640 publications from this institution
The final discussion session of the Newcastle Earthquake Conference outlines changes that need to be made in relation to earthquake engineering, hazard analysis, and response. The recommendations are based on a broad feeling of consensus by conference participants. The discussion also includes feedback of problems currently facing industry and civic professionals involved in the Newcastle earthquake of 1989., i.e insurance assessment, continuing ground movement, demolishment vs. repair, and the public perception of engineers.
In this paper, the problem of overload failure of a structural component under random loading and under random crack propagation is addressed. The problem is formulated by combining the first passage failure model with stochastic models of crack propagation. Disadvantages of the standard random variable approach to the problem are discussed, and an alternative random process approach is developed. The developed solution addresses both overload and critical crack growth failure modes, requires a single mean crack growth computation, allows the consideration of non-destructive inspections and significantly speeds life-time analysis. The random process approach leads to a first passage problem involving crossings of a random barrier level, which is solved by means of the ensemble up-crossing rate approximation. Limitations of this approximation are addressed and related to typical problem parameters. The concept of barrier failure dominance is discussed, and extended to the case of a barrier-defined failure. Sensitivity studies involving different problem variables are performed, helping to identify the appropriate solution method for specific problems.
Small changes in the composition of mild and low alloy steels can effect their immersion corrosion behaviour. A number of comprehensive test programs for coupons immersed at different locations and recovered at different times have been reported. Comparison between them has also been attempted with modest success as well as leaving some apparent inconsistencies in the effect of some alloying elements. In this paper, a new comparative analysis of previously reported observations is reported. It employs a recently reported multi-phase phenomenological corrosion–time model, with different corrosion phases governing corrosion behaviour. Each phase is a function of time. The analysis shows that metal composition can influence the first, kinetically controlled corrosion phase and also the long-term anaerobic corrosion phases. However, during the phase controlled by oxygen diffusion through the corrosion product, metal composition is largely irrelevant, in agreement with theoretical predictions. It is shown that the several observations in the literature about the effect of particular alloys can be reconciled, including apparently conflicting observations about the effect of chromium content.
Localised or pitting corrosion can be detrimental for steel pipes and containment structures, since wall perforation may cause system failure. Herein maximum pit depth quantification and its development with time are considered for samples taken from longitudinal welds on 33-year-old tubulars exposed in Newcastle Harbour. Relationships between pit depth and material metallurgy and corrosion properties were investigated by means of standard macro-etching, rest potential and zero resistance ammetry techniques. It is considered that the observed results are the result of the lack of homogeneity at the corrosion interface caused by differences in grain size, grain structure and the potential for pitting to occur preferentially along boundaries. The results are compared to measurements for longitudinal welds obtained previously on samples of API X56 Spec 5L pipe exposed in similar waters for up to 3·5 years, showing a reasonable degree of consistency between the two sets of data. The reasons for this are discussed.
A physically based mathematical model that can predict the moment‐rotation relationships of bolted extended end‐plate eave connections, using the connection dimensions as inputs is presented. The model recognizes the bounds within which the relationship must lie, viz. the initial (elastic) stiffness, the plastic moment capacity and the strain‐hardening stiffness of the connection. Comparison is made to a series of test results for a range of bolted end‐plate moment connections.
The structural service life of brittle material pipes with exterior corrosion pits is likely to depend on crack initiation and crack development and this may be influenced by pressure loading fluctuations and the possibility of material hydrogen embrittlement. Recently developed methods are used to estimate the cracking pattern, the failure state of the crack development from external pits and the rate of Hydrogen-Assisted Cracking under fluctuating loadings. The effect of hydrogen from the surrounding environment on the cracking rate is formulated using a generalized form of Paris' law. The depth of cracks initiated from surface pits is estimated as a function of pipe age. A realistic example is presented and the results discussed.
As oil and gas production increasingly moves to deeper waters the operating platforms of choice are FPSOs (Floating production storage and off-loading) ('floaters'). Station keeping is a crucial operational requirement since failure can have disastrous implications. Typically a highly redundant mooring system, consisting of chain and wire rope or synthetic rope is used. The chains have links made from 70 mm diam steel (420 mm link length) to 185 mm (1.1 m link length). Their design employs high 'factors of safety', based largely on North Sea operational experience. This reflects the high variability in loading conditions and in structural capacity as a result of fatigue and corrosion. Concern has been expressed that present design requirements may not be sufficient for operations in the Tropics. As a result, a major international Joint Industry Research project was established to study corrosion loss and pitting and also wear of mooring chain and of wire rope. The experimental work is based largely in Australia. It will provide data for revision of design and operational guidelines using modern structural reliability principles and state-of-the-art understanding and models for corrosion metal loss and pitting. The paper outlines the issues and provides the framework for the on-going project work.
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No abstract is provided for this article.
Baseplates assumed to offer so called pinned restraint only, are a common design feature for steel structures. Yet their actual behaviour has hardly been explored and rational rules for their design are not in evidence. While present design practice is undoubtedly adequate, it is nevertheless of interest to explore its limitations and its conservatism. In particular the moment capacity of nominally pinned baseplates is of interest, as this may add to structural capacity both in service and during construction. The deformation behaviour is also of interest, as is the response of the soil under the footing. The present paper gives a progress report on an investigation to obtain behaviour characteristics of two bolt, nominally pinned baseplates, founded on reinforced concrete footings and having an intermediate grout layer. The connection is subject to applied moment and axial force (a).
