The influence of frequency of alternating or infrequently reversed current on electrolytic corrosion

This paper describes experimental work done to determine the coefficient of corrosion of iron and lead in soil with varying frequencies of alternating or reversed current with 60 cycles per second as the highest frequency and a two-week period as lowest — some d-c. tests being made as a check on the methods. The results show (1), that a decrease of corrosion occurs with an increase in frequency; (2), that the corrosion is practically negligible below a five-minute period; (3), that there is, a limiting frequency above which practically no corrosion occurs; (4), that certain chemicals affect the natural and electrolytic corrosion of the two metals quite differently; (5), that the loss of lead in soil on direct current is about 25 per cent of the theoretical loss; and (6), that alternating or reversed current with as long periods as a day or a week would in the case of iron materially reduce the damage to underground structures. The importance of these results grows out of the fact that there are large areas in practically every city in which the polarity of the underground pipes reverses with periods ranging from a few seconds to an hour or more due to the shifting of railway loads. The investigation shows that the corrosion under such conditions is much less than has generally been supposed.