The hydrogen permeation of low alloy high strength steel at splash zone and the mitigation effect of a wrapping protection technique

摘要

The corrosion of steel at marine splash zone is the most severe. Due to the characteristics of this zone, the surface of the steel cannot be completely dry especially after the formation of corrosion products. Experiments show that a pH as low as below 3 can be obtained beneath corrosion products at constant wetting conditions and a fairly low potential is achieved. These conditions enable the H~+ reduction as part of the cathodic reaction except O_2 reduction and then facilitate the hydrogen entry. It was found that under same cathodic polarization potentials, the hydrogen permeation current and the total hydrogen permeated through the corrosion products covered specimens at a fixed time period are higher than those without corrosion products. High strength steel has a high SCC and HE sensitivity. This must be considered for high strength steel. A wrapping protection technique was developed in our laboratory for the corrosion protection of marine splash zone corrosion. This technique has the advantage of easy implementation not only for new structures but also for structures that have already suffered some extent of corrosion. The technique has been proved to be effective in reducing the corrosion rate at splash zone, but the effect of mitigating the hydrogen entry particularly for the corroded structures is unclear. If the technique has not only the ability in reducing the corrosion rate but also the ability in reducing the hydrogen entry, it would be very promising. Wrapping protection layers were applied to new and corroded specimens and then experiments were conducted to record the hydrogen permeation current under simulated seawater splash conditions. The hydrogen permeation currents of both the new and corroded specimens were greatly reduced. Slow strain rate tensile tests showed that the elongation of wrapped specimens without corrosion products under seawater splash conditions was close to that in air. The elongation of corroded specimens after wrapping was also larger than that without wrapping. It is concluded that the wrapping technique has potential applications in mitigating the hydrogen entry except corrosion prevention at marine splash zone.