Statistical Modeling of Corrosion Failures in Natural Gas Transmission Pipelines

Abstract

Natural gas pipelines are a critical component of the U.S. energy infrastructure.The safety of these pipelines plays a key role for the gas industry. Therefore, the understanding of failure characteristics and their consequences are very important for designing future operations, operating expenditure, and maintenance decisions.The oil and gas industry spends billions of dollars annually for the corrosionrelated cost of the transmission pipelines, the costs which increases due to aging and deterioration processes in pipeline networks. Therefore, pipeline operators need to rethink their corrosion prevention strategies. These results of corrosion failures are forcing the companies to develop accurate maintenance models based on failure frequency. Statistical methods for modeling pipeline failures and proper maintenance decisions play a key role in future safety of lines, to reduce the rate of occurrence of failures, and the cost-effective operation of pipelines.This thesis is focused on two challenges. The first challenge is to estimate the failure rate of natural gas transmission pipeline networks from the previous incidents' data in the United States. A specific objective of this part is to determine the characterization of the failure modes of the transmission pipelines, and to develop the statistical models based on the reliability of a repairable system. The second challenge is to develop the optimal preventive replacement actions by using well-developed optimization models. The objective of the second part is to choose appropriate iii maintenance policies based on the statistical models and to find the optimal maintenance policies.In this thesis, two of the most commonly applied stochastic models, which are the homogeneous Poisson process and the power law process, are used for the estimation of the failure rate. The point and interval estimators of the failure intensity function are provided and the accuracy of the stochastic models is tested for each determined failure mode. Finally, appropriate maintenance models will be presented for planning preventive maintenance and replacement activities for a repairable and maintainable system. It is assumed that pipeline systems could be restored to operation requirements by some minimal repair process instead of replacement after each failure.iv DEDICATION This thesis is dedicated to my parents who supported me throughout my studies.

An Optimal Preventive Maintenance Model for Natural Gas Transmission Pipelines

“…This study focuses on finding optimal preventive maintenance decision in natural gas pipeline networks. In this paper, the pipeline reliability models, which were developed by Cobanoglu et al (2015), were utilized to determine the optimal maintenance policy in a realistic way for pipeline systems. Moreover, the aim of this paper is to present mathematical models for scheduling preventive maintenance and replacement activities.…”

“…The failure rate, which is used to express reliability of a system, is affected by many factors such as the environmental conditions, internal variables, structural characteristics, and maintenance variables. Cobanoglu et al (2015) performed a comprehensive analysis of pipeline internal and external corrosion and concluded that the corrosion trend is dominantly deteriorating for external and internal corrosion with a few exceptions on stationary and improving. The results of the reliability trend in the pipeline systems for internal corrosion are shown in Table 1.…”

“…The final expressions are given for the cumulative number of internal failures for each predetermined decade of installation are shown in Table 1. The results of the reliability trend analysis in the pipeline systems for external corrosion are shown in Table 2 (Cobanoglu et al, 2015). Based on the results, the pipeline systems for external corrosion failures can be modeled by the power law process for all data, 1940-1949, 1950-1959, and 1960-1969.…”

Experimental and Numerical Prediction Model for the Dangerous Radius of Natural Gas Leakage in Soil

“…With the continuous growth of natural gas consumption, buried pipelines, as the main transportation method of natural gas, may leak due to corrosion, aging, or human damage during transportation. , Similar problems also exist in the subsea pipeline transportation. − The complex soil environment around the pipeline makes it difficult to detect natural gas leakage in time, which may cause serious economic losses and casualties. − …”