Fire water tank refurbishment: inspection, coating and return to service

A fire water tank is refurbished in four stages: interior and exterior inspection, abrasive blast preparation, application of an immersion lining suited to the stored water, then a return to service coordinated with the person responsible for fire protection. The outage must be managed as a fire protection impairment, with compensatory measures, in line with NFPA 25 and the requirements of the insurer and the authority having jurisdiction. NFPA 22 governs the tank's design.

A fire water tank stays full and still, often for years. Nobody looks inside while the system works, and corrosion advances quietly on the floor, at the waterline and under the roof. When an inspection reveals tubercles, pitting or a failed lining, you have to act without compromising the building's protection. This guide is for industrial facility managers in Quebec and Ontario, alongside our tank and water tower painting page.

Where does corrosion form in a fire water tank?

Corrosion forms mostly in three zones: the floor, where sediment and sludge settle; the waterline and level-change zone, where oxygen and moisture alternate; and the underside of the roof, exposed to condensation. Welds, ladder supports and pipe connections also concentrate attack.

• Floor and sediment. Under deposits, oxygen is scarce and local corrosion cells form. Bacteria find a favourable environment there, as our article on microbiologically influenced corrosion (MIC) explains.
• Waterline. The level changes little, but the wet-dry band remains the most oxygen-exposed area.
• Roof underside and upper shell. Condensation is almost constant, especially when the water is heated in winter to prevent freezing.
• Floor underside. On a foundation, soil moisture attacks the steel from outside. Our article on storage tank bottom corrosion covers the mechanism.

The outside of the tank deserves the same attention. Many fire water tanks in Quebec and Ontario are insulated and heated to prevent freezing. When the cladding is damaged, rain and melt water get behind it and stay trapped against the shell, where corrosion progresses unseen. Anchor bolts, the chime at the base of the shell and the junction with the foundation are other weak points: water and de-icing salts collect there, and the foundation can crack with freeze-thaw. An exterior survey during the same campaign lets you plan both scopes together, which avoids mobilizing twice and limits the time the tank is out of service.

How do you inspect a fire water tank?

Inspect at the frequency and with the content NFPA 25 sets for fire protection tanks, combining regular exterior inspections and periodic interior inspections. The interior inspection is done with the tank drained, or by diver or underwater camera when draining is not possible.

An inspection that is useful for planning a coating records:

• Existing coating condition. Blisters, disbonding, rust-through, mapped by zone, for example using ASTM D610 for rust grade.
• Steel thickness. Ultrasonic readings on floor, shell and roof, with a pitting map.
• Sediment and tubercles. Volume and nature, which tell you about water quality.
• Appurtenances. Ladders, manways, anti-vortex plate, heating, level indicator, vents and overflow.
• Exterior. Coating, insulation, foundation, anchors.

Our coating inspection service produces this survey and turns it into a scope of work.

Which coating should you choose for the interior?

Choose an immersion-grade lining for water, most often a high-solids epoxy in several coats, per the system defined by AWWA D102 or the project specification. If the tank also serves potable water, the lining must be listed to NSF/ANSI 61.

Our article on potable water tank coating to NSF 61 covers the combined case. To estimate the service life of an epoxy in immersion, see our article on epoxy coating service life. Interior cathodic protection can supplement the lining in immersion.

How do preparation and application work?

Preparation is abrasive blasting to the grade the system requires, usually a high grade for immersion, after draining, sediment cleaning and steel repair. Application follows the data sheet: number of coats, recoat windows, ambient conditions and cure before refilling.

• Draining and cleaning. Water discharged under municipal rules, sludge removed, surfaces washed.
• Repairs. Welding or reinforcement of thinned areas, depending on the steel assessment.
• Blasting. Containment, ventilation and dust control in the confined space.
• Stripe coat. Brushed onto welds, edges and corners before full coats.
• Full coats. Thickness checked on each coat.
• Final checks. Holiday test over the whole immersion surface, total thickness, appearance.

In winter, heating and dehumidifying the enclosure allow work within the required conditions. Our article on cold weather epoxy application explains how.

How do you coordinate the outage with fire protection?

Taking the tank out of service impairs part of the fire protection system. It is managed under the NFPA 25 impairment program: notice to the designated person, the insurer and the fire department, compensatory measures and the shortest possible duration.

• Before the outage. Risk assessment with the owner and its insurer, an alternate water source if required, a fire watch plan.
• During the outage. Active compensatory measures (fire watch, limits on hot work, restriction of some processes), daily progress tracking.
• Before refilling. Full lining cure per the data sheet, removal of all equipment, final inspection.
• Return to service. Filling, valve checks, tests required by the person responsible for fire protection, impairment closed and parties notified.

Our project management service prepares this schedule with the operator and the fire protection contractor, who remains responsible for system testing.

Which mistakes should you avoid on a fire water tank?

The costliest mistakes concern coordination and cure, more than product choice. Refilling too early, or stretching the outage without compensatory measures, creates real risk.

• Refilling before full cure. The lining blisters or softens in immersion.
• Forgotten appurtenances. Untreated ladders, supports and fittings become the first rust spots.
• Sediment left in place. It hides pitting and skews the inspection.
• Extended outage with no plan. Bad weather or an unplanned repair can stretch the outage considerably. A contingency plan is needed.

How do you get a quote?

An accurate quote starts from a recent inspection report or, failing that, photos, dimensions and the tank's history. Our crews and qualified subcontractors work from LaSalle, including in Mauricie and Centre-du-Quebec, Montreal and Ontario. This work is part of our protective coatings for immersion service.

Frequently asked questions

Can a fire water tank be coated without draining it?

A full lining requires a drained, dry tank. Some inspections are done underwater, and a few spot repairs exist with products that can be applied underwater, but they do not replace a full refurbishment.

What role does NFPA 22 play in a refurbishment?

NFPA 22 governs the design, construction and appurtenances of water tanks for private fire protection. A refurbishment must respect the original requirements, including for appurtenances and the coating.

Does a fire water tank need disinfection after coating?

Only if the tank also feeds a potable water system or the operator requires it. A fire-only tank is refilled after cure and inspection.

How much does fire water tank refurbishment cost?

Pricing is on consultation. It depends on tank size, steel condition, the chosen system, outage measures, season and access.

For a fire water tank to inspect or refurbish, send dimensions, photos, the latest inspection report and the possible outage period through our request a quote form: pricing on consultation, reply within 24 business hours.