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End-of-Life Corrosion Estimation and Profile of Ship Hull Structure: Non-Parametric Statistical Analysis of Medium Endurance Cutters
Abstract
Corrosion in hull structure of Coast Guard cutters is a primary degradation mode that accounts for a significant portion of depot budgets and the occasional unavailability of ships in general. Corrosion exhibits great variability spatially and temporally. This paper presents, summarizes, and analyzes a one-of-a-kind data set for end-of-life corrosion estimation and profile of ship hull structure. The data set was created over several years and on several vessels, and collected by maintenance personnel at several geographic locations. This study analyzes wastage data due to corrosion that were systematically collected in 2007 to 2008 from twelve 210-foot Medium Endurance Cutters, commissioned in 1964 to 1969, in the form of thickness measurement using visual inspection and ultrasonic testing methods. A total of 76,091 thickness measurements were analyzed at positions covering the entire hulls. The measured corrosion levels mean is about 0.02 to 0.04 inches (1 in. = 25.4 mm), i.e., 6 to 14% of the as-built thicknesses after no more than 43 years of use of these 12 cutters as of 2007; however, the analysis of outliers indicates that the average wastage values can be misleading in predicting extreme corrosion. A method is proposed for estimating the counts and intensity of outliers. Examining geographic locations of the operations of these cutters and corrosion revealed that southern warm water led to appreciably larger corrosion compared to the northern colder waters, at a ratio of about 1.25 to 1.5.
... The other PdM physics-based models include the prognostic model of physics-offailure Tinga & Loendersloot, 2019), the RUL model of ship hull structure profile (Ayyub et al., 2022), and ship hull tanker profile . These models were tested and evaluated by comparing them with their corresponding simulations. ...
Corrosion is a natural phenomenon that deteriorates and damages the surface of metallic material. Over time, the surface of the material deteriorates due to electrochemical reactions with the surrounding environment. If corrosion is not identified early on, it can become a major financial burden for industries, costing billions of dollars. Despite swift technological developments, preventing and maintaining corrosion progression with reactive maintenance remains difficult. Due to that, predictive maintenance has been developed to predict the deterioration, degradation, and fault over the remaining useful life of the material by using real-time data, historical data, simulation, modelling, and failure probability. Predictive maintenance allows inspectors to monitor the health and predict the corrosion level of the material. However, it is hard to predict the unexpected degradation of the material from the developed prediction model without considering the harsh environment and other external factors. Hence, there is a need to investigate these problems and their effect on predictive maintenance for corrosion detection and maintenance. Therefore, this paper reviews and compares the state-of-the-art predictive maintenance solutions developed to solve corrosion issues in various applications, industries, and academic research. The challenges and opportunities for the predictive maintenance application of corrosion detection and maintenance are also presented. This review will provide new and additional knowledge that can be used to develop prediction models for corrosion detection and maintenance, which will help prevent unexpected failures.
... The other PdM physic-based corrosion prediction models include the prognostic of physics-of-failure [131,132], RUL of ship hull structure profile [133] and ship hull tanker profile [134]. These physics models were validated and compared with the respective simulations. ...
One of the biggest problems the maritime industry is currently experiencing is corrosion, resulting in short and long-term damages. Early prediction and proper corrosion monitoring can reduce economic losses. Traditional approaches used in corrosion prediction and detection are time-consuming and challenging to execute in inaccessible areas. Due to these reasons, artificial intelligence-based algorithms have become the most popular tools for researchers. This study discusses state-of-the-art artificial intelligence (AI) methods for marine-related corrosion prediction and detection: (1) predictive maintenance approaches and (2) computer vision and image processing approaches. Furthermore, a brief description of AI is described. The outcomes of this review will bring forward new knowledge about AI and the development of prediction models which can avoid unexpected failures during corrosion detection and maintenance. Moreover, it will expand the understanding of computer vision and image processing approaches for accurately detecting corrosion in images and videos.
Traditional underwater hull inspections, which rely heavily on human divers, face significant challenges such as safety hazards and dependency on expert judgment. Recent technological advancements, such as remotely operated vehicles and artificial intelligence, offer promising alternatives to address these limitations and enhance the efficiency and safety of underwater inspections. This paper proposes a framework for planning underwater hull inspections based on computer vision and degradation assessment. The proposed modeling includes three main processes: Detect degradation, Assess degradation, and Perform maintenance decision-making. The degradation detection process utilizes Convolutional Neural Networks for computer vision to identify structural degradations such as corrosion and cracks through automatic image analysis. Then, the degradation assessment process assesses the hull degradation based on measurements such as material loss to provide a comprehensive understanding of structural integrity. Finally, the maintenance decision-making process guides the decision on maintenance tasks based on the Remaining Useful Life estimates. Through a case study, the proposed framework was demonstrated considering the operational context of Floating Production Storage and Offloading (FPSO). As a result, the proposed framework showed to be consistent in identifying different types of structural degradations based on a U-Net architecture and supporting underwater hull inspection planning.
