Evaluating the structural and corrosion performance of a steel welded joint produced via submerged arc welding

The structural integrity of SA 516 Grade 70 steel pressure vessels critically depends on welding procedures and resultant microstructures. Finite element analysis (FEA) modeled the thermal profile of welded joints and was validated by the observed microstructural transformations. High-temperature excursion in the heat-affected zone (HAZ) transformed polygonal ferrite into Widmanstätten ferrite (α w ), while acicular ferrite (α ac ) and allotriomorphic ferrite (α al ) phases formed in the weld zone (WZ). Corrosion testing revealed preferential dissolution of the WZ due to a higher galvanic current (135.4 µA/cm²) compared to the base metal-HAZ interface (104.6 µA/cm²). This galvanic interaction could be detrimental due to a low exposed area ratio between the WZ and base metal. Impact toughness dropped significantly from 140 J at 20 °C to 13 J at −40 °C, transitioning the fracture mode from ductile to brittle, as confirmed by fractographic analysis. • FEA linked thermal profiles to microstructural changes in SA 516 Grade 70 welds. • High HAZ temperatures formed Widmanstätten ferrite; WZ showed acicular and allotriomorphic ferrite. • Corrosion favored WZ dissolution with higher galvanic current (135.4 µA/cm²). • Impact toughness dropped from 140 J at 20 °C to 13 J at −40 °C, showing brittle transition. • Fractographic analysis confirmed ductile to brittle fracture mode with temperature drop.