Steel storage tanks hold fuels, crude oil, water, chemicals, food products and process liquids. Inside, corrosion attacks the floor where water and sediment collect, the roof and upper shell where condensation forms, and anywhere the stored product is aggressive to steel. Internal linings separate the steel from the contents, protect the product from contamination by rust, and extend the life of the tank between major repairs.
This guide explains how internal linings are chosen and applied, from product compatibility and surface preparation to stripe coating, cure, inspection and return to service. It is general information for tank owners, terminal and plant staff, contractors and students. A real lining project needs a specification from a qualified engineer or coatings specialist, the lining manufacturer’s data sheets and chemical resistance data, the tank inspector’s findings and the standards and owner requirements that apply.
Key takeaways
- Choose the lining for the service: product, temperature, water and sediment at the bottom, vapor space conditions and cleaning methods.
- Full or partial: many tanks are lined on the floor and lower shell only, where water collects; others need full internal linings.
- Preparation usually means abrasive blast cleaning to a high cleanliness grade with a specified profile, soluble salt control and dehumidification.
- Stripe coats on welds, edges, corners and fittings give these areas the thickness that spray coats alone often miss.
- Cure fully before filling, often with heating and ventilation, as the manufacturer specifies.
- Inspect thickness, cure and continuity, with holiday testing on immersion linings, and keep records for the next inspection.
Where corrosion happens inside steel tanks
| Zone | Typical problem |
|---|---|
| Floor | Water and sediment settle under the product; microbial activity in water bottoms can cause severe pitting |
| Lower shell and first course | Contact with water bottoms and sludge |
| Product zone of the shell | Depends on the product; often mild for hydrocarbons, aggressive for some chemicals |
| Vapor space and roof underside | Condensation, oxygen and corrosive vapors |
| Floating roof components | Wet-dry cycles, seals, pontoons |
| Nozzles, sumps, heating coils, supports | Crevices, edges and mixed metals |
Corrosion on the underside of the floor, between the tank and its foundation, is a separate problem. An internal lining does nothing for it. Engineers address it with foundation design, cathodic protection of the tank bottom and inspection methods covered by the applicable tank standards.
Tanks, inspection and lining
In the petroleum and petrochemical industry, welded steel tanks are commonly designed and built to API 650, and inspected, repaired and altered according to API 653, with API RP 652 covering linings of aboveground petroleum storage tank bottoms. Water tanks have their own standards, such as AWWA standards in North America; see coatings and linings for drinking water tanks for the separate certification rules that apply to potable water. Other industries and countries use other codes and owner standards.
A lining project often follows an internal inspection, when the tank is already out of service and cleaned. The inspection identifies plate thinning, pitting, weld defects and settlement. Repairs such as patch plates, pit filling or floor replacement are completed and approved before lining starts. The lining protects what remains; it does not make up for lost steel, and decisions about remaining thickness and repair belong to the tank inspector and engineer.
Choosing the lining
Service conditions
The specifier needs to know:
- The stored product, including additives, blends and any likely change of service. Fuels containing ethanol, biodiesel or other bio-components can affect some linings differently from conventional hydrocarbons.
- Temperature, normal and maximum, including heated tanks and steam cleaning.
- Water bottoms and sediments, which are often more corrosive than the product.
- Cleaning methods, such as hot water washing, steam or solvents.
- Mechanical exposure from roof legs, mixers, sludge removal and foot traffic during maintenance.
- Product purity requirements, for example where contamination or color pickup must be avoided.
Manufacturers publish chemical resistance data and, for many tank services, lists of products the lining has been tested with. The exact product and temperature must fall within that data; where they do not, ask the manufacturer.
Common lining types
| Lining type | Typical use | Notes |
|---|---|---|
| Epoxy phenolic and novolac epoxy | Fuels, crude, many chemicals, higher temperatures | Multi-coat; often need forced cure; check temperature limits |
| Standard amine-cured epoxy | Water, mild services, many fuels | Lower cost; limited at high temperature and with some solvents |
| Solvent-free or high-solids epoxy | Floors and shells, thicker single coats | Fewer solvent vapors; shorter pot life |
| Glass flake reinforced coatings (epoxy, vinyl ester) | Floors and aggressive services | High thickness, good barrier; specialist application |
| Fiberglass reinforced laminates | Floors with pitting or minor perforations, after repair | Thick system; not a substitute for structural repair |
| Polyurea and polyurethane | Some water and secondary services | Chemical resistance varies widely; confirm for each product |
These are general tendencies, not product claims. Typical film thickness ranges from a few hundred microns for thin-film multi-coat systems to well over a millimeter for reinforced floor systems; check the manufacturer’s data sheet. For the generic coating families, see our comparison of protective coating systems.
