Materials Performance

MAR 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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14 MARCH 2018 W W W.MATERIALSPERFORMANCE.COM Paint peeling off from the pipe-stay at the SS collar. Photo courtesy of Vinod S. Agarwala. Marine Atmospheric Corrosion Takes Toll on U.S. Army Aircraft Hangar E ngineers at the Mid-Atlantic branch of the U.S. Naval Facili- ties Engineering Command (NAV FAC Mid-Atlantic) (Nor- folk, Virginia, USA) discovered major structural damage of a nearby aircraft hangar owing to marine atmospheric cor- rosion, leading to recommendations of a number of coating refurbishments and structural f ixes to keep the hangar operational. Vinod S. Agarwala, a technical consul- tant at Iron Pillar Engineers (Philadel- phia, Pennsylvania, USA) and NACE Inter- national member, was part of the on-site technical collaboration team who exam- ined the problems. He detailed many of their findings in CORROSION 2017 paper no. 9212, "Infrastructure Corrosion Issues and Solutions on Military Bases." "Since most military naval bases have to be strategically located in coastal areas around the world, their infrastruc- ture and equipment are most subjected to the effects of corrosion," Agarwala says. "Atmospheric corrosion is a major issue for the infrastructure, as it is constantly exposed to corrosive elements of the envi- ronment such as high relative humidity, salts/dust, and airborne gases that pro- duce acids, microbial, and organic matter." In the NAV FAC Mid-Atlantic case, the group's facilities engineering team reported in 2015 that Hangar 111 at the Naval Air Station Oceana (Virginia Beach, Virginia, USA) had suffered extensive cor- rosion of its roof and its top structural cantilever roof support system, including general coating failures on roof f lashings and 12-in (305-mm) carbon steel (CS) pipe-stays along with stress corrosion cracking (SCC) found at the weld joints and hangar ceiling base plates. "There was a concern that if one pipe- stay fails in structural strength from cross-sectional metal loss due to crevice and pitting corrosion, the adjacent stays would become potentially overloaded and may cause the roof to collapse," Agarwala says. The hangar was built in 1980, which limited its anticorrosion properties, the consultant explains. "Most hangars were built over 35 years ago and were designed and fabricated with the conventional wisdom that existed at that time, with none or very lit- tle consideration of the effects of corro- sion and corrosion engineering prac- tices," Agarwala says. In addition, hangars designed at that time were gener- ally installed the same, regardless of geo- graphic location, he says. In other words, while the anticipated lifespan was ~50 years, developers likely did not take local condi- tions into account when making that pro- jection. "There was very little consider- ation on the corrosiv- ity of the environment then," Agarwala says. The hangar included a conven- tional coating system at the time, he explains, including an epoxy polyamide primer and perhaps a poly urethane top- coat. However, no evidence was found of any surface pretreatment of the steel, such as phosphoric acid (H 3 PO 4 ) or anod- izing. The stays had a f iber-reinforced polymer (FR P) wrap starting from the base-weld plate and extending to the roof. Over the f irst ~30 years of the lifespan, periodic maintenance was conducted on the hangar. For instance, whenever a water leak occurred, a resin with rein- forcing mesh was applied to seal the stay joints and f lashing. Similarly, when pipe stays were corroded—especially under- neath the paint system, where deep pits and severe crevice corrosion from the failure of the protective coating were found—stainless steel (SS) collars were placed to provide structural support. However, in many cases, the mainte- nance work was either ineffective or may have even exacerbated the underlying problem. "An SS collar attached to the pipe stays is not a good idea when attached to CS pipe stays," Agarwala says. "It creates galvanic couples and causes galvanic cor- rosion, even with the insulation between two metals. Water absorption, seepage, or moisture condensation could compro- mise the insulation via environmental degradation and may lead to initiation of crevice corrosion in the joints, and then accelerated galvanic corrosion of pipe stays." In addition, many of the coating solu- tions from prior maintenance had peeled off, leading to severe corrosion of the sub- strate metal. "The paint system was peel- ing off due to porosity in the coating sys- tem," he says. "This disbonding occurs when moisture penetrates through the topcoat and compromises the adhesion of MATERIAL MATTERS

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