API 510 Inspection Methods & Nondestructive Testing 5 — Questions and Answers
Question 1: When performing angle-beam UT on an austenitic stainless steel weld, what additional challenge must the inspector account for compared to carbon steel welds?
- Coarse columnar grain structure causing high attenuation and beam skewing (Correct answer)
- Higher surface reflectivity requiring special couplant
- Inability to use any angle above 45°
- Mandatory use of TOFD only per ASME Code
Correct answer: Coarse columnar grain structure causing high attenuation and beam skewing
Austenitic welds have coarse, anisotropic columnar grains that scatter and skew ultrasonic beams, requiring specialized techniques or lower frequencies.
Question 2: An API 510 inspector identifies a region of corrosion under insulation (CUI) on a carbon steel vessel operating at 180°F. Which damage mechanism is of greatest concern for CUI at this temperature range?
- Oxygen-concentration cell corrosion and wet H2S attack under wet insulation (Correct answer)
- High-temperature oxidation scaling
- Creep damage from sustained elevated temperature
- Hydrogen embrittlement from atomic hydrogen absorption
Correct answer: Oxygen-concentration cell corrosion and wet H2S attack under wet insulation
CUI in the 25–350°F range on carbon steel is dominated by electrochemical corrosion under wet conditions, often with oxygen concentration cells at the insulation-metal interface.
Question 3: What does the term 'sensitivity' mean in the context of liquid penetrant testing as used by an API 510 inspector?
- The minimum flaw size the penetrant system can reliably detect, related to penetrant fluorescent brightness and viscosity (Correct answer)
- The reaction of the penetrant to corrosive environments
- The time required for the developer to reveal indications
- The maximum operating temperature of the penetrant
Correct answer: The minimum flaw size the penetrant system can reliably detect, related to penetrant fluorescent brightness and viscosity
PT sensitivity refers to the system's ability to detect the smallest relevant flaw, influenced by penetrant brightness, viscosity, surface tension, and developer characteristics.
Question 4: During radiographic testing of a pressure vessel nozzle-to-shell weld, the radiograph shows a dark irregular area with fuzzy edges. What is the most likely interpretation?
- Porosity cluster — rounded voids from gas entrapment during welding (Correct answer)
- Slag inclusion — angular trapped nonmetallic material
- Lack of fusion — a planar linear flaw at the fusion face
- Incomplete penetration — linear density change at the weld root
Correct answer: Porosity cluster — rounded voids from gas entrapment during welding
Porosity appears on radiographs as rounded, dark spots with well-defined but fuzzy edges; a cluster indicates multiple gas voids in a localized area.
Question 5: According to API 510, what is the minimum wall thickness (t_min) concept used for when evaluating thickness measurement results?
- It is the calculated required thickness plus corrosion allowance to the next inspection, used to determine if the vessel can continue operation safely (Correct answer)
- It defines the original design wall thickness from the manufacturer's data report
- It establishes the maximum allowable test pressure for hydrostatic testing
- It sets the required insulation thickness for external corrosion protection
Correct answer: It is the calculated required thickness plus corrosion allowance to the next inspection, used to determine if the vessel can continue operation safely
t_min is the minimum acceptable wall thickness based on the pressure design formula; measured thickness must exceed t_min for the vessel to remain in service.
Question 6: Which NDE technique would an API 510 inspector most likely specify to confirm the presence of stress corrosion cracking (SCC) on the inner surface of a pressure vessel that cannot be entered?
- Shear-wave (angle-beam) UT from the outer surface to detect near-inner-surface planar cracks (Correct answer)
- External visual inspection with binoculars
- Pulsed eddy current through the insulation
- Magnetic flux leakage from the outer surface
Correct answer: Shear-wave (angle-beam) UT from the outer surface to detect near-inner-surface planar cracks
Angle-beam UT from the OD is the standard method to detect SCC at or near the ID surface when internal access is not available.
Question 7: When performing external inspection of a pressure vessel, the inspector notices a 'turtle-back' pattern of bulging on the lower shell above a water draw-off nozzle. Which damage mechanism does this pattern most strongly suggest?
- Hydrogen blistering (HIC blisters) caused by atomic hydrogen migration in sour service (Correct answer)
- External corrosion from rainwater pooling
- Thermal shock from rapid temperature cycling
- Creep deformation from long-term high-temperature operation
Correct answer: Hydrogen blistering (HIC blisters) caused by atomic hydrogen migration in sour service
Turtle-back surface bulging is a classic sign of HIC blisters where hydrogen accumulates at internal lamination planes, creating surface domes.
API 510 Inspection Methods & Nondestructive Testing 5
When performing angle-beam UT on an austenitic stainless steel weld, what additional challenge must the inspector account for compared to carbon steel welds?