API 510 Inspection Techniques & Nondestructive Testing 3 — Questions and Answers
Question 1: Eddy current testing (ECT) is most commonly used in pressure vessel inspection for:
- Detecting subsurface cracks in thick carbon steel shells
- Inspecting heat exchanger tubes for corrosion and pitting (Correct answer)
- Measuring weld residual stress in austenitic stainless steel
- Identifying creep damage in high-temperature carbon steel
Correct answer: Inspecting heat exchanger tubes for corrosion and pitting
ECT is widely used for rapid screening of heat exchanger tubes, detecting wall loss, pitting, cracks, and support plate wear without requiring the tube to be drained.
Question 2: A vessel inspector suspects sulfide stress cracking (SSC) in a carbon steel vessel. Which NDT method is most appropriate for detecting SSC cracks at the surface?
- Radiographic testing
- Wet fluorescent magnetic particle testing (WFMT) (Correct answer)
- Immersion ultrasonic testing
- Eddy current testing
Correct answer: Wet fluorescent magnetic particle testing (WFMT)
WFMT provides high sensitivity for detecting tight surface and near-surface cracks characteristic of SSC, which are typically too fine for RT to resolve reliably.
Question 3: According to API 510, the maximum interval between external inspections for a pressure vessel in normal service is:
- 2 years
- 3 years
- 5 years (Correct answer)
- 10 years
Correct answer: 5 years
API 510 specifies a maximum external inspection interval of 5 years for pressure vessels in normal service, though risk-based approaches may allow extensions.
Question 4: During visual inspection of the external surface of an insulated vessel, the inspector notices wet insulation at a nozzle. The primary concern is:
- Thermal efficiency loss reducing process yield
- Corrosion under insulation (CUI) on the vessel shell and nozzle neck (Correct answer)
- Electrical grounding issues from moisture accumulation
- Insulation settlement causing mechanical stress on nozzle
Correct answer: Corrosion under insulation (CUI) on the vessel shell and nozzle neck
Wet insulation traps moisture against the vessel surface, creating conditions for accelerated CUI, which can cause significant metal loss that is hidden under the insulation.
Question 5: Pulsed eddy current (PEC) testing offers an advantage over conventional ECT for pressure vessel inspection because it:
- Provides higher resolution for detecting micro-cracks in welds
- Can inspect through insulation and coatings without removal (Correct answer)
- Requires no calibration standard for each inspection
- Is unaffected by the conductivity of the base material
Correct answer: Can inspect through insulation and coatings without removal
PEC uses low-frequency pulsed fields that penetrate insulation and protective coatings, enabling corrosion screening without removing insulation—ideal for CUI surveys.
Question 6: When performing hardness testing on a pressure vessel weld using a portable Brinell tester, what is the primary purpose in an inspection context?
- Verifying dimensional tolerances of the weld bead profile
- Detecting softening or hardening associated with in-service damage mechanisms (Correct answer)
- Confirming the weld filler metal lot number
- Establishing the remaining corrosion allowance
Correct answer: Detecting softening or hardening associated with in-service damage mechanisms
Portable hardness testing on welds and HAZ can detect softening from high-temperature damage (e.g., graphitization, creep) or hardening from hydrogen embrittlement and SSC.
Question 7: In API 510 terminology, a 'condition monitoring location' (CML) differs from a 'thickness measurement location' (TML) in that a CML:
- Is limited to ultrasonic methods only
- Can include any monitoring technique, not just thickness measurement (Correct answer)
- Is used exclusively for new vessel baseline data
- Requires more frequent inspection than a TML
Correct answer: Can include any monitoring technique, not just thickness measurement
A CML is a broader term encompassing any designated monitoring point where condition is assessed—including visual, chemical sampling, or other methods—while TML specifically refers to thickness measurement points.
API 510 Inspection Techniques & Nondestructive Testing 3
Eddy current testing (ECT) is most commonly used in pressure vessel inspection for: