What Is the Difference Between Hastelloy C22 Compression and Flare Fittings?

Both are ways to make a leak tight mechanical tube connection, and Hastelloy C22 is used for either type when you need resistance to aggressive chemicals, corrosion, and high temperatures, but the two designs seal very differently and suit different applications.

Compression fittings

• Seal by using a ferrule that a nut compresses radially and axially onto the outside of the tube when tightened into a fitting body.
• The ferrule bites into or deforms slightly against the tube OD, creating a seal without needing any special tube end preparation.
• Easier to install correctly with basic tools, no special flaring tool required.
• Generally rated for high pressure and vibration resistance once properly set, and can often be disassembled and reassembled without leaking.
• Common in instrumentation, process piping, and analytical systems.
• Tube surface finish and roundness matter, but there's more tolerance for minor imperfections than with flare fittings.

Flare fittings

• Require the tube end to be flared outward using a flaring tool before assembly.
• The flared cone seats against a matching angled seat in the fitting body, and the nut draws the flare into that seat to create a metal to metal seal.
• No separate ferrule, the tube itself becomes the sealing surface, so tube quality is critical, since Hastelloy C22 work hardens readily and can crack if flared improperly.
• Tend to be preferred where a proven, simple metal-to-metal seal is wanted and where the system will see less vibration or where periodic disassembly/reassembly with reliable resealing is important.
• Installation is less forgiving, a poor flare will leak, and C22's hardness/work-hardening behavior makes flaring somewhat trickier than with softer alloys like copper or annealed stainless.