Sunday, 30 July 2017

Heating System Water & Corrosion Prevention




All I see these days in trade magazine and merchants is magnetic filters, chemicals, chemicals and some more chemicals, every page you turn in a trade magazine has either an advert for magnetic filters or chemicals, or an article telling you how important inhibitors are to the system, well I say "utter nonsense" 

Lets set some facts, todays heating systems are sealed, this means they are sealed from outside influences, including oxygen, now for corrosion to occur oxygen must be present, No oxygen = No Corrosion, so why do we need inhibitors, well in my opinion, we don't, inhibitors create a false layer on the metal components, well in the presence of water metals will create their own natural layer to protect themselves, this is called passivation of the metal,The passivation of metals is the process, when metals protect themselves against further corrosion with a thin oxide layer. The metal becomes passive and is not oxidised any further.

The problems occur with poor design and the use of poor quality materials, inhibitors and magnetic filters are in my opinion there to cover for poor quality installations, whereas we should be looking to increase knowledge and standards, also I have been to many systems that have inhibitor that are still corroding.

Lets look at other points that need to be monitored in a heating system, but are generally ignored, The pH of the heating water should be in a range of 8.2 to 10, but only 8.2 to 8.5 in presence of aluminium alloys. The function of the pH in heating systems is one of the most important factors for means of corrosion protection. with the recommended pH range the metals in the system can basically build up their natural oxide layers and keep them stable to be protected against further corrosion. As long as this mechanism is not disturbed for example incorrect pH, a high electrical conductivity, a high oxygen concentration or erosion, the formation of natural oxide layers provides a safe protection of the metals against further corrosion

Electrical conductivity, the acceptable electrical conductivity in heating systems water has to be seen in conjunction with the amount of dissolved oxygen. If there are only traces of oxygen (y0,02 mg/l) dissolved in the heating water, then the system can tolerates an electrical conductivity up to 1.500 µS/cm. But at higher concentrations of dissolved oxygen the electrical conductivity should be limited to <100 µS/cm.



In the UK the British Standard BS 7593:2006i which deals with water treatment, is very very basic and my German Colleagues actually find it laughable, in Germany, Austria and Switzerland they deal with the subject in a much more in depth manner, the German method, which I follow, in respect to heating water treatment with chemical agents the statement of the VDI 2035 is in contrast to the British Standard that such agents should only be used in limited cases by professionals with the necessary chemical education. According to VDI 2035 there is no need for chemical agents as in a well-planned operated and maintained system, with a favourable water quality, no damages caused by lime-scale and corrosion are to be expected.
I could go on, this is a big subject and it is a big passion of mine, there is a lot to cover, so I won't go on, as people lose interest quite quickly when reading blogs, but I do find it encouraging to see many installers are starting to realise there is more to controlling corrosion and I have seen a lot more installers using quality de-aeration devices, which is great, but for those who may not fully understand a de-aeration device is NOT an automatic air vent, they are very different things, an AAV should only be used for filling and venting, after these uses they should be closed, as they can and do ingress oxygen, a de-aeration device which should be fitted on the hottest part of a system, these are microbubble separators. With de-aeration of the system, the remaining carbon dioxide can be vented and thus the pH can rise to a preferable level during normal operation
I am looking at running seminars and trade breakfast mornings at Trade Merchants that may be interested
Please feel free to leave a comment if you have any questions that need answering
This blog is mainly to let you know there are other methods to system corrosion control in heating systems, there are lots of solutions out there, but I can supply products from Germany from Elector, a company I work very closely with 




2 comments:

  1. Excellent article Chris. We are fighting against vested interests who make lots of money selling chemicals and standards setters who are still living in the dark ages.

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  2. This is a fantastic article. Chris (vietec) has been highlighting this issue for many years now...some installers have now started to appreciate the importence of good system design. It is so, so sad that boiler manufacturers have never promoted deaeration but instead promoted chemicals and magnatic cleaners. You would think that the companies involved with the heart of a heating system would be getting it right...the consumers loose out...the installers get blamed and manufaturers keep manufacturing. Well done Chris, a very important article.

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