Corrosion Inhibitor

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Corrosion Inhibitor is used in the water in Hot Water ("Hydronic") Central Heating systems to protect ferrous components of the system (including steel radiators and cast-iron boiler heat exchangers) from corrosion caused by the action of oxygen dissolved in the water.

Corrosion inhibitors vary in price from about £5 to £15 (for a quantity intended to protect an average domestic installation). The chemistry of corrosion and corrosion-inhibition is, presumably, well known, so one would expect the various different makes of inhibitor to be pretty much equally effective. Unfortunately simple experiment suggests otherwise.

Corrosion Inhibitor test

Test method

  1. Four bottles were filled each with a similar quantity of water and similar number of (already slightly rusty) nails.
  2. Inhibitor was added to each of the bottles in the concentrations recommended by their manufacturers.
  3. The inhibitors used were:
    • Fernox MB-1
    • Sentinel X100
    • Purimachos Protex
    • none (control)
  4. The bottles were then placed together in a warm place (the back of an airing cupboard)
  5. Six months later the bottles were examined


Corrosion Inhibitor test - Fernox 040314.jpg Corrosion Inhibitor test - Protex 040314.jpg Corrosion Inhibitor test - Sentinel 040314.jpg Corrosion Inhibitor test - none 040314.jpg


Fernox Corrosion Inhibitor test - Fernox (2) 040913.jpg Corrosion Inhibitor test - Fernox (1) 040913.jpg
Protex Corrosion Inhibitor test - Protex (2) 040913.jpg Corrosion Inhibitor test - Protex (1) 040913.jpg
Sentinel Corrosion Inhibitor test - Sentinel (2) 040913.jpg Corrosion Inhibitor test - Sentinel (1) 040913.jpg
none Corrosion Inhibitor test - none (2) 040913.jpg Corrosion Inhibitor test - none (1) 040913.jpg

Further work

  • Other brands of inhibitor (e.g. Tower, CalChem; seen on the market since this test was carried out) could be tested.
  • The test could be repeated with the addition of copper (and perhaps other materials) to the mix to see if these either affect the effectiveness of the inhibitors or (especially in the case of Aluminium etc) suffer corrosion themselves.
  • Samples of limescale (e.g. scaled-up pipe or fittings) could be introduced to see whether any inhibitor has actual descaling properties.
  • More air could be introduced to the test samples periodically and the samples monitored over a longer period to see how well each inhibitor copes.
  • This and similar tests could be repeated by other people. The original tests were carried out by John Stumbles during 2004.

External links

uk.d-i-y thread including discussion of composition of corrosion inhibitors