Experimental Determination of the Normalizing Effect on Tensile Strength, Impact Strength, Fatigue, Residual Stress of Girth Welding on Iranian Natural Gas Transmission Pipelines

In this article, the effects of normalization heat treatment on girth weld with containing titanium oxide and titanium carbide microparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy test results show that in the normalized sample containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium carbide microparticles and titanium carbide microparticles), has been respectively increased by 33% and 18%. Also, the ultimate strength of normalized samples containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles) has been increased by 9% and 11%, respectively. The results show that the fatigue life in both normalized micro-alloy samples has been increased. The fatigue life in the normalized sample of titanium carbide microparticles has increased more than the titanium oxide microparticles. The fatigue test results show that the fatigue life (150-N force) has been increased by 36% in the normalized sample containing titanium carbide microparticles compared to the normalized sample containing titanium oxide microparticles. In this loading, the fatigue life (normalized sample containing titanium carbide microparticles compared to the no heat treatment sample) has been increased by 27%. The hole-drilling strain-gage results show that in the normalized sample containing titanium oxide and titanium carbide microparticles, hoop residual stresses have been respectively decreased by 12% and 8%compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles).