In the manufacturing of hydraulic oil tanks, the welding process is crucial for controlling residual stress on the inner wall and the risk of leakage. If residual stress is not effectively released, it can easily lead to deformation of the tank during use, and even cracks; leakage directly affects the stability and safety of the hydraulic system. Therefore, multi-dimensional coordinated control is needed, including welding method selection, process parameter optimization, welding sequence planning, pre- and post-weld treatment, and leakage detection, to reduce residual stress and improve sealing performance.
The selection of welding methods is fundamental to controlling residual stress. TIG welding, due to its high energy density and concentrated heat input, can reduce the area of the heat-affected zone, thereby reducing residual stress. For critical parts such as the inner wall of the tank, TIG welding can be used for the root pass to ensure weld root quality and avoid porosity and lack of fusion defects; MIG welding can be used for the filler layer to improve welding efficiency. This combined process ensures weld quality and suppresses residual stress by reducing the total heat input. Simultaneously, avoiding arc striking outside the bevel prevents spatter damage to the base material, further reducing stress concentration sources.
Optimization of process parameters is the core of residual stress control. Welding current, voltage, and speed directly affect the heat input. Excessive current or slow welding speed leads to excessive heat input, causing the inner wall material to overheat and expand, resulting in uneven contraction during cooling and significant residual stress. Therefore, parameters need to be dynamically adjusted according to material thickness and welding position, such as using a low-current, high-speed welding method to reduce the residence time of heat in the material. Furthermore, preheating and interpass temperature control are also crucial. Preheating reduces the temperature difference during welding and slows the cooling rate, thus reducing residual stress; excessively high interpass temperatures may cause grain coarsening and must be strictly controlled within a reasonable range.
The planning of the welding sequence has a significant impact on the distribution of residual stress. A reasonable welding sequence allows the weld to contract freely, avoiding stress concentration. For example, welding welds with larger shrinkage first, followed by welds with smaller shrinkage, allows the stress generated by subsequent welding to be offset by the shrinkage of the earlier welds. For circumferential welds on the inner wall of the tank, a segmented back-welding method can be used, dividing the long weld into several short segments and welding symmetrically from the center to both ends to reduce overall deformation. Furthermore, avoiding concentrated welding of intersecting welds can prevent stress accumulation and reduce the risk of cracking.
Pre-welding treatment is a crucial step in reducing leakage risk. Before welding, the tank plates must be beveled to ensure complete penetration at the weld root. Simultaneously, the oxide layer, oil, and rust on the plate surface must be thoroughly removed to prevent porosity and inclusions during welding. Higher cleanliness is required for the inner wall of the tank; acetone wiping or mechanical grinding can be used to ensure the welding area is free of impurities. In addition, the geometric dimensions and form and position tolerances of the plates must be checked before welding, and the plates should be fixed with clamps to prevent weld misalignment due to deformation during welding.
Real-time monitoring and adjustment during welding are important means of ensuring quality. Visual inspection and infrared thermometers can be used to monitor weld formation quality and temperature changes in real time. If defects such as porosity, cracks, or undercut are found on the weld surface, welding must be stopped immediately, the defects removed, and the welding repeated. If the temperature is too high, heat input can be controlled by adjusting the welding speed or increasing cooling measures. In addition, when using multi-layer, multi-pass welding, each weld seam must be cleaned with a wire brush to remove oxide scale and spatter, ensuring good interlayer bonding and preventing leakage due to interlayer defects.
Leakage detection is the final guarantee of welding quality control. After the oil tank is welded, its sealing performance must be checked through a kerosene test or a pneumatic pressure test. The kerosene test involves applying lime solution to the inner wall of the tank and kerosene to the outer wall, observing for any kerosene leakage. The pneumatic pressure test involves filling the tank with compressed air and detecting the pressure drop. For pressurized oil tanks, a pressure test is also required, with the test pressure being 1.5 times the working pressure, held for 2 hours without leakage. Furthermore, the inner wall of the oil tank must be coated with an oil-resistant coating, such as zinc powder or chlorinated polyethylene coating, to prevent leakage caused by media corrosion.
Welding process control in the manufacture of hydraulic oil tanks must be implemented throughout the entire process—before welding, during welding, and after welding. By rationally selecting welding methods, optimizing process parameters, planning welding sequence, strictly implementing pre-weld treatment, real-time monitoring and adjustment, and conducting post-weld inspection and coating protection, residual stress on the inner wall can be effectively reduced, the risk of leakage can be decreased, thereby improving the reliability and service life of the fuel tank.
