Tubing Pipe (409ss)

Description

The tubing the OEMs use, because it bends

409 is a ferritic stainless steel, and it is what the factories run for exhaust systems. It handles heat cycling, coastal air and summer rain far better than mild steel or aluminised pipe, but the important part for a fabricator is what it does on the bender. Where 304 work hardens, springs back and cracks at the outer radius, 409 stays soft and forms cleanly. You set your radius, pull the bend, and it holds.

Built for the bench and the bender

Run it through a hydraulic pipe bender or a mandrel bender without babying it. The 1.5mm wall is thick enough to hold its shape through a tight radius but thin enough to work quickly, cut clean and weld without burning through. It tacks easily with MIG or TIG using standard workshop consumables, and it takes a flare or an expansion at the joint when you need a slip fit rather than a butt weld.

Out the box it carries a brushed metallic finish. In service it develops a light surface patina over time instead of the flaking rust you get off mild steel, and the wall keeps its structural integrity underneath.

Why 409 over the alternatives

• Bends properly on a machine, where 304 fights back and springs
• Lasts several times longer than mild steel or aluminised pipe
• Costs less than 304 for a similar working life on an exhaust
• Holds up to coastal humidity, gravel road grit and daily heat cycling
• Magnetic and weldable with standard workshop equipment

Common applications

• Full custom exhaust systems, cat back and turbo back
• Downpipes and mid sections
• Header and manifold collector piping
• Silencer inlet and outlet necks
• Repair sections on OEM stainless systems

Specifications

Material: 409 ferritic stainless steel
Finish: brushed mill finish
Bending: mandrel and press bending

Working with it

For tight radii, use a mandrel bender to keep the bore fully open through the bend. Back purge on TIG welds where you can, and let the tube cool naturally rather than quenching it, so you keep the heat affected zone stable.