Corrosion Control In Oil And Gas Pipelines

Forensic Evaluations
Although a comprehensive corrosion-control program based on inspection, monitoring and model predictions can be an effective means for controlling pipeline corrosion, unexpected events or undocumented changes in operating conditions can still lead to premature pipeline failure. When these occur, it is essential to perform a thorough forensic evaluation of the failure to determine the failure mechanism and its root cause. By identifying the root cause of the failure, the pipeline operator will know if this resulted from an event or operating condition outside of the general conditions included in the corrosion-control program.

Steps can then be identified to mitigate future failures by eliminating recurrence of the event. If such an event is not identified as the root cause of failure, the results of the evaluation can be instrumental in identifying necessary changes to the corrosion-control program. Additionally, destructive evaluations, which are a routine part of a forensic evaluation, can be a valuable tool for validating the effectiveness of a corrosion-control program.

Summary
Aging infrastructure, increasing performance requirements, cost and safety are all driving the need for more comprehensive corrosion control. Experimental assessments of materials in extreme environments will always play a critical role in supporting material selection and design. More recently, the role of computer modeling is playing a more prominent role. As our understanding of the fundamental mechanisms of environmental effects on materials improves, our ability to model these fundamental mechanisms and predict the integrity of complex structures and systems has grown.

These models, however, require information regarding initial conditions, operational conditions, calibration and, most importantly, validation of the predictions. Inspection tools, sensors, and monitoring systems provide key information, but they cannot alone provide estimates of future performance. By coupling inspection, monitoring, mitigation, forensic evaluation, and prediction, a comprehensive corrosion-control program can be realized. Subsequent remedial actions can then be devised to counteract the effects of corrosion, thereby helping to assure the integrity of aging systems.

Acknowledgements
The authors acknowledge the research collaborations and technical support of SwRI staff members Dr. Stephen Hudak (Material and Component Integrity), Dr. Hegeon Kwun and Gary Burkhardt (Staff Scientists, Sensor Systems and Non-destructive Evaluation), Dr. Ronghua Wei (Surface Engineering and Materials Chemistry), Drs. Marta Jakab and Gustavo Vasquez (Environmental Performance of Materials), and Steven Clay (Environmental Performance of Materials). The authors also acknowledge the contributions of Dr. Ashok Sabata, Aginova Inc.

References
1. G.H. Koch; Brongers, M.P.H.; Thompson, N.G.; Virmani, Y.P.; and Payer, J.H., "Corrosion Costs and Preventive Strategies in the United States," FWHA-RD-01-156, U.S. Department of Transportation, Federal Highway Administration (2002).