640 publications from this institution
After more than 75 years continuous exposure to the Pacific Ocean waters on the Queensland coast, the 879 reinforced concrete driven piles that supported the superstructure of the Hornibrook Highway Bridge appeared to be in remarkably good condition when the bridge was demolished during 2011–2012. Detailed investigations revealed excellent, very hard concrete with pH values still around 12 and very little evidence of serious corrosion of the steel reinforcement. The concrete chloride content at the reinforcement was considerably more than the usually accepted limits. However, a few isolated occurrences of very severe localised reinforcement corrosion were found during demolition even though there was little visual external evidence. Possible reasons for the various observations are discussed, together with the practical implications.
Microbial corrosion of reinforced concrete sewer pipes is a global problem costing billions of dollars annually. In Australia a collaborative research project involving numerous industry and university bodies is underway to better understand the key in-sewer processes that drive the corrosion process. Results from an extensive program of field and laboratory work are reported which confirms that the corrosion process involves three stages. The timing and corrosion characteristics of each stage, as indicated by the early observations, are discussed.
The Monte Carlo method and its refinements can deal with quite general reliability problems. Thus the random variables may each have any appropriate probability density function, the limit state functions need not be linear and there may be many of them. The brief overview of some of the Monte Carlo possibilities given here will indicate the significant advantages they can have over other techniques. For problems which involve load processes, it is necessary, usually, to solve a stochastic load combination problem. A more direct approach is to use the concept of vector process outcrossing. Although difficult to solve analytically, recent progress has been made in using simulation techniques and this will be outlined. This type of approach is being explored at present also for use in problems in which there is time or load-cycle deterioration of material strength.
This paper describes the corrosion loss profiles of 1m long vertical steel strips attached to a raft and exposed for 1 year in calm natural seawater on the Australian eastern seaboard. The upper parts of the strips were exposed to the atmosphere and the lower parts immersed to depths varying from 0.3 to 0.9m. It was found that, irrespective of the precise ratio of atmospheric/immersion exposure, corrosion in the splash zone was much higher than that at the waterline and in the atmosphere. There was also significant corrosion in the immersion zone, immediately below the waterline, consistent with classical observations. Above the water line there was only moderate variability in corrosion between the strips but there was much greater variability in corrosion loss for the parts of the strips fully immersed. Mass loss observations are compared with observations of the corrosion and pitting patterns observed in the various zones. Potential reasons for these observations are considered. The observations have implications for explaining aspects of accelerated low water corrosion (ALWC).
The bounds calculated herein, based on the application of the static theorem and mathematical programming, form an alternative to bounds derived on the basis of collapse modes (kinematic theorem). Although semi intuitive techniques do appear to be capable of predicting the system reliability index for parallel systems when the kinematic theorem is invoked, there remains an element of uncertainty regarding the correctness of the result obtained. Exact calculation involves enumerating very many combinations of collapse modes for all but very simple problems; the technique outlined herein involves fewer variables and limit state equations, but is less accurate.
No abstract is provided for this article.
The present paper reports on four-year field investigations aimed at ascertaining internal corrosion rates for offshore wind-power generation monopiles, despite these being designed to obviate internal corrosion through oxygen exclusion. Results for mild steel strips within the enclosed, quiescent, uPVC simulated seawater environments are presented as a function of relative to mean tide level, period of exposure and localised pollution of seawater. Detailed pit depth measurements are also reported for various exposure periods, with the magnitude of such corrosion displaying a bi-modal behaviour as a function of exposure time, consistent with much other data. No evidence was found of the classical corrosion profile for vertical steel structures (e.g. piles) or of accelerated low water corrosion usually associated with microbiologically influenced corrosion caused by elevated seawater nutrient concentrations. It is proposed that the observed corrosion behaviours primarily are the result of the shielded quiescent environment. The practical implications are briefly discussed.
This paper presents an overview of the principal features of the recently developed model for the short and the long-term marine corrosion of steels. In marine environments such as immersion, tidal and coastal atmospheric, chlorides conventionally are considered to play a major role in causing corrosion loss. The actual corrosion process is considerably more complex and besides oxidation by dissolved or atmospheric oxygen there is an important influence from the metabolic products of sulphate-reducing bacteria. The model also deals with temperature, oxygen availability, pollution and various other influences. Although the fundamental corrosion processes are all electrochemical in nature, the model does not deal specifically with these. Instead the model is built around the governing corrosion-rate controlling processes. For engineering purposes the rate of loss of material is the critical issue. The main emphasis is on the behaviour of structural and other low alloy steels. The paper closes with some observations about the applicability of the model to stainless and weathering steels and its recent extension to reinforcement corrosion in concrete structures. RÉSUMÉ Cet article présente une revue d'ensemble des principales caractéristiques des modèles récemment développés pour la corrosion marine des aciers à court et long termes. Dans des environnements marins tels que l'immersion, le marnage et l'atmosphère côtière, on considère usuellement que les chlorures jouent un rôle majeur pour la perte de matériau. On montre que les processus réels de corrosion sont considérablement plus complexes et qu'audelà de l'oxydation par l'oxygène dissous ou atmosphérique, il y a une grande influence des produits métaboliques des bactéries sulphoréductrices. Le modèle tient aussi compte de la température, de la disponibilité de l'oxygène, de la pollution et d'autres influences diverses. Quoique les processus de base de la corrosion soient tous électrochimiques par nature, le modèle est plutôt bâti autour des processus qui contrôlent le taux de corrosion. Pour les applications en ingénierie, le taux de perte de matière est la question clé. L'article se termine avec quelques observations relatives à l'applicabilité du modèle pour les aciers inoxydables et il trace quelques pistes de recherche pour la corrosion des aciers du béton armé. KEYWORDS: corrosionsteelmarinemodelsmathematical modelsMOTS-CLÉS: aciercorrosionenvironnement marinmodèlesmodèles mathématiques
In the reliability estimation of complex structures, response surface methodology has been suggested as a way to estimate the actual but implicit limit state function. Typically the response surface is constructed from a polynomial function and fitted to the implicit function at a number of points. The location of these points has been noted as being an issue but the effect of varying their location has had little attention in the literature. In the present paper some simple examples are used to indicate possible effects. It is noted that the probability can be both under- and over-estimated, depending on the choice of points, but that no clear guidance for point selection can be given in any one case. A particularly disturbing feature is that for some types of problems there can be instability in the probability estimate as the location of the points is changed. This is demonstrated through a previously well-discussed example.
Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsR. E. MelchersEmail: rob.melchers@newcastle.edu.au
Data published in the 1957 Romanoff National Bureau of Standards report for the corrosion of steels buried in soils for up to 17 years are re-interpreted using the bi-modal model for corrosion in wet environments. The relevant soil properties are those of the backfill, not those of the undisturbed soil at the depth of the steel samples. Using estimated backfill properties shows that stiff clays, calcareous loams and gravelly loams corrosion transitioned from Mode 1 to Mode 2 after 4–8 years, following severe corrosion and deep pitting. For most other backfill soils, the transition occurred later and corrosion was less severe. These differences are attributed to the relative influence of differential aeration and localised corrosion caused by air-voids at the soil–metal interface. The declining rate of corrosion in the later part of Mode 2 is attributed to backfill consolidation decreasing the diffusion of oxygen and possibly also of moisture.
SUMMARY: The corrosion of ferrous water mains is a signific ant problem for the Australian Water Industry. A significant proportion of Australia’s a geing water infrastructure is composed of cast iron and steel cement lined pipes, which are prone to co rrosion on the external surfaces that are in contac t with soil. Internal corrosion is not a significant issue for cement-lined pipes. For the water industr y to manage these ageing assets effectively, quantitativ e predictions of the damage likely to result from long-term corrosion are highly desirable. Many of t he fundamental corrosion mechanisms are known and there is considerable practical experience on t he corrosion of buried iron. However, the predictio n of the long-term corrosion losses, of pit depths an d pitting extent are not well developed, including understanding and prediction of the quantitative in fluences of external soil conditions. In this paper the basic mechanisms involved in the corrosion of ferro us metals in contact with soil are reviewed and the likely effects of various influencing factors such as soil moisture content, soil type and soil water chemistry on long-term corrosion are described. The review has found that long-term corrosion is controlled by diffusion processes and is a function of soil moisture content, soil density, and soil w ater quality. The review is followed by an outline of an approach to modelling long-term corrosion of cast iron pipes. It involves developing a realistic mode l for the prediction of pipe corrosion in soil and its calibration to field and historical data. Both the modelling approach and field data collection requirements are outlined.
Welded Joints long-term integrity is of particular importance to large vessels, such as frigates or bulk carriers. Downtime due to corrosion concerns can be onerous. Ship classification organisations, such as The American Bureau of Shipping (ABS), standardises processes and product approval programmes for materials manufacturers. High-strength steels are of particular interest due to their high strength to cost ratio for large marine vessel construction. The corrosion performance of such steels has been studied, but data on the specific degradation of such metals when welded and for the welds themselves are scarce. The present paper reports marine immersion corrosion pit depth data for several ABS steel grade weld permutations and exposed to different sites for up to 2.5 years. The implications of the presented results are discussed as well as the possible influence of alloying elements and microstructural differences on the underlying corrosion kinetics.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
A load space formulation for calculating the failure probability of complex structures for which the limit state functions are implicit is described in this paper. This formulation is used in conjunction with probabilistic finite element (PEE) analysis and employs a directional simulation to calculate the structural reliability. Apart from the advantage that a lower order space is used, the main advantage of the load space formulation proposed in this paper is that the number of inversions of the structural stiffness matrix and/or its gradients with respect to the material property random variables is reduced dramatically when compared with the usual Monte Carlo simulation (MCS) method. When used in a finite element reliability analysis, this procedure can save significant amounts of CPU time. Numerical examples are presented to show the efficiency and accuracy of the proposed approach.
For environmental and for economic reasons, there is increased emphasis on extending the life of existing infrastructure and to design new infrastructure for longer, safe and effective service lives. Increasing use is being made of monitoring of performance and estimation of long-term reliability and safety, allowing also for the likelihood of long-term deterioration. To obtain optimal decision outcomes, reliance should be placed not only on data but also on accumulated scientific and engineering knowledge. In engineering, this is embodied in mathematical models. Ideally, these are of good quality, calibrated to ‘real world’ data and have prediction capabilities. Recently, developed models of this type are described for the corrosion of steel in marine environments and simplified to models suitable for engineering applications. An example is given of the prediction of the expected corrosion loss and of the likely future rate of corrosion for a mild steel structural element exposed to temperate seawater.Keywords:: corrosionmodelspredictionprobabilityremaining lifesteel AcknowledgementsThe continued financial support of the Australian Research Council through two successive Australian Professorial Fellowships and various Discovery Grants is acknowledged with gratitude.
