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NITROGEN PROTECTION AS ANTICORROSION AND FIREPROOFING MEASURE IN THE USE OF SOUR CRUDE OIL STORAGE TANKS I. I. Reformatskaya,1 I. R. Begishev,1 I. I. Ascheulova,1 and A. N. Podobaev 2

UDC 661.93

The results of using a nitrogen protection system for 15 years in a sour crude oil storage park equipped with Hazmat class II and III vertical storage tanks with a stationary roof without pontoons are analyzed. Under nitrogen protection conditions, the rate of localized corrosion of the inner surface of the roof of raw and commercial crude oil storage tanks is 0.013–0.015 mm/year, which is ∼100 times lower than the rate of corrosion under natural gas phase conditions inside the tank. Continuous operation of the nitrogen protection system ensures fire and explosion safety of the tanks. Interruptions in the nitrogen protection do not have any practical effect on the efficiency of through perforation of the roof until the end of the regulated service life of the tanks, but increase fire and explosion hazard due to the formation of pyrophoric corrosion deposits. Keywords: oil storage tanks, corrosion, steel, fire and explosion hazard, pyrophore.

One of the main reasons for the ignition of storage tanks at oil storage and processing enterprises (especially when the planned service life of the storage tank park is reached) is the corrosion of metal in contact with oil, which leads not only to the thinning of the equipment walls (up to their local through perforation), but also to formation of pyrophoric corrosion deposits that cause spontaneous combustion of oil inside the tanks. According to GOST 31385–2008 “Vertical cylindrical steel tanks for crude oil and oil products,” when using anti-corrosion protection with a guaranteed service life of at least 10 years, the service life of the tanks must coincide with the period of full technical diagnostics of the applied protective equipment. When tanks are operated without anticorrosive protection, the guaranteed service life of the tanks is estimated with allowance for corrosion. For Hazmat class II and III storage tanks with a volume of 1000–50,000 m3, the assumed service life (with full technical diagnostics at intervals of no more than 10 years) is 40 years with an average number of fillings/emptyings per year not exceeding 100. The corrosion rate of the metal is determined by the zone of its location. The overall service life of the tank is determined by the corrosion rate of the metal in the least resistant zone. Studies [1] show that the service life of storage tanks ranges between 1 and 20 years, depending on the aggressiveness of the media filling the tank and the corrosion rate of the inner surface of the tank. The storage tank park of one of the oil refineries in Russia is equipped with hazmat class II and III storage tanks with a stationary roof without pontoons (the service life of the tanks in the early 2000s was close to the regulations standard). Oil processed at the enterprise contains a significant amounts of hydrogen sulfide and sulfur compounds and is considered s