MICROSTRUCTURAL CHARACTERIZATION OF THE API X-70 PIPELINE STEEL UNDER SOUR ENVIRONMENTS

摘要

The transportation of hydrocarbides is one of the most important activities of the petroleum industry. There are many different problems related with the transportation of these products. These include stress corrosion cracking produced by H_2S, sulfide stress corrosion (SSC), embrittlement by hydrogen, etc. A microstructural and chemical characterization of the API X-70 pipeline steel focus in the longitudinal weld joint was carried out. Hardness values of 120 to 185 HV were obtained in this material. Globular inclusions over all the weld bead were observed. These inclusions have a composition based mainly in iron oxide, Mn, Ca, and occasionally some sulfides. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were used to study the microstructure and the chemical composition of the longitudinal weld joint and the base material. The stress corrosion cracking in the weld bead zone exposed to a NACE solution saturated with H_2S has also been studied.