The corrosion of welded or coated mild-steel and of wrought-iron boiler tubes in highly saline water 1

The paper describes an investigation, in collaboration with the British shipbuilding Research Association, on the corrosion of electrical resistance welded and of coated seamless tubes in sea-water using model fire-tube boilers. Previous results and the experimental equipment have already been fully described elsewhere.

Welded tubes are susceptible to deep pitting and perforation particularly in the weld region and, in marked contrast to previous results with seamless tubes, this is not reduced by increasing the copper content of the steel. Possible reasons for this difference in behaviour are discussed.

The corrosion of mild-steel tubes is markedly reduced by chromizing or phosphating but not by aluminizing or aluminium spraying. No pitting was observed on chromized tubes but these tubes had unsuitable mechanical properties, having a tendency to split on expansion into the tube plates. There is some evidence that the protection afforded by phosphating is of a temporary nature.

No wrought-iron tubes were available for experiment but several tubes with a long service life have been examined. Possible reasons for this extended life are discussed.