Every steel structure exposed to weather, water, or soil is at risk of corrosion, and the paint system protecting it is one of the most important factors in how long a fuel tank lasts in the field. Fuelchief's tanks are engineered to deliver over 35 years of protection, and that durability comes down to selecting the right paint system for the environment the tank will actually operate in.
This article covers how paint systems are selected and applied, based on the International Standard ISO 12944, which governs corrosion protection of steel structures by protective paint systems.
How Fuelchief tanks are supplied
All tanks fabricated by Fuelchief in New Zealand, including SuperVault, Praxis, Vanguard, and Pyrotector, are supplied fully painted. Factory-applied paint protects long-term durability and keeps the manufacturer's warranty intact.
Our welded range is painted to C5-I as standard, using an industrial-grade coating from Hempel (an ISO 12944 supplier) for durable, high-performance protection. A C5-M marine-grade option is also available for coastal and high-salinity environments, at an additional cost.
Understanding corrosivity categories
ISO 12944 defines five atmospheric corrosivity categories, based on how aggressive the environment is toward steel:
|
Corrosivity Category |
Exterior Examples |
Interior Examples |
|---|---|---|
|
C1 – Very Low |
N/A |
Heated buildings with a clean atmosphere, e.g. offices, shops, schools, hotels |
|
C2 – Low |
Atmosphere with minor contamination, mainly rural regions |
Unheated buildings where condensation may occur, e.g. storehouses, sports halls |
|
C3 – Medium |
Industrial and urban atmospheres with average sulphur dioxide levels; low-salinity coastal areas |
High-humidity production spaces with some air contamination, e.g. food plants, laundries, breweries, dairies |
|
C4 – High |
Industrial areas and medium-salinity coastal areas |
Chemical plants, swimming pools, ship repair yards |
|
C5-I – Very High (Industrial) |
Industrial areas with high humidity and aggressive atmosphere |
Buildings with near-constant condensation and high contamination |
|
C5-M – Very High (Marine) |
Coastal and offshore areas of high salinity |
Buildings with near-constant condensation and high contamination |
Fuelchief's welded range is painted to C5-I as standard, which covers most industrial applications. C5-M is available for tanks in marine or high-salinity coastal environments.
What to consider when choosing a paint system
When specifying paint for a custom welded tank, four factors drive the decision:
1. Environment
The conditions the tank will operate in determine everything else.
Key factors include:
- Humidity
- Temperature range
- UV exposure
- Chemical exposure
- Risk of mechanical damage from impact or abrasion
For buried tanks, ground conditions matter too:
- Soil porosity
- Moisture
- pH
- Exposure to bacteria and micro-organisms.
For submerged applications, the chemical composition of the water is significant. These factors together determine the paint type, total coating thickness, surface preparation required, and re-coating intervals.
2. Type of Protected Surface
The base material affects the choices that follow. Steel, hot-dip galvanised steel, spray-metallised steel, aluminium, and stainless steel each call for different surface preparation, primer selection, and coating thickness.
3. Durability Required
ISO 12944 defines three durability ranges for how long a coating lasts before it needs maintenance:
|
Durability |
Timeframe |
|---|---|
|
Low (L) |
2–5 years |
|
Medium (M) |
5–15 years |
|
High (H) |
More than 15 years |
Fuelchief's combined coating systems exceed the "high" category, delivering over 35 years of protection across our tank range.
4.Application Planning
Paint needs to be applied at the right point in the build process, accounting for prefabrication, on-site assembly, and completed structures. Surface preparation and drying or curing times both depend on temperature and humidity. If a tank moves between a controlled workshop environment and an on-site setting during construction, re-coating intervals need to be factored in too.
How we prepare and apply paint
For our fabricated tank range, surface preparation and application follow a strict process.
All surfaces are cleaned, dried, and checked for contamination, assessed against ISO 8504:2000, with oil or grease removed per SSPC-SP1 solvent cleaning standards. Surfaces are then abrasive blast cleaned to Sa2.5 (ISO 8501-1:1988) or SSPC-SP6, a near-white metal finish that removes almost all visible contamination. If oxidation occurs between blasting and painting, the surface gets reblasted, and any defects revealed during blasting are ground, filled, or treated as needed.
Stripe coats are applied to welds, lap joints, plate edges, corners, and any other areas where standard spray application could leave a thin coating.
The result: 35+ years of protection
This process delivers over 35 years of corrosion protection across Fuelchief's tank range, and every tank fabricated in New Zealand is audited and backed by a paint manufacturer's warranty.
