into a tube and then to suppress the three links and so on.
Welding welding of the welding method commonly used manual arc welding, gas welding and automatic welding and so on.
Zhongwei Pipe Fittings shall prepare welding procedures to guide the welding work and shall evaluate the welding process according to the corresponding specifications to verify the correctness of the welding procedure and to assess the welder's welding capacity.
Welders engaged in the welding of welded butt welds shall pass the examination of the quality and technical supervision department and obtain the corresponding qualification certificate to engage in the welding work of the relevant steel (according to the inscriptions of some industries, To obtain the industry requirements of the welder examination and welding process assessment, such as marine welding of the welding elbow to obtain the corresponding classification societies of the welder examination and welding process assessment).
Butt welding elbow in the heating and cooling process, due to the surface and the heart of the cooling rate and time inconsistency, the formation of temperature difference, it will lead to volume expansion and shrinkage uneven stress, that is, thermal stress. Under the action of thermal stress, because the surface temperature is lower than the heart, the contraction is greater than the heart and the heart of the stretch, when the end of the cooling, due to the final cooling volume of the heart can not be free to make the surface by the heart Pull. That is, under the action of thermal stress, the final surface of the workpiece pressure and the heart of the stretch.
This phenomenon is affected by the cooling rate, material composition and heat treatment process and other factors. When the cooling rate is faster, the higher the carbon content and the alloy composition, the greater the uneven plastic deformation produced by the thermal stress during the cooling process, and the greater the residual stress formed. On the other hand, the steel in the heat treatment process due to changes in the organization that austenite to martensite transformation, due to the increase in specific volume will be accompanied by the expansion of the workpiece volume, the workpiece parts have phase change, resulting in volume growth is inconsistent and produce tissue stress. The ultimate result of tissue stress changes is the tensile stress of the surface, the compressive stress of the heart, and the opposite of the thermal stress. The size of the tissue stress is related to the cooling rate, shape, chemical composition of the workpiece in the martensitic transformation zone.
Practice has proved that any butt welding elbow in the heat treatment process, as long as there is phase change, thermal stress and tissue stress will occur. But the thermal stress has been produced before the organizational transformation, and tissue stress is generated in the process of organizational transformation, in the whole cooling process, the thermal stress and the combined effect of tissue stress is the actual existence of the butt welding elbow The stress.