Crevice corrosion control in UV water treatment systems

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A Canadian commercial ultra violet (UV) radiation-based water disinfection system employs a 4-20 mA silicon carbide (SiC) photo diode sensor that is specifically tuned to the germicidal UV-C (254 nm) light used to treat the residential water. The Type 316L stainless steel casing of the sensor is prone to corrosion under specific water conditions. This poses a serious problem as corrosion fouls the quartz window, which significantly reduces the sensor's ability to 'see' the UV light. While it is well known that UV radiation can enhance passivity of stainless steels, its detrimental effects on crevice corrosion as a consequence of the enhanced passivity is not well understood, especially when considering the interplay with water temperature, pH and total dissolved solids (TDS) content. The research proposed here will (i) validate the crevice corrosion failure mode using well characterized process waters, (ii) identify the temperature TDS (or Cl-) thresholds for crevice corrosion susceptibility of Type 316L stainless steel, (iii) analyze the suitability of upgrading to Type 317L and/or 2205 duplex stainless steel and proposed changes to the design details.