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.

Advanced Circular Magnetization

Level II technicians must be able to calculate magnetization parameters for any part geometry, not just simple cylinders. This lesson covers the engineering behind circular magnetization calculations.

Direct Contact (Head Shot) - Detailed Amperage Selection

Solid cylindrical parts:
Standard formula: 300-800 A/inch of outside diameter

• Lower end (300-400 A/in): Standard sensitivity, surface cracks in carbon steel
• Mid-range (400-600 A/in): Enhanced sensitivity, finer cracks, alloy steels
• Upper end (600-800 A/in): Maximum sensitivity, subsurface detection with DC

Hollow parts - the cross-section approach:
For hollow cylinders (tubes, pipes), the effective diameter is based on the cross-sectional area:

• Effective cross-section = (OD² - ID²) × π/4
• Equivalent solid diameter = √(OD² - ID²)
• Apply the same A/inch rule to the equivalent diameter

Example: 8-inch OD pipe with 0.5-inch wall:

• ID = 7 inches
• Equivalent diameter = √(8² - 7²) = √(64-49) = √15 = 3.87 inches
• Amperage at 400 A/in: 3.87 × 400 = 1,548 amperes
• Compare: Using full OD would give 8 × 400 = 3,200 amperes - dramatically overmagnetized

Non-circular cross-sections:
For rectangular, L-shaped, or irregular cross-sections:

• Calculate the cross-sectional area
• Convert to equivalent circular diameter: D_eq = √(4A/π)
• Apply the A/inch formula to D_eq

Prod Technique - Advanced Considerations

Beyond the basic 100-125 A/inch of spacing formula:

Thin material (< ¾ inch): Reduce to 90-110 A/inch to avoid overmagnetization and through-wall heating

Thick material adjacent to a free edge: Current flows preferentially through the material near the prods. If one prod is near a plate edge, current density at the edge is higher, potentially causing overheating or arc damage

Weld crown geometry: For examinations over weld reinforcement, the prods may not sit flat. Use prod tips with appropriate profiles or grind flat spots for contact

Advanced Longitudinal Magnetization

Coil Magnetization - Engineering Details

The standard formula NI = 45,000/(L/D) assumes the part is positioned at the center of the coil. In practice, several factors modify this:

Part position within the coil: Maximum field is at the coil center. Parts positioned near the coil edge experience reduced and non-uniform field. For best results, center the part within the coil or position it against one end (for parts shorter than the coil).

Fill factor: The ratio of part cross-sectional area to coil cross-sectional area. Below 10% fill factor, most flux passes through air rather than the part, reducing effectiveness. Solutions:

• Use a smaller-diameter coil
• Add ferromagnetic pole pieces to concentrate flux into the part
• Increase amperage (within equipment limits)

L/D extremes:

• L/D < 2 (short, fat parts): Formula gives NI > 22,500 - may exceed coil or machine ratings. Consider yoke technique instead, or use multiple lower-amperage shots with the part repositioned.
• L/D > 15 (long, thin parts): NI is low but the effective field length is limited. Must reposition for multiple shots.
• L/D = 3 to 5: Sweet spot for efficient coil magnetization.

Yoke Optimization

Pole spacing selection:
The yoke's field strength between the poles depends on the pole spacing. Wider spacing covers more area per placement but produces a weaker field.

• 3-4 inches: High field strength, maximum sensitivity, but small coverage area - use for critical examinations or small parts
• 5-6 inches: Good balance of sensitivity and coverage - the standard for most field weld inspection
• 7-8 inches: Larger coverage area but reduced sensitivity - acceptable for thick structural members if lifting force verified

AC vs. DC yoke selection:
As a Level II, you specify which current type to use:

• AC: Surface cracks only (~0.5mm depth). Best for weld surface cracks, toe cracks, grinding cracks. AC provides particle mobility advantage.
• DC: Subsurface detection to ~6mm. Use when subsurface discontinuities are suspected (hydrogen cracks in HAZ, subsurface inclusions, near-surface laminations).
• In most cases, if the code doesn't specify, AC is the default for weld inspection because the vast majority of weld discontinuities are surface-breaking.

