Stainless Steel As It Relates to Woodstove and Fireplace Chimney Pipe: Class A Solid Fuel UL 127 and UL 103 HT Venting Systems

Written by: Sean Summers, National Fireplace Institute (NFI) Master Hearth Certified Technician - WoodStovePro.com

Stainless steel is a general term for a group of corrosion resistant steels containing a minimum of 10.5 percent of chromium. Varying additions of nickel, molybdenum, titanium, niobium and other elements may be present. The mechanical properties and behavior in service of the various types of steel depend upon their composition, and careful selection of the most appropriate steel grade is vital to success in any application.1

There are a few types of stainless steel, but for our purposes we’ll only focus on ferritic and austenitic (Figure 1). Ferritic stainless steels are plain chromium stainless steels, usually with low carbon content. They are magnetic and have good ductility and resistance to corrosion and oxidation. They are generally resistant to stress corrosion cracking.2 Ferritic stainless steel shares some traits with austenitic stainless steel but contains no nickel; therefore, they are less expensive to manufacture. This allows for a lower price point chimney pipe.

Austenitic stainless steels are those containing chromium and nickel with very low carbon content. They are non-magnetic, but can become slightly magnetic when cold worked. Cold working also enhances their strength. Austenitic stainless steels have excellent corrosion resistance; good formability; good weldability, and excellent mechanical properties over a wide range of temperatures.2 The addition of nickel increases corrosion resistance but also adds to the cost of the material.

Figure 2 demonstrates how austenitic stainless steels, 304 and 316, match up against ferritic stainless steels.3We can see that 304 has better corrosion resistance than 430, but 316 is an even better choice for use with corrosive materials.

Stainless steel grades 304L, 316L and 316Ti have altered compositions that have been developed to achieve different attributes. In the case of 304L and 316L, the carbon has been reduced. Carbon strengthens austenite so it is a useful alloying element in stainless steels used in applications like boiler tubes that operate at high temperature. Carbon has no other useful function and can be detrimental to corrosion resistance under certain circumstances.4 316Ti is a titanium stabilized version of 316 used where good resistance to intergranular corrosion and high temperature strength is required.5 So 316Ti is sometimes used in components that require elevated temperature strength and corrosion resistance such as flexible chimney liners.

When deciding which chimney to purchase, it is important to consider what fuel you will be burning and your budget. In most applications, 430 will do an excellent job and is cost effective. In situations where coal is the fuel of choice, a higher grade stainless steel would be a better choice. Below is a chart of various manufacturers’ chimney compositions. Woodstovepro.com carries M&G Duravent DuraTech and DuraPlus, Metal Fab TempGuard, Security Chimney Secure Temp and Selkirk UltraTemp, GalvaTemp and SuperPro.

If you have any questions, please leave a comment or send us an email. We are always happy to help.

*E-prosites has made every effort to ensure the information presented is technically correct. However E-prosites does not represent or warrant the accuracy of the information contained in this blog. This blog is for information purposes only. E-prosites, its officers and employees, disclaim any and all liability or responsibility of any kind for loss, damage or injury resulting from the use of the information contained in this publication. Please consult with pipe manufacturer for all technical specifications and advice.

1 British Stainless Steel Association - SSAS Information Sheet No.1.1 – March 2001
2 The Southern Africa Stainless Steel Development Association (SASSDA) website
3 International Stainless Steel Forum (ISSF) – The Ferritic Solution: Properties, Advantages, Applications – 2007
4 International Molybdenum Association (IMOA) – Practical Guidelines for the Fabrication of High Performance Austenitic Stainless Steels - 2010
5 Australian Stainless Steel Development Association (ASSDA) website