GPT Material Selection & Properties 3 — Questions and Answers
Question 1: Which joining method is approved for steel gas pipe connections in concealed locations?
- Compression fittings
- Flared fittings
- Welded joints (Correct answer)
- Push-to-connect fittings
Correct answer: Welded joints
Welded joints are the approved method for concealed steel gas pipe because they create a permanent, leak-free connection without mechanical components that can loosen.
Question 2: A copper tube marked 'ACR' is found on a job site. Can it be used for natural gas service?
- Yes, ACR copper is approved for all gas types
- No, ACR tubing is dehydrated for refrigerants only and not rated for gas (Correct answer)
- Yes, if pressure is below 2 psi
- No, copper cannot be used for gas under any circumstance
Correct answer: No, ACR tubing is dehydrated for refrigerants only and not rated for gas
ACR (Air Conditioning & Refrigeration) copper tubing is pre-cleaned and sealed for refrigerants and is not approved for gas service; only Type K or L labeled for gas use is acceptable.
Question 3: What minimum pipe wall thickness in inches is required for 2-inch Schedule 40 steel pipe?
- 0.083 inches
- 0.109 inches
- 0.154 inches (Correct answer)
- 0.218 inches
Correct answer: 0.154 inches
2-inch Schedule 40 steel pipe has a nominal wall thickness of 0.154 inches per ASME dimensional standards.
Question 4: Which gas piping material requires bonding to the electrical grounding system per NFPA 54?
- PE pipe
- Type K copper
- CSST (Correct answer)
- Black steel only
Correct answer: CSST
CSST requires bonding to the electrical grounding system because its thin corrugated walls can be punctured by arc damage from lightning-induced surges.
Question 5: A gas pipe runs through an exterior wall in a cold climate. Which material concern is most critical?
- Thermal expansion cracking of PE pipe (Correct answer)
- Condensation causing CSST corrosion
- Freeze-thaw stress on rigid steel fittings
- UV degradation of copper tubing
Correct answer: Thermal expansion cracking of PE pipe
PE pipe becomes brittle at low temperatures and is not approved for above-ground use, making thermal cracking the primary concern if misused.
Question 6: What does the SDR rating on PE gas pipe indicate?
- Standard Diameter Ratio (outside diameter to wall thickness) (Correct answer)
- System Design Rating for maximum pressure
- Structural Durability Rating for soil load
- Seismic Deflection Rating
Correct answer: Standard Diameter Ratio (outside diameter to wall thickness)
SDR (Standard Dimension Ratio) is the ratio of pipe outside diameter to minimum wall thickness, which determines pressure rating.
Question 7: Which fitting type is NOT approved for use in concealed or inaccessible gas piping locations?
- Welded butt joints
- Mechanically formed tee outlets
- Flared fittings (Correct answer)
- Forged steel fittings
Correct answer: Flared fittings
Flared fittings are mechanical connections that can loosen over time and must be accessible for inspection; they are prohibited in concealed locations.
GPT Material Selection & Properties 3
Which joining method is approved for steel gas pipe connections in concealed locations?