The British Refrigeration Association provides its 6th update on the UK Pressure Equipment (Safety) Regulations.
Maintaining safe working practices throughout any brazing process is paramount in the workplace and when carrying out training and assessment. Recognising the importance of brazed joints in supporting the effective and efficient operation of refrigeration and air conditioning systems, the BRA developed The simple brazing procedure specification and approval for jointing copper pipework for refrigeration systems.
There have been six issues, all incorporating a practical means of assessing an individual’s competence to braze joints for refrigeration and air conditioning pipework - in accordance with national standards used by the industry and relevant legislation. This latest revision has also considered high strength copper alloy pipe to recognise its adoption on R744 (CO2) systems and is also applicable to A2L refrigerants.
Brazing is a process of jointing that is generally applied to metals. During or after heating, the molten filler metal is drawn by capillary action into or retained in the space between the adjacent surfaces of the components being joined. Typically, the melting point of the filler metal is above 450°C, but always below the melting point of the parent metal.
Although the brazing methodologies in plumbing and the HVAC industry are the same, the high-pressure, high-temperature systems involved in HVAC and refrigeration systems means that true braze alloys are required. In contrast, a solder alloy will usually suffice in low-pressure systems that are more common in plumbing.
Specification and approval
The Brazing Procedure Specification is suitable for joints categorised by the UK Pressure Equipment (Safety) Regulations (Pressure Equipment Directive 2014/68/EU) as SEP or Cat I, for systems intended to operate on A1, A2L or A3 refrigerants. Joint Categories II and higher require recognised third party organisation (RTPO) approval of both the procedure and testing of the candidates’ test pieces. This procedure may be acceptable but should be agreed with the notified body before use.
Health and safety awareness forms an important part of carrying out any brazing process. A full risk assessment must be carried out for all the activities involved specific to the work area where the assessment is being carried out. Both the oxygen and fuel gases, together with most materials used in the brazing process, are hazardous to health. Operatives should be aware of these hazards by being familiar with method statements, risk assessments, COSHH and any specific site restrictions such as hot work permits and appropriate insurance cover.
Working areas where brazing processes are performed must be well ventilated and free from fire risk. Fumes and gases detrimental to health are emitted from most brazing processes; these must be disposed of quickly, either by use of exhaust ventilation equipment or adequate circulation of fresh air throughout the working area. If necessary, where these criteria cannot be assured, operators should wear breathing apparatus. The brazing process relies on the heat input being applied evenly below the melting temperature of the parent metal but sufficient to reach the melting temperature of the filler metal. The following precautions should be taken to ensure safe operation:
- Correct lighting up procedures (see manufacturer’s instructions)
- Avoidance of handling hot workpieces
- The use of correct protective clothing wherever required
- Adequate ventilation
- Adequate & sufficient firefighting equipment
Fluxes used in the jointing of copper pipework for refrigeration systems must be active over a lower temperature range (600°C to 750°C) and are generally based on alkali fluorides. The flux shall be applied to all joint surfaces before assembly to ensure complete flux coverage throughout the capillary joint. After completing a brazed joint, the flux residue must be removed, as it may cause corrosion.
When heat is applied to copper pipe in the presence of air, oxides form on the inner and outer surfaces of the tube. This is not generally harmful, but the scale inside the refrigeration pipework can cause blockage and damage once refrigerant and oil begin to circulate throughout the system. To overcome the formation of scale on the inside of the pipework, a suitable inert gas such as oxygen-free nitrogen (OFN) is passed through the pipework during the brazing process.
Types of joint
Three main types of configurations are used in the jointing of copper pipework for refrigeration systems. The pipework connections all form lap type joints and set out as follows:
Expanded joint: This type of joint is made by using a forming tool such as a swager where the tube (pipe) is expanded to accept another length of tube of the same circumference. Care must be taken to ensure that tube is not expanded beyond the gap size specified.
Sockets and fittings: There are several ranges of “Refrigeration” type capillary action fittings available from leading refrigeration wholesalers. These fittings are manufactured specifically for the refrigeration industry and are based on the “outside diameter” measurement of refrigeration grade copper tube. These fittings are not to be confused with the range of capillary fittings produced for the plumbing industry. HSCA fittings are specifically designed for HSCA (copper alloy tubing) and typically have a PS of 130 barg. Care should be taken to ensure the PS of the fittings is equal to or greater than the tubing they are being used to connect to. Accuracy in the fit-up components is essential for a good joint, and care must be exercised to ensure the clearance between the faces of components is not greater or less than specified.
Bi-metal joints and flanges: Bi-metal sockets and flanges are usually used where there is a need for dismantling of the pipework system during maintenance and servicing operations, e.g. bolt-on flanges and bi-metal sockets to service valves of a compressor or evaporator.