Inspection and maintenance planning of pipeline under external corrosion considering generation of new defects

Safe operation of aging pipeline systems under external corrosion can be achieved through inspection and maintenance programs. Tools used for the pipeline inspection are uncertain in detecting a corrosion defect and in sizing a detected defect. The process of generation of new corrosion pits is an uncertain process. These uncertainties must be taken into account in the reliability analysis and in the pipeline inspection and maintenance planning. In this paper the effect of corrosion defect size on the remaining pipeline strength is modeled by a Markov process. Analytical solution of the probability transition matrix is obtained by solving the Kolmogorov forward differential equation. The matrix of probability transition function, the probability of defect detection and the probability distribution of sizing a detected defect is incorporated in estimating the probability of failure. The generation of new corrosion defects is modeled by a Poisson process. The optimal inspection and maintenance schedules are selected based on the reliability constraint. The sensitivity of optimal inspection schedule to the quality of inspection tools and to maintenance criteria is illustrated through examples.     

Reliability analysis with nondestructive inspection

Nondestructive inspection tools are commonly used to inspect structures or structural components with resistance deterioration due to defect size growth. The quality of the tools is mainly defined by the rate of detecting a defect with defect size s, (s), and the accuracy in sizing a detected defect. The uncertainty of sizing a detected defect can be incorporated in limit state functions that include defect size, and a reliability evaluation can be carried out with the efficient first-order reliability method (FORM). The rate of detecting a defect can also be incorporated in the reliability evaluation of an inspected structure or structural component. This is done, in this paper, by introducing a standard normally distributed variate, Z, and defining a limit state function as a function of and (s). Advantages of using this limit state function, rather than using a limit state function based on the actual defect size and the critical defect size distributed according to the rate of detection curve, are discussed. It is shown that one only needs to use the mean rate of defect detection curve to consider the uncertainty in the rate of detection. The incorporation of the uncertainty in rate of detection for reliability updating analysis with inspection results, and for reliability-based selection of optimal inspection and maintenance schedule for resistance deteriorating structures are also presented. The proposed approach is illustrated by two examples in evaluating reliability with inspection information and in selecting an optimal inspection and maintenance schedule by minimizing the probability of time to failure before inspection and before the time at the end of remaining service life.     

Inspection and maintenance planning of underground pipelines under the combined effect of active corrosion and residual stress

In this paper, a maintenance policy is proposed for pipelines subjected to active corrosion and residual stress, by taking into account imperfect inspection results. The degradation of the pipeline is induced by uniform corrosion, leading to losses of the pipe wall thickness. Localized corrosion is not considered herein, as neither pitting nor crevice corrosion are strongly influenced by external loading conditions and, hence, are not critical in structural strength considerations. When the corroded layers are removed, strain relaxation occurs, causing a redistribution of residual stresses. In parallel, the inspection is applied to detect the corrosion defects, namely the thickness of the corroded layer, and it has a detection threshold under which no corrosion rate can be measured. Due to uncertainties, each inspection is affected by the probability of detecting small defects and the probability of wrong assessment in terms of defect existence and size. The present work aims at integrating imperfect inspection results in the cost model for corroded pipelines, where the failure probabilities are computed by reliability methods. A numerical application on a gas pipe shows the influence of corrosion rates and residual stresses on the optimal maintenance planning.     

Predictive maintenance of shield tunnels

Scientific maintenance methodologies are specially needed to enhance system reliability and safety, reduce maintenance manpower, spares, and repair costs, eliminate scheduled inspections, and maximize lead time for maintenance and parts procurement. This paper systematically presents a comprehensive methodology and framework for aggressive inspection and condition based predictive maintenance of a shield tunnel consisting of prefabricated lining rings. The framework consists of six components: maintenance purposes, data, modeling and simulation, documentation, managerial schedule, and inspection/maintenance behaviors. These components are interpreted in details as nine necessary parts in a predictive maintenance strategy. The failure mode and effect analysis approach is employed in developing a predictive maintenance strategy for a tunnel structure, with the purpose of prioritizing possible defects in the tunnel in order to facilitate the decision making on predictive maintenance. The system-level lifing analysis method is proposed for the proactive maintenance of the tunnel system. The method includes data preprocessing, risk model establishment, quantitative model validation, empirical lifing analysis, and system-level maintenance schedule. The empirical lifing analysis involves both risk prediction and damage accumulation models for service limit determination, system-level risk analysis, and system-level conditional risk for maintenance schedule. The proposed methodology is demonstrated with the inspection data collected for six typical defects observed in real-world shield tunnels.     

