Prevention of Chloride stress corrosion cracking [CSCC] in austenitic stainless steel material for closed loop water/glycol mixture are as follows:
- Elimination of oxygen is an effective measure to prevent CSCC in neutral and alkaline solutions.
- Complete removal of oxygen by means of non scaling oxygen scavengers (e.g. nitrites) is the safest approach. Oxygen levels below 0.2 PPM appear to prevent CSCC at high temperatures up to 300 °C with chloride levels up to 1000 PPM. Residual nitrite levels of 1000 PPM to 2000 PPM are sufficient for the control of oxygen to suitable levels to avoid corrosion and CSCC.
- Increasing pH up to a maximum of about 12 will enhance CSCC resistance. However this should only be used for short term deviations and should be avoided as a long term solution.
- Low chloride levels of less than 1 PPM can also prevent CSCC in the presence of oxygen.
- Removal of oxygen and maintenance of alkaline pH can also provide good corrosion resistance.
- Biological growth should not be a problem in an alkaline anaerobic cooling medium but a suitable biocide can be added.
- Do not use free chlorine biocides.
Above figure shows an example of Chloride stress corrosion cracking in Intergranular of an Inconel heat exchanger tube with the crack following the grain boundaries.