API 510 Non-Destructive Examination Methods 3 — Questions and Answers
Question 1: When conducting liquid penetrant testing on an austenitic stainless steel pressure vessel, which penetrant type is preferred to avoid stress corrosion cracking?
- High-sensitivity fluorescent penetrant with chlorine-based remover
- Water-washable fluorescent penetrant with low halogen and sulfur content (Correct answer)
- Solvent-removable visible dye penetrant with standard formulation
- Post-emulsifiable penetrant with hydrophilic emulsifier
Correct answer: Water-washable fluorescent penetrant with low halogen and sulfur content
For austenitic stainless steel, penetrant materials must have low halogen (chloride) and sulfur content because these contaminants can cause stress corrosion cracking in sensitized austenitic alloys.
Question 2: In radiographic examination, what is geometric unsharpness (Ug) primarily controlled by?
- Film speed and developer temperature
- Source size, source-to-object distance, and object-to-film distance (Correct answer)
- Lead screen thickness and density range
- Kilovoltage and milliampere-seconds settings
Correct answer: Source size, source-to-object distance, and object-to-film distance
Geometric unsharpness is a function of the radiation source size (focal spot), the source-to-object distance (SOD), and the object-to-film distance (OFD), as defined by Ug = (f × OFD) / SOD.
Question 3: What NDE limitation does API 510 specifically address when evaluating corrosion under insulation (CUI) on pressure vessels?
- CUI can only be detected after insulation removal by visual inspection
- Pulsed eddy current and profile RT can detect CUI through insulation without full removal (Correct answer)
- Magnetic particle testing is required for all CUI evaluations
- Liquid penetrant testing is the preferred method for CUI detection
Correct answer: Pulsed eddy current and profile RT can detect CUI through insulation without full removal
API 510 recognizes that pulsed eddy current (PEC) and profile radiography can screen for CUI through insulation, reducing the need for costly full insulation removal.
Question 4: During straight-beam ultrasonic thickness measurement of a pressure vessel wall, the inspector notices the digital readout fluctuates significantly on a corroded surface. What is the best corrective action?
- Accept the lowest reading as the minimum thickness (Correct answer)
- Use an angle-beam transducer to improve coupling
- Use a low-frequency transducer and apply more couplant to average out the reading
- Grind the surface smooth before taking measurements
Correct answer: Accept the lowest reading as the minimum thickness
Per API 510 and ASME inspection practice, when thickness readings fluctuate due to surface irregularity, the lowest recorded reading should be used for fitness-for-service evaluation as it represents the minimum remaining wall.
Question 5: What is the primary purpose of the IQI (image quality indicator) or penetrameter in radiographic testing?
- To identify the type of discontinuity present in the weld
- To demonstrate that the radiograph has the required sensitivity to detect relevant defects (Correct answer)
- To measure the actual thickness of the material being radiographed
- To indicate the correct exposure time for the film
Correct answer: To demonstrate that the radiograph has the required sensitivity to detect relevant defects
The IQI (penetrameter) demonstrates that the radiographic technique has sufficient sensitivity to detect discontinuities of a defined size, serving as a quality indicator for the radiographic process — not as a measurement tool.
Question 6: In magnetic particle testing, which magnetization technique is BEST suited for detecting longitudinal (axial) cracks in a pressure vessel nozzle weld?
- Circular magnetization using a central conductor through the nozzle bore (Correct answer)
- Longitudinal magnetization using a coil around the nozzle
- Yoke magnetization oriented parallel to the weld axis
- Prod technique with prods placed along the weld seam
Correct answer: Circular magnetization using a central conductor through the nozzle bore
Circular magnetization creates magnetic flux lines that encircle the part circumferentially, making them perpendicular to longitudinal (axial) cracks, which provides optimal detection sensitivity for that crack orientation.
Question 7: According to API 510, when can radiographic testing be substituted by ultrasonic testing for weld examination?
- UT can never substitute for RT on pressure vessel welds
- UT may substitute for RT when the weld geometry prevents proper RT and UT provides equivalent or better defect detection (Correct answer)
- UT substitution is allowed only on welds in low-pressure service below 150 psi
- UT substitution requires approval only from the insurance carrier
Correct answer: UT may substitute for RT when the weld geometry prevents proper RT and UT provides equivalent or better defect detection
API 510 and ASME Section V allow UT to substitute for RT when radiography is geometrically impractical or when UT provides equivalent sensitivity, particularly for thick-wall vessels or nozzle welds.
API 510 Non-Destructive Examination Methods 3
When conducting liquid penetrant testing on an austenitic stainless steel pressure vessel, which penetrant type is preferred to avoid stress corrosion cracking?