Martensitic stainless steels (SS) have been used widely for oil-country tubular goods (OCTG) because of their high strength and excellent corrosion resistance in carbon dioxide (CO2) gas wells. Cr-rich precipitates forms after tempering heat treatments of martensitic SS. These precipitates can affect the corrosion resistance of martensitic SS in environments simulating CO2 gas wells because Cr is considered to be an important element for improving corrosion resistance. The effect of chemical composition and tempering heat treatment on corrosion rates and pitting potentials were investigated to clarify the effect of precipitates on corrosion resistance of martensitic SS in environments simulating CO2 gas wells. The general corrosion index (GCI=Cr-12C+0.77Ni+10N (mass %)) was confirmed as a good index for estimating corrosion rates of martensitic SS in environments simulating CO2 gas wells. The term 'C coefficient/Cr coefficient' (-12), was defined as the amount of Cr as carbide precipitates (M23C6) in martensitic SS from the analysis of precipitates. The term 'N coefficient/Cr coefficient' was positive because soluble N was effective in improving corrosion resistance, as demonstrated by surface analysis. From electrochemical analysis, the anode reaction of martensitic SS was controlled by a high GCI. Pitting potential in environments simulating CO2 gas wells depended on Cr-12C+Mo+1.1Ni+6N (mass %). From the surface analysis, Mo corroded in solution to form molybdate (MoO4(2-)), which inhibited corrosion. Corrosion rates and pitting potentials in environments simulating CO2 gas wells were governed mainly by the amount of Cr in the matrix. This amount could be estimated by deducting the amount of pricipitated Cr from the total amount of Cr in the steel, regardless of the tempering heat treatment.
Corrosion resistance of martensitic stainless steels in environments simulating carbon dioxide gas wells
Korrosionsbeständigkeit von martensitischem nichtrostenden Stahl in Medien, die kohlendioxidhaltige Gasquellen simulieren
Corrosion, Houston ; 54 , 12 ; 1003-1011
1998
9 Seiten, 11 Bilder, 5 Tabellen, 16 Quellen
Article (Journal)
English
nichtrostender Stahl , martensitischer Stahl , Kohlenstoffgehalt , Chromcarbid , chemische Zusammensetzung , Legierungszusatz , Wärmebehandlung (Materialbearbeitung) , Korrosionsbeständigkeit , Korrosionsgeschwindigkeit , Lochfraßkorrosion , Ölfeld , Kohlendioxid , Rohrleitung , Chromstahl , Chrom-Nickel-Stahl , Chrom-Nickel-Molybdän-Stahl , Tempern
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