API 510 Inspection Methods & Nondestructive Testing 4 — Questions and Answers
Question 1: An inspector performing UT thickness measurement on a pressure vessel finds readings significantly lower than the original design thickness. Per API 510, what is the next step before determining corroded thickness retirement?
- Establish a corrosion rate using historical thickness data to calculate remaining life (Correct answer)
- Immediately take the vessel out of service
- Sandblast and recoat the vessel without further measurement
- Increase the operating pressure to test vessel integrity
Correct answer: Establish a corrosion rate using historical thickness data to calculate remaining life
API 510 requires calculating short-term and long-term corrosion rates from historical data to establish remaining life and next inspection interval.
Question 2: In radiographic testing of a pressure vessel weld, what is 'geometric unsharpness' (Ug) and how is it controlled?
- Blurring of the radiographic image caused by source size and geometry, controlled by maximizing source-to-object distance and minimizing object-to-film distance (Correct answer)
- Over-exposure caused by excessive radiation dose
- Film graininess caused by incorrect development temperature
- Scatter radiation from adjacent structures
Correct answer: Blurring of the radiographic image caused by source size and geometry, controlled by maximizing source-to-object distance and minimizing object-to-film distance
Geometric unsharpness is penumbra blur from finite source size; it is minimized by using a small source and maximizing SFD while minimizing OFD.
Question 3: Which API 510 inspection category is defined as an internal inspection performed with the vessel open and entry made by the inspector?
- Internal inspection (Correct answer)
- On-stream inspection
- External inspection
- Intrusive inspection
Correct answer: Internal inspection
API 510 defines internal inspection as a formal inspection with the vessel out of service, opened, and entered by the inspector for direct examination.
Question 4: During penetrant testing of a pressure vessel repair weld, the inspector notes a linear indication that is 3/4 inch long but fades after 7 minutes of development. What is the most likely cause?
- The indication is a wide, shallow scratch that is bleeding out slowly — the linear pattern and fading suggest a superficial mechanical mark rather than a crack (Correct answer)
- The fading confirms a through-wall crack
- The penetrant is contaminated with water
- The developer was applied too thickly
Correct answer: The indication is a wide, shallow scratch that is bleeding out slowly — the linear pattern and fading suggest a superficial mechanical mark rather than a crack
Wide, shallow scratches often produce fading linear indications because there is limited penetrant volume trapped, unlike tight cracks which continue to bleed.
Question 5: API 510 allows substitution of on-stream inspection for internal inspection under certain conditions. Which of the following is NOT one of those conditions?
- The vessel is operating above its maximum allowable working pressure (MAWP) (Correct answer)
- Appropriate NDE methods suitable for the damage mechanisms are used
- A corrosion specialist or engineer approves the on-stream inspection program
- Historical inspection data supports the use of on-stream methods
Correct answer: The vessel is operating above its maximum allowable working pressure (MAWP)
Operating above MAWP is never a condition that permits on-stream substitution; it is a violation of the vessel's design envelope.
Question 6: What is the primary advantage of pulsed eddy current (PEC) testing when inspecting an insulated pressure vessel?
- It can detect wall loss through insulation, cladding, and coatings without requiring removal of the insulation (Correct answer)
- It provides higher accuracy than contact UT for thin-walled vessels
- It is the only method approved for ASME Code vessels
- It can identify the chemical composition of corrosion products
Correct answer: It can detect wall loss through insulation, cladding, and coatings without requiring removal of the insulation
PEC penetrates insulation and coatings using time-domain analysis of induced eddy currents, enabling wall-loss detection without stripping insulation.
Question 7: When applying ASME Section VIII, Div. 1 rules for a hydrostatic test of a repaired vessel, the test pressure is typically set at what multiple of the MAWP (adjusted for temperature)?
- 1.3 times the MAWP (Correct answer)
- 1.5 times the MAWP
- 2.0 times the MAWP
- 1.1 times the MAWP
Correct answer: 1.3 times the MAWP
ASME Section VIII, Div. 1 (post-2000 editions) requires a hydrostatic test pressure of 1.3 × MAWP × (stress ratio for test temperature).
API 510 Inspection Methods & Nondestructive Testing 4
An inspector performing UT thickness measurement on a pressure vessel finds readings significantly lower than the original design thickness.
Per API 510, what is the next step before determining corroded thickness retirement?