Surface preparation
Preparation sets the life of a tank lining. Typical steps include:
- Degas and clean the tank, removing product, sludge and residues to a safe and coatable condition.
- Remove oil and grease before blasting, since blasting spreads contamination rather than removing it.
- Prepare welds and edges: grind sharp edges, remove weld spatter and laminations, and smooth undercuts, so coating can cover them at full thickness. ISO 8501-3 describes preparation grades for welds, edges and other surface imperfections.
- Abrasive blast clean to the cleanliness grade the specification and manufacturer require, often near-white or white metal for immersion service. Grades are described in ISO 8501-1 and in the joint AMPP surface preparation standards. Our guide to blast cleaning steel before coating explains the grades.
- Achieve the specified profile for the lining thickness, measured by the method in the specification.
- Test for soluble salts, such as chlorides, which cause blistering under immersion linings. ISO 8502 includes methods for assessing surface contaminants; the acceptable level comes from the specification and the manufacturer.
- Remove dust and check cleanliness before coating.
- Coat before flash rusting occurs; dehumidification is commonly used to hold the blast and allow larger areas to be prepared at once.
Climate control
Tanks are enclosed, so the air inside can be controlled. Dehumidifiers and heaters keep the steel above the dew point by the margin the specification requires. A margin of 3 °C above the dew point is a widely used rule of thumb, but the specification and data sheet decide. Ventilation removes solvent vapors to keep them well below explosive limits and to protect workers.
Application
Stripe coats
Spray coats tend to pull thin on sharp edges and miss the shadowed side of welds, bolts and brackets. A stripe coat, applied by brush or roller to welds, edges, corners, nozzles, supports and other difficult areas, adds thickness exactly where failures usually start. Specifications commonly call for stripe coats before or between full coats, often in a contrasting color so inspectors can see them.
Full coats
Each coat is applied within the manufacturer’s limits for temperature, humidity, pot life and recoat window. Wet film thickness is checked as work proceeds. Missing a recoat window on some chemistries means the surface must be abraded before the next coat.
Cure
Tank linings must be fully cured before the tank is filled. Under-cured linings can soften, absorb product, blister or contaminate the contents. Many linings need forced curing with heated, dehumidified air for a stated time at a stated temperature. Cure is typically confirmed by the method the manufacturer specifies, such as hardness or solvent rub tests, together with records of time and temperature.
Inspection and testing
| Check | When | Purpose |
|---|---|---|
| Ambient and steel conditions | Throughout | Dew point margin, temperature, humidity within limits |
| Cleanliness, profile and soluble salts | After blasting | Confirm preparation meets the specification |
| Wet film thickness | During each coat | Control thickness as applied |
| Dry film thickness | After each coat and at completion | Confirm specified thickness, for example by a sampling plan such as ISO 19840 or the specification |
| Visual inspection | After each coat | Runs, sags, dry spray, pinholes, missed areas |
| Cure confirmation | Before filling | Confirm the lining is ready for service |
| Holiday testing | After full cure, before service | Find pinholes and discontinuities in immersion linings |
Our guides to coating inspection basics and holiday testing cover the methods. Every holiday is repaired and retested, and the results are recorded for the next internal inspection.
Safety and re-entry
Tank work combines confined space entry, flammable atmospheres, toxic vapors, high-pressure blasting, high-voltage holiday testers and work at height. A safe project includes a confined space entry program, gas testing before and during entry, forced ventilation, isolation of all lines and equipment, controlled ignition sources, rescue planning and respiratory protection suited to the materials. High-voltage holiday testing must not be carried out where flammable vapors may be present unless the atmosphere has been tested and the work authorized.
Return to service is a controlled step: the lining is cured and accepted, the tank is closed up, and filling follows the owner’s procedures, which may include a slow initial fill and checks after a period in service.
Bottom line
An internal tank lining works when it suits the stored product and temperature, is applied over properly repaired steel, sits on a clean, salt-free blasted surface with the right profile, has extra thickness at welds and edges from stripe coats, and is fully cured and tested before the tank is filled. It does not restore lost steel or protect the floor underside. Selection and specification belong to qualified engineers and coatings specialists, working from the tank inspection, the manufacturer’s data and standards such as API 650, API 653 and the applicable surface preparation standards.