6.2 Follow-Up Testing & Repair Procedures

Under the F-Gas regulations, addressing leaks is not just a best practice; it is a strict legal requirement. When a leak is detected in a system containing fluorinated greenhouse gases, immediate action must be taken to stop the release of these potent climate-warming gases into the atmosphere.

Immediate Repair Requirement

If a leak is found during maintenance, servicing, or a mandatory leak check, the equipment operator (and the certified engineer conducting the work) has a legal obligation to ensure the leak is repaired without undue delay. You cannot simply top up the system with new refrigerant and walk away. Topping up a leaking system is illegal under F-Gas regulations. The system must be pumped down or the refrigerant recovered, the leak identified and repaired, and the system tested before any new refrigerant is added.

The process follows a strict sequence:

1. Identify: Locate the exact source of the leak using electronic leak detectors, UV dye, or bubble spray.
2. Recover: Remove the refrigerant from the leaking section or the entire system into a dedicated recovery cylinder.
3. Repair: Fix the leak. This usually involves replacing a component, re-making a flare joint, or re-brazing a connection.
4. Pressure Test: Perform an OFN strength and leak test to prove the repair is successful.
5. Evacuate: Use a vacuum pump to remove air, moisture, and nitrogen from the system.
6. Recharge: Put the correct quantity of refrigerant back into the system.

Statutory Follow-Up Timeline

One of the most critical legal stipulations in the F-Gas regulations is the requirement for a follow-up leak check after a repair has been made. Repairing the leak and putting the system back into operation is not the end of the process.

A certified engineer must return to the site to carry out a follow-up leak test. The timeline for this follow-up is legally mandated:

• It must be conducted within one month of the repair.
• However, it cannot be conducted on the same day. The system must be allowed to operate under normal working conditions, experiencing typical temperature and pressure fluctuations, to ensure the repair holds. Therefore, the test must be done after 24 hours but within 30 days (one month) of the system being recommissioned.

This follow-up check focuses specifically on the area that was repaired, as well as any adjacent areas that might have been stressed or affected during the repair process.

Joint Repair and Brazing Procedures

When repairing copper pipework, particularly when brazing, technicians must follow strict technical procedures to prevent system contamination and future leaks.

• OFN Purging: During any brazing operation, a constant, low-pressure flow of Oxygen-Free Nitrogen (OFN) must be passed through the pipework (typically at 0.1 to 0.2 bar or 2 to 5 CFH). This displaces atmospheric oxygen inside the tube. Without an OFN purge, the intense heat of brazing (above 600°C) causes copper to react with oxygen, forming a black, flaky layer of cupric oxide scale. Once the system is put into service, this scale flakes off and circulates with the refrigerant, clogging expansion valve orifices, blocking filter-driers, and causing mechanical damage to compressor bearings and valves.
• Mechanical Joints: Flare joints are a common source of leaks. When re-making a flare, the technician must inspect the copper tube for burrs, use a high-quality flaring tool to create a smooth, concentric flare, and tighten the flare nut using a calibrated torque wrench. Over-tightening flares is a common error that stresses the copper and causes it to split over time under vibration, while under-tightening leads to slow, persistent leaks.

Post-Repair Pressure Testing Protocols

Once a repair is complete, the technician must verify the integrity of the system before recharging it with refrigerant. This requires a two-stage pressure testing protocol using OFN:

1. Strength Test: The system is pressurised to its strength test pressure—typically 1.1 times the maximum allowable pressure (PS) for the high side or low side. This ensures the structural integrity of the repaired joint and proves it can withstand extreme operating conditions without bursting.
2. Leak Test: The pressure is adjusted to the design pressure (PS) and held. The joint is then checked using leak detection spray (bubble solution) or a digital pressure gauge. For critical repairs, a 24-hour pressure-hold test is recommended, and the final pressure reading must be corrected for changes in ambient temperature using the ideal gas laws ($P_1/T_1 = P_2/T_2$ in Kelvin).

Statutory F-Gas Record Keeping

Every repair and follow-up test must be recorded in the system's F-Gas logbook. This is a legal requirement for all systems containing F-Gas equivalent to 5 tonnes of CO2 or more. The logbook must contain:

• The name, address, and contact details of the equipment operator.
• The certified technician's name, certificate number, and their company's F-Gas registration details.
• The exact type of refrigerant and its total charge mass.
• The date and details of the leak check, including the locations and causes of any leaks found.
• The specific quantities of F-Gas added during recharging or recovered during the repair.
• The dates and results of the mandatory follow-up leak checks.

These records must be maintained by both the operator and the servicing company for a minimum of 5 years and must be made available to local environmental regulators (such as the Environment Agency in the UK) upon request.