基于成本的长输管道腐蚀缺陷检测及维修规划

提出了基于成本的长输管道腐蚀缺陷的检测及维修模型,将总成本分为检测和维修2部分,根据总成本最小原则确定最优检测及维修规划。最优的检测及维修,是在保证管道在设计工作寿命内的最大腐蚀深度小于满足强度要求的最大腐蚀裕量的基础上,使管道生命周期内总的期望费用最小。针对腐蚀缺陷的发展过程,以最早产生缺陷的尺寸为界限进行划分,对不同腐蚀程度缺陷进行分类修复。通过比较在不同的状态点下进行检测修复所产生的检测和维修总费用,确定最优的检测及维修规划。     

Updating occurrence probability and size of defect for bored piles

To ensure performance of large-diameter bored piles, integrity tests are often conducted after pile construction. It is often impractical to inspect 100% of piles due to high costs and possible delays. Accordingly, the presence of defects may not be fully detected as only a limited number of piles can be inspected. The defect sizes may also be insufficiently predicted based on limited tests. This paper proposes a procedure to predict the occurrence probability of defect and the defect size for piles at a site based on coring examinations supplemented with engineers’ experiences. This procedure is formalized in the Bayesian framework. To update and estimate the occurrence probability and size of pile defects, the concepts of occurrence probability of defect and encounter probability are presented. Then, a method to evaluate the encounter probability is formulated. The occurrence probability of defect is updated based on results from on-site coring. After measurements on encountered defects are taken, the defect size distribution is updated using the proposed procedure. Results from numerical examples indicate that the occurrence probability of defect can be estimated using the proposed procedure in a more rational way. The inspection results from on-site coring have a significant influence on the estimated occurrence probability of defect. The uncertainty in defect size is substantially reduced after being updated with the information on defect sizes from on-site coring. Analysis results can assist the specification of pile inspection program to assure given level of quality assurance.     

Attention-guided multiscale neural network for defect detection in sewer pipelines

Sanitary sewer systems are major infrastructures in every modern city, which are essential in protecting water pollution and preventing urban waterlogging. Since the conditions of sewer systems continuously deteriorate over time due to various defects and extrinsic factors, early intervention in the defects is necessary to prolong the service life of the pipelines. However, prior works for defect inspection are limited by accuracy, efficiency, and economic cost. In addition, the current loss functions in object detection approaches are unable to handle the imbalanced data well. To address the above drawbacks, this paper proposes an automatic defect detection framework that accurately identifies and localizes eight types of defects in closed-circuit television videos based on a deep neural network. First, an effective attention module is introduced and used in the backbone of the detector for better feature extraction. Then, a novel feature fusion mechanism is presented in the neck to alleviate the problem of feature dilution. After that, an efficient loss function that can reasonably adjust the weight of training samples is proposed to tackle the imbalanced data problem. Also, a publicly available dataset is provided for defect detection tasks. The proposed detection framework is robust against the imbalanced data and achieves a state-of-the-art mean average precision of 73.4%, which is potentially applied in realistic sewer defect inspections.     

Macro-crack initiation life for orthotropic steel decks considering weld heterogeneity and random traffic loading

This paper presents a multi-scale approach to predict the macro-crack initiation life (MCIL) of welded joints. This fully adaptive multi-scale technique is designed to take into account micro-scale material heterogeneity due to the existence of defects and to consider the uncertainties regarding defect occurrence and characteristics and traffic loading. The procedure of the proposed approach was introduced along with an orthotropic steel deck. Firstly, a homogenisation method was used to link defects in the heat-affected zone with the macro-scale structure. This allows for estimating the effective Paris constant, required for a Paris Law-based fatigue damage analysis. Secondly, a traffic flow, based on weigh-in-motion measurements, was used to simulate the load effects on the examined joint. Afterwards, the extended finite element method was adopted to calculate the stress intensity factors with respect to the weld geometries. Finally, the damage before macro-crack initiation was obtained using the Paris Law. In addition, Monte Carlo simulation was integrated within this multi-scale crack growth procedure to consider the randomness in pore and inclusion occurrence and characteristics. Hence, the MCIL is expressed in the form of a probability distribution. Results show that the proposed approach enables to provide a rational maintenance and inspection intervention time.     

Capacity loss evaluation of reinforced concrete bridges located in extreme chloride-laden environments

This article provides a comprehensive procedure for the structural performance evaluation and life-cycle cost (LCC) analysis of reinforced concrete highway bridges located in extreme chloride-laden environments. An integrated computational methodology is developed to simulate the chloride intrusion and to estimate the corrosion initiation time. The effects of various influential parameters on the chloride diffusion process are examined and the changes in geometry and material properties of structural members are calculated over the entire life of the bridge. In order to evaluate the global structural degradation due to the corrosion mechanisms, an inventory of bridges with different structural attributes are investigated. The extent of capacity loss is calculated using the moment-curvature and nonlinear static (pushover) analysis. Results of this study are then utilised to find the LCC of bridges. Different inspection and maintenance strategies are considered to minimise the total LCC, which includes the initial construction cost, inspection and maintenance costs and service failure costs. The proposed approach indicates the inspection and maintenance intervals in a way that the inspection and maintenance costs are optimised while the safety of the bridge is ensured.     

城市沥青路面检查井质量通病分析及工艺改进

指出检查井质量通病是市政道路的主要病害，通过近几年工程实践应用，重点从施工工艺的改进消除了该质量通病，从而提高了城市道路的整体质量，延长了沥青路面的使用寿命。     

Automated defect detection for sewer pipeline inspection and condition assessment

To regularly and proactively assess conditions of sewer infrastructure systems to ensure their structural integrity and continuity of services, it is critical to advance the state of automated pipeline inspection and condition assessment. Currently, a critical issue is to address realistic defect detection that deals with real sewer inspection data. This paper presents the findings of a research project that seeks to enable automated detection of defects in sewer pipelines from inspection videos and images. The need for and the challenges of automated defect detection in sewer infrastructure condition monitoring are presented. Based on a general detection and recognition model established in this paper, a change detection based approach which is tailored to solve the challenges in this sewer pipeline domain is described and illustrated through case study.     

Risk-based maintenance strategy for deteriorating bridges using a hybrid computational intelligence technique: a case study

The current bridge inspection and maintenance protocol that is used in most countries focuses primarily on the visible aspects of bridge fitness and underestimates the invisible aspects, such as resistance to scouring and earthquake hazards. To help transportation authorities to better consider both aspects, the present study developed a new computational intelligence system, the so-called risk-based evaluation model for bridge life-cycle maintenance strategy (REMBMS). This model considers the three main risk factors of component deterioration, scouring and earthquakes in order to minimise the expected life-cycle cost of bridge maintenance. Monte Carlo simulation is used to estimate the probability of bridge maintenance. The evolutionary support vector machine inference model (ESIM) was applied to estimate the risk-related maintenance cost using historical data from the Taiwan Bridge Management System (TBMS) database. The time-influenced expected costs were obtained by multiplying each maintenance probability with its associated cost. Finally, the symbiotic organisms search (SOS) algorithm is used to identify the bridge maintenance schedule that optimises the life-cycle maintenance cost. The present study provides to bridge management authorities an effective approach for determining the optimal timing and budget for maintaining transportation bridges.     

Statistical analysis of online strain response and its application in fatigue assessment of a long-span steel bridge

This paper covers reliability assessment of the fatigue life of a bridge-deck section based on the statistical analysis of the strain–time histories measured by the structural health monitoring system permanently installed on the long-span steel bridge under study. Through statistical analysis of online strain responses in the frequency domain using multiple linear regression, a representative block of daily cycles of strain history is obtained. It is further assumed that all cycles of online strain response during bridge service are repetitions of the representative block. The rain-flow counting method is then used to determine the stress spectrum of the representative block of daily cycles. The primary assessment of fatigue life at a given value of failure probability is undertaken for the sample component in a bridge-deck section by using the classification of details for welded bridge components and the associated statistical fatigue model provided by the British Standard BS5400. In order to evaluate bridge fatigue at any value of failure probability, a modified probability model is proposed based on BS5400. The fatigue life of the considered component in the bridge-deck section is then evaluated for some other values of probability of failure which are not included in BS5400 by use of the modified probability model. The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.     

基于寿命函数的斜拉索系统维修更换策略研究

展开寿命周期内拉索劣化规律和维修更换策略的研究,获得桥梁结构的最优成本-效益比,是缆索桥梁养护维修的重要研究内容之一。根据拉索寿命函数和拉索系统的串并联模型,研究斜拉桥拉索系统失效概率变化即结构劣化的规律,分析全寿命周期内不同维修更换措施对结构失效概率的影响。运用周期成本理论,进一步分析不同维修更换时间和更换策略的经济性。结合一斜拉桥模型,验证了模型的适用性,并且以延长使用寿命和累积维修费用最低为目标,获得该桥的最优维修策略。研究表明,寿命函数和周期成本理结合是确定斜拉桥拉索更换优化策略的有效途径,为工程拉索更换策略提供有益的参考。     

Inspection survey of 150 expansion joints in road bridges

Expansion joints are current equipment applied to almost every type of bridge with relatively high maintenance costs. Furthermore, their service life is generally short (often below 10 years) and lower than the bridge expected service life (over 50 years). In this paper, the results of an inspection campaign of 150 expansion joints in road bridges, the first comprehensive survey of the kind, are presented. They allow knowing and characterizing more properly the expansion joints installed in Portuguese roads and highways, namely in terms of their typology, pathology and rehabilitation. It was concluded that: (a) some types of joints have been systematically replaced (open joints, nosing joints with poured sealant, buried joints under continuous surfacing, steel sliding plates); (b) made-to-order joints are no longer prescribed; (c) the transition strip and the anchorage cavities need more maintenance and more frequent rehabilitation than other parts; (d) installment errors and lack of maintenance are the most frequent causes of pathology; (e) direct or indirect visual observation is still the best diagnosis method; and (f) the importance of the defects found depends a lot on the type of joint and of the defect.     

