Corrosion Behavior of API X70 Steel Welded for Process Double Submerged Arc Immersed in Different Corrosives Environments

Abstract

The steels API X70 are applied in construction and fabrication of pipeline for transport of hydrocarbons, however, to lapse time are degrade due to environment to which are exposed, influencing on mode and corrosion rate on surface base metal (BM), heat zone affected (HAZ) and fusion zone (FZ). In order to know and evaluate the corrosion susceptibility in joints of API X70 steel submitted to different corrosives environment, several tests were carried out by process of double submerged arc welding (DSAW), which were immersed in different electrolytes: Sodium Chloride (3.5% NaCl) and Water (H₂O) at room temperature for know its behavior. Electrochemical techniques were used of electrochemical noise (EN) and cyclic polarization curves (CPC) to obtain mode and corrosion rate produced for each of the samples analyzed, included the three zones: BM, HAZ and FZ. Further, characterization techniques were used such as optical microscopy (OM) and scanning electron microscopy (SEM) for superficial analysis. The welds’ majoirity have a mixed corrosion, with higher corrosion rate in 3.5% NaCl.

Key-words
Corrosion; Electrochemical techniques; Double submerged arc welding