SPF Saves Digester Tanks with Emergency Repair

 By Stephanie Marie Chizik

When two digester tanks in the city of Riverside, California, began leaking methane gas in 2006, some serious decisions had to be made. Since methane gas — associated with the decomposition of organic substances — is flammable, the first decision was to complete temporary emergency repairs to the tanks. The city hoped that these quick repairs could stop the gas from leaking out of the perimeter seals and bolts and give them time to decide on a long-term solution.

 With little time to waste, the city decided on spray polyurethane foam (SPF) and called in an insulation crew they knew could get the job done quickly and correctly, The city arranged for Hydro Seal Construction Co., Inc., to complete the quick rehab on the 1.75-million-gallon and 1.05-million-gallon tanks. The crew quickly learned that they were handed a full plate.
 

Spotlight on Safety

Within a week after the decision was made, Hydro Seal’s five-man crew arrived on the job site a mere five miles from their headquarters. They started the rehab process by pressure-washing the tanks, a 2,000-square-foot job. To remove all of the rust and dirt from the hold-downs and steel lids — 88 and 75 feet in diameter — they used a 4,800 psi pressure-washer from John Deere. It took the Hydro Seal crew less than a day to wash each of the tanks completely. Then, they came in and applied a petrolatum tape wrap to each of the bolts, and masked off handrails and guardrails. This wrap, Trenton’s #2 wax tape, was used to protect the tanks from rusting and was intended to allow the temporary coating to be removed easily when the formal repair eventually started.

With the seams covered, the crew was able to begin the spray application of the emergency urethane coating. With the tanks at 50 feet tall each, insulating and coating was a challenge. First, the crew installed open-weave netting along the perimeter. The netting was particularly important on windy days; without it, the guardrails and any cars in the parking lot would have been subject to possible SPF overspray.

Along with protecting exterior surfaces, the crew was concerned with protecting themselves. A safety plan was extremely important to the Hydro Seal crew. To the National Fire Protection Association (NFPA), it was mandatory.

The digesters, which remained in operation throughout the repairs, were classified as Class 1, Division 1 in regard to the NFPA 820 — the Standard for Fire Protection Wastewater Treatment and Collection Facilities. To accommodate the needs of this classification, the crew made sure to take “special precautions for any open flames or sparks,” said Hydro Seal’s owner, Heinz Lapper. With methane gas escaping from the tanks — and power tools working nearby — it was no surprise that safety on this job was tight.

In addition to using a safety plan, the Hydro Seal crew wore 3M respirators and safety ropes and belts from Miller and Rose. With methane gas lurking around the tanks, the crew wasn’t taking any risks.
 
SPF SOS

When the scene was set, the crew was ready to spray-apply the first coat of their emergency renovations. To seal any cracks, they applied a solid urethane primer. They used a Graco EXP 3 to apply 40 mils of the Hydrothane product.

Immediately after they’d finished applying the urethane, the Hydro Seal crew returned to install the SPF. The crew used the same equipment to apply BASF Polyurethane Foam Enterprises’ (PFE) 1.7-pound FE348 foam. They applied two inches of the foam before returning to give one more 40 mil coating of the Hydrothane. This quick coating gave the acrylic topcoat — the final layer — a surface to which it could stick. The crew applied the Hydroseal topcoat at 18 mils (DFT) with a Graco King 45:1. The topcoat’s job was to give the tanks protection from UV rays and top off the rehab coating system. In 16 to 24 hours — with the topcoat completely cured — the Hydro Seal crew was ready to wrap up (or unwrap, rather) the Water Quality Control Plant project.

Leak-Free Solution

With the temporary insulation system complete, the tanks were re-pressurized to five to seven psi. With the tanks confirmed to have no leaks — and the nets, masking tape, and masking paper removed — the crew’s job was complete. After eight days and four separate layers, the Hydro Seal crew finished their part in the overall tanks’ repair: the emergency system was in place. Since then, the city has yet to find a long-term solution.

 “No formal repair has been scheduled, and since the emergency repair, this seems to be a long-lasting solution,” explained Lapper. A few changes will eventually need to be addressed. All of the seals will need to be replaced, and the digester will need to be shut down for an extended period of time during the repair—things the Hydro Seal crew would be honored to be involved with. In the meantime, though, they’re happy knowing that the work they completed for the emergency repair is not only still in working order, but is also helping the city of Riverside accomplish environmental achievements.

Two years after Hydro Seal finished their emergency repair on the two digester tanks, the city of Riverside was recognized as one of the Leaders Combating Southland Air Pollution. The city won a 2008 Clean Air Award from the South Coast Air Quality Management District for Model Community Achievement. On a separate occasion, the digester project also won the Tanks and Vessels category at the 2008 SPFA National Industry Excellence Awards.

These awards continue to prove to Hydro Seal that their work was not only a success for the survival of the tanks, but also for the betterment of the Riverside community.

For more information on the Clean Air Awards, check out the South Coast Air Quality Management District Web site at www.aqmd.gov. For more information on the 2008 SPFA Contractor Awards, check out www.sprayfoam.org.
 

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