NDT Material Properties & Inspection Standards 3 — Questions and Answers
Question 1: What NDT method is most effective for detecting surface-breaking cracks in ferromagnetic boiler components?
- Ultrasonic testing
- Magnetic particle testing (Correct answer)
- Radiographic testing
- Eddy current testing
Correct answer: Magnetic particle testing
Magnetic particle testing (MT) is highly effective for detecting surface and near-surface discontinuities in ferromagnetic materials such as carbon and low-alloy steels.
Question 2: What is 'creep' in boiler material behavior?
- Sudden fracture under impact loading
- Slow, time-dependent plastic deformation under sustained load at elevated temperature (Correct answer)
- Rapid corrosion in the presence of oxygen
- Grain boundary attack by sulfur compounds
Correct answer: Slow, time-dependent plastic deformation under sustained load at elevated temperature
Creep is the gradual, permanent deformation of a material under constant stress at high temperatures over an extended period.
Question 3: According to ASME standards, what is the minimum required weld joint efficiency for a double-welded butt joint in a pressure vessel subjected to radiographic examination?
- 0.70
- 0.85
- 1.00 (Correct answer)
- 0.60
Correct answer: 1.00
A double-welded butt joint that has been fully radiographed is assigned a joint efficiency of 1.00 per ASME Section VIII, Division 1.
Question 4: In material science, what does the 'modulus of elasticity' (Young's modulus) represent?
- The stress at which permanent deformation begins
- The ratio of stress to strain in the elastic region (Correct answer)
- The energy absorbed before fracture
- The maximum stress a material can withstand
Correct answer: The ratio of stress to strain in the elastic region
Young's modulus is the slope of the linear portion of the stress-strain curve and measures a material's stiffness in the elastic range.
Question 5: Which of the following inspection standards is used specifically for the qualification of NDE personnel in the US?
- ASME Section V
- AWS D1.1
- ASNT SNT-TC-1A (Correct answer)
- ASTM E709
Correct answer: ASNT SNT-TC-1A
ASNT SNT-TC-1A is the recommended practice for the qualification and certification of NDE personnel in the United States.
Question 6: What does 'sensitization' mean for austenitic stainless steel used in boiler applications?
- Increased susceptibility to hydrogen embrittlement after heat treatment
- Precipitation of chromium carbides at grain boundaries, reducing corrosion resistance (Correct answer)
- Increased hardness due to work hardening
- Loss of magnetism after exposure to high temperatures
Correct answer: Precipitation of chromium carbides at grain boundaries, reducing corrosion resistance
Sensitization occurs when austenitic stainless steel is heated in the 425–870°C range, causing chromium to diffuse to grain boundaries and form carbides, depleting the surrounding area of chromium.
Question 7: When performing a liquid penetrant test, what is the purpose of the developer?
- Remove excess penetrant from the surface
- Clean the surface prior to penetrant application
- Draw penetrant out of discontinuities to form visible indications (Correct answer)
- Increase the viscosity of the penetrant liquid
Correct answer: Draw penetrant out of discontinuities to form visible indications
The developer absorbs penetrant trapped in discontinuities through capillary action, forming enlarged, visible indications on the surface.
NDT Material Properties & Inspection Standards 3
What NDT method is most effective for detecting surface-breaking cracks in ferromagnetic boiler components?