We all complain about rising prices at the gas pump
This is the story of a preventative maintenance coatings project at a diesel and unleaded gasoline storage tank farm that spans the course of two years. It is the story of how cutting-edge coatings technology made that expansive job more efficient. And of how one coatings crew worked for two years, utilizing the new technology to quickly and competently line the tanks and protect the nation's fuel supply.
A LINING TO LAST
As Cliff Haskins, Vice President of Marketing for Specialty Products, Inc. explains, 'Allied Energy Corporation knew that they were facing a problem. Their tank farm was aging and they needed corrosion- and chemical-resistant linings for the interiors of their fuel tanks - specifically their tanks used to store a trans-mix of diesel and unleaded gasoline before it is processed into usable fuel. These tanks have capacities ranging from 12,000 barrels to 54,000 barrels.' So this would be no small project. And since the cost of taking fuel storage vessels off-line is so high (See 'Crude Oil Tank Farm: Coatings Help Investors Make Money,' CoatingsPro online article, April 2010, www.coatingspromag.com), the job would be done slowly - on an on-going basis, one tank at a time.
SMC Commercial Services Inc., was the contractor hired to complete the project and Benny Abbott, owner of Abbott Consulting and Coating Inspections, was hired as the inspector/consultant.
During the course of the project, 'We worked on several tanks - seven in all - in various sizes from late 2007 until March of 2009,' explains Abbott. 'The smallest was approximately 30' (9.14m) in diameter. The largest was approximately 90' (27.43m) in diameter. And not all of the tanks were spec'ed for polyurea, but most were. We ended up using about 20,000+ square feet (1,858.06m2) of it.' That is a lot of polyurea - especially given the fact that it was applied at 100 to 125 mils (2.54mm to 3.18mm) DFT.
'It is,' Abbott agrees. 'But the owners wanted to make sure that the tanks were well-protected and that everything was done right.'
On a job of this size and scope, making sure that everything was done right was a detailed process. Each tank was approached as an individual project. 'We would write a specification for each tank, since each one was different,' says Abbott. For the purposes of this article, we'll focus on the application used in the majority of the tanks - SPI's PTU Chemical Resistant Polythiourea. As SPI's Haskins explains, 'Allied Energy Corporation had previously used PTU successfully in their bio-diesel, unleaded gasoline, and diesel fuel storage tanks and they felt confident to continue using the same product to provide a protective lining to coat another tank.'
As for the tanks themselves, they were in a mixed bag of conditions. 'Some of the tanks were brand new carbon steel,' Abbott describes. 'Others dated from 1952 and were in very poor shape. A few of these had thin areas and even holes in the bottoms.'
Before Abbott and the coatings crew stepped onto the job site, the owners drained the tank to be coated. Then it was time for the four-to-six man coatings crew to suit up and enter the tank.
Working with chemicals in a tank that has housed fuel immediately raises a red flag and on this job site, nobody took any chances. 'We wore air-supplied or standard full-face air-purifying respirators (APRs) and the ventilation system that we had established helped keep the fumes away too,' explains Abbott. In addition the crew wore Tyvek suits designed to withstand chemical service, as well as gloves and hardhats. They checked in and out with a safety monitor whenever they entered the tank. Not only did SMC provide their own company safety training, but also 'there was a mandatory site-specific training program run by the facility owner as well,' Abbott says.
Dressed to coat, Abbott and the coatings crew first cleaned the freshly drained tank using a Mighty Mite 4,000 psi (27.6MPa) pressure washer and a multiple mix of water, Krud Kutter (a water-based surfactant), and a micro-biological agent. This cleaning process took from two to four days depending upon the size of the tank. And the tanks weren't all that was getting cleaned.
'The dirty water was then vacuumed out of the tank via vacuum trucks and sent to Allied Energy's micro-biological on-site treatment system,' Abbott recounts. 'There, at the treatment center, micro-organisms actually eat the dirt and toxic particles in the water. By the time the processed water leaves the treatment facility, it is cleaner than drinking water.'
