ABSTRACT
Pipeline integrity programs require validation techniques such as in-line inspection (ILI), pressure testing (PT), or direct assessment (DA). Many unpiggable pipelines present operational restrictions for the use of ILI tools. DA is applied through four steps: data gathering; indirect examination (IDi); detailed examination (DEx); and post-assessment. The flow and corrosion models used for the IDi are physics- based and do not quantify the uncertainties in the variables, the models, nor the corrosion process. The selection of verification sites for the DEx from the IDi, is not risk based. The post-assessment does not include a formal risk evaluation. The purpose of this paper is to present a framework for the integrity assessment of unpiggable pipelines, which are subject to internal corrosion. This integrity assessment is done by combining probabilistic flow and corrosion models with risk assessment. The flow model calculates variables that affect the corrosion process, thereby enhancing the predictability of the corrosion model. A risk analysis combines the information from the corrosion model with a consequence model to define the verification sites, and field verification is used to update the corrosion model. Risk evaluation uses the output of the risk analysis to recommend optimal inspection, maintenance, and risk mitigation strategies.
INTRODUCTION
Natural resources in the form of oil and gas are the predominant forms of energy used to satisfy the requirements of modern society1. The exploration and production of these resources often occurs in remote locations and pipelines are used to deliver the raw resources to processing facilities in more populated regions. Pipelines, serving as the transportation infrastructure for oil and gas, are essential throughout all stages of the production process. When compared to rail or highway tankers, pipelines are considered to be one of the safest methods to transport hazardous liquids and gases1-5. Despite their safety, pipelines sometimes fail due to different causes. These causes include design and construction errors; incorrect operations or maintenance; unintentional damage; vandalism; degradation mechanisms; and natural forces2,6. Figure 1 presents a summary of the causes of pipeline failures in Alberta, Canada, as identified by the Alberta Energy Regulator7. The consequences of pipeline failure include human casualties, environmental impact, and asset destruction8. Failures can lead to direct and indirect costs. Direct costs form part of the operating expenses (Opex) and include loss of product, property damage, personnel injury or death, clean-up and recovery, and repair costs9. Indirect costs, in contrast, do not form part of the Opex and include environmental clean-up, negative impact on an operator's public image, legal costs, and loss of throughput9. In order to reduce the risk of failure, operators implement pipeline integrity programs (PIPs) to improve the safety of pipelines.
