SPED Valve & Fitting Selection 3 — Questions and Answers
Question 1: In ASME B16.5, what does the Class 300 pressure-temperature rating for a carbon steel flange signify?
- Maximum allowable pressure of 300 psi at all temperatures
- A pressure-temperature rating group that varies with temperature (Correct answer)
- Minimum tensile strength of 300 ksi
- A flange bore diameter of 3.00 inches
Correct answer: A pressure-temperature rating group that varies with temperature
ASME B16.5 Class designations represent rating groups where the maximum allowable working pressure decreases as temperature increases, following published tables.
Question 2: Which type of valve disc design in a butterfly valve provides improved sealing performance at high differential pressures?
- Concentric (centric) disc
- Single-offset disc
- Double-offset (high-performance) disc
- Triple-offset disc (Correct answer)
Correct answer: Triple-offset disc
Triple-offset butterfly valves use a conical seat geometry that produces zero friction during opening/closing, enabling tight metal-to-metal shutoff at high pressures.
Question 3: A fitting used to connect two pipes of different schedules (wall thicknesses) with the same nominal pipe size is called a:
- Swage nipple (Correct answer)
- Concentric reducer
- Barrel nipple
- Insert coupling
Correct answer: Swage nipple
Swage nipples transition between different pipe schedules while maintaining the same nominal diameter, providing a smooth bore transition.
Question 4: For a valve in chlorine gas service, which packing material should be avoided due to attack by wet chlorine?
- PTFE (Teflon)
- Graphite
- Carbon fiber reinforced PTFE
- Neoprene elastomer (Correct answer)
Correct answer: Neoprene elastomer
Neoprene (polychloroprene) and most elastomers are attacked by dry or wet chlorine gas, making PTFE or graphite-based packings the correct choice.
Question 5: What is the purpose of a spectacle blind (figure-8 blind) in a piping system?
- To regulate flow rate between two process lines
- To provide visual confirmation of isolation or flow status between equipment (Correct answer)
- To protect instruments from high-pressure surges
- To allow bidirectional flow control
Correct answer: To provide visual confirmation of isolation or flow status between equipment
A spectacle blind provides a permanent, positively isolating blind or spacer that can be flipped, with the open or blind position visually verifiable at the flange.
Question 6: Which fitting is used to close the open end of a female-threaded pipe fitting?
- Plug (Correct answer)
- Cap
- Blind flange
- Hex nipple
Correct answer: Plug
A plug has male external threads and is screwed into a female-threaded fitting to seal an open end.
Question 7: According to API 6D, what is the minimum required closure time for a 24-inch full-bore ball valve used in pipeline service?
- Instantaneous closure is acceptable
- Closure time is not specified by API 6D
- Slow-closing operation is preferred to prevent water hammer, with time defined per system analysis (Correct answer)
- Exactly 30 seconds, regardless of size
Correct answer: Slow-closing operation is preferred to prevent water hammer, with time defined per system analysis
API 6D does not prescribe a single closure time; the pipeline engineer must determine the safe closure time based on surge pressure analysis for each specific system.
SPED Valve & Fitting Selection 3
In ASME B16.5, what does the Class 300 pressure-temperature rating for a carbon steel flange signify?