Failure analysis of an AISI 316 steel pipe elbow exposed to the weather for three years after 16 years of operating at 515 °C
Análise de falha de uma curva de tubulação de aço AISI 316 exposta ao tempo por três anos após 16 anos operando a 515 °C
Flavio Pereira de Moraes; Emanuelle Machado Amaral; Flávio Beneduce Neto; Angelo Fernando Padilha
Abstract
The failure of an AISI 316 austenitic stainless-steel pipe used in a hydrotreatment plant was investigated. Circumferential cracks starting from outside the pipe and parallel to the weld were identified in the pipe elbow. The failure occurred after three years of plant inactivity and exposure to the atmosphere. The pipe was operated regularly for 16 years at a temperature of 515 °C before failure, having undergone phase transformations that made the steel susceptible to intergranular attack, followed by stress corrosion cracking at room temperature. The preferential precipitation of chromium-rich M23C6 carbides at the grain boundaries allowed the occurrence of sensitization, which, associated with the residual tensile stresses caused by the welding process and the presence of chlorine from industrial atmosphere concentrated under insulation, were responsible for the failure by stress corrosion cracking.
Keywords
Resumo
Foi investigada a falha de um tubo de aço inoxidável austenítico AISI 316 utilizado em uma estação de hidrotratamento. Trincas circunferenciais partindo do lado externo em uma curva de tubulação e paralelas ao cordão de solda foram detectadas. A falha foi identificada após 3 anos de inatividade da instalação, exposta à atmosfera e temperatura ambiente. O tubo operou por 16 anos regularmente a 515 °C antes da falha, tendo sofrido transformações de fase que tornaram o aço suscetível ao ataque intergranular seguido de trincamento por corrosão sob tensão ao tempo na temperatura ambiente. A precipitação preferencial dos carbonetos ricos em cromo do tipo M23C6 nos contornos de grão foram responsáveis pela sensitização, que associada às tensões residuais de tração causadas pelo processo de soldagem e à presença de cloro proveniente da atmosfera industrial concentrado sob o isolamento térmico foram responsáveis pela falha por corrosão sob tensão.
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Referências
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Submetido em:
15/05/2023
Aceito em:
04/09/2023
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