Development of advanced reliability assessment models with applications in integrity management of onshore energy pipelines

This thesis addresses some of the predominant engineering challenges involved in the reliability-based integrity management of energy pipelines. The aim is to conjointly consider realistic safety threats and integrity management strategies, such as in-line inspections, criteria for excavation and direct assessment of energy pipelines. Towards this, advanced algorithmic model-based approaches are developed and proposed, based on fundamental principles of structural reliability analyses, stochastic degradation processes, machine learning through Bayesian statistics, multivariate data analysis, hazard modelling and interval probabilities, in an effort to quantify uncertainties that impose threats and define risks to the integrity of energy pipelines. First, the quantification of failure probabilities for onshore gas pipelines subjected to external metal-loss corrosion is addressed. The probabilistic methodology proposed is based on a robust integration of stochastic processes within a structural reliability analysis (SRA) framework. It comprehensively accounts for the temporal uncertainty of multiple metal-loss corrosion defects and efficiently predicts long-term time-dependent reliability at the pipe segment level. The application of the methodology is illustrated through two case studies, based on two distinct inspection and maintenance strategies. In specific, an industry-consistent maintenance strategy is considered in one of them, namely External Corrosion Direct Assessment (ECDA). The reliability, originally evaluated at the segment level, is incorporated in an investigation of the influence of imperfect ECDA actions at the system level. The methodology is also applied considering a realistic maintenance and repair strategy based on in-line inspections (ILI). Again, it deals with multiple metal-loss corrosion defects, facilitates the identification of the critical ones and provides expected reliability forecasts for the whole lifecycle of the pipe segment. Second, two distinct statistical models are proposed that can account for multiple integrity threats, since historical failures form an integral part of informed integrity management strategies. For the implementation actual incidents are employed, derived from the Pipeline and Hazardous Material Safety Administration (PHMSA) database, which contains data of incidents of existing gas transmission pipelines, providing useful insights into their state at the time of the analysis. In both statistical models, a non-repairable system approach is considered, as opposed to the repairable system approach commonly adopted in energy pipeline studies. In the first one, a well-established approach from reliability and survival analysis is employed, known as nonparametric predictive inference (NPI). This method provides interval probabilities, also known as imprecise reliability, in that probabilities and survival functions are quantified via upper and lower bounds. The focus is on the rupture of a future pipe segment, due to a specific cause among a range of competing risks. The second statistical methodology adopts a parametric hybrid empirical hazard model, complemented with a robust data processing technique, i.e. the non-linear quantile regression, for reliability analysis and prediction. It provides inferences on the complete lifecycle reliability of the average pipe segment of a region under study. For the purpose of cross-verification, the results of the second statistical model are compared with these of the second aforementioned structural reliability model, which is based on the ILI maintenance and repair strategy. Finally, a robust methodology for estimation of small posterior failure probabilities for gas pipelines based on available inspection data is presented. The analysis of the data is based on the BUS (Bayesian Updating with Structural reliability methods), which sets an analogy between Bayesian updating and a reliability problem. The structural reliability method adopted is Subset Simulation (SuS) and the whole analysis is referred to as BUS-SuS. Two case studies are carried out to illustrate and validate the proposed methodology. In the first case study, hierarchical BUS-SuS is implemented on an existing gas pipeline containing metal-loss corrosion defects and is validated against field data. The reliability of the pipe segment is evaluated in terms of three distinctive failure modes, namely small leak, large leak and rupture. In the second case study, the Bayesian updating is conducted by using BUS-SuS in conjuction with the data augmentation (DA) technique. Simulated data, corresponding to an existing gas pipeline with high-pH stress corrosion cracking (SCC) features and constant internal pressure loading, are employed to illustrate and validate the proposed model. Furthermore, the dependence among the growths of different crack features is taken into account, using the Gaussian copula. At the end, the sensitivity of both the stochastic growth model and pipe segment reliability to different dependence scenarios is investigated. All the aforementioned proposed methodologies aim to assist pipeline operators in decision making and informed implementation of integrity management strategies

