	Background

More than 2.7-million miles of pipeline transport roughly two-thirds of our  nation’s domestic energy supply. (See fig. Gathering pipelines: Gas gathering pipelines collect natural gas and  other gases from production areas, while hazardous liquid gathering  pipelines collect oil and other petroleum products from oil well heads. However, external coatings  can be damaged by construction or degrade over time. Cathodic  protection involves applying an electrical current onto the pipeline to  control external corrosion. Pipeline Operators Use Steel, Plastics, and Various Corrosion Prevention Technologies, Which Have a Range of Benefits and Limitations

		Nearly All Federally Regulated Pipelines Are Constructed of Steel or Plastic, Which Involve Various Benefits, Limitations and Costs

The vast majority (over 95 percent) of U.S. gas and hazardous liquid  pipeline miles that PHMSA regulates are constructed of either steel or  plastic, with relatively minor use (less than 5 percent) of other materials,  including composites and iron, according to our analysis of PHMSA data  from 2015. In practice, steel’s strength to withstand high  operating pressures and other design characteristics generally  facilitate its use across all portions of the pipeline network. According to  operators and expert stakeholders, coatings and cathodic protection are  generally a cost-effective way to protect steel pipelines against external  corrosion and stress corrosion cracking, and operators and expert  stakeholders said that coatings and cathodic protection are a relatively  small portion of total pipeline cost. PHMSA Uses Data on Pipelines and Corrosion Prevention to Prioritize Inspections, but Lacks a Process to Assess and Validate the Effectiveness of Its Approach

PHMSA uses data on pipelines and corrosion collected from operators in  its Risk Ranking Index Model (referred to as RRIM) to determine the  frequency of PHMSA’s inspections of operators based on threats to  pipeline integrity, such as ineffective coatings. Moreover,  PHMSA has not used data to assess the model’s overall effectiveness  and lacks a process to do such an evaluation. Without documentation and  a data-driven evaluation process, both of which are consistent with  federal management principles, PHMSA cannot demonstrate the  effectiveness of RRIM in allocating PHMSA’s limited inspection resources  according to pipeline threats or targeting its limited resources to the  greatest threats. PHMSA officials said they used professional judgment to select threat  factors, to determine their associated weights, and to establish the risk  tiers and inspection frequency, but they did not document the rationale or  justification for their decisions, including how, if at all, they used data as  part of developing this approach. The officials said they conducted sensitivity  analyses to calibrate the threat factor weights when they designed  RRIM in 2012, but did not document these analyses. Recommendations for Executive Action

To assess and validate the effectiveness of PHMSA’s RRIM in prioritizing  pipelines for inspection, we recommend that the Secretary of  Transportation direct the Administrator of PHMSA to take the following  two actions: document the decisions and underlying assumptions for the design of  RRIM, including what data and information were analyzed as part of  determining each component of the model, such as the threat factors,  weights, risk tiers, and inspection frequency. The Department of Transportation and NTSB also  provided technical comments, which we incorporated as appropriate. This appendix provides perspectives obtained from  interviews with a nongeneralizable sample of eight pipeline operators and  eight additional stakeholders with expertise on pipeline materials and  corrosion (expert stakeholders) on (1) the use of pipeline materials and  corrosion prevention technologies internationally, and (2) the potential  improvements in pipeline materials and corrosion prevention  technologies. Appendix II: Objectives, Scope and Methodology

The objectives of this report were to determine (1) the pipeline materials  and corrosion prevention technologies that are used in the gas and  hazardous liquid pipeline network and their respective benefits and  limitations; (2) how selected pipeline operators train personnel to manage  corrosion and the challenges that exist in ensuring personnel are  qualified, and (3) how the Pipeline and Hazardous Materials Safety  Administration (PHMSA) uses data on pipelines and corrosion prevention  to inform its inspection priorities. We assessed the data’s reliability by  reviewing PHMSA reports, analyzing the data to identify any outlier  values, and interviewing PHMSA officials.
Why GAO Did This Study

The U.S. energy pipeline network is composed of over 2.7-million miles of pipelines transporting gas and hazardous liquids. While pipelines are a relatively safe mode of transportation, incidents caused by material failures and corrosion may result in fatalities and environmental damage. PHMSA, an agency within the Department of Transportation, inspects pipeline operators and oversees safety regulations.
2016 pipeline safety legislation included a provision for GAO to examine a variety of topics related to pipeline materials and corrosion. This report addresses: (1) the materials and corrosion-prevention technologies used in the pipeline network and their benefits and limitations and (2) how PHMSA uses data on pipelines and corrosion to inform inspection priorities, among other topics. GAO analyzed PHMSA's 2010–2016 data; reviewed PHMSA regulations; and interviewed PHMSA officials and representatives of nine states selected based on pipeline inspection roles, eight pipeline operators—providing a range of sizes, geographic locations, and other factors—and eight stakeholders selected for expertise on pipeline and corrosion issues.

What GAO Found

The U.S. gas and hazardous liquid pipeline network is constructed primarily of steel and plastic pipes, both of which offer benefits and limitations that present trade-offs to pipeline operators, as do corrosion prevention technology options. According to data from the Pipeline and Hazardous Materials Safety Administration (PHMSA), over 98 percent of federally regulated pipelines that gather natural gas and other gases and hazardous liquid products, such as oil, and transmit those products across long distances are made of steel. An increasing majority of pipelines that distribute natural gas to homes and businesses are made of plastics. Steel pipelines are manufactured in various grades to accommodate higher operating pressures, but require corrosion protection and cost more than plastics, according to operators and experts. In contrast, plastics and emerging composite materials generally are corrosion-resistant, but lack the strength to accommodate high-operating pressures. Operators use a range of technologies to protect steel pipes from corrosion, including applying coatings and cathodic protection, which applies an electrical current to the pipe. (See fig.) While such technologies are generally considered effective, operators and experts stated that coatings degrade over time and that cathodic protection requires ongoing maintenance and costs to deliver the current over long pipeline distances, among other considerations.
PHMSA uses materials and corrosion data collected from operators in its Risk Ranking Index Model to determine the frequency of PHMSA's inspections of operators based on threats, such as ineffective coatings, to pipeline integrity. PHMSA officials said they used professional judgment to develop their model, but did not document key decisions for: (1) the threat factors selected, (2) their associated weights, or (3) the thresholds for high, medium, and low risk tiers for pipeline segments inspected by PHMSA. Moreover, PHMSA has not used data to assess its model's overall effectiveness, as would be consistent with federal management principles. PHMSA officials said they have not established an evaluation process because they consider the model to be effective in prioritizing inspections. Although PHMSA officials said they analyzed the model when they developed it in 2012, they have not done so since that time and did not document the results of this initial analysis. Without documentation and a data-driven evaluation process, PHMSA cannot demonstrate the effectiveness of the model it uses to allocate PHMSA's limited inspection resources.

What GAO Recommends

GAO recommends that PHMSA document the design of its Risk Ranking Index Model and implement a process that uses data to periodically assess the model's effectiveness. The Department of Transportation agreed with our recommendation and provided technical comments, which we incorporated as appropriate.