Long-term marine corrosion of welds on steel piling

Welds on mild and low alloy steels exposed to the marine environment are known to be prone to high levels of corrosion. Pitting usually is the critical form of attack. Quantification of the relative and absolute maximum pit depths that occur is important for predicting future and remaining structural life but longterm data is scarce. The present paper reports on a study of the statistical characterization of pit depths measures on longitudinally welded steel piling exposed for some 33 years in Newcastle harbour. The investigation is based on the hypotheses that the lack of homogeneity at the corrosion interface caused by differences in grain size, grain structure and the potential for pitting to occur preferentially along boundaries is responsible for the observed effects. The pit depth results obtained are compared with the results reported earlier for maximum pit depths measured on welded steel coupons exposed to similar Pacific Ocean 20oC seawaters for up to 3.5 years. It is shown that there is a reasonable degree of consistency between the two sets of results, adding confidence to the possibility of extrapolation of medium term data to the longer term.