Bayesian analysis of small probability incidents for corroding energy pipelines

This paper presents a new methodology for estimation of small posterior failure probabilities for underground energy pipelines, based on external corrosion inspection data. The analysis of the data is based on the BUS (Bayesian Updating with Structural reliability methods) that sets an analogy between Bayesian updating and a reliability problem. The structural reliability method adopted herein is Subset Simulation (SuS) and the whole analysis is referred to as BUS-SuS. Corrosion data obtained from multiple in-line inspections (ILI) of an underground natural gas pipeline are used to illustrate and validate the proposed methodology. The growth of the corrosion defects is modelled through an hierarchical Bayesian framework and the ILI associated measurement errors are comprehensively considered. Through this efficient method, it is ensured that the final samples have reached the posterior distribution. It is also more advantageous over other methods typically employed for Bayesian analysis of corroding pipelines, because it allows the estimation of small posterior failure probabilities directly within the same framework. The proposed methodology can be incorporated in a reliability-based pipeline integrity management program to assist engineers in selecting suitable maintenance strategies

Reliability prediction for corroding natural gas pipelines

This paper aims to evaluate time-dependent reliability of a corroding onshore underground natural gas pipeline system over its lifetime. The reliability analysis is segment-based, as opposed to defect-based and the pipe segment is examined with respect to external metal loss corrosion. The non-homogeneous Poisson process (NHPP) and an empirical power law model are employed for generation of corrosion defects over time and for defect growth, respectively. The time-dependent probability of failure is evaluated by employing the limit state function for burst under internal pressure. Internal pressure is modelled using a Poisson square wave process-based method (PSWP). Thereinafter, the study uses the aforementioned analysis, in conjunction with a heuristic model, in order to investigate the influence of imperfect repairs on the reliability prediction of the pipeline system. The heuristic method is known as split system approach and it is used to describe the changes in reliability of the pipeline system over its lifetime with the consideration of multiple maintenance actions. A numerical example of the described methodology is presented based on a chosen maintenance policy. A parametric study is conducted to examine the impact of instantaneous generation rate of NHPP model, PSWP model and reliability control limit on the results of the numerical application. The proposed methodology aims to assist engineers in the decision making with regard to corrosion maintenance strategies

Statistical model and structural reliability analysis for onshore gas transmission pipelines

The reliability of gas pipelines against rupture can be estimated based on historical failure data and theory of structural reliability. In this study, an integrated model for reliability analysis of failure data is presented jointly with a robust structural reliability model for the purpose of comparison and cross-verification. The statistical model adopts a parametric hybrid empirical hazard model complemented with a robust data processing technique known as the nonlinear quantile regression for reliability analysis and prediction. This model provides inferences on the complete lifecycle reliability of the average pipe segment in the region under study. The structural reliability model is segment based and estimates rupture probabilities due to external metal loss corrosion. The non-homogeneous Poisson process is used to model the generation of new defects and the Poisson square wave process is used to model the growth of defects. The internal pressure load is modelled as a discrete Ferry-Borges stochastic process. Then, an inspection and maintenance plan is incorporated based on ASME B31.8S code of practice, for the service life considered. The probability of detection and measurement error of the inspection tools is also incorporated in the model. A numerical example of these models in an industrial context is presented. Onshore gas transmission pipeline rupture data for the period from 2002 to 2014, was obtained from the United States Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) database and analysed. The comparative study of the proposed methodologies can assist gas pipeline operators in the informed implementation of optimal maintenance strategies based on risk prioritization

Competing risks survival analysis of ruptured gas pipelines: A nonparametric predictive approach

