ASNT Level II Magnetic Particle Testing

Level I Review - Magnetism Fundamentals

As a Level II candidate, you are expected to have thorough command of Level I concepts and be able to apply them independently. This chapter provides a focused review of the critical principles that underpin all Level II activities.

Magnetic Fields and Flux

The core of MT is flux leakage - when flux flowing through a ferromagnetic material encounters a discontinuity oriented perpendicular to the flux direction, the flux is forced out of the material at the surface, creating a localized leakage field. Magnetic particles are attracted to this leakage field, forming visible indications.

Key relationships a Level II must know cold:

• B = μ × H (flux density = permeability × magnetizing force)
• Ferromagnetic materials have very high μ (hundreds to thousands), concentrating flux inside the material
• Reluctance is the magnetic analog of electrical resistance - air gaps and non-ferromagnetic inclusions have high reluctance
• Discontinuities perpendicular to flux produce strong leakage; those parallel produce none
• Two perpendicular magnetization directions are always required for complete coverage

Hysteresis and Material Response

The hysteresis loop (B-H curve) determines how a material responds to magnetization and demagnetization:

• Retentivity (Br): Residual flux after magnetizing force removed - determines suitability for residual technique
• Coercivity (Hc): Reverse force to demagnetize - determines demagnetization difficulty
• Permeability (μ): Ease of magnetization - affects amperage requirements
• Saturation (Bs): Maximum flux density - defines the upper limit of useful magnetization

As a Level II, you will select magnetization parameters, choose between continuous and residual techniques, and specify demagnetization procedures. These decisions all require understanding the material's hysteresis behavior.

Equipment and Techniques - Level II Perspective

At Level II, you are expected to independently set up, calibrate, and operate all MT equipment types. Your Level I training covered the mechanics - Level II adds the engineering judgment for selecting and optimizing.

Equipment Selection Logic

Bench (stationary) units: Best for production environments with repetitive parts. Head shots (circular) and coil shots (longitudinal) provide complete coverage on parts that fit between headstocks. Central conductors handle hollow parts without arc burn risk.

Portable prod units: Field inspection of large weldments, structural connections, pressure vessel welds. Prod spacing 3-8 inches, amperage per ASTM E709 formulas. Critical awareness: arc burn prevention requires firm contact before energizing and de-energizing before lifting.

Portable yoke units: The most common field MT tool. AC for surface cracks (most weld inspections), DC for subsurface detection. Lifting force verification at the actual spacing to be used. Articulating legs for curved surfaces.

Multidirectional units: Production bench units that apply circular and longitudinal fields in rapid sequence, eliminating the need for separate magnetizations. Requires careful setup and verification with QQI shims in multiple orientations.

As a Level II, You Must Be Able To:

1. Select the optimal technique(s) for a given part geometry, material, and discontinuity type
2. Calculate amperage or verify field adequacy for each technique
3. Determine if continuous or residual technique is appropriate
4. Specify particle type, carrier, and application method
5. Define coverage strategy (number of passes, overlap requirements, magnetization sequence)
6. Recognize when equipment performance is degraded and take corrective action
7. Troubleshoot unexpected results (no indications when expected, excessive background, false indications)

The Level II Mindset Shift

The transition from Level I to Level II is not just an increase in technical knowledge - it is a fundamental shift in responsibility and approach.

Level I mindset: "I follow the procedure exactly as written and record what I see."
Level II mindset: "I understand why each step exists, can select the optimal approach, diagnose problems, and make accept/reject decisions with confidence."

This shift manifests in every aspect of MT:

• Equipment selection: Level I uses what's available. Level II selects the optimal equipment for the specific application and can justify the selection.
• Parameter setting: Level I applies the procedure's specified values. Level II calculates optimal values, understands the trade-offs, and adjusts based on field conditions.
• Indication evaluation: Level I records indications. Level II determines whether each indication is relevant, classifies it, measures it, and applies acceptance criteria.
• Problem solving: Level I reports problems to the Level II. Level II diagnoses root causes and implements solutions.
• Supervision: Level II reviews Level I work for completeness and accuracy, providing training and guidance.

The Level II in Quality Assurance

The Level II serves as the quality gatekeeper for MT examinations. Every accept/reject decision you make directly affects structural integrity and public safety.

Quality Responsibilities

• Verify that Level I personnel follow the procedure exactly
• Ensure all system checks (bath concentration, UV intensity, equipment calibration) are current
• Review Level I reports for completeness and accuracy before signing
• Identify training needs when Level I performance is inconsistent
• Report procedure deficiencies to the Level III for revision

The Weight of the Decision

When you accept a weld, you are stating that the examination was performed correctly and no rejectable indications were found. If that weld later fails in service and investigation reveals that a detectable discontinuity was present at the time of examination, the Level II's competence and the adequacy of the examination technique will be scrutinized.