Storage Tank Linings
Internal linings that keep aboveground and underground storage tanks from corroding — and keep stored fuels, chemicals and process liquids clean — through years of immersion service.
Key takeaways
- A tank lining is an immersion-grade coating system that must remain continuous, adherent and chemically resistant under constant contact with the stored product.
- Lining selection starts with the stored product — its chemistry, concentration, temperature and any water bottoms — then considers cleaning, cycling and cathodic protection.
- Thin-film linings suit sound steel; thick-film and reinforced linings are used to bridge pitting on older tank bottoms and resist mechanical damage.
- Most premature lining failures trace to surface contamination, inadequate cure, holidays or exceeding the lining’s temperature or chemical limits.
Storage tank linings protect the interiors of tanks that hold crude oil, refined fuels, biofuels, chemicals, process water and many other liquids. Without a lining, carbon steel tanks can suffer pitting from water and sediment at the bottom, corrosion at the vapor space and liquid line, and contamination of sensitive products by rust. Linings extend tank life, reduce leak risk and help keep product on specification. Drinking-water tanks have their own requirements and are covered in potable water tank coatings.
Where and why tanks corrode
- Tank bottoms — water and sludge settle out of crude and fuel products, creating a corrosive, often microbially active layer. Bottom pitting is a leading cause of leaks in aboveground petroleum tanks — see microbiologically influenced corrosion.
- Lower shell — also wetted by water bottoms and sediment; linings commonly extend a few feet up the shell.
- Vapor space and roof — condensation, oxygen and corrosive vapors such as hydrogen sulfide attack the upper shell and roof underside.
- Floating roof seal zones and liquid line — wetting and drying cycles and mechanical wear.
- Underside of bottom plates — not reachable by the lining and typically protected by cathodic protection and foundation design.
Lining types and chemistries
| Lining | Typical service | Strengths | Watch points |
|---|---|---|---|
| Amine-cured epoxy (thin film) | Crude, fuels, water, mild chemicals | Versatile, economical, good adhesion | Limited for strong solvents, some biofuels, high heat |
| Novolac epoxy | Acids, ethanol and fuel blends, hotter service | Higher chemical and temperature resistance | More brittle; tighter recoat windows |
| Epoxy-phenolic / phenolic | Solvents, aromatics, product purity | Excellent solvent resistance | Often needs heat cure; thin, careful application |
| Vinyl ester (often glass flake or reinforced) | Strong acids, oxidizers, hot chemicals | Broad chemical resistance | Shrinkage stress; skilled application |
| Fiberglass-reinforced epoxy or vinyl ester | Pitted petroleum tank bottoms | Bridges pits, impact resistant | Thicker, costlier; inspection more complex |
Product-specific chemical resistance charts from the lining manufacturer should be checked for the exact commodity, concentration and temperature. For the resin families, see novolac epoxy coatings and vinyl ester coatings and linings.
Thin-film versus thick-film and reinforced linings
Thin-film linings, commonly in the range of about 12–40 mils (300–1,000 µm), are applied in two or more coats or as a single-coat high-build 100% solids system. They suit new tanks and tanks with limited pitting once repaired. Thick-film reinforced linings, often 60 mils (1.5 mm) or more with chopped glass or woven mat, are used on older bottoms with extensive pitting or where impact and mechanical damage are expected. For aboveground petroleum tanks, API 652 provides guidance on lining selection, surface preparation, application and inspection of tank bottoms, and API 653 governs tank inspection, repair and alteration.
Surface preparation
Immersion linings demand the highest standards of preparation. Typical requirements include:
- Clean and degas. Remove product and sludge, ventilate and certify the tank safe for entry.
- Repair steel. Weld-repair or fill pits, grind sharp edges and weld spatter, and patch-plate thin areas as required by the tank inspector — see edge and weld preparation.
- Remove contaminants. Degrease per SSPC-SP 1 and wash to remove soluble salts, then verify salt levels against the specification.
- Blast clean. Typically to white metal (SSPC-SP 5/NACE No. 1) or near-white (SSPC-SP 10/NACE No. 2) with an angular profile, often in the 2.5–4 mil (65–100 µm) range, measured by ASTM D4417.
- Control conditions. Dehumidify to hold blasted steel without flash rust and keep surface temperature above the dew point during application and cure.
Tank interiors are permit-required confined spaces with fire, explosion and toxic atmosphere hazards, especially when residual hydrocarbons or solvent vapors are present. Follow the safety data sheet, the entry permit, continuous atmospheric monitoring and the employer’s safety program.
Application and cure
Linings are applied by airless or plural-component spray, with stripe coats on welds, edges, nozzles and roof supports. Many systems are specified with contrasting colors between coats to show coverage. Cure is critical: an under-cured lining placed into service can soften, absorb product and blister. Manufacturers specify minimum cure time at temperature before immersion, and some linings require forced heat curing. Cure can be verified by hardness or solvent-rub tests where appropriate — see testing coating cure.
Inspection and testing
Quality control for tank linings typically includes environmental readings, profile and cleanliness checks, wet and dry film thickness (for example by SSPC-PA 2 sampling), and 100% holiday testing of immersion surfaces. High-voltage spark testing is generally used for thicker linings and low-voltage wet sponge testing for thinner films, following NACE SP0188 and the manufacturer’s voltage recommendations. All holidays are marked, repaired and retested.
Record the as-built lining — product, batch numbers, DFT map and holiday test results — in the tank file. When the tank comes out of service years later, inspectors can compare condition with the original installation and make a far better repair-or-replace decision.
Frequently asked questions
Does the whole tank need to be lined?
Not always. Many petroleum tanks are lined on the bottom and the first few feet of shell, where water and sediment collect. Chemical, product-purity and some fuel tanks are fully lined. The owner’s specification and product requirements decide.
How long does a tank lining last?
Properly selected and applied linings often last many years, sometimes until the next major inspection cycle or beyond, but service temperature, product changes and mechanical damage all shorten life.
Can a lining be applied over pitted steel?
Pits must be cleaned and filled or welded first. Shallow, widespread pitting on tank bottoms is often addressed with a reinforced thick-film lining.
Educational reference. Coating performance varies by formulation. Always follow the manufacturer’s product data sheet, safety data sheet and your project specification.
