CRST Piping, Tubing & Brazing Techniques 1 — Questions and Answers
Question 1: Which type of copper tubing is specifically manufactured, internally cleaned, and sealed for use in refrigeration and air conditioning systems?
- Type L plumbing tubing
- Type M plumbing tubing
- Type K plumbing tubing
- ACR (Air Conditioning and Refrigeration) tubing (Correct answer)
Correct answer: ACR (Air Conditioning and Refrigeration) tubing
ACR tubing is deoxidized, internally cleaned, dehydrated, and sealed at the factory to keep the interior free of moisture and contamination for refrigerant service.
Question 2: When brazing copper-to-copper refrigeration joints, which brazing alloy family is self-fluxing and most commonly used in the industry?
- 50/50 tin-lead solder
- Silver-phosphorus-copper (BCuP) alloys (Correct answer)
- Aluminum brazing rod
- Zinc-tin alloy
Correct answer: Silver-phosphorus-copper (BCuP) alloys
BCuP (silver-phosphorus-copper) alloys are self-fluxing on copper-to-copper joints because phosphorus acts as its own flux, making them the industry standard for refrigeration brazing.
Question 3: What is the primary purpose of flowing dry nitrogen through refrigeration piping during the brazing process?
- To cool the pipe rapidly after brazing is complete
- To prevent internal oxidation and copper oxide scale formation inside the tubing (Correct answer)
- To increase the brazing temperature at the joint
- To simultaneously pressure-test the joint while brazing
Correct answer: To prevent internal oxidation and copper oxide scale formation inside the tubing
Nitrogen purging displaces oxygen inside the tubing during heating, preventing the formation of copper oxide scale that could contaminate the refrigerant system and damage components.
Question 4: What is the correct preparation sequence before brazing a refrigeration copper fitting joint?
- Apply refrigerant oil inside the tube end to lubricate the fit
- Clean mating surfaces with emery cloth until bright, then apply flux if joining dissimilar metals (Correct answer)
- Heat the joint first to drive off moisture, then insert the fitting
- Apply water to the joint area to prevent overheating
Correct answer: Clean mating surfaces with emery cloth until bright, then apply flux if joining dissimilar metals
Surfaces must be mechanically cleaned to bare, shiny metal, and appropriate flux applied when needed, to ensure proper brazing alloy flow and a leak-free joint.
Question 5: What minimum refrigerant velocity is generally required in vertical suction line risers to ensure adequate oil return to the compressor?
- 100-200 fpm
- 700-1,000 fpm (Correct answer)
- 3,000-4,000 fpm
- 50-100 fpm
Correct answer: 700-1,000 fpm
Vertical suction line risers require approximately 700-1,000 fpm minimum velocity to carry entrained oil droplets upward against gravity back to the compressor.
Question 6: Which type of joint connection is recommended for permanent refrigerant piping installations in commercial refrigeration systems?
- Threaded NPT connections
- Brazed connections (Correct answer)
- Compression fittings
- Push-to-connect quick couplings
Correct answer: Brazed connections
Brazed connections provide permanent, leak-resistant joints that withstand pressure cycling, thermal expansion, and vibration typical in refrigeration systems over their service life.
Question 7: When a long horizontal suction line transitions into a vertical riser, what piping configuration is recommended at the base of the riser?
- Install a check valve to prevent backflow
- Install a P-trap (inverted trap) to accumulate and batch-transport oil up the riser (Correct answer)
- Increase the pipe diameter by one size at the riser base
- Install a Y-strainer to collect debris
Correct answer: Install a P-trap (inverted trap) to accumulate and batch-transport oil up the riser
A P-trap at the base of a vertical suction line riser collects oil so that once a sufficient slug accumulates, refrigerant velocity can carry it upward in a batch rather than a thin film.
CRST Piping, Tubing & Brazing Techniques 1
Which type of copper tubing is specifically manufactured, internally cleaned, and sealed for use in refrigeration and air conditioning systems?