The early tests showing the advantages of weathering steel were carried out in the USA using a particular grade of weathering steel called Cor-Ten A. In the grade used in bridge construction, Cor-Ten B, the alloying composition was altered and in tests carried out by the British Steel Corporation in the UK the B grade corroded at a higher rate than the A grade. Also, corrosion rates in the UK were generally higher than those measured in the USA.
At Thorney Island there was considerable variation in the corrosion rate of the different sheltered
specimens for both steels. The I-section specimens corroded far more than the others but these were positioned in a different bay from the weight loss coupons. The coupons attached
to the web also gave much lower corrosion rates than the specimens placed on racks. The web
specimens faced in one direction only whereas the rack specimens were corroding from both sides. Agreement between the two methods of measurement presupposes that there is no major
effect of direction on corrosivity. However at marine sites the main influence on corrosion is wind borne chlorides from the sea so that the prevailing wind direction could be of importance. The specimens attached to the web faced away from the prevailing wind. To check whether this could account for some of the variation in the results further sets of specimens were exposed on each side of the web along with a further set of rack specimens.