Impact of Water Quality in Coal Handling and Preparation Plants

This project evaluated water chemistry impacts on the corrosion rates of other common construction and fabrication materials. Different construction and fabrication materials are each affected differently by different aspects of water chemistry. For example, it is known qualitatively that chloride concentration does not affect mild steel corrosion but has a very large impact upon stainless steel corrosion.

Earlier project C28059 involved placement of reference mild steel corrosion coupons in each of eight CPPs, and the water quality at each CPP was monitored over an 18 month period. Despite the success of the project, some limitations of the approach were identified, including:

• Different environmental and water temperature conditions at each site; and
• Impossibility of locating test coupons in exactly the same exposure scenario at each site.

As a consequence it was recommended that a different approach (laboratory-based Linear Polarisation Resistance - LPR, and Electrochemical Impedance Spectroscopy - EIS testing) be applied for this project which would simplify logistics and eliminate many of the extraneous variables which may have introduced variability to the pervious study.

Using the LPR-EIS approach the project has successfully correlated laboratory EIS corrosion rate data with either two or three key water quality parameters, for each of bright mild steel, hot dipped galvanised steel, and aluminium grade 6060. Three stainless steels (304, 316 and 3CR12) were also tested but the corrosion rates for those materials were all below 0.001 mm/year.

Stereo microscope and scanning electron microscope images of the test piece surfaces have been generated.