When Tube Fitting Material Should Not Match Tubing Material (Part 2)

How do you know which material of fittings and ferrules to choose with your tubing? 

 In an earlier post, Use Ferrules and Fittings that Match the Material of the Tubing, we explained the general rule to follow with respect to materials selection — but warned there are exceptions. Review exceptions here, then take advantage of free downloads that fill in more detail.

This Swagelok video goes over how to choose fittings, ferrules, and tubing materials to match your applications.

Like materials (usually) heads off trouble

Generally, we suggest that you use like materials. So if you have stainless steel tubing, use stainless steel ferrules and fittings. On plastic tubing, use plastic ferrules and fittings.

As we wrote in the previous article:

The reason for matching materials is simple: You want the ferrules to be stronger than the tubing so that the ferrules can swage onto the tubing and lock into place. If the ferrules are made of softer material than the tubing, you won't get that swaging action. Brass, for instance, is softer than stainless steel. So brass ferrules won't give you the full swaging action on stainless steel tubing.

Exceptions

However, on copper tubing we suggest using brass ferrules and fittings. Since brass is an alloy of copper and zinc, you are still using like materials.

In this video we reviewed dos and don'ts of tube fitting installation, then showed results of a burst test with copper tubing.

Sometimes you don't want the swaging action of the ferrules. Suppose you are using a thermocouple or some other sensor probe. You want to insert the probe into the fluid line, but you don't want to lock it into place because you'll need to remove the probe.

Or suppose you are using glass tubing, and you are worried that hard metal ferrules will fracture the glass.

In those cases you might want to use plastic ferrules. Perhaps you'll want a front ferrule made of Teflon because it's the most chemically compatible material. For the back you might want nylon. It's a little harder than Teflon, so it will help deform the front ferrule. You'll still get a good seal when you tighten them down, but you won't get the full swaging action.

Get details

"Just about every metal corrodes under certain conditions," explains the Swagelok Materials Selection Guide. "Corrosion occurs when a metal atom is oxidized by a fluid, leading to a loss of material in the metal surface. This loss reduces the wall thickness of a component and makes it more prone to mechanical failure."

Help options

1. Support: Our friendly experts are happy to help you choose the right components and materials for your application. Request support →
2. Urgent technical support: Have an urgent technical issue? Get help diagnosing & resolving fluid system issues with our 24x7 Field Advisory Services On-Call Technical Support. Call 780-237-7109.
3. Custom assemblies: Consider using our team to design, fabricate, and/or build assemblies for you. Get in touch →

Also see:

• Materials for Oxygen Service (with Ignition Example Photos)
• Anatomy of a Swagelok Hose: What's Going on Inside and Out
• Building Up Swagelok's Inventory of Special Alloys