Publications

Reliability estimation of pressurised pipelines subject to localised corrosion defects

This paper describes a probabilistic method for the assessment of the suitability of corroded pipelines under pressure loading. The method takes into account the uncertainties of the variables that influence suitability. The paper starts with a review of the various available techniques for the assessment of failure pressure of corroded pipelines and then develops a probabilistic limit state model from the available deterministic failure equations. The advanced first-order second moment method is then employed to estimate reliability. This approach is then applied to some typical examples. The results are presented in graphical form.

The marine corrosion of structural steels in brackish and fresh waters

High-quality models are required to describe the corrosion of structural steels in marine, brackish and fresh waters and these models should, preferably, be based on a proper understanding of the corrosion processes involved. The models should then be used to interpret field data, rather than attempting to derive models empirically from field data. On this basis a multi-phase corrosion–time model has been proposed previously for mild and low alloy steels subject to immersion in 'at-sea' conditions. This model is reviewed and extended to brackish and fresh waters in this paper. The scientific principles show that salinity is not the critical issue for the corrosiveness of water. Instead, the critical parameters are the temperature, pH and calcium carbonate solubility when corrosion is governed by oxidation. For later corrosion, governed by anaerobic bacterial activity, the available nutrient level and rate of supply of nutrients control the observed rate of corrosion. The data available at the present time for estimating all the parameters of the new model are somewhat preliminary and new corrosion monitoring programmes will be required to augment the information and to fully characterize the corrosivity of coastal and harbour waters. However, indicative trends for the parameters, based on currently available data, are given and permit the construction of corrosion loss curves for practical applications.

Decision model for overview checking of engineering designs

Overview checking occurs whenever an engineering design is reviewed by another engineer without specifically carrying out checking calculations or following through the design process in detail. Results are reported herein of a survey examining the effectiveness of overview checking. The respondents were requested to assess whether a structural design should be considered “undersized”, “correct” or “oversized”. Using the responses as a basis, a decision model is proposed for the effectiveness of overview checking as a function of error magnitude and of checker's experience. It is concluded that correct assessment of a design as “safe” is not a function of experience. However, it appears that more experience is beneficial in selecting economical designs.

Corrosion Performance of Low Alloy Steels in Sub-Arctic Natural Seawater

Corrosion mass loss trends for low alloy and for high-strength structural steels of grades A, B, D, AH, and DH exposed for up to 5 years in sub-Arctic seawater near Vladivostok are compared with tr...

Corrosion uncertainty modelling for steel structures

Marine environments are well-known to be very corrosive for mild and low alloy steels. For reasons of economy, such steels are still the preferred materials for off-shore structures, ship hulls, sheet piling and harbour-side facilities. Despite some quite extensive, long-term experimental test programs, the prediction of the likely corrosion loss of material is still rather simplistic, even though the various factors that can influence marine corrosion are known. However, precise understanding of the mechanics of marine corrosion has been slow to develop and mathematical formulation has been largely neglected. This paper reviews the various factors of importance in marine corrosion, outlines previous models and describes on-going work aimed at developing a probabilistic phenomenological model for time-dependent material loss of mild and low alloy steels in immersion conditions.

SYNOPSIS OF PAPER 7622. COMPUTER ANALYSIS OF REINFORCED CONCCRETE TANKS.

"SYNOPSIS OF PAPER 7622. COMPUTER ANALYSIS OF REINFORCED CONCCRETE TANKS. ." Proceedings of the Institution of Civil Engineers, 55(3), pp. 672

Reliability of large structural system

No abstract is provided for this article.

RELIABILITY OF UNDERGROUND PIPELINES SUBJECT TO CORROSION. DISCUSSION AND CLOSURE

A discussion of a paper with the aforementioned title by Ahammed and Melchers, published in this journal (Volume 120, Number 6, November/December 1994), is presented. Discusser Prevost begins by suggesting that the authors confirm that the material of the pipes addressed is steel. He then moves on to discuss the two types of loadings separately, assuming steel pipes only are considered. Discusser Prevost also states that elastic limit is not a criterion of failure but a permanent feature. He concludes by pointing out that the paper lacks a discussion on jointing systems. Discussion is followed by closure from the authors.

