Research on welding technology and properties of composite wear-resistant plate
At present, with the development of acid gas fields, gas pipelines are facing more and more severe corrosion environment. Many gas pipelines fail due to serious corrosion, and even cause explosions, threatening personal safety, polluting the environment, and the consequences are very serious. With the rapid development of the steel pipe manufacturing industry, the composite wear-resistant plate has been widely used because of its mechanical properties of carbon steel or alloy steel, but also has the advantages of stainless steel corrosion resistance.
However, because the two materials of the composite wear-resistant plate have different chemical compositions and physical properties, it is easy to cause the diffusion of the fusion zone C and the dilution of alloying elements during the welding process, causing the deterioration of the performance of the welded joint and affecting the welding quality. This makes the welding of composite wear-resistant plate and post-welding heat treatment complicated, which increases the difficulty of on-site welding construction.
In order to avoid the dilution of alloying elements and the migration of carbon elements at the interface between the coating and the substrate during the welding of the composite wear-resistant plate, different welding materials are commonly used, but this method increases the welding workload and the risk.
In this study, a new welding process of composite steel pipe with a size of 355.6mm×(10+3)mm was developed. First, the composite steel pipe end is pretreated by surfacing welding in the factory, and then the same type of welding material is used in the construction site. The welding process not only reduces the amount of welding engineering, but also reduces the welding complexity of the composite wear-resistant plate.
The test material is the butt welding composite wear-resistant plate, the composite wear-resistant plate based tube size is 355.6mm×10mm, the material is L360QS seamless steel pipe, and the tube manufacturing requirements and performance should comply with the relevant provisions of GB/T9711-2001; The inner lining is 316L austenitic wear-resistant plate with a wall thickness of 3mm, and the processing type of composite wear-resistant plate is mechanical composite. The chemical composition of the base steel pipe of L360QS/316L composite steel pipe with mechanical composite molding is very different from that of the lining pipe, and there is a certain difference in the thermal expansion and cold contraction speed, which is easy to lead to hot cracks or crystallization cracks in the transition layer. Coupled with the dilution of the composition of the weld metal by the base material in the welding process, it is very easy to lead to cracks.
In this study, a welding material ERNiCrMo-3, suitable for both base and inner lining, has good plasticity and toughness, and can also ensure the welding quality of the transition layer. At the same time, in order to ensure the quality of composite wear-resistant plate welding, semi-automatic TIG welding is adopted. The test results show that:
(1) The performance evaluation results of the welded joint obtained by TIG surfacing welding pretreatment and argon protection TIG butt welding process show that the joint meets the requirements of appearance inspection and non-destructive testing; The tensile properties and impact toughness meet the mechanical properties requirements of relevant standards, and the transition between the hardness of the joint and the base material is smooth. Especially, the hardness of the 316 steel pipe lined after surfacing welding is small in the fusion zone and HAZ zone. The welded joint has good resistance to intergranular corrosion and SCC cracking.
(2) Prefabricating a layer of ERNiCrMo-3 welding material around the composite steel pipe can effectively prevent cracks caused by the difference of thermal expansion and cold contraction rates during the welding of the composite wear-resistant plate transition layer; The alloy elements in the transition layer metal are prevented from being diluted by carbon steel, which plays a good isolation role for the transition layer.
