Keywords
Citation
(2002), "Galvanizing in scotland lasts longer", Anti-Corrosion Methods and Materials, Vol. 49 No. 1. https://doi.org/10.1108/acmm.2002.12849aaf.003
Publisher
:Emerald Group Publishing Limited
Copyright © 2002, MCB UP Limited
Galvanizing in scotland lasts longer
Keywords: Galvanizing, Coatings
Galvanizing in Scotland is lasting longer and longer, and that's official! ....
UK Government figures show that the levels of atmospheric pollution North of the Border have dropped dramatically over the last decade, as in the rest of the U.K. Consequently galvanized coatings are lasting much longer. This we are informed has been confirmed by an extensive two-year survey.
The findings follow a comprehensive Zinc Millennium Map Project carried out jointly throughout the UK and Ireland by Galvanizers Association and the Agricultural Development Advisory Service (ADAS).
It shows how, as there has been a steep reduction in sulphur dioxide (S02) levels in the air, so zinc corrosion rates have fallen.
This in turn has significantly raised the life expectancy of steel that has been hot dip galvanized for rust-free protection: it is atmospheric S02 which mainly determines the rate at which the essential raw material for galvanizing - zinc - will corrode on steel structures.
Stephen Milnes, director and general manager at Scottish Galvanizers, one of the largest galvanizer in Scotland, commented: "We know that a typical galvanized heavy steel structure, outside with average pollution levels, might now have a corrosion-free lifespan of up to a hundred years.
"A new galvanized steel bridge had a life expectancy of 38 years when it was built in 1990. But, because the atmosphere is getting cleaner, that same bridge can now be expected to last at least 55 years."
Similar surveys were carried out by ADAS in 1986 and again in 1991. The results are determined by how atmospheric pollution has reduced the weight of a sample of zinc in a year - and the better the atmosphere, the lower the corrosion rate is, so the lower the weight loss.
A special Zinc Millennium Map has been produced to show the new findings. It is divided into 10km squares, shaded in different colours, to depict the relevant figures at-a-glance. The figures are averages and depict "background" corrosion rates - they do not account for local conditions such as someone throwing salt on the galvanizing.
The lifetimes (in years) of an average galvanized coating (85m) in urban Scotland are shown in Table I.
For the 'mechanics' of the new survey, small zinc canisters were weighed and mailed to volunteers in different environments in different parts of the UK.
The canisters were located outside above the ground for a period of two years. The canisters were then returned to the organizers and re-weighed to determine how much zinc had been eaten away by the atmosphere over the two-year period.
"Global warming may be having a changing effect on our climate, but it's now a proven fact that zinc corrosion rates are coming down!" said Stephen Milnes.
He believes a mixture of factors have led to rapid falls in S02, or "acid rain", in the air - including environmental protection measures, legislation on industry, lead-free petrol, and the switch away from coal-fired power stations.
Scottish Galvanizers Ltd, of MacLellan Street, Glasgow, serves customers throughout Scotland. The company is a member of UK- wide Wedge Group Galvanizing, which has plants in 16 different locations, and the ability to handle pieces as diverse as washers 1.6 millimetres thick right up to structural steel 29 metres long, with quality assurance to BS EN ISO 1461.
1986 | 1991 | 2000 | |
Edinburgh | 22 | 27 | 57 |
Glasgow | 22 | 27 | 57 |
Aberdeen | 22 | 34 | 34 |
Inverness | 34 | 42 | 42 |
Perth | 26 | 42 | 57 |
Dundee | 26 | 42 | 57 |
Table I
Details available from: Scottish Galvanizers Ltd. Tel: +44 (0) 141 427 3041; Fax: +44 (0) 141 427 4981; E-mail: scottish@wedge-galv.co.uk