A semi-empirical model predicting the life of cathodically protected 0.15 % C steel under conditions of water-borne erosion from suspended solids in potential UK tidal barrage draught tube wall applications, has been developed. The model has shown that the erosion rates of mild steel are sufficiently low for this application. Upstream of the runner blades, predicted wear rates are insignificant. In the section including, and downstream of, the runner blades, wear rates are higher owing to the swirl component in the flow. Over the 120-year design life of the barrage the model predicts a maximum worst case wear of only 28 mm adjacent to the runner blades, failing to around 2 mm, some 15 mm downstream of the runner blades. Empirical relative life models for dioritic and quartzitic concretes and the 0.15 % C steel show that the erosion resistance of steel is very significantly better than that of the concretes over the full range of conditions encountered in the draught tube. Relative life values for these conditions based on 0.15 % C steel life = 1.0, range from 0.003 to 0.100 for the quartzitic concrete. Under some draught tube conditions, the wear resistance of harder quenched and tempered low alloy steels can be up to 2.5 times greater than that of mild steel. The application of polymer coatings to the steel surface for corrosion protection, either alone or in combination with cathodic protection systems, is also able to significantly enhance steel life. Elastomeric polyurethanes had up to eight times the wear resistance of mild steel making these highly suitable for this application. However, some of the less wear resistant, lower cost coating materials examined could also be considered, depending on the position of application in the draught tube. Erosive wear has been seen to be highly sensitive to operating parameters including erodent particle shape, speed, approach angle and concentration. Steels wore by plastic flow and cutting mechanisms, whilst for concrete, wear takes place largely by brittle fracture processes. Polymers too exhibited classical erosive wear ductile-brittle behaviour. Mild steel, with a polymeric coating and/or cathodic protection, a very cost-effective and reliable solution for tidal barrages.
Erosion-corrosion in steels for tidal power generation
Erosionskorrosion von Stählen in Gezeitenkraftwerken
1998
170 Seiten, 62 Bilder, 50 Tabellen, 19 Quellen
Report
English
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