Corrosion: An Integrity Threat to the Entire Oil and Gas Asset Value Chain

Introduction

In spite of the many improvements in pipeline integrity management over the last decade, pipeline operators continue to experience both internal and external corrosion problems. In the 2002 Cost of Corrosion¹ study, the cost of corrosion to the transmission pipeline industry alone was estimated between $5.4 and $8.6 billion dollars annually. Corrosion damage leading to leaks and ruptures increases pipeline operating risks associated with health, safety, the environment, product deliverability, and can result in regulatory actions and litigation against pipeline operators.

The causes of internal and external corrosion vary, however the common thread for nearly all corrosion is contact between the pipe metal and some form of water. The potential for external corrosion is influenced by factors such as the environment in which the pipeline is installed (e.g., atmospheric, buried, or submerged), coating type and condition, efficacy of cathodic protection, soil type, construction practices, and operating temperatures. In general, these factors apply consistently to all pipelines regardless of the fluids transported. The potential for internal corrosion, on the other hand, is closely tied to the type of fluids transported by the pipeline and to operating conditions, such as flow rate, pressure, and maintenance practices.

Data collected by the PHMSA on US regulated pipelines² shows that internal corrosion incidents from 1994 through 2013 represented 9% of all hazardous liquid incidents, 12% of all gas transmission incidents, and 49% of all gas gathering incidents. These statistics illustrate how different fluid compositions affect susceptibility to internal corrosion, as gas gathering systems often transport natural gas and hydrocarbons containing condensed and produced water. Gas and crude oil transmission pipelines are far less likely to experience water accumulations as compared to gathering pipelines and therefore, they are relatively less susceptible to internal corrosion.

Since the transported fluids and operating conditions vary across the oil and gas value chain, corrosion susceptibility also varies significantly, along with the strategies needed to manage corrosion. The “value chain” runs from the production well to the end user of the hydrocarbon, progressing from downhole, to production gathering, to processing, to transmission and storage, to refining, and finally to distribution. To effectively manage asset integrity relative to the threat of corrosion, it is essential that integrity and risk management professionals clearly understand the unique conditions that may promote external and internal corrosion in their assets.

In managing corrosion, a continuous process of threat assessment, prevention and mitigation, and monitoring is typically applied. However, the overall success of the process rests upon correctly assessing the corrosion threat mechanisms that are most relevant. Understanding the common factors that promote corrosion threats in the oil and gas value chain helps operators create effective inspection strategies.