Lock bucket cone strip welding process

In recent years, high-temperature and high-pressure corrosion-resistant pressure vessels used in petrochemical and coal chemical industries have grown significantly in size. To ensure both strength and corrosion resistance, the inner walls of large-scale equipment often require surfacing with austenitic stainless steel or nickel-based alloys. To enhance production efficiency and product quality, submerged arc surfacing technology has become widely adopted for large-area inner wall surfacing. However, due to the complex shape of conical sections, successful implementation of this technique remains rare in China. By combining practical factory conditions, focusing on production feasibility and reliability, and developing specialized equipment, the process was optimized through detailed research and parameter setting. This approach improved productivity while ensuring consistent quality in the surfacing process. The factory was contracted to produce lock cylinder containers for a coal chemical project. These containers were classified as Class II (SAD), with a base material of 16MnR and a corrosion-resistant layer of 00Cr17Ni14Mo2. The design parameters are outlined in Table 1. The container had an inner diameter of 2190 mm and a length of approximately 8586 mm. A 5 mm thick corrosion-resistant layer was required, making the welding process challenging. The conical section ranged from DN2200 to DN350 mm, with a length of 2170 mm. The surface of the welds needed to be smooth, with no more than 1 mm depression between adjacent welds. The device structure is illustrated in Figure 1. Before surfacing, the base metal surface must undergo 100% magnetic particle testing to ensure there are no cracks or defects. Each weld overlay layer must be tested with 100% penetrant testing, followed by ultrasonic testing after completion. After the transition layer is applied, stress relief heat treatment is performed before applying the surface layer. The chemical composition within 3 mm of the surface must match that of the surface layer. Additionally, the ferrite content of the weld overlay must be between 4% and 10%. Electrode surfacing offers several advantages, including cost-effectiveness, speed, lower dilution rates, and higher deposition rates compared to other techniques. It allows precise control over penetration depth, resulting in a high-quality weld overlay. The flux-to-solder ratio is 0.4–0.5, which saves material and reduces costs. Moreover, it minimizes the loss of alloying elements and enhances the plasticity and toughness of the surfacing layer. The selected materials included E309MoL-15 for the transition layer and E316L-15 for the surface layer, with H309LMo and H316L welding wires, along with SJ304 flux. Their chemical compositions are listed in Tables 2 and 3. To evaluate the surfacing process, tests were conducted according to JB 4708-2000. The test piece size was 300 mm × 600 mm × 25 mm, and the optimal welding parameters were determined, as shown in Table 4. Surface chemical compositions are also presented in Table 5. For the conical section, a special tire was designed to ensure uniform rotation during welding. Due to the varying diameters, the welding parameters were adjusted gradually, reducing current and voltage while slowing the welding speed. The tire design was patented under ZL200820111544.5. Figures 2, 3, and 4 illustrate the surfacing setup and field application. A detailed surfacing process was developed, starting with 100% magnetic particle inspection of the base metal surface. Preheating to around 150°C was implemented to reduce hydrogen diffusion and residual stress. An integral heating box was used for the entire cone, with specific heating methods to maintain continuity. Post-weld dehydrogenation and stress relief treatments were carried out as per the process. The surface layer was then tested with 100% PT and UT. Ferrite content was measured at 18 points, confirming values between 4% and 10%, meeting the requirements. Common welding defects such as excessive current, poor insulation, and inadequate cleaning were addressed through strict parameter control, proper insulation, and thorough pre-weld preparation. In conclusion, following the described process and conducting non-destructive testing according to JB4730 ensured high-quality surfacing. The welded products met all standards, proving the effectiveness of the method. A well-designed conical tire and appropriate welding parameters, combined with preheating and post-weld heat treatment, were critical to achieving the desired results.

Stainless Steel Non-standard Bearing

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