Effect of welding procedure on the properties of microalloyed steel-welded joints for metal piping

Abstract

The objective of this work was, in the first step, to compare the mechanical properties and microstructure of the corrosion-resistant steel hydrogen-induced cracking, alloyed with Nb–Ti–Cu–Ni, to those of a normal steel NOR, microalloyed with Nb–V–Ti, characterized through chemical analysis, hardness measurements, metallographic studies and tensile and Charpy-V properties. The preheating temperature was established using Tekken tests at different temperatures, according to the JIS Z 3158 standard. Circumferential welds were carried out on piping manufactured from both steels, designing procedures for the use of coated electrodes on the one hand (shielded metal arc welding, with electrodes from various suppliers) for all passes, and for a first pass using automatic welding with low-CO₂ solid wire on the other (gas–metal arc welding) and the rest with self-shielding tubular wire (flux-cored arc welding, self-shielding). The welds were classified in accordance with the API Code 1104. The results of the metallographic analysis and the mechanical traction, hardness and impact tests of the welded joints revealed the influence of the welding consumables and of the base metal on the properties of the joints. Differences were observed between the properties of the joints welded with consumables of equal specification and different suppliers. From the different combinations tested, optimum values for the welding of these steels were defined.

Keywords:

• microalloyed steel
• weldability
• piping
• SMAW
• FCAW-S

Acknowledgements

The authors are deeply grateful to Air Liquide Argentina and the Lincoln Electric Company for the donation of the consumables.