Non-Pressurized Horizontal Storage Tanks Are Typically Made Of Steel
Non-pressurized horizontal storage tanks are typically made of carbon steel, with stainless steel, fiberglass-reinforced plastic (FRP) and polyethylene used when chemical compatibility, hygiene or corrosion resistance demands it.
Definition: A non-pressurized horizontal storage tank is a cylindrical vessel mounted on its side, operating at or near atmospheric pressure, and used to hold liquids such as fuel, water, chemicals or process fluids. Horizontal tank references describe this layout as common where low profile, stable support and easy access matter.
Atmospheric tanks are generally designed for internal pressures of roughly 0 to 2.5 psig (about 17 kPa) or less. Vessels operating above that range are built to pressure-vessel codes instead, as this explanation of tank pressure types outlines.
Carbon steel tanks are the default because the metal is strong, weldable, cost-effective and easy to fabricate into custom sizes. In Canada, common aboveground steel designs are built to UL 142 (steel aboveground tanks for flammable and combustible liquids) or the ULC equivalent.
Common Materials and How to Choose Between Them
Five materials cover almost every non-pressurized horizontal tank. Each one trades cost, strength and chemical resistance differently.
Carbon steel
Carbon steel offers high strength, low cost, and easy welding and customization. It needs internal linings or external coatings for corrosive products and outdoor exposure. That's why most carbon steel tanks leave the shop with a protective system already applied.
Stainless steel (304 and 316)
Stainless steel resists corrosion and cleans easily, so it's preferred for food and beverage, pharmaceutical and aggressive chemical service. Grade 316 adds molybdenum for better chloride resistance. The upfront cost is higher. Our guide to 304 stainless steel properties covers the common grade in more detail.
Aluminum
Aluminum is lightweight and corrosion resistant. It's used for certain fuels and non-corrosive products. It has lower strength than steel, and it isn't suited to some chemicals, particularly strong alkalis.
Fiberglass (FRP)
FRP resists many acids, caustics and corrosive chemicals, and it handles underground corrosion well. Impact strength is lower than steel, and temperature limits depend on the resin used.
Polyethylene (HDPE)
Polyethylene is lightweight, corrosion-proof and economical for water and many chemicals. It's limited by temperature, UV exposure (stabilizers are needed) and structural capacity at large sizes.
Material comparison table
| Material | Strengths | Limitations | Typical products | Typical standards |
|---|---|---|---|---|
| Carbon steel | Strong, weldable, low cost, easy to customize | Needs linings or coatings for corrosive or outdoor service | Fuel, lubricants, water, process fluids | UL 142, ULC-S601, API 650, API 12F |
| Stainless steel (304/316) | Corrosion resistant, hygienic | Higher upfront cost | Food-grade liquids, pharmaceuticals, aggressive chemicals | Project specification, plus tank code as applicable |
| Aluminum | Lightweight, corrosion resistant | Lower strength, not compatible with some chemicals | Certain fuels, non-corrosive liquids | Product and jurisdiction dependent |
| FRP | Resists acids and caustics, good underground | Lower impact strength, resin-dependent temperature limits | Acids, corrosive chemicals | UL 1316 |
| Polyethylene | Lightweight, corrosion-proof, economical | Temperature, UV and size limits | Water, many chemicals | Manufacturer and product standards |
Other manufacturers list tank types on their sites. This guide adds a side-by-side material comparison, standards references and use-case guidance so you can narrow your options faster.
Selection factors
Work through these questions before you choose a material:
- Chemical compatibility: Does the material resist the stored product at its concentration?
- Temperature: What are the operating and ambient ranges?
- Exposure: Will UV, snow, wind or buried conditions apply?
- Capacity: Large volumes usually favour steel or FRP.
- Hygiene: Does the product need sanitary surfaces?
- Budget: Compare lifecycle cost, not just purchase price.
- Regulations: Which codes apply where the tank is installed?
