Certified Pipefitter Steam Traps and Steam Systems — Questions and Answers
Question 1: What is the primary function of a steam trap in a steam distribution system?
- To increase steam pressure before it enters process equipment
- To discharge condensate and non-condensable gases while retaining live steam (Correct answer)
- To reduce steam velocity in long distribution mains
- To filter particulates from the steam supply
Correct answer: To discharge condensate and non-condensable gases while retaining live steam
A steam trap automatically discharges condensate (water that has condensed from steam) and air/non-condensable gases while preventing the escape of live steam. Allowing condensate to accumulate reduces system efficiency and creates conditions for water hammer.
Question 2: Which type of steam trap uses a floating ball that rises with accumulating condensate to mechanically open a discharge valve, providing continuous condensate removal?
- Inverted bucket trap
- Thermodynamic disc trap
- Float and thermostatic (F&T) trap (Correct answer)
- Balanced-pressure bellows trap
Correct answer: Float and thermostatic (F&T) trap
The float and thermostatic (F&T) trap uses a float that rises as condensate accumulates, mechanically opening the discharge valve. A separate thermostatic air vent releases non-condensable gases at startup. It discharges condensate continuously and handles high condensate loads well.
Question 3: What is 'water hammer' in a steam piping system?
- A routine vibration produced by high steam velocity in undersized pipe
- The violent pressure shock wave generated when high-velocity steam contacts a slug of subcooled condensate (Correct answer)
- The sound produced by a pressure relief valve opening
- Normal condensation occurring inside insulated steam mains
Correct answer: The violent pressure shock wave generated when high-velocity steam contacts a slug of subcooled condensate
Water hammer occurs when fast-moving steam collides with a slug of cooler, liquid condensate that has accumulated in the line. The sudden deceleration creates a severe pressure shock wave that can split pipe, destroy fittings, and damage equipment.
Question 4: What distinguishes superheated steam from saturated steam at the same pressure?
- Superheated steam contains moisture droplets; saturated steam does not
- Superheated steam has been heated above its saturation temperature and contains no liquid water (Correct answer)
- Superheated steam is produced only in electric boilers, not fire-tube boilers
- Superheated steam has a lower energy content than saturated steam at the same pressure
Correct answer: Superheated steam has been heated above its saturation temperature and contains no liquid water
Saturated steam exists at the boiling point for its given pressure and may carry moisture. Superheated steam has been heated further — above the saturation temperature — so it contains no liquid droplets, carries more energy, and behaves more like a gas. It is used where dry steam is critical (e.g., turbines).
Question 5: Why should steam mains be pitched (sloped) in the direction of steam flow?
- To increase steam velocity and improve system efficiency
- To reduce heat loss through the pipe walls
- To allow condensate to drain by gravity to trap stations and prevent accumulation (Correct answer)
- To comply with OSHA minimum slope requirements for pressurized piping
Correct answer: To allow condensate to drain by gravity to trap stations and prevent accumulation
Proper pitch (typically 1/8" to 1/4" per foot) ensures condensate drains by gravity toward steam trap stations rather than pooling in low spots. Accumulated condensate is the primary cause of water hammer and can also accelerate internal corrosion.
Question 6: What is 'flash steam,' and where does it occur in a steam system?
- Steam that passes through a failed-open steam trap at full line pressure
- Steam generated when high-pressure, high-temperature condensate is discharged to a lower-pressure zone (Correct answer)
- Steam that has been superheated in an attemperator to above 600°F
- Steam produced by a safety relief valve discharge during an overpressure event
Correct answer: Steam generated when high-pressure, high-temperature condensate is discharged to a lower-pressure zone
When high-pressure condensate (which is above the boiling point at lower pressure) is released to a lower-pressure area such as a condensate return header, a portion instantly re-evaporates into steam — called flash steam. It can be recovered and reused as a low-pressure steam source, or vented safely.
Certified Pipefitter Steam Traps and Steam Systems
What is the primary function of a steam trap in a steam distribution system?