The present study reviews the recent advances in modelling and analyses the strength of corroded ship structures. Firstly, the time-variant methodologies that consider only the mean structural element thickness loss due to corrosion degradation are identified. Corrosion degradation is regarded as the phenomenon that causes uneven thinning of specimens. This has been captured by various researchers as the loss of mechanical properties of structural steel components. A review of the existing experimental and numerical studies shows significant interest in this field of study. The advances in modelling and analysis of structural behaviours of different ship structural components of larger sizes (including plates, stiffened plates and panels, and entire hull girders) are outlined. Research on the impact of general and pitting corrosion degradation is reviewed separately since the phenomena are different in terms of modelling and analysis. Additionally, recent advances concerning the reliability analysis of corroded ship structural components have also been reviewed. Finally, the general conclusions are drawn and future research topics are outlined.
This paper presents the results of a parametric study of probabilistic modelling of the ultimate strength of ship plates with non-uniform corrosion represented by random fields. The load-shortening behaviour of the plates with non-uniform reduction of thickness due to corrosion under longitudinal compression is obtained using a general-purpose nonlinear finite element analysis program. A nonlinear time-dependent corrosion model is used to define the probabilistic characteristics of the random fields based on corrosion data measured in plate elements at different locations of bulk carriers. Based on the probabilistic models derived by Monte Carlo simulation, equations to predict the mean and the 5 % characteristic value of the ultimate strength of plates with non-uniform corrosion are developed. Finally a regression equation is proposed to take into account the effect of non-uniform corrosion patterns in the predictions of the ultimate strength of plates with uniform corrosion.
This paper presents a semi-probabilistic approach to assess the time-varying ultimate strength of aging tanker's deck plate considering corrosion wastage. The procedure includes (1) defining the limit state function of deck plate failure, (2) determining the time-varying probability density function of corrosion wastage and values for selected severity levels of corrosion, (3) calculating the time-varying ultimate strength of deck plates corresponding to the selected levels of corrosion wastage, (4) determining the time-varying maximum nominal stress, (5) calculating when the deck plate reaches the ultimate strength limit state, and (6) determining the inspection intervals based on the risk of ultimate strength failure. A nonlinear corrosion model was proposed for deriving the time-varying probability density function of deck plates' corrosion wastage. The probability density function was determined based on a statistical analysis of the American Bureau of Shipping (ABS) corrosion wastage database [Wang G, Spencer J, Sun HH. Assessment of Corrosion Risks to Aging Oil Tankers In: 22nd International Conference on Offshore Mechanics and Arctic Engineering, Cancun, Mexico, 8–13 June 2002]. To simplify the calculations of ultimate strength, a semi-probabilistic model was adopted. Three levels of corrosion severity were considered, and the corresponding values of corrosion wastage were used instead of the probability density function. The increasing nominal stresses as ships age were also taken into account considering the loss of global hull girder section modulus. The loads of still-water-induced and wave-induced bending moments were treated as deterministic values. The ultimate strength calculation was based on the latest International Association of Classification Societies (IACS) – Common Structure Rule (CSR) formula [Common Structural Rules for Double Hull Oil Tankers, http://www.iacs.org.uk/; 2007]. Deck failure was defined as deck plate's ultimate strength becoming lower than the maximum nominal stress. An inspection should be conducted before such failure takes place. A total of nine sample tankers, designed in 1970s, 1980s and 1990s were selected for demonstrating this approach. Time to deck plate's failure by ultimate strength varies in a wide range depending on the initial designs and corrosion severity at both local plate and global hull girder levels.
This study considers different environmental factors affecting corrosion under marine immersion conditions and proposes a mathematical model incorporating their effects on corrosion degradation through the ship life. The study adopts a nonlinear function of time as the reference corrosion model calibrated with operational corrosion data at long term average conditions to represent the corrosion behaviour under standard environmental conditions. Based on previously obtained field data, a corrosion deterioration model is developed, in which a correction factor is proposed to account for the effect of each environmental factor. These multiplicative factors correct the standard prediction of corrosion degradation to obtain short term estimates under any specific environmental condition. Then, a long term estimate of corrosion degradation is determined by summing the short term corrosion contributions during the various discrete time periods in which the ship life can be decomposed. A numerical example of a representative application of the new empirical based corrosion model is presented, to demonstrate how to apply the model.
The stochastic deterioration of ship structural elements is both time and spatially dependent. In this paper, a formulation of the time-variant ship hull girder reliability subjected to corrosion is proposed by taking into consideration the spatial variability of corrosion growth, geometric and material properties of structural elements. The joint probability distribution of the spatially dependent variables is constructed by the Gaussian, Gumbel, Clayton, and Frank copulas. Monte Carlo simulation is used to compute the probability of hull failure. A ship hull girder is employed to illustrate the application of the developed method. The impact of the degree of dependence and the selected copula on the estimated failure probability is investigated. The results indicate that this probability can differ assuming different levels of spatial dependence and different dependence structures of corrosion growth, geometric and material properties. In addition, a higher dependence of variables tends to produce higher probability of hull failure.