Durability and the factor method of ISO 15686-1

Interest in the service life of buildings and components and the future need for maintenance is growing, and the methodology for service life planning is starting to appear in standards. The standard ISO 15686 prescribes a factor methodology for deciding about the expected service life of a component with a prescribed probability of earlier failure. The methodology is based on extensive knowledge about materials and building technology, and examples of the use of this methodology on building components are of value for the discussion on service life planning. Results from a condition survey of timber windows are used to define the service life and effect of the factor method in the Standard. Wood is a very variable material, and for wooden windows maintenance plays a key role in the durability of the component. In this instance, condition assessment is, therefore, not sufficient to estimate the service life. Information about former maintenance and refurbishment is also needed. The results from a condition assessment and the house owner's answers to a questionnaire are combined to evaluate the estimated service life of the windows. The factors for the standardized method for estimating service life with a given confidence limit are shown to have a wide range in values that give considerable uncertainty to the practical use of the standardized methodology. For example, it is shown that the estimated service life with an 80% confidence limit is much lower than the average service life. Thus, the question is posed whether there is any meaning in estimating the lower limit of service life.     

Durability and the factor method of ISO 15686-1

Interest in the service life of buildings and components and the future need for maintenance is growing, and the methodology for service life planning is starting to appear in standards. The standard ISO 15686 prescribes a factor methodology for deciding about the expected service life of a component with a prescribed probability of earlier failure. The methodology is based on extensive knowledge about materials and building technology, and examples of the use of this methodology on building components are of value for the discussion on service life planning. Results from a condition survey of timber windows are used to define the service life and effect of the factor method in the Standard. Wood is a very variable material, and for wooden windows maintenance plays a key role in the durability of the component. In this instance, condition assessment is, therefore, not sufficient to estimate the service life. Information about former maintenance and refurbishment is also needed. The results from a condition assessment and the house owner's answers to a questionnaire are combined to evaluate the estimated service life of the windows. The factors for the standardized method for estimating service life with a given confidence limit are shown to have a wide range in values that give considerable uncertainty to the practical use of the standardized methodology. For example, it is shown that the estimated service life with an 80% confidence limit is much lower than the average service life. Thus, the question is posed whether there is any meaning in estimating the lower limit of service life.     

Value of information-based decision analysis of the optimal next inspection type for deteriorating structural systems

Deteriorating infrastructure systems require inspections and maintenance to ensure safe operation. System operators are often required to decide the optimal type of inspection to perform, where some inspections are of higher accuracy, and correspondingly higher cost. Life cycle analysis is typically used to determine the optimal inspection type. While life cycle analysis is effective at determining the optimal inspection type, it is also inefficient, requiring analysis of the entire decision sequence throughout the system life cycle. This paper presents an efficient methodology to approximate the decision of the optimal next inspection type without performing a life cycle analysis. This methodology determines the range of the value of information provided by only the next inspection. When the inspection cost is outside the range of the value of information then this method yields the decision of which inspection type to choose, negating the need for life cycle analysis. When the inspection cost for some inspection types lies within the bounds then a subsequent life cycle analysis is required, but perhaps some inspection types can be eliminated, simplifying the life cycle analysis. Thus, this method is complimentary to life cycle analysis, functioning as a quick preliminary assessment. The methodology is demonstrated through a numerical example of a corroding pipeline.     

Allocation of effective maintenance limit for railway track geometry

Abstract

The objective of this study has been to develop an approach to the allocation of an effective maintenance limit for track geometry maintenance that leads to a minimisation of the total annual maintenance cost. A cost model was developed by considering the cost associated with inspection, preventive maintenance, normal corrective maintenance and emergency corrective maintenance. The standard deviation and extreme values of isolated defects of the longitudinal level were used as quality indicators for preventive and corrective maintenance activities. The Monte Carlo technique was used to simulate the track geometry behaviour under different maintenance limit scenarios and the effective limit was determined which minimises the total maintenance cost. The applicability of the model was tested in a case study on the Main Western Line in Sweden. Finally, a sensitivity analysis was carried out on the inspection intervals, the emergency corrective maintenance cost and the maintenance response time. The results show that there is an optimal region for selecting an effective limit. However, by considering the safety aspects in track geometry maintenance planning, it is suggested that the lower bound of the optimal region should be selected.