| Abstract |
The erosion corrosion of carbon steel steam pipelines at Wairakei steam field and power station, first observed in the 1970's has been attributed to a reduction in separated water separators being present in the steam lines. This led to improvement in steam condensate quality and erosion corrosion rates of up to 0.5 that seriously threatened to diminish the life of pipelines expected to last in excess of 20 years. Initiation of corrosion can be attributed to wet shutdown conditions leading to acid dissolution of the normally protective magnetite film and dislodging of the film from condensate under operating conditions or to slow dissolution of magnetite in high purity water. Injection of separated geothexmal water into each steam pipeline has proven effective in controlling the corrosion by stabilising magnetite filmsand allowingthe formation of new films on the previously corroding patch-like areas. Dissolved silica has been identified as the principal corrosion inhibitor, although the mechanism for the corrosion control remains elusive. Steam turbine silica scaling and the potential for chloride induced corrosion are controlled by ensuring that the chemical and thermodynamic conditions which exist withinsteam pipelines, the header and turbine inlets are such that concentrating mechanisms are avoided. Erosion in power station headers, where the steam quality is controlled, for protection of the turbines, remains as a maintenance problem. |