Preventing Corrosion on Pre-corroded Mild Steel Surfaces and the Benefits of Proper Cleaning

A number of techniques including weight loss coupons and corrosion probes have been used to study mild steel corrosion in system water typically used in domestic central heating systems. These techniques have also been applied to the study of the effectiveness of a corrosion inhibitor on pre-corroded mild steel surfaces.
The corrosion in domestic central heating systems can be controlled by correct system installation and commissioning, including the addition of an appropriate chemical corrosion inhibitor to the circulation water.  Nevertheless poor practice is common and many systems accumulate significant amounts of corrosion products in the form of voluminous sludge. This paper reports the results of an independent study to examine the effect of such system corrosion debris has on boiler energy efficiency and system effectiveness. By measuring boiler efficiency and analysing using thermal imaging, the study shows quantitatively that progressively fouling the system with corrosion deposits serves to substantially reduce active radiator area whilst decreasing boiler efficiency.  Replacing the boiler, often the first 'knee-jerk' response, does not improve either system or boiler efficiency. In contrast, correctly cleaning and power flushing the system was shown to fully restore the system's hydraulic balance, increasing fundamental heat transfer capabilities of radiators, increasing overall boiler energy efficiency thereby minimising domestic boiler CO₂ emission. UK heating systems account for 30% of the country's CO₂ emissions and even a modest restoration of boiler efficiency (or prevention of efficiency loss) as a result of improved practice could have significant impact on this figure.