Understanding Copper Tube Flare Connections
Flare connections are one of the most reliable methods for joining copper tubes in refrigeration, HVAC, gas distribution, instrumentation, and hydraulic systems. The flare joint creates a metal-to-metal seal between the flared tube end and a matching conical seat in the fitting body. Unlike soldered joints, flare connections are mechanical — making them ideal for applications requiring disassembly or vibration resistance.
Types of Flare Connections
37° Flare (SAE / AN / JIC)
- Standard: SAE J512, ISO 4564, ASME B16.26
- Flare angle: 37° included angle
- Applications: Refrigeration, hydraulic systems, fuel lines, instrumentation
- Pressure rating: Up to 6,000 psi depending on tube size
45° Flare
- Standard: EN 1254-3, EN 1254-4
- Flare angle: 45° included angle
- Applications: Gas piping, some HVAC connections
Important Note:
37° and 45° flares are NOT interchangeable. Attempting to connect a 37° flare fitting to a 45° flare will result in leakage.
Standards and Specifications
| Standard | Scope | Angle |
|---|---|---|
| SAE J512 | Automotive and industrial tube fittings | 37° |
| ISO 4564 | Hydraulic fluid power fittings | 37° |
| ASME B16.26 | Wrought copper alloy flared joint fittings | 45° |
| EN 1254-3 | European copper fittings for gas/water | 45° |
Copper Tube Preparation
Tube Selection
- Material: Typically C12200 (DHP copper) per ASTM B88 or EN 1057
- Temper: Soft (annealed) for flaring; hard temper requires annealing first
Cutting and Deburring
- Cut the tube square using a tube cutter (not a saw)
- Deburr the outside edge with a deburring tool
- Deburr the inside edge to restore full bore
- Clean the tube end to at least 2× the flare depth
Flaring Procedure
- Slide the compression nut onto the tube before flaring
- Insert the tube into the flare block
- Tighten the flare yoke clamp
- Advance the flare forming tool into the tube end
- Form the flare until the cone contacts the block
- Retract the cone, open the clamp, and inspect
Flare Quality Inspection
- Smooth surface: No scratches, cracks, or tool marks
- Uniform shape: Symmetric cone with even thickness
- No splits: No visible splits at the flare edge
Assembly and Torque
- Apply a thin film of compatible lubricant to the flare face and nut threads
- Align the tube and fitting
- Hand-tighten the compression nut until finger-tight
- Use two wrenches for final tightening
Torque Values
| Tube OD | Torque (N·m) |
|---|---|
| 6mm (1/4″) | 12–15 |
| 8mm (5/16″) | 18–22 |
| 10mm (3/8″) | 25–30 |
| 12mm (1/2″) | 35–42 |
| 15mm (5/8″) | 50–60 |
| 18mm (3/4″) | 65–75 |
| 22mm (7/8″) | 85–100 |
| 28mm (1-1/8″) | 120–140 |
Leak Testing Methods
- Nitrogen pressure test: Pressurize to 1.5× working pressure. Hold for 24 hours.
- Soap bubble test: Apply leak detection solution to all connections.
- Electronic leak detector: For refrigeration systems.
- Helium mass spectrometer: For ultra-tight leak detection.
Common Installation Errors
- Forgetting the nut before flaring
- Over-flaring (thin, cracked flare)
- Under-flaring (incomplete seat contact)
- Using wrong flare angle (37° vs 45°)
- Dirty sealing surfaces
- Reusing old flares
- Overtightening
CoreMetal Steel — Precision Copper Tube for Flare Connections
CoreMetal Steel supplies precision copper tube in soft annealed temper, available in sizes from 6mm to 54mm OD. All products comply with ASTM B88, ASTM B280, and EN 1057.
Email: tracy@coremetalsteel.com | Phone: +86 18291910632