CORROSÃO SOB TENSÃO EM SOLDA CIRCUNFERENCIAL DE AÇO API 5L X70 EM CONTATO COM ETANOL
STRESS CORROSION CRACKING OF CIRCUMFERENTIAL WELDING JOINT IN API 5L X70 LINE PIPE IN ETHANOL ENVIRONMENT
Vinícius Girogetti, Javier Alejandro Carreno Velasco, Rodrigo Vieira Landim, Vitor Luiz Sordi
Resumo
As juntas de solda de campo circunferenciais usadas na construção de dutos para transporte de petróleo e derivados constituem regiões susceptíveis a defeitos que podem levar a falhas em operação. Neste trabalho uma junta circunferencial de um duto de aço API 5L X70 foi produzida em laboratório e avaliada por meio de ensaios de dureza, tração e impacto; a corrosão sob tensão promovida pela exposição ao etanol combustível foi avaliada em ensaios de tração com baixa taxa de deformação em corpos de prova com entalhes posicionados nas distintas regiões da solda; as microestruturas do material de base e da região soldada foram caracterizadas por microscopia ótica e as superfícies fraturadas foram analisadas ao MEV. A análise da fratura após em ensaios de tração e de impacto indicou que as descontinuidades da solda, ainda que qualificada, interferem significativamente no mecanismo de fratura, tendendo à fragilização, especialmente nos testes de impacto. A susceptibilidade à corrosão sob tensão ficou evidente, tanto na zona termicamente afetada quanto no metal de solda, promovendo perda de ductilidade e acelerando o processo de fratura nos ensaios de baixa taxa de deformação em presença de etanol.
Palavras-chave
Abstract
Circumferential field-welding joints of oil pipelines are susceptible to defects that may lead to failures when in operation. In this work a circumferential joint of an API 5L X70 line pipe was produced in a laboratory and evaluated by hardness, tensile and impact tests; stress corrosion cracking promoted by exposition to fuel ethanol was evaluated by slow strain rate tensile tests using notched specimens; the micro-structures were characterized by optical microscopy in the different regions of the welded joint and the fractured surfaces were analyzed by SEM. The fracture surface of the welding metal after tensile and impact tests indicated that the presence of welding discontinuities may strongly affect the fracture behavior, leading to embrittlement, especially in the impact tests. Stress corrosion cracking occurred in both evaluated regions (welding metal and heat affected zone) of the welds when subjected to slow strain rate tensile tests in contact with ethanol.
Keywords
Referências
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