Risk analysis based on historical failure data can form an integral part of the integrity management of oil and gas pipelines. The scarcity and lack of consistency in the information provided by major incident databases leads to non-specific results of the risk status of pipes under consideration. In order to evaluate pipeline failure rates, the rate of occurrence of failures is commonly adopted. This study aims to derive inductive inferences from the 179 reported ruptures of a set of onshore gas transmission pipelines, reported in the PHMSA database for the period from 2002 to 2014. Failure causes are grouped in an integrated manner and the impact of each group in the probability of rupture is examined. Towards this, nonparametric predictive inference (NPI) is employed for competing risks survival analysis. This method provides interval probabilities, also known as imprecise reliability, in that probabilities and survival functions are quantified via upper and lower bounds. The focus is on a future pipe component (segment) that ruptures due to a specific failure cause among a range of competing risks. The results can be used to examine and implement optimal maintenance strategies based on relative risk prioritization

Bicycles paths in Greece-The example of the city of Larisa

247 σ.Η παρούσα διπλωματική έχει ως αντικείμενο την καταγραφή των εξελίξεων και των προοπτικών σε ότι αφορά την κατασκευή ποδηλατοδρόμων στις ελληνικές πόλεις στο πλαίσιο της βιώσιμης κινητικότητας. Συγκεκριμένα, η εργασία ασχολείται με τα εξής ζητήματα: • Την ανάλυση της ανάγκης που προκύπτει παγκοσμίως στις σύγχρονες πόλεις για βιώσιμη ανάπτυξη και για ύπαρξη βιώσιμης κινητικότητας σε αυτές. • Την εξέταση παραδειγμάτων από ευρωπαϊκές πόλεις στις οποίες το ποδήλατο είναι διαδεδομένο μέσο μετακίνησης και των ωφελειών που προκύπτουν από τη χρήση του. • Την ανάγκη για αλλαγή φιλοσοφίας στον πολεοδομικό και κυκλοφοριακό σχεδιασμό των ελληνικών πόλεων και για ένταξη του ποδηλάτου. • Την ανάγκη ένταξη του ποδηλάτου ως κύριου μέσου και όχι ως μέσου αποκλειστικά για αναψυχή. • Την αναφορά των τεχνικών προδιαγραφών για κατασκευή ποδηλατοδρόμων στην Ελλάδα. • Την εξέταση του νομικού πλαισίου που αφορά το σχεδιασμό του χώρου στην Ελλάδα και καθώς και αυτού που αναφέρεται στο ποδήλατο. Σκοπός της εργασίας είναι να αναδείξει τους λόγους οι οποίοι κάνουν σήμερα επιτακτική την ανάγκη μείωσης της χρήσης του αυτοκινήτου στο εσωτερικό των πόλεων και ένταξης του ποδηλάτου ως μέσου εξυπηρέτησης καθημερινών αναγκών μετακίνησης καθώς και να παρουσιάσει το ισχύον τεχνικό και νομικό πλαίσιο για την ένταξη του ποδηλάτου στις ελληνικές πόλεις. Η Μεθοδολογία που ακολουθήθηκε ήταν η προσέγγιση και ανάλυση του τρόπου με τον οποίον είναι δυνατόν να ενταχθεί το ποδήλατο στην ελληνική πόλη καθώς και οι λόγοι που η ένταξη αυτή θεωρείται αναγκαία. Κατόπιν, αναλύθηκε το θεσμικό πλαίσιο που συνοδεύει την ένταξη αυτή και με βάση αυτά παρουσιάστηκε το παράδειγμα της πόλης της Λάρισας. Πηγές της εργασίας αποτέλεσαν πανεπιστημιακά συγγράμματα του Εθνικού Μετσόβιου Πολυτεχνείου, η βιβλιοθήκη του Ε.Μ.Π., η βιβλιοθήκη του Τ.Ε.Ε., πρακτικά συνεδρίων και άλλων εκπαιδευτικών φορέων μηχανικών, πληθώρα ιστοσελίδων στο διαδίκτυο καθώς και το έργο της Μονάδας Βιώσιμης Κινητικότητας της σχολής Αγρονόμων και Τοπογράφων Μηχανικών του Εθνικού Μετσόβιου Πολυτεχνείου. Η μελέτη διαρθρώνεται σε 7 ενότητες: Στο κεφάλαιο-εισαγωγή διατυπώνεται η σκοπιμότητα της μελέτης και περιγράφονται οι κύριοι στόχοι της. Το πρώτο κεφάλαιο παρουσιάζει συνοπτικά τις έννοιες της βιώσιμης ανάπτυξης και της αστικής κινητικότητας στις σύγχρονες πόλεις. Στο δεύτερο κεφάλαιο παρουσιάζονται οι κοινοτικές