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Steel Pipe Network Introduction High Pressure Oil Pipeline Welding Process Evaluation from Four Points
(1) Bevel Form: All joints are horizontal fixed pipe-to-tube butt joints (5G), with a bevel angle of 60 degrees. This specific joint configuration ensures proper fusion and weld quality, especially when working with high-strength materials like 30CrMo steel.
(2) Selection of Welding Consumables: To meet the requirements of tensile strength, impact toughness, and corrosion resistance in oil field environments—particularly sulfur resistance—appropriate welding materials were chosen. The base material is 30CrMo quenched and tempered steel, which should not contain nickel in the weld seam. The selected filler wire is 4 mm HJ8CrMoA, and for the cover pass, West 3.2 mm low-hydrogen J857Cr electrodes (AWS E12015-G) were used. These consumables provide good mechanical properties and resistance to environmental degradation.
(3) Determination of Preheating and Interpass Temperatures: Based on the carbon equivalent formula from the International Institute of Welding (IIW), the Ceq of 30CrMo was calculated as 0.52% to 0.73%. Using the American Welding Society (AWS) formula, the CE value ranged from 0.55% to 0.77%. Both values indicate that 30CrMo has poor weldability and requires preheating before welding. According to ASME IX, the minimum preheat temperature is 129°C, and the maximum interpass temperature should not exceed 310°C. In practice, the preheat temperature was set at 200°C, and the interpass temperature was maintained between 180°C and 240°C to ensure consistent weld quality.
(4) Post-Weld Heat Treatment: To prevent cold cracking, improve impact toughness, and reduce hardness in the heat-affected zone (HAZ), post-weld heat treatment (PWHT) was carried out immediately after welding. The welded joint was heated to 600°C and held for 2 hours. The heating and cooling rates were controlled to no more than 150°C/h. If PWHT could not be performed promptly, an alternative method involved maintaining the joint at 400°C for 400 hours to achieve similar results. This step is crucial for ensuring long-term structural integrity and performance in harsh environments.