On the Corrosion of Sea Water Pipes

Abstract

In this paper authors give the information in designing sea water pipes and their fabrication in relation to the corrosion, that is, about the investigation on corrosion tests and the cause of corrosion suffered by the solder wiped copper pipes and plain copper pipes. Authors also express the results of the investigation on the corrosion rate of steel pipe and galvanized steel pipe joined in series through which passed sea water involving air bubbles and also on the state of galvanic corrosion in a case a steel pipe and a copper pipe were joined. The followings are the particulars of the investigation. 1) The cause of pitting that developed on solder wiped copper pipes in a very short time was due to the production of noble copper tin alloy in the boundary of the copper-solder. Experimentally it was ascertained that the potential of this alloy rapidly roses in the percentage, copper-tin contents 50-50, and becomes nobler than the copper. Copper pipes also corrode sometimes within comparatively short time, but such is mostly erosion. Ships now tend to be built much larger and of much higher speed, under such circumstance, the mixture of air bubbles in sea water is bound to become higher in percentage and which is assumed to be one of the causes of the promotion of corrosion. 2) Under such unfavourable condition, the galvanized steel pipe seems to be highly resistant to erosion and at the same time to have sufficient resistibility against corrosion. At the corrosion test of pipes with running sea water about one month, the corrosion rate of galvanized steel was unexpectedly small. 3) The development of galvanic corrosion, when a copper pipe and a steel pipe were connected, was limited within a close neighbourhood of the connection, and is concentrated within the range of, in a still water about 2-3 times of the diameter and in running water about 1.5 times of the diameter. To insert a zinc anode at connection is very effective, but just for the purpose of eliminating galvanic corrosion, Swedish iron (pure iron) serves the purpose just as well.