Water-filled cooling systems are always subject to some degree of corrosion, and left un-checked, holes can appear in the system allowing the coolant to leak out. Consequently, it is always advisable to use a carefully selected corrosion inhibitor in the water which may well reduce corrosion rates to almost negligible levels. Probably the most common examples of such systems are domestic central heating and car engine cooling systems.
In older systems where some corrosion has already occurred, this may have caused the formation of layers of scale on the walls of the system. These materials have an adverse effect on heat transfer, so the question arises about the need to use a chemical “cleaning” agent which will remove such layers. The dilemma which crops up here is that the use of such a cleaning agent may opens up some leaks. Prior to the cleaning, small pin holes in the metal had been blocked up by the corrosion product itself and use of the cleaning agent un-plugs the hole. It is at this stage that old proverbs like “let sleeping dogs lie” and “if it ain’t bust, don’t fix it” come to mind.
The concerns about the use of cleaning agents do not stop there. Having introduced the agent in to the cooling system, it very important that it is thoroughly flushed out before the system is put back in to standard service. The reason for that is that cleaning agents can often cause corrosion if left in the system long-term.
So what advice can we offer?
Firstly, take advice from the maker of the system; in the case of the heating system the maker of the boiler is usually the place to start. It is often the case that they will have approved one or more brands of corrosion inhibitors and cleaning agents. In the UK, the ‘Fernox’ company is generally regarded as one of the benchmark brands of inhibitors and cleansers.
Secondly, one technique you can use to assess the severity of scaling in radiators and heat exchangers is the use of thermal imaging cameras. These will reveal any area which is abnormally hot or cold and may infer severe scale formation
Thirdly, one way of ensuing that you have removed a cleaning agent is to compare the electrical conductivity of the water leaving the system with that of the water entering the system. If the conductivity of the water leaving the system is higher than that going in, it may infer that traces of the cleaning agent are still present and further flushing is required.
Copyright Edotek Ltd 2013