Crevice Corrosion Risk Evaluation of UNS S31603 and UNS S32205 Alloys for Low-pH Flocculants in Offshore Water Injection Systems

Abstract The corrosion behavior of 316L stainless steel (UNS S31603) and 2205 duplex stainless steel (UNS S32205) was evaluated in three low-pH flocculants (FLOCT-PIX, FLOCT-7844, and FLOCT-ALS)(1) under simulated North Sea water injection service. Coupons were immersed for 30 days at 25 °C and 50 °C per ASTM G48(2) using standardized crevice assemblies.1 Although field inspections revealed crevice-like damage in flocculant storage and injection systems, no crevice corrosion was reproduced in the laboratory. Instead, distinct alloy–chemistry interactions were observed:2,3 316L showed low general corrosion but isolated susceptibility to deep pitting, including a 39.5 μm pit in FLOCT-7844 at 50 °C, while 2205 exhibited higher general corrosion rates—up to ~3× those of 316L—but only shallow, non-propagating pits (≤20 μm). FLOCT-7844 proved the most aggressive, FLOCT-PIX (pH ~0.4–0.5) caused less attack than expected, and ALS was essentially benign. These results demonstrate that corrosion severity depends more on alloy–chemistry interactions than bulk acidity. Replacing 316L with 2205 reduces the risk of catastrophic localized failures, while reformulating flocculants toward pH > 4 further mitigates risk. The study clarifies field–lab discrepancies and supports improved material selection, flocculant design, and corrosion management strategies for offshore injection systems.