Causes and Prevention of Corrosion: IN TAR STILLS

Although the importance of the problem of corrosion of tar stills has diminished over the past 20 years with the replacement of mild‐steel pot‐stills by continuous tube stills, it remains a problem of some magnitude. In 1934, Mann and Parkes estimated that the average cost per ton of tar distilled due to corrosion was 4d. Considering the rise in costs of both materials and labour over the past two decades, this figure will be nearer 1s. a ton today and since, at present, rather more than a million tons p.a. are processed in pot‐stills, the cost to the industry on this score alone is of the order of £50,000 p.a. When one adds to this the cost of stoppages and plant replacements due to wastage of continuous pipe stills, which have their own corrosion problems, and the cost of alkali addition which is almost universally practised on continuous plant as a corrosion prevention measure, the total cost to the tar distilling industry almost certainly runs into six figures.