Piping Engineering 4 — Questions and Answers
Question 1: What is the Darcy-Weisbach equation used for in piping engineering?
- Calculating pipe wall thickness under pressure
- Determining frictional head loss in pipe flow (Correct answer)
- Evaluating thermal expansion of pipe
- Sizing relief valves for overpressure protection
Correct answer: Determining frictional head loss in pipe flow
The Darcy-Weisbach equation calculates the pressure drop due to friction in a pipe as a function of pipe length, diameter, velocity, and friction factor.
Question 2: What is the purpose of a steam trap in a piping system?
- To reduce steam pressure to a safe level
- To discharge condensate while preventing steam from escaping (Correct answer)
- To filter particulates from steam lines
- To measure steam flow rate
Correct answer: To discharge condensate while preventing steam from escaping
A steam trap automatically drains condensate and non-condensable gases from steam systems while preventing live steam from escaping, maintaining system efficiency.
Question 3: In ASME piping codes, what does 'allowable stress' depend on primarily?
- Pipe diameter and schedule only
- Material yield strength and tensile strength at operating temperature (Correct answer)
- The pipe installation method
- The pipe manufacturer's specifications
Correct answer: Material yield strength and tensile strength at operating temperature
Allowable stress values in ASME codes are derived from material yield and tensile strengths at temperature, divided by appropriate safety factors.
Question 4: What is the difference between a wye (Y) fitting and a tee fitting in piping?
- A wye branches at 45 degrees while a tee branches at 90 degrees (Correct answer)
- A wye is used for liquids and a tee for gases
- A wye is threaded and a tee is welded
- A wye handles higher pressure than a tee
Correct answer: A wye branches at 45 degrees while a tee branches at 90 degrees
A wye fitting connects a branch line at a 45-degree angle to the main run, while a tee connects the branch at 90 degrees, making the wye better for flow-through applications.
Question 5: What does PWHT stand for in piping fabrication?
- Pre-Weld Heat Treatment
- Post-Weld Heat Treatment (Correct answer)
- Pipe Wall Hardness Test
- Pressure Weld High Temperature
Correct answer: Post-Weld Heat Treatment
Post-Weld Heat Treatment (PWHT) is a controlled process of heating and cooling welded pipe to relieve residual stresses and improve mechanical properties.
Question 6: Which flow regime is characterized by fluid particles moving in parallel layers with no lateral mixing?
- Turbulent flow
- Transitional flow
- Laminar flow (Correct answer)
- Choked flow
Correct answer: Laminar flow
Laminar flow occurs at low Reynolds numbers (Re < 2300) where fluid moves in smooth, parallel layers with viscous forces dominating inertial forces.
Question 7: What is the primary reason for installing a strainer upstream of a control valve?
- To reduce the pressure drop across the valve
- To protect the valve trim from damage by particulates (Correct answer)
- To increase the flow coefficient of the valve
- To prevent reverse flow through the valve
Correct answer: To protect the valve trim from damage by particulates
Strainers upstream of control valves capture solid particles that could damage or clog the precise valve trim components, extending valve service life.
Piping Engineering 4
What is the Darcy-Weisbach equation used for in piping engineering?