API-L450 및 X65강으로 제조된 파이프의 고장력강 용접봉 종류별 용접조건과 인장시험 연구

Welding Conditions and Tensile Tests for High-Strength Steel Welding Rods of Pipes Manufactured with API-L450 and X65 Steel

Currently, welding is performed in parallel with inert gas tungsten arc welding (GTAW: TIG) and shielded metal arc welding (SMAW: MMAW) in the field of 6G-certified welding of pipes manufactured with API-L450 and X65 steel. When performing inert gas tungsten arc welding, the gas flow rate is set to 15 (ℓ/min) and only the E9016-G (LC-600) welding rod is selected for shielded arc welding with high electric current. It was found that the high gas rate and high electric current rate caused the welding rod to generate a large amount of spatter, and the slag flow was excessive. Consequently the workability was not suitable. This study was carried out to compare the effects of using high-strength steel welding rod in the welding process and to select the appropriate welding rod and welding conditions applicable to the various industrial fields. This empirical study was conducted to select welding electrodes with similar chemical composition or mechanical properties as L450 and X65 steel pipes. After inert gas tungsten arc welding was performed with a soft-tipped electrode (TGC-50), shielded arc electrodes [E7016 (KH-500LF), E9016-G (LC-600) and E9016-G (KK-60)] were selected. The welded pipes were subjected to nondestructive testing and defect-free areas were sampled; then tensile tests were carried out under the same conditions. The test results showed that two specimens were broken using the E7016 (KH-500LF) and E9016-G (LC-600) electrodes, while one specimen was broken using the E9016 (KK-60) electrode. The E9016 (KK-60) high tensile steel welding rod showed satisfactory results in welding L450 and X65 steel pipes with sufficient mechanical properties, weld defect prevention, improvement in working method.