Since hydraulic fracturing, or “fracking,” was developed in the 1940s, the practice has played an increasingly important role in domestic oil and gas production. Hydraulic fracturing involves forcing viscous fluids into oil and gas wells at pressures that are high enough to unlock deposits trapped deep underground. According to the Interstate Oil and Gas Compact Commission, nine out of 10 gas wells in the U.S. currently use fracturing fluids. And the American Petroleum Institute (API) reports that more than 1 million U.S. wells have used hydraulic fracturing technology.

Use of fracturing fluids has increased in recent years with the exploration of deep gas fields and drilling in areas like the Marcellus Shale in Pennsylvania and Colorado’s Roan Plateau. Fluids used in hydraulic fracturing range from water or compressed gasses, to mixtures of sand and chemical additives that are pumped underground at high pressure to break up blockages. The fracture creates cracks or fissures for easier flow of the oil or gas back to the well bore. Some of these mixtures are proprietary to the companies that provide these services. Typically, 150,000 gallons of fracking fluids containing 800 gallons of chemicals are used per well.

Over-the-road steel tankers, ranging in size from 4,000 to 5,000 gallons, are used to haul hydrochloric acid and solvents such as xylene or toluene to well sites for hydraulic fracturing. “An acid trailer would typically pick up a load of acid from a production or storage facility, haul it to a well site, and offload it for use in fracturing operations,” according to Tnemec coating consultant Lane Salvato. “During high oil or natural gas prices, it is not uncommon for these trailers to work around-the clock.”

Fluids used in the fracking operation are typically hauled to a site in an oilfield that is undergoing well treatment and offloaded into steel “frac” tanks. “For every acid hauler in service, there are roughly 15 frac tanks,” Salvato noted. “A pumper truck is connected to the frac tanks and the chemicals are emptied into the well head very precisely to generate a fracturing of the oil or gas bearing formation inside the well. Chemicals used in fracturing may include inhibiting agents, solvents, and weak acids.”

During hydraulic fracturing operations, frac tanks may also be used to hold mud, water, and residual chemicals pumped back up out of the well during the operation. “Frac tanks don’t really transport products as much as hold them on-site,” Salvato explained. “At the end of the operation, the frac tanks are loaded onto trailers, or in the case of transportable tanks, hooked to transport trucks, and hauled to another location.”

Acid transport trailers and frac tanks are lined with chemical-resistant coatings designed to prevent the leakage of fracturing fluids in transit or on-site. Major operators of acid transport equipment have written single-source specifications for Series 390 Bridgeport Glass Armor 90, a thick-film, reinforced, modified epoxy for corrosion control in chemical tanks and aggressive chemical immersion. “This lining is an alternative to vinyl ester coatings, which have been the standard in the acid hauler market for years,” Salvato observed. “One coat of Series 390 combines the adhesion of epoxies to prepared steel substrates with a hard-tile finish.”

Frac tanks are typically lined with either Series 390, or Series 330 Bridgeport Glass Armor 300, a thick-film, reinforced, modified epoxy that reduces coating stresses caused by mechanical, thermal, or physical forces. “Series 330 has better properties for frac tanks, which are somewhat flexible,” Salvato advised. “The same coating is used for corrosion protection in aluminum oil collection trailers and vacuum trailers that are used to haul oil and saltwater from holding tanks in the oilfield to pipelines or refineries.”

Glass Armor lining systems are manufactured and distributed by Tnemec under license from Bridgeport Chemical. They are spray-applied as a single coat at 30 mils dry film thickness (DFT), which is an advantage over other types of liners such as vinyl ester which require two coats. “With fast-curing epoxy linings, it’s possible to conduct high-voltage holiday testing within hours of application, then repair the holidays and return the trailers to service, usually within 24 to 36 hours,” Salvato said. “Turnaround time is always an issue on trailers and frac tanks used for hydraulic fracturing.”

Salvato added that a well-maintained trailer can be in service for years before it requires relining. “On the other hand, a company that mixes chemicals inside a trailer, may see a lining system fail in as little time as one year due to the high temperatures generated when acids are mixed with water or bases,” Salvato added. “An exothermic reaction can produce temperatures as high as 600 degrees F on the surface of the coating system. And a company that hauls chemicals for which the lining system is not rated to withstand is looking at a shortened service life as well.”

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