Liner vs. lining vs. coating
People use these words loosely, and owners, contractors, and tank paperwork do not always mean the same thing by them. On this page they mean the following.
Liner — a separate membrane installed inside the tank shell to hold the water, common in bolted and some field-erected tanks. It is a sheet material, not paint.
Lining — the general word for whatever protective layer is on the inside of the tank. It can mean a liner, a coating, or both.
Coating — a layer applied directly to the interior surface of the tank shell, floor, and roof to protect the material underneath.
Your tank records or the firm that installed the interior protection will tell you which one your tank has. The rover inspection works the same way for each: it records what is visible on camera.
What an in-service rover can see on a liner
The pilot flies the rover along the walls and across the floor of the tank and records what the camera sees. Everything in the findings is an observation from that video.
Visible conditions the video can show
Wrinkles and folds in the liner. Areas where the liner appears to have separated from the wall or floor. Tears or punctures that are visible on camera. Discoloration or staining. Debris and sediment on the tank floor, and how much of the floor it covers. FLOW describes what is visible and where it is; it does not grade the liner as passing or failing, and it does not call a condition a code violation. That judgment belongs to the owner, the owner’s qualified firm, and the AHJ.
What video cannot determine
A camera shows the surface, so the video cannot tell you the liner’s thickness, how well a coating or liner is bonded to the tank (adhesion), or what condition the material is in underneath. The rover does not do ultrasonic (UT) or other thickness testing, and it does not test the liner material. Sediment on the floor can also hide what is beneath it; FLOW does not remove silt or sediment, so the video shows the floor as it is. If the findings raise a question the video cannot answer, the owner takes it to a qualified liner or coating firm.
How the in-service liner inspection works
The tank stays full
The tank is not emptied. The pilot puts the rover into the water through an access point and flies it from outside the tank, so the fire protection water supply stays in service during the visit and there is no water to replace afterward.
The pilot flies the liner surfaces
The rover is flown over the wall and floor surfaces the camera can reach, with attention to seams, corners, the floor, and areas around penetrations where a liner is more likely to show wrinkles or separation. The pilot records continuous video.
Video and findings report
FLOW sends the inspection video and a findings report to the tank owner. The report describes the visible liner condition, where each observation was seen, and the floor debris and sediment the camera recorded. Keep it with the property’s NFPA 25 records.
More on the method: underwater rover (ROV) tank inspection, in service.
What happens with the findings
The findings go to the owner, who decides what to do next and can share the video and report with their qualified liner or coating firm. That firm decides whether anything needs repair, recoating, or relining, and does that work. FLOW does not repair, recoat, or reline tanks. If the firm or the AHJ wants a closer look with the tank out of service, FLOW refers that drained inspection to a licensed partner firm.
NFPA 25 Chapter 9 context
NFPA 25 Chapter 9 covers water storage tanks, including periodic interior inspection, with the interior interval set by tank type and whether the tank has corrosion protection. Our NFPA 25 tank requirements page lays out those intervals by edition.
Virginia enforces NFPA 25-2020 through the Statewide Fire Prevention Code. Other states and localities may adopt a different edition. Confirm the adopted edition, and whether an in-service rover inspection is accepted for your tank, with your AHJ before you schedule.
The full table by tank type and edition is on our NFPA 25 tank interior requirements page. The short-cycle checks are on the tank inspection overview, and the wider standard is on What is NFPA 25?.
When the tank has to come out of service
Some questions need a drained tank: the AHJ may want a drained interior inspection, or the owner’s qualified firm may want hands-on access to the liner or coating. FLOW does not drain, empty, or refill fire water tanks and does no out-of-service tank visits. Those inspections are referred to a licensed partner firm. The in-service video is still useful to that firm, because it shows where to look first.
Service area
FLOW is based in Richmond, Virginia, and serves Virginia, Washington DC, Maryland, North Carolina and South Carolina. When you request a free quote, tell us where the tank is, what it is made of, whether it has a liner or a coating, and how the rover can get into the water.
