Avaliação da susceptibilidade á fragilização por hidrogênio de juntas soldadas de aço API 5L XBO com diferentes combinações de consumíveis.

Abstract

This paper presents a study of susceptibility to embrittlement by API 5L XBO welded gaskets, evaluating the influence of welding procedures, process and consumables. Were used the Processes with Coated Electrode (SMAW), with Tungsten and Inert Gas Protection (GTAW or TIG) and Tubular Wire (FCAW). For consumables, AWS E6010 electrodes were used. for the root pass and the AWS E8Q10, E 9010, E8018 and E9018-G electrodes for hot and filling passes in the SMAW process with electrodes removed from the greenhouse and directly from the box. The GTAW process was used only for the root pass welding using AWS ER70S-3 wire as consumables. In the FCAW process AWS E91T8-K8 consumables were used. self-shielding and AWSE91T1-G the latter with gas shielding consisting of (Ar25). The hydrogen perilization tests were performed according to the ASTM G129-2006 standard with an aqueous solution (solution A - NACE TM0177 / 2005), but using sodium thiosulfate microadditions (Na2S203) instead of bubbling H2 & According to values ​​of reduction, area reductions and rupture time, it was observed that all the joints were susceptible to hydrogen embrittlement grounds. Al6m from In addition, all joints showed a distinct change in tensile fracture mode. and presented secondary cracking on the specimen surface. These results were still associated with the microstructural characterization of weld metal and lifting the hardness profile of each joint; what made it possible to evaluate the degree of influence of the change of consumables on the hydrogen embrittlement foundation. At the end of the results it can be verified that all fractures occurred in the weld metals, and that the joint that obtained the better result in embrittlement tests; was that welded using the GTAW process from scratch with AWS ER70S-3 consumables, the process SMAW in the hot pass with AWS E8010 consumables and the FCAW process in the filling and finishing passes using wire as consumables AWSE91T1-G with gas protection. This welding condition presented for the central region of the weld metal the highest percentage of acicular ferrite (AF} ~ (43%), the lowest hardness value (147.6HV) and the best result for the Ration of Area Reduction (RRA) - (0.59), which identifies it as the welded joint less susceptible to the phenomenon of hydrogen embrittlement.