Development of high strength low alloy steels for marine applications: Part 1: Results of long term exposure tests on commercially available and experimental steels

Abstract

High strength low alloy (HSLA) steels, both commercially available and experimentally prepared, were immersed at 45 and 90 m depths in the North Sea for periods ranging from 1·6 to 7·2 years. General corrosion, pitting corrosion, and crevice corrosion behaviour were evaluated after immersion. The influence of alloying elements, particularly of carbon (0·01 and 0·15%), aluminium and chromium (0 and 1·5%), and molybdenum (0, 0·5, and 1·5%), was investigated in the experimental series. It was concluded from the statistical analyses that general corrosion properties are influenced beneficially by aluminium and chromium additions and that pitting resistance is detrimentally influenced by aluminium and molybdenum. The general corrosion rates of the best alloys are afactor of 2–4 lower than those of an unalloyed reference steel similar to steel Fe52. It is also shown that this low general corrosion rate can be combined with a low tendency to pitting corrosion. Notwithstanding the lack of a sound statistical basis, the same general trend could be detected in the influence of aluminium and chromium on the commercial steels. However, the effect of alloying elements on pitting corrosion behaviour was not clear. Crevice corrosion presents no significant problems for the present HSLA steels in sea water.