July 2017

Welcome to ‘Stainless Solutions’ from IMOA. Each month, we will cover a different stainless steel issue with tips on design and specification, and links to technical resources.  This month’s issue provides information on stainless steel performance in fire.
Stainless Steel Fire Performance & Radiant Heat Transfer

Fire resistance, containment, and prevention are important aspects of building and structure design. The ability of a loaded structural material to retain its strength when exposed to fire can provide additional valuable time for building evacuation or prevent collapse of a structure like a bridge. Both bare structural sections and stainless steel concrete reinforcement have been studied.

The capacity of a metal to limit the spread of fire is not restricted to structural sections.  Barriers like fire doors, roofing, insulated equipment enclosures and other panel systems, chimney linings, and other metal components can help to reduce the spread of fire. However, the metals used in architecture exhibit significant performance differences, even with only brief exposure to high temperatures.

A longer version of this article is available on IMOA’s website with more data and paper references.

Metal Basics
For large projects it is advisable to conduct fire engineering assessments. Country specific code guidance should be used to determine fire protection requirements for limiting temperature increase during fires.

Copper and aluminum start to experience strength reductions at fairly low temperatures. Aluminum alloys begin to show a reduction in strength at temperatures above 212ºF (100ºC). At 400ºF (204ºC), the strength of copper has decreased about 25% and that of 6061-T6 aluminum has decreased by about 60%.

Steels are able to retain their strength up to higher temperatures. The traditional method of ensuring sufficient fire resistance is to ensure that the temperature of carbon steel does not rise above 700ºF (370ºC) so that it retains all of its strength. By the time carbon steel reaches 930ºF (500ºC), it has lost about 30% of its strength. Unprotected weathering steel loses about half of its strength above 1000ºF (538ºC).

Results from research to determine the structural performance of different alloys of stainless steel in fire have been included in both Eurocode 3: Part 1.2 and the AISC Steel Design Guide 27: Structural Stainless Steel. Austenitic stainless steels generally retain a higher proportion of their room temperature strength than carbon steel above temperatures of about 1000° F (550°C). All stainless steels retain a higher proportion of their stiffness than carbon steel over the entire temperature range. There is further information available in these resources:

Stainless Steel Fire Testing
The first comprehensive fire testing on stainless steel was done by Darchem Engineering in the early 1990’s after a North Sea oil platform fire. The program included testing the fire and radiant heat resistance and heat conduction through fittings and walls of:

  • galvanized carbon steel
  • fiberglass-reinforced plastic (FRP)
  • aluminum
  • molybdenum-containing Type 316 stainless steel.

FRP and aluminum failed the tests. Stainless steel surpassed the requirements of all of the tests and had less deflection than carbon steel. A copy of this report, Stainless Steel for Durability, Fire-Resistance, and Safety (10042), can be downloaded from the Nickel Institute website and a video of some of this testing can be viewed by following the link below.

Click on the image to watch a video of the fire resistance and fire radiation testing programs. Credit: Nickel Institute

Significant testing has subsequently been conducted to meet the requirements of structural design codes and guides. Stainless steel’s ability to retain stiffness better than carbon steel at elevated temperatures has been repeatedly demonstrated. Furthermore, molybdenum containing Type 316 stainless steel retains its strength better than Type 304 stainless steel.  Figure 1 shows the stiffness retention behavior of stainless and carbon steels at elevated temperatures and Figure 2 compares the strength retention. (See the Eurocode and AISC Design Guide for further information.)

By 1472ºF (800ºC), carbon steel has a stiffness retention level of about 10%, while stainless steel retains approximately 60%. This may make it possible to eliminate stainless steel fire protection if the expected failure mode is governed by stiffness retention.

Figure 1: Comparison of stainless and carbon steel stiffness retention at elevated temperature

Figure 2: Comparison of different stainless steel alloys and carbon steel strength retention factors

Continued research and innovations in stainless steel structural design will allow designers and engineers to create ever more compelling structures that capitalize on the fire resistance of bare metal to express details as sculptural design elements.

Stainless Steel Library

Download a free Stainless Steel Library (zip file, 559 MB) with over 360 pdfs covering building and construction applications, selection, specification, fabrication, sustainability and other common questions.

Stainless Solutions e-newsletter archive

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Continuing Education – American Institute of Architects (AIA)

IMOA is an AIA continuing education system approved provider with eight 1-hour programs that are registered for both live face-to-face and distance learning credit.

1. Stainless Steel Sustainable Design
2. Bioclimatic Design With Stainless Steel Weather Screens
3. Stainless Steel Structural Design
4. Stainless Steel Specification For Corrosive Applications
5. Deicing Salt: Stainless Steel Selection to Avoid Corrosion
6. Stainless Steel Finish Specification
7. Advanced Stainless Steel Specification and Problem Avoidance
8. Specification of Stainless Steel Finishes and Grades For Corrosive Applications

For more information or to schedule a workshop contact Catherine Houska, 412-369-0377 or email chouska@tmr-inc.com.

What is IMOA?

IMOA (International Molybdenum Association) is a non-profit industry association, which provides technical information to assist with successful specification of molybdenum-containing materials. Molybdenum is an element. When it is added to stainless steel, molybdenum increases its resistance to corrosion caused by deicing salts, coastal atmosphere and pollution.

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