Initiation and propagation of a single pit on stainless steel using a local probe technique.

Stéphane Heurtault,Raphaël Robin,Vincent Vivier,Fabien Rouillard

doi:10.1039/c4fd00252k

Abstract

Experiments about single pit initiation and propagation were performed on 316L stainless steel with the aim to determine the pitting corrosion behaviour for nuclear waste containers. The experimental setup permits to control the pit development at will and to create reproducible single pits in three dimensions. Radial and deep evolutions of a disc shaped pit were studied for propagation times of up to 10 hours. These evolutions were used to determine what limiting mechanism takes place during long-term pit propagation. Special attention has been paid to the chloride ion action on pitting. A minimum chloride concentration was found to be necessary in the bulk electrolyte to support pit propagation. The existence of a critical pit depth of 230 μm was also underlined.

Highlights

Pitting corrosion is an important issue for the long-term behaviour of nuclear waste containers
This paper aims at bringing new insight on the pit propagation description on 316L stainless steel
A similar current evolution between the 11 identical tests shows that the experimental setup permits to obtain reproducible single pits

Summary

Introduction

Pitting corrosion is an important issue for the long-term behaviour of nuclear waste containers. With the presence of humid zones formed on the inner 316L stainless steel container surface, the HCl gas completely dissolves and may form highly concentrated hydrochloric acid zones. Under these conditions, pits can initiate and propagate. Pitting corrosion has been widely studied in the last decades on stainless steel,[1,2] but since it is a stochastic process, it remains difficult to study experimentally. Adding an aggressive anion, such as chloride ion, to the electrolyte leads to the formation of several pits with different stages of development on the material surface making any pitting analysis very difficult. Many statistical studies have been performed to determine the pitting susceptibility of a

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