Hydrogen induced cracking HIC resistance in HSLA API 5L X65 e 5L X80 steels

In the oil and natural gas production chain the structures for transport and extraction of the product are damaged by the conditions they are exposed to, which generally contain H₂S, reducing the properties and the good performance of these pipes. In this work, we studied an API 5L X65LMN tube and another API 5L X80 with different levels of C and, mainly, Mn and Nb. The inclusions were examined by optical microscopy (OM) and scanning electron microscopy (SEM), the microstructure was examined by scanning electron microscopy (SEM) and the chemical analysis by Dispersive Energy Spectroscopy (EDS) of the inclusions was performed. As for the hydrogen-induced crack resistance in H2S containing media, the procedures of NACE TM0284-11 were used. The materials were subjected to the HIC test in solution A saturated with H2S of said standard. After the HIC, the characterization of the samples by Scanning Electron Microscopy (SEM) was performed. The API 5L X65LMN tube showed inclusions homogeneously distributed in the matrix, whose classification was of the type oxide-sulphide fine series, with maximum size of 5.6 μm and rounded format mainly with presence of Ca, Al, Ti and Mn. For tube X80 Presented irregular inclusions of type D-globular oxide-sulfide sserie coarse with a maximum size of 7.2 μm, with presence of Mn, O and S inclusions, with respect to the microstructural characterization of the tube X65 presented ferritic matrix, with presence of microconstituent M / A (Martensita / Austenite) and perlite in the cross section with lamination direction and grain size of 6.8 μm, the API 5L X80 tube presented ferritic matrix, with presence of M / A (Martensite / Austenite) and maximum grain size of 4.6 Mm. The results of the Hydrogen Induced Cracking Resistance (HIC) tests showed that the API 5L X80 tube showed cracks initiated on the D-globular oxide-sulphide coarse series inclusions, showing the deleterious effect of these inclusions on HIC resistance. It is important to note that the API 5L X80 tube has higher mechanical strength, which contributes to its lower resistance to HIC.