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Fig. 3. The internal surface of a tube showing extensive pitting (x 3)

Fig. 4. The EDS results of the greenish-white deposits found on the internal surfaces of the tubes.

3. METALLOGRAPHY

Samples from the tubes examined were prepared for metallographic analysis using standard
grinding and polishing techniques. Etching was carried out in acidified ferric chloride. The typical
microstructure observed in all cases consisted of large equi-axed grains, indicating that the tubes
were in the annealed condition.