All through the oil refining course of, water used to cool production items can attain temperatures in excess of 140 levels F, creating a need for numerous cooling tower constructions that adjoin the processing units. Heated water despatched to these cooling towers to be cooled and saved for reuse comprise minerals and salt that can turn out to be concentrated, causing corrosion on steel surfaces in basins, partitions and structural steel helps. Highly corrosive surfaces are typically located in or near the intake and updraft sections at the base of the towers, where giant volumes of contaminated air are drawn previous steel and concrete supports to meet water falling from the top of the tower.
Usually, maintenance is carried out on cooling tower elements whenever its processing unit is scheduled for a “turnaround,” which is a planned, periodic shutdown to examine, repair or substitute gear that’s worn out or damaged. Based on the Vitality Data Administration (EIA), routine turnarounds on key fuel manufacturing models are deliberate for every three-to-5 years and can result in a unit being offline for several weeks to several months. “During a significant unit turnaround, as many as 1,500 to 2,000 skilled contractor employees could also be introduced on site to carry out a myriad of interrelated jobs that require significant coordination and safety measures,” the EIA explained.
During the turnaround of an alkylation (alky) unit at a significant Gulf Coast oil refinery in Louisiana, staff found 4 badly corroded headers in the unit’s cooling tower. “The protecting coating system that was beforehand used on the headers had not only failed, nevertheless it had failed prematurely, resulting in severe corrosion and pitting of the steel,” recalled Tnemec coating advisor Eddie Borne. “There was blistering, rust and corrosion, so the steel was abrasive blast-cleaned all the way down to naked steel and primed.”
The headers had been prepared in accordance with SSPC-SP 10/NACE No. 2 Near White Blast Cleansing to remove all the rust and corrosion, then primed with Sequence 90G-1K97 Tneme-Zinc, a sophisticated expertise, single part zinc-wealthy polyurethane. The coating system was scheduled to obtain a 15.Zero to 20.0 mils DFT topcoat of Sequence 46H-413 Hello-Construct Tneme-Tar, a corrosion-resistant polyamide coal-tar epoxy, however the alky unit was put back into service earlier than it could be applied.
Six years later, during another scheduled turnaround of the alkylation unit, the headers were inspected and located to be “almost excellent with no corrosion on them,” Borne reported. “The efficiency of the Tneme-Zinc primer was so good that it stopped the corrosion on those headers, even after six years of service in a reasonably aggressive surroundings containing corrosive chemicals and salts. It’s much more exceptional when you think about that a number of the pitting in the headers was 1/eight of an inch, or 125 mils, which is 40 occasions the DFT of the primer. So even though all of those deep pits have been sprayed with only three.0 mils of primer, the very fact there was no rust on the headers indicated the primer sprayed on uniformly and adhered evenly across the edges of the pitted steel.”
The corrosive effect of water from the cooling tower is not limited to the structure’s inside, however can even outcome from the mist that is launched into the ambiance. “When the cooling tower is in service, it is putting out what looks like a big fog that may cowl the complete refinery, depending on the path of the wind,” Borne defined. “When this mist containing salts and contaminants settles on steel surfaces, it could possibly lead to corrosion, which is what occurred on the floating roofs of steel storage tanks at a significant oil refinery in Texas. The coatings on these roofs failed, inflicting sufficient corrosion that the refinery ended up replacing the roofs at a price of $1 million for every substitute.”
In addition to cooling tower fallout, roof and sidewall coatings are subject to ultraviolet (UV) mild, rain water accumulation and ponding, and elevated temperatures for crude and distillate storage of one hundred twenty to 140 levels F. “These tanks experience the widest vary of corrosive situations and offer the greatest potential for superior technology coatings for use,” Borne added.