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The exterior surfaces of cast iron pipes buried in clay soils for up to 129 years show clustering of pits of similar depth at progressively greater overall corrosion pit depth. Within experimental accuracy, the pit depth increments are approximately constant over the whole range of pit depth for each soil. They increase with lower soil pH and appear insensitive to other soil properties and to burial period. These new findings are interpreted relative to pitting electrochemical potential and compared with field observations for pitting in marine corrosion of steel. Implications for modelling maximum pit depth development are considered.
Data from the US NBS study for corrosion of buried objects are employed to show that average annual atmospheric precipitation directly influences corrosion of ferrous objects buried in various soils. This is attributed to the softness of precipitation waters and their delivery of oxygen. Also, as surrogate for time of wetness at the buried object within the soil, atmospheric precipitation has a clearer effect on corrosion loss and localised corrosion than does ground surface time of wetness. The relationship and the amount of corrosion also depend on soil type, a matter not previously considered. The results allow an explanation for the generally higher rate of corrosion of cast iron water pipes in cities such as Sydney with mainly clay-loam soil backfill and high precipitation compared with many locations in the UK with much lower annual average precipitation.
A stress corrosion model of a glass fibre is used within the framework of the finite element theory to predict the life of a unidirectional composite. The approach proposed here seeks to construct plausible models of comparative behaviour such that data and experience gained from short-term durability tests can be extrapolated and used to predict long-term behaviour. It is based on numerical simulation. Its significance comes from the fact that it makes use of the finite element method at the microstructural level. The finite element can capture reasonably well all aspects of damage mechanisms taking place in the microstructure.
This paper is concerned with estimating the failure probability associated with the intersection of two or more non-linear limit state functions. Previous work has relied on the use of general non-linear minimization routines to establish the intersection point of the limit states and then to use tangents to bound the region for estimating the failure probability. The present paper outlines two approaches based on successive approximation both to find the intersection point and to estimate the intersection probability. It is shown that the results for selected examples converge to the probabilities estimated using Monte Carlo analysis. Comments about extending the results to using second order or asymptotic probability estimates close the paper.
No abstract is provided for this article.
No abstract is provided for this article.
The traditional procedure for employing the virtual work equation to calculate structural deflections of statically indeterminate structures requires the solution of the internal action state of the structure to be available or to be calculable. This is not always convenient, for example, in design problems for which strength proportioning is based on plasticity theory, or for thermo elastic problems. The present paper demonstrates an alternative method for calculating the linear elastic deflection of statically indeterminate structures using the virtual work approach. However, in contrast to conventional applications, the internal action state under applied loading is not required to be known.
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When steel sheet piling suffers accelerated low water corrosion the webs and flange-web regions of individual piles often perforate first, for reasons not fully understood. To investigate this, samples of the cross-sections of typical U and Z profile sheet piling were exposed to natural seawater for 1, 2 and 3years. They showed localized corrosion in the central region and also near the flange-web junctions. These locations were found to have more material defects and segregation and show composition differences. It is proposed these observations are linked to localized sheet pile perforation after long exposure to seawater.
The apparently premature corrosion of steel reinforcement in reinforced concrete structures exposed to marine environments continues to be a matter of concern in practice despite decades of research effort and much research funding expenditure and despite much practical experience. Herein results are reported of a long-term (10 year) study of the influence of alkalis on the corrosion initiation and progression of 6mm diam. reinforcing bars centrally embedded in 40x40x160mm concrete specimens. These were made with seawater as mixing water and with a variety of mix proportions including some with added alkalis. All were equally well compacted by vibration. After 10 years continuous exposure in a fog-room only a limited amount of corrosion initiation was observed. These results are in stark contrast with those reported in the famous paper by Shalon & Raphael (1959) who found serious corrosion of reinforcement after only 1-2 years exposure for all mixes. It is shown herein that the corrosion loss trends in those tests are similar to those of steel exposed directly to seawater. This indicates that in the 1959 tests the concrete provided little protection against reinforcement corrosion. The reasons for this are considered herein and the practical implications discussed.
