Materials Performance Supplements

Corrosion Management for Pipeline Integrity 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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4 JUNE 2018 W W W.MATERIALSPERFORMANCE.COM CORROSION MANAGEMENT FOR PIPELINE INTEGRIT Y SUPPLEMENT TO MP Pipeline Protection Articles and tape-wrap coatings. Because coatings can degrade over time, CP is also utilized to apply an electrical current onto the pipe- line. Both protective coatings and CP work together to protect the pipeline to disrupt the chemical processes that could lead to external corrosion. To prevent internal cor- rosion, applying plastic liners and additives such as biocides and inhibitors are among common strategies, along with pigging programs. In the field, the degree of protection often depends on a pipeline's age. Starting in 1971, the combined use of external coat- ings and CP became mandated for metallic pipes. However, nearly 50% of U.S. gas trans- mission, distribution, and hazardous liquid pipelines in use today were built before 1970. 2 This means that some of the existing infrastructure was built with materials that are no longer used today. 3 Based on the varying strategies and ages of each pipeline, the RRIM uses data col- lected from operators to assess the proper frequency with which to inspect. The model gives a numeric score to each segment based on weighted "threat factors," including the use of an ineffective external coating; recent significant incidents and enforcem ent actions; the mileage of bare pipe without a protective coating; and miles that were welded prior to 1970 using a low-frequency electric-resistance welding technique, which is a risk factor for corrosion. The risk score determines whether the system is assigned to the high-, medium-, or low-risk tier, and inspected at least every three, five, or seven years, respectively. Regional inspectors are given the opportunity to raise or lower the priority, because in some cases, the inspec- tors on the ground may be able to take addi- tional factors into consideration. These could include the operator's management experience and public concerns about a given pipeline, the GAO says. Each year, PHMSA inspects a portion of the total number of pipeline systems within its purview, which in 2016 was 655 systems. In 2016, PHMSA used RRIM to prioritize 79 systems to be inspected the following year. Of those, 29% were considered high risk, 53% medium risk, and 18% low risk. However, according to the GAO study, PHMSA has not documented its decisions or validated the effectiveness of its models. Specifically, in designing RRIM, GAO says PHMSA did not document its rationale for the selection of the various "threat factors" and their associated weights, or the thresh- olds for risk tiers, and the frequency of inspection associated with each risk tier. "PHMSA officials said they used their professional judgment to select threat fac- tors, to determine their associated weights, and to establish the risk tiers and inspec- tion frequency, but they did not document the rationale or justification for their deci- sions, including how, if at all, they used data as part of developing this approach." For example, RRIM's design places a greater relative weight on longer pipeline units, under the assumption that longer pipeline segments have a greater relative risk than shorter units, the GAO explains. In 2016, the average length of a high-risk inspection system was 1,841 mi (2,963 km), while the average length of medium-risk and low-risk systems was 358 and 49 mi (576 and 79 km), respectively. " While this generally results in more frequent inspections for longer pipeline systems—which may be desirable from PHMSA's perspective—without documen- tation, the rationale for the chosen mileage weighting and the assumed risk of this fac- tor relative to other factors is unclear," the GAO writes. In addition to a lack of documentation, the GAO study also finds that PHMSA lacks a data-driven process to assess the ongoing effectiveness of RRIM and validate that it a pp r o p r i a t e ly p r i o r it i z e s i n sp e c t i o n s . PHMSA officials told GAO that they con- ducted sensitivity analyses to calibrate the weights in RRIM when it was first designed in 2012, but those analyses were not docu- mented . As a result, GAO says because PHMSA has not documented the basis for the design and key decisions of the model and has not formally evaluated its effective- ness, it is unclear how effective the model has been in helping PHMSA manage its inspection resources or maximize benefits to public safety. Example of an external coating and cathodic protection installation and application. Images courtesy of GAO. The U.S. government study recommends that pipeline regulators document the design of a new risk ranking model and implement a process that uses data to periodically assess the model's effectiveness.

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