Industry Material and Procedure – Wrought Iron
The drop in casualties can be attributed to two factors. First, the methods companies use to replace their old, corroded pipelines are becoming safer for workers. Second, as the pipeline industry becomes more profitable, more money is being spent on research and development into the construction of safer pipelines. In the past, pipelines were constructed out of low carbon, iron-based metals, which are corrodible. Pipeline built and placed in the 1950s and 60s accounts for approximately 50% of the total pipeline infrastructure (PHMSA, 2011a). According to a report by the US Department of Transportation, 24% of hazardous liquid pipeline system incidents are the result of corrosion (PHMSA, 2011a). The most failure-prone material used in active pipelines is wrought iron. State and federal incentives have brought the amount of wrought iron in America’s pipeline system down significantly. Wrought iron, which remains in only 2.3% (PHMSA, 2014b) of active main pipelines, but still account for 10.2% of incidents along gas distribution mains, is four times as likely to fail as the rest of the pipeline system, and in the case of failure, is over twice as likely to cause a fatality or injury (PHMSA, 2014b).
While no company constructs new pipeline made of wrought iron, one dangerous possibility for the future of wrought iron pipelines is to reactivate them without replacing their material. Tennessee Gas Pipeline Co. has proposed to repurpose a wrought iron pipeline which was partly laid in 1940 (Bruggers, 2014). Tennessee Gas Pipeline Co. wants to use this pipeline to carry natural gas liquids from a fracking well. Both the federal PHMSA and the local residents are against this repurpose. The pipeline is within 200 feet of citizens’ houses and travels over the Dix River and nearby caves, a major problem if a leak were to occur, because both landforms connect to the local water supply (Bruggers, 2014). The concern is based on histories of repurposed pipelines failing, such as a 20-year-old pipeline which spilled 20,000 barrels of crude oil over a North Dakota wheat field (Tackett, 2013). The failure, a hole a quarter-inch in diameter, was likely caused by the pipeline rusting over and corroding due to the age of the pipeline.
Industry Material and Procedure – New Material
Newly implanted pipelines are made of plastic or steel. Plastic is the primary material used for underground natural gas transportation to limit corrosion, to which metal is prone (Underground, 2015). Due to thermodynamic fluid mechanics favoring the transportation of fluid at the same viscosity, the thermal benefits of steel make it the primary material used for pipelines carrying liquids (Thermodynamics, 1992). The industry standard for steel pipelines is steel grade X70, an iron alloy. Occasionally, either X60 or X80 will be used. The grade refers to the pressure in pounds per square inch (psi) the steel can withstand before becoming stressed and deformed. X60 withstands up to 60,000 psi, X70 up to 70,000 psi, etc. (White, 2012). The new alloys are not impervious to fatigue and eventual failure from exposure to compounds such as hydrogen gas, sulfur dioxide, and carbon dioxide (Drexler, et al., 2013, Xiang, et al., 2013), but compared to wrought iron are vast improvements.