Abstract
Austenitic stainless steel, when heat-treated at 550-850 °C, became susceptible to intergranular corrosion in acids. This phenomenon, know as sensitization, it is result from the precipitation of chrome carbides in the grain boundary, making these areas less resistant to corrosion. Two different electrochemical reactivation tests are compared with a destructive test and related to the classification of its respective microstructures. It was established a quantitative methodology to evaluate the degree of sensitization in AISI 304 and also to compare the correspondence of the results with the data of the automatic and portable EPR device for non-destructive field measurement of the degree of sensitization. The used electrochemical techniques were the EPR (Electrochemical Potentiokinetic Reactivation) or single loop test and the PRP (Pasivation Reactivation Potentiokinetic) or double loop test. The destructive test used was boiling, 120 h ferric sulfate-50 % sulfuric acid, according to the standard practices ASTM A-262 practices B. The classifications of each structures were according to the standard practices ASTM A-262 practices B.
Highlights
Two different electrochemical reactivation tests are compared with a destructive test and related to the classification of its respective microstructures
It was established a quantitative methodology to evaluate the degree of sensitization in AISI 304 and to compare the correspondence of the results with the data of the automatic and portable EPR device for non-destructive field measurement of the degree of sensitization
Para el cálculo del parámetro cuantitativo, Pa, se asume que solamente los límites de grano son atacados y que el ancho de ataque es constante
Summary
Los aceros inoxidables austeníticos se utilizan en la industria petroquímica por su excelente resistencia a la corrosión y características mecánicas; sin mebargo, se han producido fallas inesperadas en equipos industriales en determinadas condiciones de servicios, siendo una de las causas principales la corrosión intergranular cuando este acero se encuentra en estado sensibilizado y en contacto con soluciones corrosivas' \. S.ANTOS prolongada del acero a una solución acida en ebuIlición, determinando el grado de sensibilización por pérdida de peso, siendo tediosas y destructivas. Las pruebas de reactivación electroquímica se usan frecuentemente debido a la cualidad de detectar bajos grados de sensibilización, que no pueden ser detectados por otros métodos, permitiendo obtener una medida cuantitativa, fácil y rápida de realizar. Se determinaron las ventajas y desventajas para detectar el grado de sensibilización de un acero inoxidable AISI 304 por esta herramienta y su correspondencia con los métodos anteriormente descritos. Las diferentes variaciones en el grado de sensibilización de las muestras se lograron con un tratamiento de sensibilización a 670 °C, temperatura de máxima sensibilización del acero inoxidable^ , para tiempos de exposición de 0,2, 0,4, 0,7, 1, 2, 3, 4, 5, 6, 7, 30, 50, 70 h y posteriormente templadas en agua
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