Onshore/Offshore Facilities

Localized Pitting Corrosion of Superduplex Stainless Steel in a Seawater Application

During the dismantling and removal of fire-water-pump columns of superduplex stainless steel barely 1 year after plant startup in a redeveloped brownfield offshore Nigeria severe localized pitting corrosion was observed in the columns. This paper explores the findings and identifies the reasons.

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The corrosion and holes observed in the column. Source: Paper SPE 189091.

During the dismantling and removal of fire-water-pump (FWP) columns of superduplex stainless steel barely 1 year after plant startup in a redeveloped brownfield offshore Nigeria, the unexpected was observed: severe localized pitting corrosion affected the columns. This paper explores the finding that, even though seawater chlorination was present, the chlorination was not the dominant factor that led to the corrosion; instead, manufacturing imperfections were responsible.

Introduction

After failures of duplex stainless steels in extreme environments (such as in solutions containing chloride, bromide, sulfides, or hypochlorite ions) were noted, superduplex stainless steel was developed. Since the 1970s, superduplex stainless steel has been preferred for use in a variety of marine and seawater applications and so far has recorded proven high performance. Superduplex stainless steel typically has high resistance to pitting and crevice corrosion, which is the most likely type of corrosion seen in other stainless steels.

Material resistance to pitting corrosion is measured by a pitting resistance equivalent number (PREN) value, used as the value to evaluate the resistance to pitting in an overall corrosive environment.

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