The bimodal model previously shown to be applicable to long term corrosion loss of mild steel in seawater is examined herein for hard freshwater at elevated temperatures. Laboratory data reported in the literature are reinterpreted using conventional corrosion theory and the bimodal model. The data fit the trends for the parameters of the model extrapolated from water temperature observations. One different set of data earlier can be reconciled if allowance is made for the effect on corrosion of water velocity. Overall the results show the bimodal model is applicable to freshwaters to 70°C.
The external corrosion of buried cast iron water mains is a significant problem for the Australian Water Industry. To improve maintenance and replacement strategies for these mains the water industry requires a method to estimate their remaining service lives. Predictions of long-term corrosion losses, pit depths and pitting extents are therefore required. A conceptual model for the prediction of long-term corrosion has been developed and the external soil conditions influencing corrosion were identified in a previous study. To calibrate the model, long-term data of corrosion (average losses and maximum penetration) and associated soil parameters for pipes in service is required. Field data has been collected at 18 condition assessment sites within Hunter Water Corporations network. This paper presents the field observations from the first 11 sites, the model calibration procedure and results of the calibration. The evidence gathered in this work suggests that the long-term maximum corrosion penetration increases with increasing soil wetness (measured using degree of saturation) for the sites investigated. The initial model calibration produced model parameters for cast iron pipes buried at standard depths in relatively homogeneous, low-permeability, soils with degrees of saturation equal to 0.66 and 0.76.
Highly polished coupons (25 by 25 by 1.5 mm) sourced from the same steel sheet were continuously immersion-exposed either to natural coastal seawater or to seawater from the same source subjected to filtration and UV irradiation to eliminate microbiologically influenced corrosion as much as possible. This was continued for 943 days (2.6 years). Dissolved oxygen levels were very similar in both environments. On average the UV-treated seawater was 2°C warmer, but all coupons exposed to it showed less localized corrosion than those exposed to natural seawater. The typical topographical difference was about 60% as measured by surface roughness parameter Sa. Mass losses in UV-treated seawater were about 10% higher than in natural seawater, but after temperature correction were similar to natural seawater for the first year and tended to be lower subsequently. At all exposure periods the rusts in UV-treated seawater were less voluminous than the rusts in natural seawater. Eventually they also contained a higher proportion of magnetite.
The reinforced concrete (RC) caissons, code-named Phoenix, still visible off the coast of Arromanches, France, have been exposed to marine immersion, tidal, splash and atmospheric conditions since 1944. Little evidence of corrosion of the steel reinforcement was observed during inspections in 2011, 2015 and 2019, although there was much structural damage. Archival material from the Second World War reveals the caissons were designed to low safety margins, without consideration of durability and constructed at a very fast rate mostly with unskilled labour, minimal material usage, without additives and no restrictions on adding water to aid concrete workability. Analysis of data that has recently become available indicates the concretes had a high cement content and were made with calcareous aggregates. It is concluded that these factors contributed to the high strength, low permeability and high remaining alkalinity of the concretes and hence to the very low evidence of reinforcement corrosion. When interpreted using recent experimental observations, these observations have implications for the design of new RC structures in marine exposures and for the prediction of the remaining life of older marine-exposed RC structures.
Most available data sets for the long-term corrosion loss of various grades of weathering steel exposed to marine atmospheric environments are demonstrated to be consistent with the multi-phase corrosion model previously proposed for steels exposed to marine environments. This means that the early corrosion of weathering steels by oxidation is gradually inhibited by the build-up of corrosion products. These produce anoxic and sub-oxic conditions that may permit microbiological activity to govern the longer-term corrosion loss process. This new interpretation for the long-term corrosion of weathering steels may have implications for the design of such steels.
