Avaliação do nível de tensão residual e susceptibilidade à fragilização por hidrogênio em juntas soldadas do aço API 5L X80 utilizados para o setor de petróleo e gás.

Abstract

This study aimed to evaluate the residual stresses and susceptibility to hydrogen embrittlement in API 5L X80 steel welded joints used for oil and gas area. Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW) and Flux-Core Arc Welding (FCAW-Self-protected) process were used and four weld joints were obtained by varying process, consumable and welding parameters. The residual stress was evaluated by x-ray diffraction in the top, bottom and along the thickness of the welded joints. Electrochemical tests of hydrogen permeation were carried out according to ASTM G148-97-R11 (2011). The susceptibility to hydrogen embrittlement caused by Sulfide (Sulfide Stress Cracking - SSC) was evaluated according to G 129-00-R06 (2006) employing the A solution proposed by the NACE TM0177/2005 standard with additions of sodium thiosulfate. Hydrogen-Induced Cracking (HIC) Tests were performed according to standard NACE TM0284/2003. It was verified that in the upper regions of the welded joints the use similar Heat Input, but with higher welding current intensities and welding speed, the residual stress were more compressive in Weld Metal (WM). For different welding conditions employed, it was found that the use of high currents implies more compressive residual stresses along the WM in the top surface. On the bottom of welded joint, with higher Heat Input were obtained higher tensile residual stress in the WM. All welded joints were susceptible to SSC, as verified through the Elongation Ratio (ER) obtained and the analysis of the fracture surfaces of the samples. It was found that the solubility and diffusivity can’t be considered the only factors considered in susceptibility to SSC. Although shown in some cases tensile residual stress along the thickness, the joints showed no cracks in HIC tests in solutions simulating low concentrations of H2S.