Effects of novice developed TIG welding parameters on the microstructures and hardness of API 5L X65 High-Strength Low-Alloy (HSLA) Steel

Abstract

API 5L X65 is a commonly utilized pipeline material for gas transportation by Sui Northern Gas Pipelines (SNGPL) Private Limited, which employs submerged arc welding (SAW). Three samples, sourced from in-service seamless pipe with a 3x6 inches cross-section, were subjected to TIG welding experiments. Basic techniques, including gas, lathe, shaper, and hacksaw cuttings, were employed to prepare the samples. The microstructural analysis and hardness test results indicated that the lowest current was optimal, as per Ohm's law (V = IR). The low current in amperes (A) and high resistance resulted in a higher melting temperature, increasing molten puddle flowability and ease of control. Conversely, high current welding (120 A) led to the formation of porosity defects, as confirmed by radiographic tests, which also showed a lack of penetration (LOP). The hardness testing further supported HV (HRB) scale values for the low current welded samples, while the high current welded sample exhibited poor hardness due to low temperatures and insufficient weld zone fusion. In summary, the results from microstructural analysis, radiographic testing, and hardness testing, all indicate that TIG welding is a suitable procedure for repairing API 5L X65 steel due to the ease of controlling microstructures at low currents in the weldment.