Analysis of the defects of the ring welds of stainless steel welds lined with the end of the pipe

In recent years, plastic-coated steel pipes are one of the most widely used pipes in water conservancy and hydropower projects. The anti-corrosion of the inner wall mainly uses fused epoxy powder (FBE) thermal spraying. During the construction process, the high heat generated by the pipe butt welding will burn the paint. Plastic layer, causing problems such as peeling off the anti-corrosion layer at the interface. In order to avoid damaging the coating layer of the plastic-coated steel pipe during the welding construction, the double-sealed welded plastic-coated steel pipe can be used to overcome the above problems, that is, the stainless steel ring whose inner liner width exceeds the welding heat influence range at the end of the steel pipe is sealed by the pipe end. Welding effectively combines carbon steel and stainless steel. The main purpose of this design is to protect the FBE coating during girth welding, while reducing the anti-corrosion coating repair process at the interface location. Nozzle welding is similar to butt welding of mechanical composite pipes. Therefore, more stringent requirements are put forward for the control of the welding process.

When welding the ends of low-carbon steel pipes with stainless steel rings, two different metal materials have different physical properties, which will produce different physical and metallurgical changes. In addition, due to process and technical limitations, carbon steel pipes and stainless steel The steel rings are completely welded together by sealing and welding, which will increase the probability of metal thermal deformation and cracks. This study analyzes the defects in the construction process of the pipe end lining stainless steel pipe used in a domestic water supply project to provide technical support for preventing weld cracks. The steel pipe used in the test is made of Q345C, and the pipe end is designed with OCrl8N9 (s304) stainless steel strip with a wall thickness of 15mm as the inner lining. The material is cut according to the inner diameter of the pipe, inserted into the pipe port 120mm, fixed with stainless steel electrode spot welding, and then 309 stainless steel The welding rod fully welds the inner circumferential welding seam, the longitudinal welding seam and the port circumferential welding seam, so that the stainless steel sleeve and the inner wall of the steel pipe are closely combined, and a 30 groove transition with the nozzle is formed, as shown in Figure 1.