Multidirectional Magnetization - Level II Engineering

Multidirectional units apply circular and longitudinal fields in rapid alternation, creating a resultant field that sweeps through multiple orientations. As a Level II, you must understand the engineering behind these systems.

Timing and Phase Control

Modern multidirectional units use rapid-switching electronics to alternate between circular and longitudinal pulses. The timing parameters are:

• Pulse duration: Typically 0.5-2 seconds per direction
• Overlap: Some units provide brief overlap where both fields are active simultaneously, creating a rotating resultant
• Sequence: Circular → longitudinal → circular → ... (or simultaneous with phase offset)

Verification Requirements

As a Level II setting up a multidirectional system, you must verify:
1. Field adequacy in both the circular and longitudinal directions independently
2. Coverage in all intermediate orientations using a cross-pattern or circle-pattern QQI
3. No dead spots where both fields are simultaneously too weak
4. Particle application timing synchronized with the magnetization sequence

When to Use Multidirectional vs. Separate Passes

• Multidirectional: Production environments with repetitive parts, where setup time per part is critical
• Separate passes: Field work, complex geometries, non-standard configurations where independent control of each direction is needed

Coil Shot Engineering - Level II Application

The coil shot creates a longitudinal field through the part. The Level II must calculate the correct parameters and understand the limitations.

Coil Amperage Calculation

For a coil with N turns, the required amperage is: NI = 45,000 / (L/D)

Where:

• N = number of turns in the coil
• I = current in amperes
• L = length of the part
• D = diameter (or largest cross-sectional dimension)
• L/D ratio must be between 2 and 15 for this formula

Fill Factor Considerations

The fill factor is the ratio of the part's cross-sectional area to the coil's internal area. For best results, the fill factor should be at least 10%. Low fill factors (large coil, small part) create weaker fields at the part surface and may require higher amperage.

Effective Zone Limitations

The coil shot creates an effective field within approximately 6-9 inches of the coil face in each direction. Parts longer than 18 inches require repositioning within the coil or multiple coil placements.

Central Conductor Technique

For hollow parts (rings, tubes, flanges), passing a conductor through the bore and energizing it creates a circular field in the part wall. The advantage: no direct contact with the part (no arc burn risk). The current required is calculated the same as for a head shot, using the part's OD.

Optimizing Field Direction

A Level II MT technician must not only achieve adequate field strength but also optimize the field direction relative to expected discontinuities. This is the difference between performing MT and performing effective MT.

The Angular Sensitivity Relationship

A discontinuity is most detectable when it is oriented perpendicular (90°) to the magnetic flux direction. As the angle between the discontinuity and the flux decreases:

• 90° (perpendicular): Maximum flux leakage, strongest indication - ideal detection
• 60-75°: Good detection - leakage is reduced but still produces clear indications
• 45°: Marginal detection - indications are faint, easily missed without careful examination
• 30°: Very poor detection - most discontinuities at this angle will not produce sufficient leakage
• 0° (parallel): No detection - flux flows along the crack without interruption

This angular sensitivity is why two-directional coverage at 90° apart is the minimum requirement. With two perpendicular passes, the worst-case orientation for any discontinuity is 45° - at the edge of marginal detectability but still within the detection range for most significant defects.

Planning Coverage for Specific Applications

Butt welds (linear welds):
Pass 1 - Field perpendicular to weld axis (yoke straddling weld, or prods perpendicular to weld). Catches longitudinal defects (most common).
Pass 2 - Field parallel to weld axis (yoke along weld, or prods parallel). Catches transverse defects.

Circumferential pipe welds:
Pass 1 - Field perpendicular to weld (circumferential field). Catches longitudinal cracks in the weld.
Pass 2 - Field parallel to weld (axial field). Catches circumferential cracks.
Note: On small-diameter pipe, yoke placement may require articulating legs or alternative techniques.

Nozzle-to-shell connections:
Complex geometry requires multiple placements at different angles around the nozzle circumference. The weld is curved, so the field direction relative to potential cracks changes as you move around the nozzle. A minimum of 4 yoke placements at 90° intervals around the nozzle is typical.

