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Paper mill maintenance painting: Safe work practices, state-of-the-art coatings solve application problems, Solutions!, Online Exclusives, November 2002

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PAPER MILL MAINTENANCE PAINTING:
SAFE WORK PRACTICES, STATE-OF-THE ART
COATINGS SOLVE APPLICATION PROBLEMS


By: Dave Schutz, The Sherwin-Williams Company

Productivity and safety rank as top priorities for pulp and paper mill managers. But how do these priorities apply when it comes to plant maintenance painting projects?

Georgia-Pacific Corp. is a leading manufacturer of tissue, towel and other paper products for both the home and away-from-home markets. The Old Town paper mill, a former Fort James Corp. facility in Orono, Maine, just north of Bangor, has an exemplary maintenance painting program that is part of the mill’s overall corrosion control program.

Two recent projects at the mill—the refurbishment of a chemical tank and the repainting of a steel and concrete ceiling deck above a kraft paper machine—demonstrate the effective use of teamwork, innovative safety techniques and advanced coatings technologies to put safety concerns to rest, minimize productivity disruptions and maximize equipment service life.

Spider speeds application
The chemical tank, a caustic soda storage tank located in the bleach plant building, is used to feed the papermaking process. The tank’s carbon steel exterior showed significant rusting. The tank is surrounded by nearby operating equipment, walkways and structural support steel. This posed a challenge for on-site painting contractor Corrosion Control Inc., along with mill maintenance and engineering personnel, to develop a painting plan that would minimize any unwanted effect on the nearby equipment.

The painting contractor’s three-year maintenance contract at the site runs concurrently with a three-year supplier contract from The Sherwin-Williams Company. Corrosion Control, based in Smithfield, Maine, employs only 15 or 20 full-time painters, yet the company keeps a full-time safety director on staff and has an outstanding safety record. Ted Ocana, a site engineer employed by the Old Town mill, oversees the purchase of coating materials with input from the painting contractor.

The group determined that a portable "spider staging" that would move up and down the sides of the tank to conduct surface preparation and coating application would help ensure safety and eliminate the potential for damage to nearby structures. "The fact of the matter is that safety today is so much more than making sure you have a belt on," said Jim Marston of Corrosion Control. "It’s a science."

All old coating and rust were removed from the tank’s exterior using a combination of different techniques. Power tool cleaning to bare metal (SSPC-SP-11) was accomplished over most of the accessible surfaces. This was supplemented with abrasive blast cleaning using baking soda, which effectively cleaned and removed any of the old coating and remaining rust. Baking soda is also environmentally friendly and can be easily washed off any nearby equipment with water.

The mill chose a three-coat moisture-cure urethane system to allow fast recoatability and quick curing. The primer, COROTHANE® I Zinc, was spray applied to achieve 3 to 4 mils dry film thickness (DFT). The intermediate coat, COROTHANE® I Mastic, was applied to achieve 2 to 3 mils DFT. Finally, the topcoat, COROTHANE® I Aliphatic, matched to the mill’s beige color, was applied at 2 to 3 mils DFT.

Close Cooperation
Corrosion Control finished applying three coatings within three days. There was minimal disruption in the operational area and the tank received a sound corrosion protection system. The equipment surrounding the area also went unharmed.

Despite working in gritty, industrial environments, Corrosion Control pays attention to the appearance of its projects. "Sometimes you’ll encounter the attitude that since this is industrial paint, you just have to throw it on," said Marston. "That doesn’t work with us. I’m very fussy. It has to look good."

That can be a challenge in paper mills, where concrete ceilings and steel infrastructure, processing units and machines function in hot, humid environments. Temperatures at the ceiling during "on-the-run" painting operations can eclipse 130°F and the relative humidity is constantly at or near 100 percent. These conditions create unique challenges in specifying coatings for long-term performance, and for coatings application.

Ocana has a clear understanding of the Old Town mill’s coating needs and is capable of writing specifications for virtually any coatings job in the plant, Marston said. That helps, he added, because "at some places, the customer just says, ’Go paint it.’ That can be tough because you’re the scapegoat if something goes wrong. Some will tell you to paint right over grease, but you’ve got to remember that your name is going to be on the job when it’s done."

Marston and Ocana were supported by Jim Bouier, the Sherwin-Williams Industrial and Marine Coatings representative. High-performance coatings—such as the Sherwin-Williams COROTHANE® family of moisture-cure urethanes-are designed with high-humidity applications in mind. Marston is also pleased with the results he’s experienced with Sherwin-Williams DURA-PLATE® 235 Epoxy Coating.

"For mill work, we look for a coating that can tolerate minimal surface preparation and still perform," said Marston, who calls for surface preparation of SP-11 for most steel finishing tasks in the mill. However, surface prep remains the most important aspect of any job in the mill. "Without it, product won’t mean a thing," Marston said.

A breath of fresh air
Both surface preparation and product were critical when the mill gave Corrosion Control the task of developing a plan to clean and repaint the concrete decking and structural steel above kraft paper machine #1—while the paper machine continued to operate. "Downtime on these machines is US$ 50,000 an hour. At the mill, they’ve got to be comfortable that we can not only work safely, but do so without dropping anything onto processing equipment."

Close inspection of the ceiling showed some spalling of the concrete deck panels. The steel support members showed considerable rust but no significant loss of thickness. No wholesale replacement of steel or concrete was considered necessary, but some concrete panels required cement patching done before a moisture-proof barrier coating could be applied.

Essential to the project was the construction of a work platform to allow repainting of the ceiling without disrupting the paper machine’s production. The platform was designed with flexible air ducts feeding into it to pump and continually circulate cool air through the work area. Without the much-needed relief offered by the cooler air, painters would have had to work in the 130°F temperatures generated by the paper machine. The platform also had to prove "air tight," keeping any debris generated from the surface preparation process away from the machine.

Abrasive blasting was ruled out as a preparation method on the steel due to the proximity of the paper machine. Instead, worked used hand tool and power tool cleaning (SSPC-SP-2 and 3). They patched the concrete to cover any exposed rebar.

The addition of the air ducts considerably improved the working environment and application of the coatings. The painters were able to work for extended periods of time, avoiding any potential for dehydration or heat exhaustion. Painters first brushed and rolled the Sherwin-Williams primer, MACROPOXY® 920 Pre-Prime, onto the steel to achieve the recommended 1 to 2 mils DFT. This low viscosity, epoxy primer is designed to penetrate into any remaining rust. The resultant surface is ready to receive a high performance topcoat.

The topcoat, DURA-PLATE® 235, is a two-part high build epoxy designed to withstand the heat and high humidity that comes off the paper machine. DURA-PLATE 235 was applied at 6 to 8 mils DFT. After the concrete patching operation, workers applied an acrylic elastomeric coating. This provided a moisture barrier against the high humidity given off of the paper machine.

The addition of air ducts and the work platform allowed painters to work through the extreme temperatures and humidity to successfully complete the ceiling project. The work platform also allowed the paper machine to continue operation without interruption. The specification and application of state-of-the-art coatings accommodated limits on surface preparation without compromising coating performance. By working with its supplier and contractor, the Old Town mill was able achieve a highly effective pulp and paper mill maintenance painting program.

About the author: Dave Schutz is product information specialist, The Sherwin-Williams Company, Industrial and Marine Coatings.