Atmospheric pitting corrosion of stainless steel

Mohammed Ali, Haval Bashar (2016). Atmospheric pitting corrosion of stainless steel. University of Birmingham. Ph.D.

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Abstract

Atmospheric pitting corrosion of austenitic stainless steels 304L and 316L under droplets of MgCl2 have been studied under conditions of relevance to long-term storage of nuclear waste containers using automated deposition of arrays of droplets.

The effect of microstructure on the morphology of atmospheric corrosion pits in 304L stainless steel plate was investigated. The presence of retained delta ferrite was found to influence the morphology of pits. Ferrite bands were preferentially attacked, and pits were found to have layered attack morphology dependent on the rolling direction and plane of the metal surface.
Solution annealing of stainless steel resulted in ferrite reduction and formation of faceted pits.

Pits can grow with an initial shallow dish, which may propagate via ‘earring’ or small satellite pits. The size and morphology were seen to vary with exposure humidity, chloride deposition density and distance from the droplet edge.

Pits propagated readily above chloride densities of ~10-4 µg/cm2, depending on alloy and exposure time. Below this value much smaller pits were observed due to a discontinuous solution layer.

The formation of secondary spreading and micro-droplet formation was observed for MgCl2 droplets on stainless steel when pits form close to or at the droplet edge. Small pits developed beneath these micro-droplets at lower humidities.

This work provides a basis to make recommendations for long-term storage conditions of intermediate nuclear waste (ILW) in order to minimise the risk of pitting corrosion.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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