In the subsea oil and gas industry, all super duplex stainless steels are considered equivalent regarding pitting and crevice corrosion resistance; but are they?
In this work, presented at the 16th Nordic Corrosion Conference, we investigated the correlation between localized corrosion resistance and alloy composition and microstructure. The objective of the research was to quantify the seawater pitting corrosion resistance of two 25-wt% Cr SDSS:
- a conventional low-tungsten grade (a modified UNS S32750) and
- a W-bearing SDSS (UNS S39274) using electrochemical techniques.
Cyclic potentiodynamic polarization (CPP) testing was used to determine the effect of composition and different σ-phase volume fractions on the corrosion response of the system as a function of temperature. CPP tests were conducted at various temperatures, ranging from 25 to 90°C, to determine the effect of deleterious phases on critical pitting and crevice temperatures (CPT and CCT, respectively).
The final presentation can be viewed below.
M. Næss, E. Haugan, M. Iannuzzi, and R. Johnsen, Paper No: 26 Session No 2: "Use of electrochemical techniques to determine localized corrosion resistance of 25-wt% Cr Super Duplex Stainless Steels: effect of tungsten", 16th Nordic Corrosion Conference (Stavanger, Norway, May 20-22, 2015).