Throughout the oil refining process, water used to cool manufacturing models can attain temperatures in excess of 140 levels F, creating a need for quite a few cooling tower constructions that adjoin the processing units. Heated water despatched to those cooling towers to be cooled and saved for reuse comprise minerals and salt that can turn into concentrated, inflicting corrosion on steel surfaces in basins, walls and structural steel supports. Extremely corrosive surfaces are typically located in or close to the intake and updraft sections at the bottom of the towers, the place massive volumes of contaminated air are drawn previous steel and concrete helps to fulfill water falling from the highest of the tower.

Typically, maintenance is carried out on cooling tower elements whenever its processing unit is scheduled for a “turnaround,”聺 which is a planned, periodic shutdown to examine, repair or substitute tools that’s worn out or broken. In keeping with the Energy Data Administration (EIA), routine turnarounds on key fuel production items are deliberate for each three-to-5 years and can result in a unit being offline for a number of weeks to several months. “Throughout a significant unit turnaround, as many as 1,500 to 2,000 expert contractor workers may be introduced on site to carry out a myriad of interrelated jobs that require vital coordination and security measures,”聺 the EIA defined.

In the course of the turnaround of an alkylation (alky) unit at a significant Gulf Coast oil refinery in Louisiana, staff found four badly corroded headers in the unit’s cooling tower. “The protecting coating system that was previously used on the headers had not only failed, but it had failed prematurely, leading to severe corrosion and pitting of the steel,”聺 recalled Tnemec coating consultant Eddie Borne. “There was blistering, rust and corrosion, so the steel was abrasive blast-cleaned down to naked steel and primed.”聺

The headers were ready in accordance with SSPC-SP 10/NACE No. 2 Close to White Blast Cleaning to take away all of the rust and corrosion, then primed with Collection 90G-1K97 Tneme-Zinc, a complicated know-how, single component zinc-rich polyurethane. The coating system was scheduled to obtain a 15.0 to 20.Zero mils DFT topcoat of Sequence 46H-413 Hi-Build Tneme-Tar, a corrosion-resistant polyamide coal-tar epoxy, but the alky unit was put again into service earlier than it might be utilized.

Six years later, during another scheduled turnaround of the alkylation unit, the headers had been inspected and located to be “practically perfect with no corrosion on them,”聺 Borne reported. “The efficiency of the Tneme-Zinc primer was so good that it stopped the corrosion on these headers, even after six years of service in a fairly aggressive surroundings containing corrosive chemicals and salts. It’s much more remarkable when you consider that some of the pitting within the headers was 1/8 of an inch, or 125 mils, which is forty times the DFT of the primer. So although all of these deep pits have been sprayed with solely 3.Zero mils of primer, the very fact there was no rust on the headers indicated the primer sprayed on uniformly and adhered evenly around the edges of the pitted steel.”聺

The corrosive effect of water from the cooling tower isn’t restricted to the construction’s inside, however can also result from the mist that’s launched into the atmosphere. “When the cooling tower is in service, it’s placing out what seems to be like an enormous fog that can cowl all the refinery, relying on the course of the wind,”聺 Borne explained. “When this mist containing salts and contaminants settles on steel surfaces, it could result in corrosion, which is what happened on the floating roofs of steel storage tanks at a significant oil refinery in Texas. The coatings on those roofs failed, causing enough corrosion that the refinery ended up replacing the roofs at a value of $1 million for every substitute.”聺

Along with cooling tower fallout, roof and sidewall coatings are subject to ultraviolet (UV) gentle, 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 best potential for superior know-how coatings to be used,”聺 Borne added.