Hiring a certified Level II Magnetic Particle Testing (MT) technician is more than just verifying a certificate. It’s about ensuring they have the practical skills and theoretical knowledge to make critical judgments about asset integrity. A weak link in your NDT team can lead to missed defects and catastrophic failures. To truly vet a candidate, you need a comprehensive interview process that combines sharp questions with a hands-on skills assessment.

This interview kit is designed to give you everything you need to confidently screen your next Level II MT hire. It’s broken into two key parts: a robust question bank and a step-by-step guide to conducting a practical screening test.

Part 1: The Interview Questions

A Level II technician must be able to do more than just follow a procedure; they need to understand the “why” behind it. These questions are designed to probe their technical knowledge, problem-solving skills, and understanding of relevant codes and standards.

Theoretical & Technical Questions

1. Explain the basic principle of Magnetic Particle Testing.
   • What to listen for: A clear explanation of inducing a magnetic field in a ferromagnetic material and applying iron particles that will accumulate at flux leakage fields created by discontinuities.
2. What is the difference between ferromagnetism, paramagnetism, and diamagnetism? Which category is essential for MT?
   • What to listen for: The candidate should correctly identify ferromagnetic materials (like iron, nickel, and cobalt) as strongly attracted to magnetic fields and essential for the MT method.
3. Describe the difference between a linear and a rounded indication. According to a common standard like ASME Section VIII, what makes an indication relevant?
   • What to listen for: They should define a linear indication as having a length greater than three times its width. A relevant indication is one that exceeds a certain size, typically 1/16th of an inch, and requires evaluation.[1]
4. When would you choose the dry powder method over the wet fluorescent method?
   • What to listen for: An understanding that dry powder is generally better for rough surfaces and detecting slightly subsurface defects, while the wet method is more sensitive to very fine surface-breaking cracks.
5. Explain the difference between longitudinal and circular magnetization. Provide an example of how you would achieve each using common equipment.
   • What to listen for: A clear distinction: longitudinal magnetization (using a coil or solenoid) finds transverse defects, and circular magnetization (using a headshot or prods) finds longitudinal defects.
6. What is residual magnetism, and when is the residual method of testing appropriate?
   • What to listen for: The candidate should explain that residual magnetism is the field left after the magnetizing force is removed. The residual method is suitable for materials with high retentivity and is often used to increase inspection speed.
7. According to ASTM E1444, what are the daily system performance checks required for a wet fluorescent MT system?[2][3]
   • What to listen for: Mention of checking UV-A light intensity, verifying ambient visible light levels in the inspection booth, and performing a wet particle concentration or settling test.[2][3]

Situational & Experience-Based Questions

1. You are tasked with inspecting a large weldment on-site. What equipment would you choose and what are the key steps you would take from start to finish?
   • What to listen for: A logical workflow: surface preparation, selecting a portable yoke, applying contrast paint (if using visible particles), magnetizing in two perpendicular directions, applying particles, inspecting, and post-cleaning/demagnetization.
2. You find an indication that you believe is non-relevant, such as one caused by geometry change (e.g., at the toe of a weld). What steps do you take to confirm this before dismissing it?
   • What to listen for: A cautious approach. The candidate should mention cleaning the area and re-inspecting, possibly changing the angle of magnetization, and using their knowledge of the manufacturing process to make an informed judgment.
3. You’re performing a yoke inspection and the particles are not showing clear indications on a known test piece. What are the first three things you would troubleshoot?
   • What to listen for: A systematic troubleshooting process: 1) Check the yoke’s lifting power to ensure it’s properly magnetized. 2) Verify the particle concentration or the quality of the dry powder. 3) Ensure proper contact between the yoke legs and the part surface.
4. Describe your experience working with specific codes like AWS D1.1 or ASME Section V, Article 7. How do their acceptance criteria differ?
   • What to listen for: Specific examples of using these codes. They should be able to articulate that different codes have different allowable indication sizes based on the type of component and its service conditions.
5. Why is demagnetization important after an MT inspection, and what challenges can you face during the process?
   • What to listen for: An understanding that residual magnetism can interfere with subsequent machining processes or in-service performance. Challenges include complex part geometries that can make complete demagnetization difficult.

Part 2: The Practical Screen

No interview is complete without a hands-on demonstration. This practical test verifies that the candidate can operate equipment safely, follow procedures, and accurately report their findings.

Objective: To assess the candidate’s ability to perform routine equipment verifications, conduct an MT inspection using the yoke technique, and properly document the results according to a provided procedure and acceptance criteria.

Required Items:

• AC Electromagnetic Yoke
• 10-pound certified weight block[4][5]
• Test specimen with known, relevant discontinuities (a welded plate with toe cracks or porosity is ideal)
• Dry, visible magnetic particles (e.g., black powder)
• White contrast paint
• Cleaning supplies (rags, solvent)
• A sample inspection procedure and report form (can be your company’s standard forms)
• A defined acceptance criteria (e.g., from ASME Section VIII, Div. 1, Appendix 6: “No relevant linear indications. Relevant rounded indications > 3/16″ are unacceptable.”)[1][6]

Step-by-Step Practical Test Instructions

Step 1: Pre-Use Equipment Verification (5-10 minutes)

1. Instruct the Candidate: “Before beginning the inspection, please perform the required pre-use verification check on this AC yoke.”
2. Observe: The candidate should, without prompting, correctly perform a lift test. This involves placing the yoke legs at their maximum spacing and verifying it can lift the 10-pound weight.[4][5] They should document this check on the report form.

Step 2: Part Inspection (15-20 minutes)

1. Provide the Materials: Give the candidate the flawed test specimen, contrast paint, and dry magnetic particles.
2. Instruct the Candidate: “Please inspect this weld for surface-breaking discontinuities using the AC yoke and dry powder method. Follow the provided procedure and document your findings on the report form. Evaluate any indications against the provided acceptance criteria.”
3. Observe the Process:
   • Surface Prep: Do they properly clean the surface and apply a thin, even coat of contrast paint?
   • Magnetization Technique: Do they magnetize the part in at least two directions, roughly perpendicular to each other, to ensure full coverage?
   • Particle Application: Is the powder applied lightly and evenly while the yoke is energized?
   • Evaluation: Do they correctly identify and map the location and orientation of the known indications on the report form?
   • Interpretation: Do they correctly classify the indications (e.g., linear vs. rounded) and compare their size to the acceptance criteria?

Step 3: Reporting (10 minutes)

1. Instruct the Candidate: “Complete the inspection report, ensuring all required fields are filled out, including your final accept/reject decision for the part.”
2. Review the Report:
   • Completeness: Is the report filled out accurately with all equipment details and inspection parameters?
   • Accuracy: Did they correctly identify and map the flaws?
   • Clarity: Is their description of the indications clear and concise?
   • Judgment: Did they make the correct accept/reject decision based on the provided criteria?

By combining insightful interview questions with a rigorous, hands-on screening, you can move beyond the resume and certify that your next Level II MT hire is not just qualified on paper, but truly competent in their craft.

Sources

1. scribd.com
2. youtube.com
3. qualitymag.com
4. trinityndt.com
5. inspection-for-industry.com
6. scribd.com