Seawater hydrogen embrittlement

Figure 11.18 Reduction in area as a function of the strain rate for type AISI 4340 steel subjected to cathodic polarization in seawater leading to hydrogen embrittlement (o) polarization of 0.76 V ( jpolarization of 0.61 V. The grey zone shows values typically found in air.

The described behavior applies only if crack propagation involves anodic dissolution at the crack tip. If local hydrogen embrittlement is the cause of cracking, there is no lower hmit, since the crack tip is not blunted by corrosion. Figure 11.18 shows experimental measurements taken on a steel specimen, subjected to cathodic polarization at two different potentials, in artificial seawater. The results indicate that hydrogen embrittlement of the metal occurs under these conditions. 

Figure 11.19 Stress-strain curve of cold rolled steel with and without hydrogen embrittlement (a) stress-strain curve measured in air with a strain rate of 10 mm s (b) stress-strain curve measured in seawater in the presence of H2S at a strain rate of 10 mm s . ...

Figure 11.26 Effect of potential on crack propagation rate of high strength steel (1190 Mpa) susceptible to hydrogen embrittlement in seawater at ambient temperature [12],...

In general, cathodic protection can be applied to any material susceptible to corrode, but this method is commonly used to protect carbon steel stmctures in diluted or alkaline electrolytes, such as seawater and soil The corrosion mechanism of iron or carbon steel was introduced in Section 13, Chapter one and Chapter four. Nevertheless, the corrosion product may be an unstable ferrous hydroxide [Fe OH) solid compound, which reacts in the environment to form ferric hydroxide compound [Fe (OH) ] or hydrated ferric oxide (FezOs-SH ) known as mst. The formation of this corrosion product is avoidable using cathodic protection. However, careful application of an external potential to a structure must be considered because hydrogen evolution may be induced leading to destmction of any coating and Hydrogen Embrittlement [1]. 

This alloy may be susceptible to hydrogen embrittlement under some conditions. Custom 455 should be considered when ease of fabrication, high strength, and corrosion resistance are required. Custom 455 alloy is suitable to be used in contact with nitric acid and alkalies. It also resists chloride SCC. Materials, such as sulfuric acid, phosphoric acid, hydrochloric acid, hydrofluoric acid, and seawater will attack custom 455. 

Ignored by most implementations of the CCS framework, ohmic drop can not only lead to passive-to-active transitions, but also can, in the context of environmental cracking, make hydrogen evolution, and therefore embrittlement, more viable at the crack tip. The IR framework has been successfully demonstrated in several model metal/environment systems [34, 35], and has been invoked to rationalize the practically important case of the crevice corrosion of Alloy 625 in chlorinated seawater [32, 33]. 

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