Zinc Millenium MapZinc Millenium Map

The Definitive Geographical Guide to the Differential Corrosion Levels of Galvanised Steel Construction Products

You can visit the Zinc Millennium Map website HERE.

These findings have a particular significance for those with responsibility for sanctioning construction projects where whole life costs, longevity and maintenance are important considerations.

For most sites on this map, an average hot dip galvanized coating will last between 40 to 100 years highlighting the potential for significant financial savings when galvanizing is specified.

Hot dip galvanizing, in conjunction with its many other benefits including lowest life time cost, reliability and coating toughness, is the most effective corrosion protection system available.

The resistance of galvanizing to atmospheric corrosion depends on a protective film which forms on the surface of the zinc. When the steel is withdrawn from the galvanizing bath, the zinc has a clean, bright, shiny surface. With time this changes to a dull grey patina as the surface reacts with oxygen, water and carbon dioxide in the atmosphere. A complex but tough, stable, protective layer is formed which is tightly adherent to the zinc. Contaminants in the atmosphere affect the nature of this protective film.

The most important contaminant for zinc is sulphur dioxide, SO2 and it is the presence of  SO2  which largely controls the atmospheric corrosion of zinc.

The corrosion rate for zinc is generally linear for a given environment. A major advantage of this is that it allows predictions of ultimate life to be made on the basis of interim
assessments of coating thickness.

The Zinc Millennium Map is the latest in a series of maps showing zinc corrosion rates under atmospheric exposure. Initially data was gathered over England and Wales (map published in 1982) and then across the UK (maps published in 1986 and 1991). This latest update includes the Republic of Ireland for the first time.

Early work on determination of atmospheric corrosion rates for zinc were made by Mr T Shaw, during extensive testing to determine the acidification of the atmospheric environment across the UK (Corrosion Map of the British Isles (1972) Shaw T. R. Construction Industry and Research and Information Association (CIRA), London). The acidification level was determined from, amongst other things, the weight loss of zinc reference canisters from sites. A test regime ASTM STP 646: 1978 was developed by Shaw to determine the acidification in particular areas. Zinc corrosion rate data was calculated from these weight loss results.

A modified form of this simple method has been used once more to collect zinc corrosion rate data for 1998 - 2000 from around 1000 sites to create the Zinc Millennium Map.

The zinc corrosion rate results from reference canisters throughout the UK and the Republic of Ireland have been used to establish background corrosion rates for 10km x 10km square grids (limited data for Ireland)

Corrosion rates for each 10 km square have been calculated from scattered data using the "Thiessen" method (see Agricultural Development Advisory Service - ADAS Consulting) Project Report available through Galvanizers Association.

Acknowledgements

  • Agricultural Development Advisory Service (ADAS Consulting) for project management
  • Mr Tom Shaw for consultancy services throughout the project and for application of the Thiessen method to the project data
  • Britannia Zinc Limited for provision of laboratory facilities
  • Mr John Curtin (consultant) and Mr Michael Taylor (Britannia Zinc Limited)
    for valuable project assistance
  • All those who provided sample sites for the project

Cartographic reproduction by Lovell Johns Limited
Copyright : Galvanizers Association 2001
Based upon the Ordnance Survey 1:1,500,000 map with the permission of the controller of The Stationery Office.

Galvanizers Association wishes to thank ‘The Engineering Industries Directorate’ of the DTi and the National Corrosion Service for their assistance.

ADAS Consulting and GA are grateful to Orange Plc for provision of survey sites in the UK and the Irish Electricity Supply Board for survey sites that allowed corrosion rates at key Irish locations to be included in the Zinc Millennium Map. Further studies are planned to extend survey coverage in the Republic of Ireland. For areas not yet covered, the rates indicated for comparable areas may be used as an indication of likely corrosion rates.