Pitting Resistance of Engineering Materials in Geothermal Brines—I. Low Salinity Brine

The resistance of carbon steel, E-Brite 26-1, Type 316L stainless steel, Haynes Alloy 20 Mod, Carpenter Alloy 20 Cb-3, Inconel Alloy 625, Hastelloy Alloy G, Hastelloy Alloy C-276, Titanium 50A, and TiCode 12 to pitting in a low salinity geothermal brine (Nowlin No. 1) was determined. The behavior of coupons exposed to the "fresh," unflashed wellhead brine was compared with the behavior of coupons exposed to unflashed brine collected at the wellhead and transported to the laboratory. Pitting potentials were also determined in laboratory tests. There was excellent agreement between laboratory and field test data. The two titanium alloys were completely resistant to pitting under all experimental conditions, Hastelloy Alloy C-276 was the nickel base alloy most resistant to pitting, and Haynes Alloy 20 Mod was the most resistant iron base alloy. The breakdown potentials for the high chromium ferrous alloys satisfy the thermodynamic requirements for pit initiation via oxidative dissolution of manganese sulfide inclusions in the passive film.