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Friday, January 23, 2009

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Recommended :Earlier post "Crevice Corrosion Mechanism & Prevention" has briefly discussed mechanism of crevice corrosion and its prevention. As discussed, one of the preventive measures is to select correct material to resist crevice corrosion. Stainless Steel (SS) is known to resist to general corrosion by forming a thin, protective oxide film on it external surface, SS still susceptible to localized corrosion i.e. Chloride stress corrosion cracking (CSCC), crevice corrosion, pitting corrosion, etc once this protective film is partly damage. Stainless steel once expose to water (present of Chloride) with temperature higher than 60 degC, CSCC is potentially occurred. On the other hand, temperature lower than 60 degC, crevice and pitting corrosion is potentially occurred.

There are different grade of Stainless Steel i.e. SS304, SS316, S31803, S32205, etc. How Chloride [Cl] concentration, Sulfate [SO4] concentration, pH level, temperature, oxygen level, etc affecting crevice corrosion for different Stainless Steel ?



The Crevice Corrosion Engineering Guide for Stainless Steels (CCEG) is a program available FREE to check type of Stainless Steel susceptible to crevice corrosion in water under particular conditions and impurities. The CCEG is a program with predictive mathematical model of crevice corrosion to assist with the selection of stainless steels for use in chloride and sulphate containing waters, including sea water. It was jointly developed by Nickel Development Institute (NiDI) and Sheffield Testing Laboratories Ltd.





Application Range
This program has been developed with the following application range :
  • Fluid : Water
  • Operating temperature : 5 - 85 degC
  • Chloride [Cl] concentration : 1-30,000 ppm
  • Sulphate [SO4] concentration : 0-10,000 ppm
  • Total Dissolved Solids (TDS) concentration : 0 - 65000 ppm or mg/L
  • * Can be calculated base on 1.65 [Cl] + [SO4]
  • Alkalinity : 0 - 10000 mg/L (as concentration of CaCO3 in mg/L)
  • Hardness : 0 - 20000 mg/L (as concentration of CaCO3 in mg/L)
  • pH : 5 - 9
Stainless Steel Grade Can be Checked
The program will check for following material :
  • S30400
  • S31600
  • S31700
  • S31803
  • S32205
  • N08904
  • 6% Mo SS

Example
Let take a water with following parameters :
  • Chloride (ppm) : 1000
  • Sulphate (ppm) : 100
  • Hardness (as CaCO3 mg/L) : 100
  • Alkalinity (As CaCO3 mg/L) : 100
  • TDS (mg/L) : 1798
  • pH : 7
  • Temp (C) : 25
  • Oxygen level (ppm) : 7
CCEG predict corrosion will not occur with S31803 however corrosion will initiate in days with S31600.

Download : Click here to download the program (1.17 MB).
Source : Nickel Development Institute (NiDI)

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posted by Webworm, 2:32 AM

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