This paper deals with a comprehensive investigation of fatigue life enhancement on semiautomated Gas Metal Arc Welding (GTAW) butt weld joint which is found almost everywhere in Malaysia welding structure steel sectors. The selected material in this study was high strength low alloy steel S460G2+M commonly used extremely in steel structure due to its outstanding mechanical properties. In this investigation, the method for joining the butt weld was conducted by unprofessional welder using semi-automated GMAW. At first, suitable welding parameters were identified and formulated into welding procedure specification (WPS) qualification conforming to AWS D1.1 standard. The test specimens were prepared and tested to ensure the welding quality. Further, the HFMI using Pneumatic Impact Treatment (PIT) technique were applied at the weld toe of the butt weld as tool for fatigue life enhancement. To investigate the influence of HFMI/PIT on the fatigue strength, the specimens were undergone fatigue test using universal fatigue machine using a constant amplitude loading. Finally, the comparison of the fatigue strength of as welded and treated specimens to indicate the beneficial influence of the treatment. Yes, the conduction by unprofessional welder using semi-automatic GMAW, the findings showed the improvement of fatigue strength and slope of S-N curves. In addition, the fracture location of test specimen shows physically affected by shifting from critical weld transition to base metal. The tensile test and hardness value also showed a slight difference as compared to untreated specimens.

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.

This research deals with the fatigue life investigation using experiment and FEM simulation on longitudinal fillet weld of structural offshore steel S460G2+M with a thickness of 10mm. The experimental fatigue test is conducted based on nominal stress (NS) approach while the simulation uses the effective notch stress (ENS) approach for fatigue life assessment. The investigation begins with the preparation of the longitudinal fillet weld fatigue specimen using Milling Machine based on the IIW fatigue specimen design recommendation and joined using the semi-automatic GMAW process following the AWS D1.1 procedure. Fatigue testing on non-load carrying fillet weld is conducted using the Instron Fatigue Machine with a stress ratio of 0.1 with constant amplitude loading and stress loading from 50%-75% of the yield strength of the base material. For the simulation approach, the 3D longitudinal fillet weld geometry is created using CAD based on the ENS design procedures of IIW where the sizes and dimensions are similar to the experimental fatigue specimen. The static elastic stress analysis of the model is conducted using MSC Marc/Mentat FEM software. Based on the IIW fatigue data evaluation, it is found that the natural mean curve of the longitudinal fillet weld obtained 146 MPa of FAT class which exceeds approximately 106% from the IIW FAT class recommendation for a longitudinal fillet joint. However, the characteristic curve of 97.7% failure probability of the parts only attained 95 MPa of FAT class, but still exceeds approximately 33% form the IIW FAT class. In the ENS fatigue assessment of the 3D longitudinal fillet weld, it is found that the model obtained 195MPa of FAT class which is inferior approximately 15 % from the FAT class recommendation of IIW. Also, it is found that both S-N curves of NS after conversion to ENS system have a good agreement with the S-N curve of ENS of 3D longitudinal fillet weld model and the IIW recommendation due to only 16 % and 34% lower as compared with the IIW FAT class recommendation for ENS.