Previously, it was suggested that in the bi-modal model for corrosion loss as a function of exposure period the instantaneous corrosion rate increases by a factor of about 4 through the transition phase from mode 1 to mode 2. Recent experimental observations (from Part 1 [Melchers and Jeffrey, Corrosion 78, 5 (2022): p. 415]) and other experimental observations covering a range of corrosion influencing parameters closely support this value. The reason for it is examined through a model of the development of corrosion through the transition zone, based on interpretations of the data presented in Part 1. It is shown that pitting plays a crucial role in lowering local pH conditions and permitting transitioning of the corrosion process from oxygen reduction (in mode 1) to hydrogen evolution (in mode 2) as the thermodynamically possible cathodic reaction. In both cases, the rates of corrosion are controlled by diffusion considerations, not electrochemical kinetics. This also permits a theoretical basis for the observed ratio of around 4. Further, eventual long-term corrosion, usually observed as close to a linear trend in time, is proposed as representable a system in quasi-static equilibrium, involving both the hydrogen evolution reaction at the corrosion interface and loss of ferrous ions from the external face of the rust layers.
Perforation of steel plate is of considerable interest for the longer-term safety and integrity of ships hulls and tanks and for nuclear containment systems. This paper reports on the preliminary random field characterization of the surface of two sample corroded steel plates as a trial towards generating numerically the surface topology of larger areas of steel plate. Of particular interest is the maximum depth of penetration and its dependence structure across the plate area. The potential applications and the background to the modelling of corrosion loss and pitting are reviewed briefly to set the scene for appropriate surface characterization. Contrary to the assumptions often made for the statistical characterization of maximum pit penetrations, they are highly dependent. This makes representation using extreme value probability distributions questionable. An alternative probability-based form of representation is proposed.
Understanding the mechanisms of environmental stress corrosion is very important for assessing the durability and damage tolerance predictions of composites using glass as the main reinforcement. A mechanistic model describing these mechanisms for unidirectional GFRP in tension is described. The model is based both on the chemical behaviour of glass, and in particular that of glass flaws, and on more recent models of stress corrosion. These were combined with fracture mechanics, the shear lag theory, and a probability model for flaw size. The results are very encouraging. The model shows that it is possible to obtain mechanisms of GFRP breakdown, which corresponds to observed experimental behaviour.
No abstract is provided for this article.
The remaining strength and the fatigue life of externally pitted corroded metallic pipeline are often assessed using an idealization to model the pit morphology, typically semi-ellipsoidal and cuboidal. Such idealized pit geometries are shown herein to underestimate Stress Concentration Factors (SCFs). By implication this leads to significant overestimates of fatigue life for pitting corroded pipes under sustained cyclic loading which could be the reason behind some of the recent unexpected pipeline failures. Further investigation clarified that this can occur only when there is little or no plastic deformation within the pit which is typical for pipelines constructed from brittle and quasi-brittle materials. Therefore, applying the conventional approach that uses simplistic geometries to model corrosion pits is not reliable for stress/fatigue analysis of pipelines with brittle or quasi-brittle materials such as cast iron or high-grade steel. However, for pipelines made of ductile materials, there is a specific internal pressure, termed critical operating pressure herein, below which there is no plastic flow within the pit and simple idealization of pit morphology results in underestimated SCFs. A semi-empirical equation is developed herein to allow this critical operating pressure to be calculated, based on which a protocol is outlined for correct estimation of the SCFs of pitting corroded pipelines. The conclusions of this study are supported by numerical results validated against novel full-scale burst capacity tests with both simplistic and complex-shaped pits.
Corrosion is the key factor responsible for the degradation of ship structures and in no place is this truer than water ballast tanks. Coating protection system is a continual research interest for classification societies and coating industries. Up to now, most coating performance analyses are qualitative not quantitative. Coating life prediction is almost always based on experience and various assumptions, due to unavailability of practical data support systems. This paper describes a preliminary impartial investigation of coating life carried out with interviewees from the Australian Defence Science and Technology Organization (DSTO), shipyards, coating supplier and an independent expert. Plate surface, edges and welds in ballast tank were considered and the influences of dry film thickness (DFT) and surface preparation (SP) are addressed. The investigation gives some insight into the life of practical coating systems for water ballast tanks. Coating life is proposed to be representable by a normal distribution when corrosion breakdown is below 10% of plate thickness, which is of practical implication.
The longer-term serviceability and structural safety of steel infrastructure exposed to seawater conditions may be affected by global warming and by seawater nutrient pollution. These may affect abiotic and biotic (microbial) corrosion. A model for long-term corrosion is developed from data obtained from steel piling exposed for 33 years in a seawater harbour. The effects on corrosion losses on the structural reliability of steel sheet piling as used in harbours world-wide were investigated as a function of seawater temperature rise from global warming and of seawater nutrient pollution. The results show that structural reliability is more sensitive to likely nutrient pollution than to predicted increases in seawater temperature, noting also that global warming also could increase nutrient pollution from anthropological sources.