EXAMINATION OF PUBLISHED CASES OF STRUCTURAL FAILURE

Examination of the conclusions which may be drawn from the study of cases of structural failure show these to be inconsistent between various investigators. It is suggested herein that to resolve these problems, detailed studies of the causes and underlying mechanisms for structural failure are required, even though this severely limits the data that can be employed. Starting from the development of a quite general model of the causes of structural failure, together with a set of plausible hypotheses, implications are derived for the type of information that can be obtained using limited data. It is suggested that the study of well- reported cases of failure can be useful in identifying error- causing- potentials in the conceptualization, detail design, documentation and execution of structural projects, but that only socially weighted relative values can be established from such a study. Particular attention is given to the relative importance of so- called uncertainty type (or gross) errors compared to errors arising from natural variability. Finally, it is suggested that the manipulation of control processes is likely to be an effective practical means of reducing structural failure. (Author/TRRL)

Guest editorial

No abstract is provided for this article.

Structural performance of 45 year old corroded prestressed concrete beams

No abstract is provided for this article.

An observation-based model for corrosion of concrete sewers under aggressive conditions

Development of rational mathematical models for prediction of the likely present and future internal corrosion of reinforced concrete sewers requires understanding of the important physico-chemical processes, preferably based on field evidence. Samples of new and 70year old pre-corroded concretes were exposed for up to 31months in an aggressive sewer environment at 26°C, 98% relative humidity and 79ppm H2S concentration (averages). During the initial months of exposure the pH of the new concrete surfaces reduced rapidly however little corrosion loss was observed during this period. Subsequently pH reduced further, mass loss commenced and new concrete losses reached around 24mm after 2years. During the same period the old concrete corroded at an approximately constant rate. The presence of the corrosion product layer had negligible influence on corrosion losses. A bilinear corrosion loss model is proposed for practical applications.

Discussion of “Structural Analysis of Reinforced Concrete Tanks”

No abstract is provided for this article.

Corrosion and odour management in sewers: the state of the art and key challenges

Long-term immersion corrosion of steel subject to large annual variations in seawater temperature and nutrient concentration

The corrosion of steel in open seawater is influenced mainly by water temperature. If nutrients critical for bacterial activity are available, it also may be influenced by microbiological activity. The combined effect is investigated here for the case of large variations both in the seawater temperature and in concentration of dissolved nutrients. A theoretical analysis is given for these effects acting in conjunction, with or without time-dependent differences. Field observations of corrosion losses for steel sheet piling exposed at three different locations at sea sites near Vladivostok, Russia, are used in conjunction with local temperature and nutrient concentration data to obtain trends for longer term corrosion. The main objective of the paper is to build a new long-term predictive model of corrosion which may be effectively used in conditions with large variable seasonal in water temperature and in nutrient availability.

Reinforcement Corrosion in Concrete Exposed to the North Sea for More than 60 Years

Of the some 1,000 almost identical, precast, reinforced concrete elements forming the 1.5-km-long, more than 60-year-old promenade railing immediately adjacent to the North Sea at Arbroath, Scotland, more than 90% still appear to be in remarkably good condition with little evidence of external rust staining or reinforcement corrosion. However, the elements that have been replaced, some only about 15 years ago, mostly show severe reinforcement corrosion. Concrete quality, density, and cover to the reinforcement are generally similar, but concrete permeability does not correlate well with reinforcement corrosion. Detailed investigations show some of the original, apparently sound concrete elements to have severe highly localized reinforcement corrosion, in some cases with a complete loss of steel. This was accompanied by limited amounts of mainly black corrosion product that x-ray diffraction (XRD) analysis showed to have a strong presence of magnetite. The ends of some reinforcement bars showed tunnelling corrosion, a phenomenon not previously reported for reinforcement. It is proposed that the observations show that the long-term corrosion of reinforcement in high-quality concretes involves processes more complex than simply oxidation of the steel under chloride conditions.

Human error in simple design tasks

This report deals with a preliminary investigation into human error rates incurred in three relatively simple structural design tasks. The tasks were (i) table look up, (ii) multiplication of two or three numbers on an electronic pocket calculator, and (iii) ranking exercise. Error rates and frequency distributions for the three tasks are reported (a).

Ballast Tank Corrosion using Naval Ship Operational Profiles

The sustainability of Royal Australian Navy (RAN) ships is affected by structural deterioration, including corrosion, which results in material loss through the oxidation of exposed steel. Deterioration through corrosion is one of the determining factors in developing the operational planning and economic aspects of structural maintenance management. The extent of corrosion depends on many environmental parameters making it difficult to predict efficient repair strategies using periodical time based maintenance. With this consideration, and the fact that the RAN owns an increasingly ageing fleet, new and innovative ways are required to effectively manage a ship. Presently there is no simulation tool available to the RAN that allows ship corrosion to be predicted. Tools such as these have been developed empirically for some commercial ships, however the corrosion loss models exhibit a high variability. By taking into consideration the operational parameters of the vessel a greater accuracy in modelling corrosion can be achieved.