What are the fire resistance requirements for steel pipes used in structure works?

Steel pipes are a backbone of modern structural engineering. They appear in building frames, bridge trusses, foundation piles, platform structures, and countless industrial installations. But when a fire breaks out, steel does not behave the way it does at room temperature. Its strength drops, its stiffness fades, and the structure it supports can be put at risk. That is why fire resistance requirements for steel pipes used in structure works are written into building codes and project specifications. This article explains what those requirements mean, what determines how well a steel pipe resists fire, and how to specify the right product for your project.

How structural steel behaves in a fire

The good news about steel is that it is not combustible. It will not feed a fire or add fuel to it. The challenge is different: steel loses both strength and stiffness as its temperature rises. At around 500°C, a carbon steel member can lose roughly half of its room-temperature strength. By the time the steel reaches about 700°C, the loss is severe and the member can deform noticeably under load.

To put those numbers in perspective, consider the widely referenced behavior of structural steel: at 427°C (800°F) steel retains at least 85% of its yield strength, but at 704°C (1300°F) only about 20% of the yield strength remains. Because steel is also a good conductor of heat, a fire can raise the temperature of a pipe quickly, which is why protection is almost always needed.

What a fire resistance rating actually means

A fire resistance rating is expressed in hours, and it describes how long a structural member can keep doing its job during a standard fire. The rating covers three things: the ability to carry the design load (load-bearing capacity), the ability to stop flames and hot gases from passing through (integrity), and the ability to limit heat transfer (insulation).

Ratings are established through standardized furnace tests. In North America, the benchmark is ASTM E119, also known as UL 263, which exposes an assembly to a temperature-time curve that reaches about 538°C at five minutes and continues climbing to roughly 1093°C at four hours. In Europe and many other regions, the equivalent framework comes from the EN 1363 test series and the fire design rules in Eurocode 3 (EN 1993-1-2).

Most building codes set a minimum fire resistance of one hour for structural members, and many require two or three hours depending on the occupancy, building height, and the role of the member. A bare, unprotected steel pipe typically achieves only 20 to 30 minutes, which is why fire protection is rarely optional.

Factors that determine the fire resistance of steel pipes

Several factors decide how long a structural steel pipe can hold up in a fire, and they are worth understanding before you choose a product:

• Section geometry and mass-to-area ratio. A member with more steel mass relative to its exposed surface heats up more slowly. For hollow sections, this ratio is the cross-sectional area of steel divided by the perimeter (A/P). A thicker-walled pipe therefore earns a longer rating than a thin-walled one of the same size.
• Wall thickness. Thicker walls absorb more heat before reaching a critical temperature, which is one reason heavy structural sections and pipe piles perform better than light members.
• Steel grade and chemical composition. Alloying elements such as chromium, nickel, and molybdenum improve high-temperature performance and slow oxidation. Stainless steel, with its high chromium content, generally holds up better in a fire than plain carbon steel, which is why corrosion-resistant and high-temperature grades are specified for demanding structural and industrial service.
• Restraint and connection conditions. How a member is connected and whether it can expand freely changes its fire behavior. Restrained members behave differently from simply supported ones, and design codes account for this.

Fire protection options for structural steel pipes

When the required rating exceeds what bare steel can provide, there are three practical routes: cover the steel, paint the steel, or fill the steel.

• External insulation. Gypsum board, spray-applied fire-resistive materials (SFRM), and mineral wool or ceramic fiber blankets form an insulating layer between the fire and the steel, slowing the temperature rise. These are the most common and economical methods for columns and beams.
• Intumescent coatings. Applied like paint, these coatings swell when heated, expanding up to roughly 100 times their original thickness to form a charred insulating barrier. They are the preferred choice when the clean look of the steel must be preserved.
• Concrete-filled hollow sections. Filling a hollow structural section with concrete turns the tube into a permanent form. The concrete acts as a heat sink, releases steam as it heats, and adds redundant load capacity that carries the structure as the steel weakens. This approach keeps the exterior finish flexible and is a recognized prescriptive solution, typically up to a two-hour rating.

Fire resistance requirements by application

The exact requirement depends on where and how the steel pipe is used:

• Building frames and columns. Structural columns and load-bearing members in high-rise and public buildings typically need one to three hours of fire resistance, with the highest ratings reserved for tall buildings and high-occupancy spaces.
• Bridges and infrastructure. EN 10210 steel hollow sections and similar hot-finished structural products are widely used in load-bearing frames, where the fire rating is set by the governing bridge or infrastructure code and the fire scenario considered for the structure.
• Foundation and marine structures. Steel tubular piles and driven pipe piles carry heavy axial loads, and their fire resistance is assessed on the load-bearing capacity they must keep during a fire, often combined with protective measures at exposed sections.
• Industrial structures. Petrochemical and power facilities often impose stricter requirements because the consequences of a structural failure during a fire are severe, and high-temperature alloy or stainless grades are frequently specified.

Testing, certification, and documentation

Fire resistance is verified by testing and backed by documentation. Standard furnace tests such as ASTM E119 and EN 1363 produce the rating in hours, and certified assemblies are published in recognized databases. For the steel itself, what matters on site is traceability: mill test certificates, material grade confirmation, and evidence that the product meets the specified standard.

A reliable supplier should be able to provide this paperwork without being asked twice. For structural steel pipe, look for a manufacturer that operates under a recognized quality system, holds product certifications for the relevant standards, and performs the checks that matter, such as hydrostatic testing, ultrasonic inspection, and positive material identification. These controls give you confidence that the grade, wall thickness, and dimensions you specified are exactly what was delivered.

How to specify fire-resistant steel pipes for structure works

When you are ready to specify, work through these steps:

1. Confirm the required rating. Check the governing code for your project and the fire resistance period in hours for each structural member.
2. Choose the right section and grade. ｓｅｌｅｃｔ the standard, grade, and wall thickness that meet both the structural load and the fire performance target.
3. Plan the protection method. Decide whether the member will be bare with a higher rating, insulated, coated, or concrete-filled, and confirm this with the fire engineer.
4. Verify documentation. Require mill test certificates, grade confirmation, and any required testing records as part of the supply contract.

Fire resistance is not a single property of a pipe. It is the result of material, geometry, protection, and quality control working together. Choosing a manufacturer that understands structural applications and can supply the full range of carbon, alloy, and stainless structural products with the right documentation makes the difference between a specification that looks good on paper and a structure that performs when it matters.