Behaviour on corrosion of API X70 steel welded using the process of double submerged arc welding immersed in corrosive media

ABSTRACT

API X70 steels are used for manufacturing and constructing pipes for transporting hydrocarbons; however, they deteriorate over time due to the environment to which they are exposed; influencing the rate and type of corrosion on the surfaces of the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ). In order to find out and evaluate the susceptibility to corrosion in joints made from API X70 steel subjected to different corrosive media, various tests were carried out using the process of double submerged arc welding, which were immersed in different electrolytes: sodium chloride (3.5% NaCl) and water (H₂O) at ambient temperature in order to find out about behaviour. Electrochemical noise techniques and cyclic polarization curves were used to obtain the rate and type of corrosion produced in each of the analysed samples, including the three zones: BM, HAZ and FZ. In addition, characterization techniques such as optical microscopy and scanning electron microscopy were used for surface analysis. Most welds show mixed corrosion, with higher corrosion rates in 3.5% NaCl.

KEYWORDS:

• Corrosion
• electrochemical techniques
• double submerged arc welding

Acknowledgments

The authors thank the people involved in developing this work, which was carried out at the Corporación Mexicana de Investigación en Materiales, S.A. de C.V. in conjunction with the Centro de Investigación e Innovación en Ingeniería Aeronáutica de la FIME Nuevo León and the external support of the team belonging to the Asociación de Investigación Metalúrgica del Noroeste de Porriño, Pontevedra, Spain.