TURBINE GENERATOR windings are cooled in a closed air cooling system, employing water-cooled copper tubes. To maintain a high heat transfer efficiency the tubes are cleaned every few weeks to remove scale deposited from hard cooling water. A 16 to 20 percent solution of hydrochloric acid, inhibited with one percent of a commercial acid inhibitor, is flushed through the system until removal of scale is complete.
The tubes began to leak within a year after the removal of scale was begun with hydrochloric acid solution. Inspection indicated that the leakage was caused by excessive corrosion on the interior of the tubes, apparently from attack by the acid.
Although copper is not fully resistant to hydrochloric acid, the rate of attack ordinarily is not excessive at concentrations up to about 24 percent. (The exact rate varies appreciably with the degree of aeration.) Figure I shows that in 18 percent unaerated hydrochloric...