Fillet welds:
The weld toe is the critical zone. Place the yoke to maximize field perpendicular to each weld toe line. For T-joints, this means at least 4 passes: perpendicular to each weld toe on each side.

Complex Joint Coverage Planning

The Level II must plan coverage strategies for joint configurations that go beyond simple butt welds. Each joint type presents unique coverage challenges.

Nozzle-to-Shell Connections

The weld is circumferential around the nozzle, but the potential crack orientations include both longitudinal (axial) and circumferential. Coverage requires:

• Minimum 4 yoke placements at approximately 90° intervals around the nozzle circumference
• At each position, two magnetization directions (radial and circumferential)
• Total: 8 minimum magnetization shots

Multi-Pass Fillet Welds on T-Joints

T-joints have four weld toes (two on each side of the web). Each toe must be within the effective field of at least one magnetization pass:

• Pass 1: Yoke on the flange, straddling the fillet - examines flange-side toes
• Pass 2: Yoke with one pole on the web, one on the flange - examines web-side toe and root area
• Pass 3: Rotate 90° - catches transverse indications in both orientations

Repair Weld Examination

Repair welds require the same (or more thorough) examination as original welds. Coverage must extend beyond the repair boundaries to include:

• The repaired zone
• The transition between repair weld and original weld
• The base metal adjacent to the repair (check for new HAZ cracking)

Prod Spacing - Engineering the Effective Zone

Prod spacing determines both the effective examination area and the field intensity. The Level II optimizes spacing for maximum coverage efficiency while maintaining adequate sensitivity.

Spacing Rules

• Minimum spacing: 3 inches - closer spacing concentrates current and risks arc burns
• Maximum spacing: 8 inches - wider spacing reduces field intensity below detection threshold
• Optimal spacing: 6-8 inches for most applications - provides the largest effective area with adequate field strength

The Effective Examination Zone

The effective zone between prods is roughly oval-shaped:

• Length: Equal to the prod spacing
• Width: Approximately 1/3 of the prod spacing on each side of the prod-to-prod centerline

For 6-inch spacing: Effective zone ≈ 6 inches long × 4 inches wide = ~24 square inches per shot

Coverage Planning

For a weld with 1-inch reinforcement height and 1-inch HAZ on each side:

• Examination width = 1 + 1 + (2×1) = 4 inches
• For 6-inch prod spacing: One pass along the weld covers the full width
• Overlap consecutive prod placements by at least 10% of the spacing (0.6 inches for 6-inch spacing)

Amperage Selection

The standard rule: 100-125 A/inch of prod spacing

• 6-inch spacing: 600-750 A
• 8-inch spacing: 800-1000 A

Verify with a field indicator at the examination surface - the rule provides starting values, not guarantees.

Residual vs. Continuous - Level II Selection Guide

The Level II selects the examination technique based on material properties, expected discontinuity types, and procedural requirements.

Continuous Method

Particles are applied while the magnetizing current is flowing.

• The field is at maximum strength during particle application
• Particles are held by both the applied field and the leakage field
• Detection sensitivity is at maximum
• Required for low-coercivity materials (annealed, normalized) that cannot retain adequate residual magnetism
• Required by most codes as the standard technique

Residual Method

The part is magnetized first, then particles are applied after the current is removed.

• The field depends entirely on the material's remanence
• Only works on high-coercivity materials (Q&T steels, hardened steels) that retain significant magnetism
• Lower sensitivity than continuous method
• Advantage: Particles can be applied more carefully without timing constraints
• Used when the continuous method is impractical (immersion bath, automated systems)

Selection Decision

Default: Use the continuous method unless the procedure specifically authorizes the residual method.

The residual method is only acceptable when:
1. The material has sufficient retentivity (verified by Gaussmeter after magnetization)
2. The procedure explicitly authorizes residual technique for the specific material
3. The sensitivity demonstration (QQI or known-defect specimen) confirms adequate detection capability

Field Strength Control for Level II

As a Level II, you are responsible for specifying and verifying that the magnetic field at the examination surface is within the correct range - strong enough for reliable detection but not so strong that it produces excessive background.