Then, the crew used Clemco's 6-cubic-foot blast pots with 1 1/2' (3.81cm) piping and Harsco's Black Beauty media, to sweep blast the tank's floor as well as 4' (1.22m) up onto the walls of the tank. 'We blasted the steel substrate to the NACE No. 3/SSPC-SP 6 Commercial standard in order to remove any mil scale and/or rust,' states Abbott. Then, a third-party inspection firm was hired to inspect the tank according to American Petroleum Institute (API) standards using ultrasonic equipment.
'For this job, we followed the API 652 standard for the lining of petroleum tank bottoms. It wasn't specifically stated in any of the specifications, but that is what we used when we approached the coating of each tank. We also followed all NACE/SSPC standards,' explains Abbott.
HIGH SALTS ANS GAS
Once the tank passed API standards, sub-contracted welders arrived on site to perform any necessary repair work.
After all of the third-party work was finished, it was time to re-clean the tank. Abbott and the coatings crew re-entered and, using a Chlor-Rid kit, tested the substrate to be coated for salts, chlorides, nitrates, and sulfides. 'We found high levels of salts,' says Abbott. 'So we applied the Chlor-Rid solution and removed it using plain water run through the 4,000 psi (27.6MPa) pressure washers. The water was then vacuumed out and recycled through the plant's micro-biological treatment facility.' The cleaned surface was re-tested for salts and found to be within acceptable levels.
Next, using Black Beauty media and the same Clemco 6-cubic-foot abrasive blasting pots with 1 1/2' (3.81cm) piping, 130 lbs. (58.67kg) of pressure, and nozzles ranging in size from #7 to #8, the crew abrasively blasted the tank's floor and 4' (1.22m) up onto the tank's walls to the NACE No. 1/SSPC-SP 5 White Metal standard. 'This created the 5 to 6 mil (0.13mm to 0.15mm) anchor profile specified for tank corrosion protection,' Abbott states. The spent media was vacuumed out and the tank walls were 'blown down with clean, dry, compressed air in preparation for the coating application.'
The coating process itself was perhaps the quickest part of the entire job as the team used state-of-the-art materials and equipment to get the job done. Every day that a tank is out of service represents a monetary loss, so speed was paramount. Given this, the specs called for the use of PTU, a chemical-resistant, spray-applied, polythiourea elastomer from Specialty Products, Inc.
PTU is self-priming which meant that the crew could spray the 100% solids, no VOC coating directly onto the cleaned and prepped carbon steel substrate without having to apply a primer - thus trimming time and money off of the project's bottom line.
They used a Gusmer 20/35 Pro hydraulic proportioner and a Graco Fusion mechanical-purge gun to spray-apply 100 to 125 mils (2.54mm to 3.18mm) DFT of the PTU onto the tank floor and 4' (1.22m) up onto the tank walls.
'The mechanical-purge gun has the best properties for spraying this material,' Abbott says. 'We never experienced any down-time due to gun-related problems during the course of this entire project. And no, I don't have an endorsement deal to say that,' he adds. 'It just consistently works really well.'
After spraying the PTU, the crew checked for DFT and Shore D hardness. 'We used a gage from PTC Instruments to check for Shore D hardness. We used DeFelsko's PosiTector 6000 to measure the coating thickness. And we used Tinker & Rasor's AP model, high voltage holiday detector to check for any voids or holidays in the coating,' Abbott says.
FILL 'ER UP
Once all of the various inspections had been performed the crew exited the tank for the final time. 'After completion, the tank sat for 72 hours before it was placed back into service,' recounts Abbott. 'This ensured a full cure.' According to the technical data, PTU will cure to recoat from minutes after the original application up to six hours, so a 72 hour window for curing was more than enough for the fast-curing coating. And it would seem that the patience has paid off.
'Every tank has now been opened, drained, and cleaned and no problems have been found with the linings,' Abbott explains. 'In fact, the tank with the oldest lining - one that we coated in the fall of 2007 - was recently opened and the lining looked good.' SPI's Haskins concurs, 'The owner is very pleased with PTU's performance.'
Two years, seven tanks and counting. Seems like no matter what the issue, when the discussion turns to fuel, the numbers keep increasing. This, however, is one instance in which that increase represents a savings in time and money -- thanks in part to coatings technology and the men who apply it. CP