Piping Piping Inspection and Testing 2 — Questions and Answers
Question 1: What is a 'pneumatic test' for piping, and when is it used instead of hydrostatic testing?
- A test using nitrogen or air at high pressure, used when the system cannot be exposed to water due to process contamination concerns or structural limitations (Correct answer)
- A test that checks for air pockets in water-filled piping
- A test for gas leaks using a combustible gas detector
- A preliminary check before hydrostatic testing
Correct answer: A test using nitrogen or air at high pressure, used when the system cannot be exposed to water due to process contamination concerns or structural limitations
Pneumatic testing uses compressible gas (typically nitrogen) and carries higher risk than hydrostatic testing; it is used when water would cause process contamination, structural overloading, or when freezing is a risk.
Question 2: What does 'deadleg inspection' specifically look for in process piping?
- Fatigue cracking at support attachment points
- Corrosion, pitting, and deposits in stagnant zones where process fluid does not flow (Correct answer)
- Flow-induced vibration damage
- Erosion at pipe bends
Correct answer: Corrosion, pitting, and deposits in stagnant zones where process fluid does not flow
Deadlegs accumulate corrosive by-products, sediment, and microbiological growth in stagnant fluid, often causing rapid corrosion that requires focused inspection attention.
Question 3: What is 'external corrosion' most commonly caused by in above-ground process piping?
- Internal process fluid attack
- Moisture trapped under insulation (Corrosion Under Insulation — CUI) or atmospheric corrosion on uninsulated pipe (Correct answer)
- Galvanic attack from cathodic protection current
- High-temperature oxidation above the pipe's maximum temperature rating
Correct answer: Moisture trapped under insulation (Corrosion Under Insulation — CUI) or atmospheric corrosion on uninsulated pipe
CUI is the most prevalent external corrosion mechanism in insulated piping, occurring when water infiltrates insulation and creates a wet environment on the pipe surface.
Question 4: What is the purpose of a 'hammer test' or 'coin tap' inspection on piping?
- To measure pipe wall thickness by resonance frequency
- To detect delamination, disbonded linings, or hollow spots by listening for changes in sound when tapping the pipe surface (Correct answer)
- To check if the pipe is properly supported
- To identify cracked flanges by acoustic response
Correct answer: To detect delamination, disbonded linings, or hollow spots by listening for changes in sound when tapping the pipe surface
Tapping the pipe surface with a hammer or coin produces different sounds when disbonded or damaged areas are present, providing a quick qualitative screening method.
Question 5: In a risk-based inspection (RBI) program for piping, what are the two factors that determine inspection priority?
- Age of the piping and material grade
- Probability of failure (PoF) and consequence of failure (CoF) (Correct answer)
- Last inspection date and current wall thickness
- Operating pressure and temperature
Correct answer: Probability of failure (PoF) and consequence of failure (CoF)
RBI prioritizes inspection resources by combining the probability of failure (based on corrosion mechanisms and rates) with the consequence of failure (safety, environmental, and economic impacts).
Question 6: What nondestructive method is best suited for detecting stress corrosion cracking (SCC) in stainless steel piping?
- Radiographic Testing (RT)
- Eddy Current Testing (ET) or Phased Array Ultrasonic Testing (PAUT) (Correct answer)
- Hydrostatic testing
- Magnetic Particle Testing (MT)
Correct answer: Eddy Current Testing (ET) or Phased Array Ultrasonic Testing (PAUT)
Eddy current and PAUT are effective for detecting SCC cracks in stainless steel; MT cannot be used on non-ferromagnetic austenitic stainless steel.
Piping Piping Inspection and Testing 2
What is a 'pneumatic test' for piping, and when is it used instead of hydrostatic testing?