General tank design guidance reinforces that product properties and operating conditions drive these choices.
Linings and coatings
Epoxy, polyurethane and specialty linings extend carbon steel life and widen the range of compatible products. They protect the interior from the product and the exterior from weather. Our tank paint and coating guide explains how tanks are protected after fabrication.
Standards that apply
- UL 142 and ULC-S601: aboveground steel tanks
- UL 58 and ULC-S603: underground steel tanks
- API 650: larger welded atmospheric tanks
- API 12F: shop-fabricated tanks
- UL 1316: FRP tanks
API 650 governs atmospheric tanks up to about 2.5 psig, while API 620 covers low-pressure tanks up to about 15 psig. API 650 vs API 620 breaks down the difference. For a practical example of the larger-tank standard, see our custom API 650 storage tanks. Transport Canada and UN requirements apply to portable transport containers, not fixed storage tanks. A quick reference on pressure classifications helps separate these categories.
Real-world applications
Mining and oil and gas operations store fuel and lubricants in horizontal steel tanks. Chemical plants hold process chemicals. Food and beverage producers use stainless tanks for food-grade liquids. Municipal and industrial plants rely on atmospheric tanks for treatment steps, as our article on industrial tank design for wastewater treatment shows.
Custom fabrication
Custom builds allow tailored nozzles, saddles, baffles, heating and fluid handling integration. We fabricate steel tanks in-house across 100,000+ sq. ft. of Ontario facilities, with 40+ years of experience. See our custom process equipment for tailored options.
Frequently Asked Questions
What are non-pressurized horizontal storage tanks usually made of?
Non-pressurized horizontal storage tanks are usually made of carbon steel because it's strong, weldable and economical. Stainless steel is used for corrosive or hygienic products, while fiberglass (FRP) and polyethylene are common for chemicals and water. Aluminum is used less often. The right choice depends on the stored product, temperature, UV exposure and regulations.
Are intermodal tanks pressurized or nonpressurized?
Both exist. Intermodal (ISO) tank containers are built in types suited to different cargo. Low-pressure or non-pressurized tanks typically carry liquids such as food-grade products and many chemicals, while higher-pressure tanks carry liquefied gases and certain hazardous goods. Check the tank's rated pressure and approval markings, as this overview suggests.
When is stainless steel specified over carbon steel?
Stainless steel is chosen when the product is corrosive, purity matters, or sanitary cleaning is required, as in food, beverage and some chemical service. Grade 304 suits many uses; 316 is better for chloride exposure. Carbon steel with a lining is often cheaper for less demanding products. Our carbon steel vs stainless steel tanks comparison goes deeper, and you can browse our stainless steel tanks.
Can polyethylene be used for horizontal storage tanks?
Yes. Polyethylene tanks are lightweight, corrosion-proof and economical for water and many chemicals. Limits include temperature, UV degradation without stabilizers, and lower strength at very large capacities, so steel or FRP is often used for demanding service. Our polyethylene tank buyer's guide explains when plastic makes sense.
What standards apply to non-pressurized horizontal tanks?
Common standards include UL 142 and ULC-S601 for aboveground steel tanks, UL 58 for underground steel tanks, API 650 for larger welded atmospheric tanks, API 12F for shop-fabricated tanks, and UL 1316 for FRP. Requirements vary by product, location and jurisdiction. Tank design references provide further background.
How is a horizontal storage tank different from an IBC?
A horizontal storage tank is typically a fixed installation for bulk storage, while an IBC is a portable container (commonly 450 to 3,000 litres) designed for handling and transport and certified to UN and Transport Canada standards. See IBC sizes and standards for details.
Choosing a Tank Manufacturer
Before you specify a tank, confirm the manufacturer's applicable standards, in-house fabrication and material expertise. Our guide on how to choose an industrial tank manufacturer covers what to ask. If you'd like help matching material and design to your product and site, see our manufacturing capabilities or talk to our team.