The welding process for large-diameter thick-walled stainless steel pipes is a highly challenging and critical technology in industrial manufacturing. These pipes are widely used in industries such as petrochemicals and nuclear power engineering, often requiring long-term service in harsh environments with high pressure, high temperature, and strong corrosion. Therefore, the quality requirements for welding are extremely stringent. Sufficient mechanical properties (such as strength, toughness, and hardness) must be ensured, along with excellent corrosion resistance and sealing performance. Furthermore, due to the large diameter and thick walls, welding faces challenges such as insufficient penetration, stress concentration, and susceptibility to cracking. Therefore, it is essential to rationally select welding methods such as plasma welding, argon arc welding, and submerged arc welding based on the characteristics of different materials, and to formulate targeted process parameters and operating specifications to ensure welding quality.

The welding characteristics of different stainless steel materials vary significantly. Austenitic stainless steel, whose main components are chromium and nickel, possesses excellent corrosion resistance, plasticity, and toughness. However, when welding at temperatures within the sensitization temperature range of 600-850℃, intergranular corrosion is prone to occur. Secondly, austenitic stainless steel has a large coefficient of linear expansion, which generates significant thermal stress and deformation during welding, and its high weld shrinkage rate makes it prone to hot cracking. Ferritic stainless steel mainly relies on chromium for corrosion resistance, with its chromium content typically between 11% and 30%. During welding, ferritic stainless steel is prone to rapid grain coarsening at high temperatures (above 900℃), leading to decreased low-temperature toughness. Furthermore, ferritic stainless steel has poor thermal conductivity and a low coefficient of thermal expansion, making it susceptible to stress concentration and cold cracking. Martensitic stainless steel contains a high carbon content, resulting in high strength and hardness, but poor plasticity and toughness. Duplex stainless steel contains both austenitic and ferritic phases, combining the toughness and corrosion resistance of austenitic stainless steel with the high strength of ferritic stainless steel. The key to welding duplex stainless steel is maintaining the austenite-ferrite ratio in the weld, typically requiring an austenite phase volume fraction of 30%-50% to ensure good mechanical properties and corrosion resistance of the welded joint. During welding, excessive heat input or slow cooling will result in an excess of ferrite phase, increasing weld brittleness; insufficient heat input or rapid cooling will result in insufficient austenite phase, reducing weld corrosion resistance and toughness.

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