ZHITONG PIPE VALVE TECHNOLOGY CO.,LTD , https://www.ztongvalve.com
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 configuration ensures proper penetration and weld quality, especially for thick-walled sections.
(2) Selection of Welding Consumables: To meet the mechanical properties and corrosion resistance requirements of 30CrMo quenched and tempered steel—specifically tensile strength, impact toughness, and sulfur resistance—the appropriate welding materials were selected. The wire used is 4mm HJ8CrMoA flux-cored wire, while the filler material consists of 2.4mm J857Cr low-hydrogen electrodes (AWS E12015-G). These consumables ensure good metallurgical compatibility and minimize hydrogen-induced cracking.
(3) Determination of Preheating and Interpass Temperatures: Based on the carbon equivalent formula from the International Institute of Welding (IIW), the Ceq value for 30CrMo ranges from 0.52% to 0.73%. Using the American Welding Society (AWS) formula, the CE value was calculated as 0.55% to 0.77%. Both values indicate that 30CrMo has poor weldability, necessitating preheating before welding. According to ASME IX, the minimum preheat temperature should be 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 avoid thermal stress and cracking.
(4) Post-Weld Heat Treatment: To prevent cold cracking, improve joint toughness, and reduce hardness, especially in the heat-affected zone (HAZ), post-weld heat treatment (PWHT) was performed 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 per hour. If PWHT could not be carried out promptly, an alternative method was applied: the joint was kept at 400°C for 400 hours to simulate the same effect. This step is crucial in maintaining the integrity and performance of the welded structure under harsh service conditions.