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Although computational methods have been separately developed to predict corrosion and fatigue crack growth rates for metallic structures, challenges remain in implementing a methodology that considers the combined effects. In this work the output from a galvanic model is used to determine the spatial distribution of corrosion damage; providing a guide for the location of discrete corrosion damage features that can be analyzed using stress fields from structural models. In order to build confidence in this approach the galvanic models are validated by comparing predicted results to surface damage measurements from test specimens subject to ambient atmospheric exposure. There was good comparison between the predicted spatial distribution of corrosion damage and the measured surface damage profiles obtained from the galvanic test specimens. Following this exercise novel computational corrosion damage features were developed to represent simplified cracks shapes emanating from corrosion pits. Stress intensity factors (SIF) for these newly developed hybrid pit-crack features were determined and these solutions compared to cases where the pit is assumed to be an equivalent crack. The impact of the local, cavity induced stress field, on the SIF solutions is discussed. Building on these findings a fatigue crack growth simulation was performed using an initial flaw emanating from a hemispherical cavity (corrosion pit) located at the edge of hole in a plate. A reasonable comparison, of the predicted number of crack growth cycles, to available experimental test results was achieved.
Key words: Galvanic Corrosion, Atmospheric Exposure Measurements, Corrosion Pitting, Fracture Mechanics, Computational Modelling
This paper will present both laboratory and field trial results as evaluated with ASTM D610 for Zn-Ni nanolaminated and comparative coated fasteners and discuss how utilizing ASTM D610 helps to ensure objective, consistent red rust measurements.
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The application of Corrosion Resistant Alloys (CRA) in harsh environments and severe services is gaining a leading position across the Industry. Among the different CRA Duplex & Superduplex stainless steels (DSS) represent an often-interesting choice in terms of cost-benefit ratio. Duplex and superduplex stainless steels as a matter of fact offer a competitive cost excellent corrosion resistance in many environments and good mechanical properties; they are often replacing and upgrading traditional stainless steels by closing the application gap with more noble alloys such as nickel and copper alloys. The quality control of DSS fabrications that involve welded joints cannot underestimate the possible influence of the welding process itself on the localized corrosion resistance of the material. Such alloys are characterized by a somewhat complex metallurgy which involves during welding the possible precipitation of undesirable phases & compounds that can induce an important loss of corrosion resistance in particular considering localized corrosion phenomena (e.g. pitting corrosion).During welding and materials qualification steps the most commonly specified test for checking localized corrosion resistance of CRA in particular in chloride-containing environments is the Ferric chloride ASTM G48 [1] corrosion test. So many End-User material & fabrication specifications have taken up this procedure by incorporating it and often customizing it. This is because the procedure described in the ASTM standard does not cover or define in detail many particular aspects of the test itself. This creates a number of free interpretations of the test procedure that can be associated with more or less severe test conditions and more or less easy-to-reach requirements. It can be useful to remember that the test itself is in any case not a real fitness for purpose test but more a quality control one; it is carried out under very severe conditions often more severe than the actual conditions in which components will be exposed. This also means that even small variations in the test procedure welding variables or welding metallurgy can tip the balance in the pass/fail equilibrium. The purpose of this work is to describe some fundamental aspects of test procedure and results evaluation somehow customizable with respect to the ASTM standard which may influence the test outcome itself also considering a possible review of the standard toward a more unified procedure. In this context taking into account that manufacturers find themselves in need to optimize the welding process with the aim to overcome G48 corrosion test during qualification the work also describes typical issues related to welding that could induce a negative verdict of ferric chloride pitting test.
Understanding environmental conditions experienced during shipping (both domestic and export) and/or storage is critical when determining the most effective corrosion control system for metal components. Temperature and humidity sensors were used to help understand the conditions within industrial packaging applications during different overseas shipping routes and during warehouse storage. The effect of secondary packaging (i.e. polyethylene film) on temperature and humidity within a package was also evaluated. The scope of this paper is to compile and analyze the data and utilizing it to help develop the best corrosion prevention strategies.Key words: Sensor corrosion control packaging overseas shipping