This research deals with a method and procedure for enhancing the structural life of the commonly used steel structure in oil and gas industries HSLA S460G2+M with a thickness of 10 mm. The type of joint and welding process is T-joint with transverse and longitudinal attachment welded using semi-automated GMAW. Filler wire ER80S-Ni1 and mixed shielding gas (80% Ar / 20% CO2) is used as material consumables. At first, the best suitable welding parameters are comprehensively investigated, prepared, tested and qualified according to welding procedure specification (WPS) qualification requirements. Further, the weld toe is treated by using HFMI/PIT with a frequency of 90Hz, 2 mm pin radius and air pressure of 6 bars. In accordance with the recommendation of the International Welding Institute (IIW), fatigue test is conducted using constant amplitude loading with the stress ratio of 0.1 and loading stresses from 55% to 75% of the yield strength of the material. Finally, the results of the fatigue experimental are compared with the fatigue recommendation of as-welded and HFMI/PIT of IIW as well as the untreated raw material. As a conclusion, it is observed that the fatigue life is increased up to 300% compared to IIW and 70% to as-welded. It is also obvious that treated transverse T-joint shows significant improvement than the longitudinal attachment.