Aboveground storage tanks dedicated to water storage are used most often for fire protection and potable water. Water tanks for fire protection are used in numerous applications including fire sprinkler systems supply, water source for firefighting, to create a fire perimeter, and as a source of water at fire departments to fill up trucks. Potable water storage tanks have many applications in commercial and residential circumstances. Water tank inspections are generally conducted in accordance with National Fire Protection Association (NFPA) – 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems and American Water Works Association (AWWA) M42 Steel Water Storage Tanks. Compared to aboveground storage tank inspections of petroleum product tanks, water tank inspection is typically less complex and expensive since the water is not a hazardous material, non-flammable, and clear. Water clarity allows for excellent in-service tank testing with remotely operated vehicles (ROVs) that provide high quality video of the tank internal coating, shell, and nozzle conditions. However, precautions must be made that any ROV used for water tank inspection does not contaminate the water. Well defined rigorous sanitation processes must be applied to all tools entering the tank before water tank inspections. These guidelines are outlined in AWWA C652 – Disinfection of Water Storage Facilities. This article discusses some of the in-service water tank inspection guideline and the non-destructive testing (NDT) technology to support water tank testing.
Introduction to Water Tank Testing
The videos above and below show typical water tank testing video footage, from the interior of water tank, acquired from a tethered ROV. In the first clip, the ROV is approaching a 12” diameter outlet to assess condition. The water tank ROV assesses the coating condition clearly and effectively with illuminated high-resolution capabilities. The second video demonstrates the ROV’s capability to detect subtle paint blistering and coating failure.
There are a variety of fire protection and potable water tank types that require periodic in-service and out-of-service tank inspection, typically in 3-5 year inspection frequencies. Fire protection tanks are often ground level above ground storage tanks made from welded steel, riveted steel or concrete. Additional configurations for potable water tank inspections include single pedestal, leg tank, standpipe, fluted column and composite elevated. Figure 1 shows a water tank that was inspected in-service by TKS in accordance with NFPA 25 - Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. The 250,000 gallon capacity heated tank, 35’ high tank – 37; diameter tank, was equipped with insulation.
Figure 1 In-service fire water tank testing to NFPA 25 - Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems