Multi-Objective Structural Optimization of a Large- Effect of Welding Current and Voltage on Weld Defects and Corrosion Resistance of HF-ERW ST37 Steel Pipes

Abstract

The High-Frequency Welding (HFW) process is one of the most frequently employed fabrication techniques to manufacture longitudinally welded steel pipes in pipeline transport for oil and gas transmission applications. In this study, the impact of current strength and electrical potential on radiographic features and corrosion properties of HFW-steel ST37 pipes was analyzed. A 12 inches diameter ST37 steel pipe with a wall thickness of 6 mm was manufactured using the High-Frequency Electric Resistance Welding (HF-ERW) method by varying the current of welding between 1100 and 1130 A and keeping the frequency equal to 180 Hz. Radiography was performed to assess defectiveness and porosity structure. Also, electrochemical corrosion properties were studied using Tafel polarization curves in 3.5 wt.% NaCl medium. Electrochemical parameters, such as corrosion current density (icorr), corrosion potential (Ecorr), and polarization resistance (Rp), were obtained from Tafel polarograms using Stern–Geary equation. The radiography revealed that the increase in welding current and voltage led to a remarkable increase in porosity formation in welds owing to intensive heat exposure. The results of the electrochemical analysis show that the welds subjected to higher current intensities had a high corrosion current density and low polarization resistance, meaning a lower resistance to corrosion. The test sample with the highest porosity level performed poorly in terms of corrosion since pores and voids served as preferred locations of electrochemical corrosion and the entry of chloride ions into the metal matrix. The findings prove the importance of controlling HFW conditions to reduce corrosion in ST37 pipelines.