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Water tank maintenance
September last year, the City of Dayton in Ohio awarded a maintenance project of two very large (two million gallon) multi-leg elevated water tanks to a local painting contractor.
The tanks are supported by a large central riser column, and 12 legs around the circumference. These tanks are completely contained with tarps that can be raised or lowered in high wind conditions.
Access is via swing stages and catwalk platforms that are suspended between the columns. The 15-year-old tanks have a total surface area of 73,000 square feet (or 6,782 square metres) with a 25-30mm intact coating.
Internal surface area is 28,000 square feet (2,601 square metres) while external is 45,000 square feet (4,181 square metres). The contractor performed abrasive blasting on the first tank using Coal Slag with the following results:
| Abrasive consumption | 380 tonnes | |
|---|---|---|
| Total man-hours | 1,728 hours | |
| Nozzle used | 6 to 7 for 12 hours per day | |
| Clean-up | 670 man-hours. Disposal coast $22,000 |
|
| Down time | Refilling pot 2-3 times per day |
For the second tank which had a much thicker costing than the first, recommended a combination of GMA SpeedBlast and two high production bulk blaster each equipped with a 1,600cfm compressor. The results were:
| Abrasive consumption | 220 tonnes |
|---|---|
| Total man-hours | 1350 hours |
| Nozzles used | 5 to 6. 10 hours per day. |
| Clean-up | 390 man-hours, disposal cost $0, as product was returned Free of Charge for beneficial reuse |
| Down time | Minimal. Reloading only once a day compared to two to three times previously. |
The foreman was amazed with the excellent visibility after the blasting session.
“I can work shorter days as I don’t have to stop to let the dust clear to see what we are doing! There is basically nothing to clean up!”
The contractor was happy with a savings of 22% on the total project cost over the previous tank. Moreover, he was able to move the equipment on a week ahead of schedule to start the next project.
