There is little data available in the public domain on the performance of 316L in concentrated anoxic brines saturated with CO2 in the absence of H2S. Where limits of use are stated in the literature the origin of these limits may be obscure and unreliable for validation of materials selection undertaken during engineering design. Given the limited ‘good quality’ data available a series of laboratory tests was performed aimed at assessing the suitability of 316L for downhole sand screens and as a potential cladding material for a gas production separator where the chloride concentration of the produced water was up to 200000mg/l. The following text describes the tests performed and the results obtained.This work involved autoclave pitting corrosion tests conducted with 316L sand screen wire mesh (30-day duration) and 316L sheet samples (7-day and 30-day duration). The pitting exposure tests were supplemented by electrochemical polarisation curves on 316L sheet samples only. Autoclave tests and polarisation curves were performed with brine concentrations from 100000mg/l up to 250000mg/l with temperatures varying from 25 °C to 112 °C and CO2 partial pressures from 1 bar to 4.8 bar; the in-situ pH varying naturally with a fixed bicarbonate concentration.The results of pitting corrosion tests on the 316L strip showed that with 200000 mg/l chloride 316L was susceptible to pitting corrosion at 65°C. Increasing the test temperature to 112°C resulted in initiation of pitting corrosion on both wire mesh and strip but the corrosion attack was less severe than that observed at 65°C. Also the wire mesh (with an as-received surface finish) was less susceptible to corrosion than the 316L sheet (600 grit finish). In tests with 183000 mg/l chloride at 112°C the surface of 316L strip specimens exhibited tarnished areas but the wire mesh remained burnished in appearance. No pitting was evident on either wire mesh or strip.The electrochemical test results obtained showed good correlation between the pitting and re-passivation potentials obtained from the polarisation curves and the presence or absence of pitting corrosion in the autoclave tests. It was found that pitting potentials and re-passivation potentials were lowest at 65°C which coincided with the greatest weight loss in the autoclave tests. At lower and higher temperatures (25°C and 112°C) the pitting and re-passivation potentials were nobler than the corresponding values at 65°C over the chloride range tested.At 112°C there was little change in the pitting potentials over the range 100000-200000 mg/l chloride but a small increase in pitting potential was observed in tests with 250000 mg/l chloride. At 65°C there was little change in the pitting potentials in tests with 200000 mg/l chloride and 250000 mg/ chloride. At 25°C a decrease in pitting potential was observed in tests with 250000 mg/l chloride compared with tests with 200000 mg/l chloride.It is postulated that the increased risk of corrosion at 65°C is due to the competing effects of increasing pH and decreasing CO2 solubility vs. increasing temperature. The results show that 316L can be used at very high chloride concentrations in anoxic CO2 saturated brines. However in order to ensure safe use it is necessary to understand that the highest exposure temperature is not necessarily the point at which the risk of passive film breakdown is highest in contradiction to normal expectations.

Key words: 316L, pitting, chloride, anoxic, polarization