Corrosion takes place in the life cycle of ships, resulting in degradation of structural strengths. Corrosion effects with uncertainty on ultimate strength for container ship structures are studied in this paper. On one hand, the ultimate strength of container ship hull girder subject to combined moments of bending and torsion is studied by Nonlinear Finite Element Analysis (NFEA), and the limit state of failure is derived through Minimum Square Error (MSE) technique based on a series of NFEAs, and the probabilistic characteristics under simultaneous uniform corrosions (however, with different scales) in longitudinal structures are studied for the cases of pure bending, pure torsion and combination of both, which can be a useful reference for the scheduled maintenance of container ships. On the other hand, the ultimate strength of bottom stiffened panel under longitudinal thrust derived from hogging conditions is studied considering effects of key factors such as initial deflection, element sizes, simplified boundary conditions, and lateral seawater pressure etc. Uniform and not simultaneous corrosion across different structures is studied, and surrogate models by Gaussian Process (GP) are built, and the corresponding ultimate strength probabilistic characteristics and its dependency on correlation between different structures’ corrosion are studied.
Corrosion in ship structures is influenced by a variety of factors that are varying in time and space. Existing corrosion models used in practice only partially address the spatial variability of the corrosion process. Typical estimations of corrosion model parameters are based on averaging measurements for one ship type over structural elements from different ships and operational conditions. Most models do not explicitly predict the variability and correlation of the corrosion process among multiple locations in the structure. This variability is of relevance when determining the necessary inspection coverage, and it can influence the reliability of the ship structure. In this paper, we develop a probabilistic spatio-temporal corrosion model based on a hierarchical approach, which represents the spatial variability of the corrosion process. The model includes as hierarchical levels vessel - compartment - frame - structural element - plate element. At all levels, variables representing common influencing factors (e.g. coating life) are introduced. Moreover, at the lowest level, which is the one of the plate element, the corrosion process can be modeled as a spatial random field. For illustrative purposes, the model is trained through Bayesian analysis with measurement data from a group of tankers. In this application it is found that there is significant spatial dependence among corrosion processes in different parts of the ships, which the proposed hierarchical model can capture. Finally, it is demonstrated how this spatial dependence can be exploited when making inference on the future condition of the ships.
In this paper, phenomena of general corrosion are assumed to be the results of three sequential processes; degradation of paint coatings, generation of pitting point, and progress of pitting point. A consistent corrosion model is proposed which can evaluate the generation and progress of corrosion quantitatively by introducing appropriate simple probabilistic models for each process. This probabilistic corrosion model can be identified by analyzing existing data collected from plate thickness measurements. Applicability of this model is verified by computing the estimated behavior of corrosion progress and dispersion with those from actual data.
A formulation is presented for the assessment of the reliability of longitudinal members of a ship hull as a result of fatigue and corrosion under combined loading. The model allows for the existence of multiple cracks and it accounts for the crack growth process. The time dependent degrading effect of corrosion and crack growth on the midship section modulus are modelled as random processes. The reliability is predicted by a time variant formulation and, using a two-failure criterion, the effects of maintenance actions in increasing the reliability are shown. The sensitivity of the reliability estimates with respect to different loading combinations is also studied. The formulation has been applied to a tanker.
A model is proposed for the non-linear general corrosion wastage in a plate, which is able to describe an initial period without corrosion due to the presence of a corrosion protection system, and an exponential increase in wastage up to a steady-state value. The influence of adopting this model instead of a linear one is demonstrated by studying the reliability of a corrosion-protected plate subjected to compressive loads, and maintenance actions. The paper examines how the plate collapse strength will vary in time as a result of generalised corrosion and plate repair. In the presence of general corrosion, the plate thickness will decrease at a random rate as a function of time and will affect the net plate section resisting the applied load. The collapse strength against compressive loading is described by a function of time and the resulting reliability is quantified. The sensitivity of the reliability estimates with respect to several parameters is also studied. The reliability is predicted by a time-variant formulation and the effects of repair actions in the reliability assessment are shown.
This study investigates the effects of temperature, carbon dioxide and hydrogen sulphide concentrations on the corrosion behaviour of ship steels subjected to crude oil tank atmospheres. A new corrosion wastage model is proposed based on a standard non-linear time dependent corrosion model modified by the effect of the different environmental factors contained in the crude oil tank atmosphere. The new corrosion model assesses the corrosion degradation under stationary environmental conditions denoted as “short-term”. The long-term corrosion degradation is assessed by considering the succession of the various environmental conditions that can be present in the tank and adding the corrosion damage incurred during each of them. Corrosion records depending only on time are used to calibrate the standard model while the effect of environmental factors in increasing or decreasing the corrosion rate is based on formulations published by other authors. A numerical example of a representative application of the new corrosion model is presented, to demonstrate how to apply the model.