Corrosion Control In Oil And Gas Pipelines

By Ben H. Thacker, Glenn M. Light, James F. Dante, Elizabeth Trillo, Fengmei Song, Carl F. Popelar, Kent E. Coulter and Richard A. Page, Southwest Research Institute® San Antonio, TX | March 2010 Vol. 237 No. 3

RFEC system for inspection of unpiggable pipelines.

In the United States, the annual cost associated with corrosion damage of structural components is greater than the combined annual cost of natural disasters, including hurricanes, storms, floods, fires and earthquakes(1). Similar findings have been made by studies conducted in the United Kingdom, Germany, and Japan.

According to the U.S. Department of Transportation Office of Pipeline Safety, internal corrosion caused approximately 15% of all reportable incidents affecting gas transmission pipelines over the past several years, leading to an average cost of $3 million annually in property damage, as well as several fatalities. The need to manage and mitigate corrosion damage has rapidly increased as materials are placed in more extreme environments and pushed beyond their original design life.

Typical corrosion mechanisms include uniform corrosion, stress corrosion cracking, and pitting corrosion (Figure 1). Corrosion damage and failure are not always considered in the design and construction of many engineered systems. Even if corrosion is considered, unanticipated changes in the environment in which the structure operates can result in unexpected corrosion damage. Moreover, combined effects of corrosion and mechanical damage, and environmentally assisted material damage can result in unexpected failures due to the reduced load carrying capacity of the structure.

corr1.JPG
Figure 1: Localized corrosion in process piping, such as in the stainless steel pipe shown here, can lead to through-wall penetration (inset).

Ensuring long-term, cost-effective system integrity requires an integrated approach based on the use of inspection, monitoring, mitigation, forensic evaluation, and prediction. Inspections and monitoring using sensors can provide valuable information regarding past and present exposure conditions but, in general, they do not directly predict remaining life. Carefully validated computer models, on the other hand, can predict remaining life; however, their accuracy is highly dependent on the quality of the computer model and associated inputs. Mitigation (corrosion prevention) methods and forensic evaluations play a key role in materials selection, assessment and design. All of these corrosion-control elements represent long-standing areas of research and development at Southwest Research Institute® (SwRI®).

Pipeline Inspection
A significant portion of many pipeline systems cannot be inspected through traditional methods. Nondestructive evaluation (NDE) and inspection tools are critical to assessing the integrity of pipelines. Traditional NDE methods involve the use of pipeline inspection gauges (PIGs), which travel through the inside of a pipe and detect the presence of mechanical damage or corrosion.

Researchers at SwRI have developed an inspection system for inspecting pipelines that cannot accommodate traditional PIGs (Figure 2). This system uses remote field eddy current (RFEC), and was designed for use with the Carnegie Mellon Explorer II Robot. However, this technology can be adapted to other transport mechanisms. The system can expand to inspect 6-8 inch (150-200 mm) diameter lines. The sensor arms retract to accommodate line restrictions, such as elbows, tees and gate valves.

corr3.JPG
Figure 2. RFEC system for inspection of unpiggable pipelines.