Pipefitter Valves, Fittings, and Pipe Materials 5 — Questions and Answers
Question 1: A needle valve is best suited for applications requiring:
- Full open/full closed service only
- Precise flow metering and throttling (Correct answer)
- High-volume flow control
- Backflow prevention
Correct answer: Precise flow metering and throttling
The needle valve's tapered stem and small orifice allow very fine, precise adjustments to flow rate.
Question 2: When threading black steel pipe, the correct taper for NPT threads is:
- 1/16 inch per inch (Correct answer)
- 1/8 inch per foot
- 1/4 inch per foot
- 1/16 inch per foot
Correct answer: 1/16 inch per inch
National Pipe Taper (NPT) threads have a standard taper of 1/16 inch per inch (3/4 inch per foot) of thread length.
Question 3: Galvanized steel pipe should NOT be used for which of the following services?
- Cold potable water
- Natural gas distribution
- High-temperature steam above 212°F (Correct answer)
- Compressed air
Correct answer: High-temperature steam above 212°F
High temperatures cause the zinc coating to deteriorate and flake off, contaminating the system and weakening the pipe.
Question 4: What is the function of a strainer installed upstream of a control valve?
- Regulate flow velocity
- Remove debris that could damage the valve seat (Correct answer)
- Increase line pressure
- Provide isolation for maintenance
Correct answer: Remove debris that could damage the valve seat
A strainer catches particulates and scale before they can score or damage the precision-machined surfaces of a control valve.
Question 5: A full-port ball valve is specified instead of a standard-port ball valve when:
- Lower cost is the priority
- Minimum pressure drop and unrestricted flow are required (Correct answer)
- Precise throttling is needed
- Space is extremely limited
Correct answer: Minimum pressure drop and unrestricted flow are required
A full-port ball valve has a bore matching the pipe ID, providing virtually no restriction or pressure drop when fully open.
Question 6: Which pipe material is most resistant to corrosion in seawater or highly corrosive chemical service?
- Carbon steel
- Galvanized iron
- CPVC
- Hastelloy or high-nickel alloy (Correct answer)
Correct answer: Hastelloy or high-nickel alloy
Nickel alloys such as Hastelloy C provide exceptional corrosion resistance in aggressive chemical and marine environments where other metals fail.
Question 7: A concentric reducer connects pipes of different sizes and is distinguished from an eccentric reducer because it:
- Has both centerlines aligned on the same axis (Correct answer)
- Keeps the bottom of the pipe flat
- Is used only for vertical runs
- Has a longer lay length
Correct answer: Has both centerlines aligned on the same axis
A concentric reducer maintains a common centerline between both pipe sizes, making it suitable for vertical piping and non-critical horizontal runs.
Pipefitter Valves, Fittings, and Pipe Materials 5
A needle valve is best suited for applications requiring: