Instrumentation Fittings: Material Compatibility, Tube Hardness, Wall Thickness, and Temperature

Instrumentation fittings help create leak-resistant tubing systems for fluid and gas service. Their performance depends on the fitting, the tube, and the application conditions working together, so selection starts with compatibility rather than thread size alone.

Material Compatibility

The fitting material should be compatible with the media being contained and with the tubing material. Like materials are often paired: stainless fittings with stainless tubing, brass or iron with compatible tubing, and so on. Mixing unlike materials can create corrosion, sealing, or mechanical problems.

Tube Hardness

The fitting must be able to grip the tube properly. For ferrule-style fittings, the fitting and ferrule material should be harder than the tube so the ferrule can bite or swage as intended. Stainless tubing is often limited to a hardness such as Rb 80 or less for reliable ferrule action.

Wall Thickness

Wall thickness affects pressure capability and ferrule sealing. In gas service, the ferrule must be able to seal small surface imperfections to create a gas-tight joint. Tubing that is too thin, too hard, or poorly prepared can compromise that seal.

Temperature Conditions

Media temperature and ambient temperature affect both tubing and fittings. Not every material or seal can handle elevated temperature and pressure together. Before installation, confirm the material, pressure rating, tube wall, temperature range, and corrosion exposure.