Piping, Brazing & Leak Detection Flashcards

When brazing copper-to-copper refrigerant joints, which brazing alloy is most commonly specified?

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.

Why must dry nitrogen be purged through copper tubing during the brazing process?

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.

What is the minimum recommended overlap length for a brazed socket joint in refrigerant copper tubing?

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.

When cutting copper refrigerant tubing, which tool provides the cleanest cut with the least internal deformation?

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.

What is the primary hazard when brazing refrigerant lines that have not been fully purged of refrigerant vapour?

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.

Which flux is required when brazing copper tubing to a brass or steel fitting?

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.

What nitrogen flow rate is typically recommended when purging copper refrigerant piping during brazing?

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.