οδηγίες και οι πολιτικές προώθησης του ποδηλάτου και της βιώσιμης κινητικότητας από την Ευρωπαϊκή Ένωση , ενώ δίνονται παραδείγματα ποδηλατικών υποδομών από συγκεκριμένα κράτη-μέλη. Το τρίτο κεφάλαιο παρουσιάζει την ελληνική υστέρηση στον τομέα της βιώσιμης κινητικότητας και του ποδηλάτου και παρουσιάζει τις προσπάθειες που γίνονται. Στο τέταρτο κεφάλαιο παρουσιάζεται η τεχνογνωσία στην οποία βασίζεται η κατασκευή ποδηλατικών υποδομών στην Ελλάδα. Στο πέμπτο κεφάλαιο παρουσιάζεται το νομικό πλαίσιο σχεδιασμού του χώρου στην Ελλάδα καθώς και οι αναφορές του Κώδικα Οδικής Κυκλοφορίας στο ποδήλατο. Στο έκτο κεφάλαιο παρατίθεται το παράδειγμα της πόλης της Λάρισας η οποία πραγματοποιεί αποφασιστικά βήματα για τη διάδοση της χρήσης του ποδηλάτου στο εσωτερικό της. Η εργασία ολοκληρώνεται με ορισμένες προτάσεις-συμπεράσματα εφ’όλης της ύλης. (έβδομο κεφάλαιο)This diploma thesis is to record developments and prospects in terms of the construction cycle in the Greek cities in the context of sustainable mobility. Specifically, the work addresses the following issues: • The analysis of the need arising in the modern world cities for sustainable development and existence of sustainable mobility in them. • Examining examples from European cities where cycling is a widespread means of travel and the benefits resulting from its use. • The need for paradigm shift in urban planning and traffic of the Greek cities to join the bike. • The need to integrate cycling as a main instrument and not as an instrument solely for recreation. • The reference of the technical specifications for construction of bicycle paths in Greece. • Examining the legal framework for the design of a site in Greece, as well as that specified on the bike. The purpose of the paper is to highlight the reasons which now make it imperative to reduce car use in inner cities and the integration of cycling as a means of handling everyday transport needs and to present the current technical and legal framework for the integration of cycling in Greek cities. The methodology used was the approach and analysis of how they can join the bike in the Greek city and the reasons for this integration is necessary. Then analyzed the institutional framework that accompanies such integration on the basis of these presented the example of the city of Larissa. Sources of work have textbooks from the National Technical University, NTUA's library, the library of TEE, conference and other educational institutions engineering, multiple sites on the Internet and the work of the Unit for Sustainable Mobility of School of Rural and Surveying Engineering of NTUA. The study is divided into 7 sections: This chapter out-introduction feasibility study and outlining the main objectives. The first chapter outlines the concepts of sustainable development and urban mobility in modern cities. The second chapter presents the EU directives and policies to promote cycling and sustainable mobility in the European Union and cycling infrastructure are examples of specific states. The third chapter presents the Greek behind the field of sustainable mobility and cycling and shows the efforts being made. The fourth chapter presents the expertise on which the construction of cycling infrastructure in Greece. The fifth chapter presents the legal framework of the design space in Greece and the reports of the Highway Code on the bike. The sixth chapter shows the example of the city of Larissa, which makes decisive steps towards increasing the use of the bicycle at home. The work concludes with some suggestions, conclusions Comprehensive. (Seventh chapter)Κωνσταντίνος B. ΠεσίνηςΙωάννης Σπυρόπουλο