Band 30, Heft 5-6

The concept of time of wetness (TOW) is extensively used in the atmospheric corrosion disciplines for such purposes as corrosion prognostics and environmental corrosivity classification. Time of wetness can generally be defined as the amount of time a metal surface remains wet during atmospheric exposure. Although the basic concept and importance of TOW in governing atmospheric corrosion is generally agreed upon, what is meant by “wet” has generally remained ambiguous and its practical determination has been widely varied throughout its history. The objective of this review is to demystify TOW in terms of definition and measurement and identify issues that inhibit this parameter from providing deeper insight into the effect wetness duration has on atmospheric corrosion. Specifically, this paper summarizes the current state of TOW determination methods along with the parallel concept leaf wetness used in environmental science. Furthermore, wetting and drying phenomena associated with atmospheric corrosion and thought to control TOW are overviewed. From this framework, current issues and limitations of TOW are identified and avenues for further improvement suggested.

The external surfaces of all underground oil and gas pipelines are protected by polymeric coatings and cathodic protection. The polymeric coatings are classified under two types: mainline coating and girth weld coating. Most of the modern mainline coatings are applied in the mill as line pipes are made. The mainline-coated line pipes are shipped to the construction site where they are joined by welding. Over the weld joint – commonly known as girth weld – coatings are applied in the field. The mainline coating, girth weld coating, and cathodic protection all should function in a complementary fashion. The standards developed by various associations for evaluating and selecting mainline coatings were previously reviewed. In this article, three international standards for girth weld coatings developed by the Canadian Standards Association, National Association of Corrosion Engineers, and International Standards Organization have been reviewed and compared with those for mainline coatings. It should be noted that in addition to these international standards, other country-specific standards are also available.

The rupture behavior of an anodized aluminum surface was investigated in a borate buffer solution using an in situ micro-indentation test, in which transients of the indentation load and flowing current were monitored during loading and unloading of a sapphire indenter. A pair of anodic current peaks emerged during both downward and upward drives of the indenter due to rupture and repair of an anodic oxide film. The total area of film ruptured during both drives, as well as the area of radial cracks, increased with an increase in film thickness and with a decrease in electric field applied while an area of circular cracks was almost constant. It was suggested that the film–rupture owing to radial cracks formation was enhanced by tensile stress accumulated in the anodic oxide film by thickening of the oxide film and lowering of the electrostriction.