In the main water supply pipeline system under high temperature and high pressure conditions, the reliability of the welded gate valve directly determines the safety of the entire pipeline network operation. As the core control device, the quality of the welding joint of the Z962Y-160 electric welded gate valve directly affects the pressure bearing capacity and sealing performance of the valve body. Let’s discuss how the welding process of the gate valve should improve the welding quality.

1. Analysis of key characteristics of welding process

The valve body of Z962Y-160 electric gate valve is made of ASTM A217 WC9 chromium-molybdenum alloy cast steel material, which has the characteristics of maintaining good mechanical strength at a high temperature of 590℃, but there is obvious thermal crack sensitivity during welding. The groove design of the connection between the valve body and the pipeline adopts a U-shaped composite groove structure. This design increases the difficulty of accurately controlling the amount of deposited metal filling while ensuring the welding strength.

The main contradictions that need to be overcome in the welding process are reflected in two aspects: first, the residual stress generated by the welding of thick-walled parts is easy to cause delayed cracks, and second, improper temperature control between multiple weld layers will lead to grain coarsening in the heat-affected zone. In particular, the annular weld between the valve body flange neck and the pipeline, as the main load-bearing structure, must meet the highest level requirements specified in the ASME B16.34 standard for welding process optimization.

2. Technical route for welding process optimization

Dual control mechanism is implemented in the material pretreatment stage, and the welding area of ​​the Z962Y-160 electric gate valve is penetrated to ensure that the base material is defect-free. At the same time, an infrared heating device is used for gradient preheating. The traditional overall preheating is changed to partitioned dynamic preheating. The temperature within 100mm on both sides of the groove is evenly monitored by thermocouples in real time to reach 180±10℃, effectively reducing the risk of hydrogen-induced cracks.

In terms of welding parameter optimization, a combined process of pulsed argon arc welding primer and flux-cored wire gas shielded welding filling is adopted. During the base welding, the heat input is controlled within the range of 9-12kJ/cm, and the welding speed is adjusted to 80% of the conventional process to ensure that the root is fully melted and there are no unfused defects. In the filling welding stage, the interlayer oscillation welding technology is used to widen the molten pool width by lateral swing of the welding gun, so that the width of each weld is increased by 30%, significantly reducing the number of welding passes.

The post-heat treatment process introduces a computer temperature control system, and immediately after welding, a 350℃×2h dehydrogenation treatment is carried out, followed by a step-by-step heating annealing. The traditional continuous heating is changed to multi-stage insulation, and three insulation platforms are set below the AC1 phase change temperature, so that the residual stress elimination rate reaches more than 92%, while avoiding excessive loss of material strength.

3. Engineering application verification and improvement

In the main water supply system renovation project of the thermal power plant, the optimized welding process was successfully applied to the installation of 32 Z962Y-160 gate valves. The first-time pass rate of the weld was increased from the original 86.7% to 98.2%, and there was no leakage after the 48MPa water pressure test after installation. After 18 months of operation monitoring, no stress corrosion cracks were found in the weld area, and the attenuation value of the ultrasonic detection signal was stable in the ideal range of -14dB to -18dB.

On-site feedback showed that the optimized process reduced the welding time of a single valve body by 40% and reduced the consumption of auxiliary materials by 25%. Especially in confined space operations, the improved narrow gap welding technology showed significant advantages, solving the problem of interlayer slag inclusion that is easy to occur in the traditional process when welding large-diameter valves above DN400.

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