Failure modes carbon corrosion

If carbon or low alloy steel cannot be safely used, corrosion resistant alloys must be evaluated. The production environment must be dupHcated in alloy corrosion tests in the same manner as for carbon or low alloy steels. Standard corrosion tests modified to use the production environment are conducted for the corrosion resistant alloys with due consideration given the probable failure modes, e.g., crevice and pitting corrosion for stainless steels. On completion of this test sequence, the corrosion resistant alloy or alloys to use for tubulars, wellheads, and facilities construction are specified. 

Durability is the capability of a PEM fuel cell stack to resist permanent change in performance over time. A durability failure may not cause catastrophic failure in the fuel cell. However, this mode of failure will decrease the performance of the fuel cell. It also can involve irreversible failures, such as electrochemical surface area reduction, carbon corrosion, etc., and losses mainly related to ageing [12]. 

Failure modes studied included fuel starvation and cell reversal, partial fuel starvation, carbon corrosion, membrane thinning and hole formation oxidant starvation excessive drying and flooding, air and fuel contamination, freeze-start and freeze-thaw degradation. 

This mode of failure is possible in all the copper alloys. The principal environment involved is ammonia. The evidence also exists for other media such as citrates, tartrates, nitrites, sulfur dioxide, carbonates, nitrogen oxides and phosphates to be conducive to a stress-corrosion cracking mode of failure of copper alloys. 

One method of preventing the catastrophic failure of components by chloride SCO would be the use of austenitic stainless steel as an internal cladding. The highly branched mode of any cracking would effectively prevent the development of stress raisers. Carbon or low alloy steel base metal would not be susceptible to cracking in chloride solutions, but some localized corrosion may occur. This type of construction would also provide resistance to cracking when chlorides are hable to contact the outside of the components, as in external insulation, for example. 

---