313A Piping, Brazing & Leak Detection 1 — Questions and Answers
Question 1: When brazing copper-to-copper refrigerant joints, which brazing alloy is most commonly specified?
- Soft solder (50/50 tin-lead)
- BCuP-2 (copper-phosphorus, no silver)
- BCuP-5 (15% silver, copper-phosphorus) (Correct answer)
- BAg-7 (56% silver)
Correct answer: BCuP-5 (15% silver, copper-phosphorus)
BCuP-5 (15% silver) is the industry standard for copper-to-copper refrigerant joints because it is self-fluxing on copper and flows reliably at brazing temperatures.
Question 2: Why must dry nitrogen be purged through copper tubing during the brazing process?
- To cool the tubing faster after brazing
- To prevent cupric oxide scale from forming inside the pipe (Correct answer)
- To increase the flow rate of the brazing alloy
- To pressure-test the joint immediately after brazing
Correct answer: To prevent cupric oxide scale from forming inside the pipe
Flowing dry nitrogen displaces oxygen inside the pipe, preventing the formation of copper oxide scale that can contaminate compressor valves and metering devices.
Question 3: What is the minimum recommended overlap length for a brazed socket joint in refrigerant copper tubing?
- Equal to the tube wall thickness
- Equal to the tube outside diameter (Correct answer)
- Half the tube outside diameter
- Three times the tube wall thickness
Correct answer: Equal to the tube outside diameter
The minimum overlap for a brazed socket joint should equal the tube outside diameter to provide adequate joint strength and a leak-free seal.
Question 4: When cutting copper refrigerant tubing, which tool provides the cleanest cut with the least internal deformation?
- Hacksaw
- Reciprocating saw with metal blade
- Wheel-type tubing cutter (Correct answer)
- Angle grinder with a cutoff disc
Correct answer: Wheel-type tubing cutter
A wheel-type tubing cutter produces a clean, square cut with only a small internal burr that is easily removed by reaming, while saws leave rough edges and metal filings.
Question 5: What is the primary hazard when brazing refrigerant lines that have not been fully purged of refrigerant vapour?
- The brazing alloy will not bond to the copper
- Phosgene gas can form from refrigerant decomposition in the flame (Correct answer)
- The torch tip will overheat and require replacement
- Excessive oxidation will blacken the outside of the tubing
Correct answer: Phosgene gas can form from refrigerant decomposition in the flame
Residual refrigerant or oil vapour exposed to an open flame can decompose into phosgene, an acutely toxic gas, making complete purging and ventilation critical before brazing.
Question 6: Which flux is required when brazing copper tubing to a brass or steel fitting?
- No flux is needed on any copper joint
- A proper brazing flux (AWS Type FB3-A or equivalent) must be applied (Correct answer)
- Standard paste solder flux is sufficient
- Flux is only required when using oxygen-acetylene equipment
Correct answer: A proper brazing flux (AWS Type FB3-A or equivalent) must be applied
BCuP alloys are self-fluxing only on copper-to-copper joints; when joining copper to brass or steel, a dedicated brazing flux must be used to prevent oxidation and ensure proper flow.
Question 7: What nitrogen flow rate is typically recommended when purging copper refrigerant piping during brazing?
- As high as possible to ensure complete purging (above 50 CFH)
- A low positive flow just sufficient to displace oxygen (1–5 CFH) (Correct answer)
- Nitrogen pressure must match the system working pressure
- No specific flow rate — opening the valve briefly is adequate
Correct answer: A low positive flow just sufficient to displace oxygen (1–5 CFH)
A low positive flow of 1–5 CFH maintains an inert atmosphere inside the pipe without creating turbulence or wasting nitrogen, which is all that is needed to prevent oxide formation.
313A Piping, Brazing & Leak Detection 1
When brazing copper-to-copper refrigerant joints, which brazing alloy is most commonly specified?