Overview
Pipework connects every component in a refrigeration system and must be installed to the highest standard to prevent leaks, ensure proper oil return, and maintain system efficiency. Poor pipework installation is a leading cause of refrigerant leakage — a key concern under EU F-Gas Regulation 517/2014. Brazing, flaring, and pipe routing are all practical skills assessed under EU Implementing Regulation 2015/2067 for Category I and II technicians.
Copper Pipe Standards
- Refrigeration-grade copper pipe is dehydrated, deoxidised, and sealed at both ends to prevent moisture and debris ingress.
- Pipe is specified by outside diameter (OD) in millimetres (e.g., 6.35 mm, 9.52 mm, 12.7 mm, 15.88 mm).
- Wall thickness must be suitable for the system’s maximum working pressure. Higher-pressure refrigerants like R-410A require thicker-walled pipe than R-22 or R-134a.
Brazing
Brazing is the primary method for making permanent joints in refrigeration pipework.
- A silver-alloy brazing rod (typically 2–5 % silver content) with a suitable flux or a phosphorus-copper alloy (self-fluxing on copper-to-copper joints) is used.
- The joint must be heated evenly until the brazing alloy flows by capillary action into the gap between the tube and fitting.
- Nitrogen purging is essential during brazing: a slow flow of OFN through the pipe prevents internal oxide scale formation. Oxide scale can block filter driers, damage compressor valves, and cause expansion valve failure.
- Never braze near flammable materials. Use fire-resistant mats and keep an extinguisher to hand.
Flare and Mechanical Joints
- Flare fittings are used where a joint must be removable (e.g., at service valves, equipment connections).
- The flare must be smooth, concentric, and free of cracks. A poor flare is a common source of leaks.
- Compression (bite-type) fittings are acceptable for certain applications but are not suitable for all refrigerants or pressures. Check manufacturer specifications.
Pipe Routing and Oil Return
- Suction lines must be sized to maintain adequate gas velocity for oil return to the compressor, especially on vertical risers.
- Horizontal suction and discharge lines should slope slightly in the direction of flow.
- Traps at the base of suction risers help entrain oil during low-load operation, but excessive traps add pressure drop.
- Liquid lines are less critical for velocity but must avoid excessive vertical lifts that could cause flash gas.
Insulation
- Suction lines must be insulated to prevent condensation (which causes corrosion and dripping) and to minimise heat gain, which reduces system capacity.
- Liquid lines should be insulated where they pass through warm areas to prevent subcooling loss and flash gas formation.
- Insulation material must be closed-cell (e.g., elastomeric foam) to resist moisture absorption.
Exam Tip: Always nitrogen-purge when brazing — this is one of the most frequently tested practical points. Know the consequences of not purging (oxide scale, blockages, acid formation). Also be ready to explain why suction lines are larger in diameter than liquid lines (lower-density vapour requires more volume to achieve adequate velocity).