Tangential Field Measurement with Gaussmeter

The Hall-effect Gaussmeter is the definitive tool for quantitative field measurement. The probe measures the tangential (parallel to surface) component of the field at the surface.

Measurement procedure:
1. Place the Hall probe flat on the part surface with the sensing element parallel to the surface
2. Orient the probe to measure in the direction of the applied field
3. Apply the magnetizing current
4. Read the Gaussmeter display

Acceptable ranges (per ASTM E709 and common specifications):

• Minimum tangential field: 30 Gauss (2.4 kA/m) - below this, leakage fields from small cracks may be too weak to attract particles
• Maximum tangential field: 60 Gauss (4.8 kA/m) - above this, background noise from domain effects and surface roughness increases
• Some specifications allow up to 70-80 Gauss for coarse surface conditions or when searching for subsurface discontinuities

Over-Magnetization vs. Under-Magnetization

Under-magnetization symptoms:

• Pie gauge shows faint or absent division lines
• QQI shim shows incomplete or faint artificial defect indications
• Gaussmeter reads below 30 Gauss
• Known defects (from previous examinations) fail to produce indications
• Particles do not accumulate at known geometry changes (threads, holes)

Over-magnetization symptoms:

• Heavy, "furry" background of particles across the entire surface
• Difficulty distinguishing real indications from background noise
• Gaussmeter reads above 60-70 Gauss
• Non-relevant indications at every minor surface feature
• Particles attracted to the yoke poles so strongly they pile up rather than spreading across the examination area

Level II response:

• Under-magnetized: Increase amperage, reduce prod/pole spacing, verify contact, check equipment calibration
• Over-magnetized: Reduce amperage, increase prod/pole spacing, use lower sensitivity particle type (dry instead of wet fluorescent)

Troubleshooting Magnetization Issues

As a Level II, you must diagnose and resolve magnetization problems that a Level I would simply report. Here are the most common issues and their solutions:

Problem: No Indications Where Expected

Potential causes and Level II actions:

1. Insufficient field strength - Measure with Gaussmeter. If below 30 Gauss, increase amperage or adjust technique.
2. Wrong field direction - The field may be parallel to the expected discontinuity orientation. Rotate magnetization direction 90°.
3. Excessive coating thickness - Measure with DFT gauge. If coating exceeds the procedure maximum, remove and re-test.
4. Dead particles - Check bath concentration (settling test). Verify particles fluoresce under UV. Replace if degraded.
5. Equipment malfunction - Ammeter may read correctly but actual output may be reduced. Verify with a known test piece (reference standard).

Problem: Excessive Background

1. Over-magnetization - Reduce amperage. Background should diminish.
2. Excessive particle application - Apply less powder/bath. Remove excess with gentle air.
3. Contaminated bath - Check settling test for debris, discoloration, or layering. Replace bath if contaminated.
4. Rough surface - Particles trapped mechanically. Consider grinding the surface or switching to a different particle type.
5. Prior residual magnetism - Demagnetize the part, then re-magnetize at the correct amperage.

Problem: Intermittent/Inconsistent Indications

1. Marginal field strength - The field is at the detection threshold. Increase amperage slightly to move above marginal range.
2. Non-uniform contact - Prod tips or yoke poles not making consistent contact. Clean contact surfaces, check for damage.
3. Variable coating thickness - Indication appears where coating is thin, disappears where it is thick. Achieve uniform coating.
4. Environmental interference - Wind blowing away dry particles, condensation on surface, bath temperature too cold. Address environmental conditions.

Equipment Selection - Level II Decision Framework

As a Level II, you select the optimal equipment for each application. This selection considers part geometry, material, expected discontinuity types, access constraints, and environmental conditions.

Equipment Selection Matrix

Small cylindrical parts (bolts, pins, studs):
→ Bench unit with head shot (circular) + coil (longitudinal)
Rationale: Complete coverage in two shots, controlled conditions, high throughput

Hollow parts (rings, bearing races, tubes):
→ Central conductor (circular) + coil (longitudinal)
Rationale: No current through the part (no arc burns), examines both ID and OD

Large flat surfaces (plates, tank walls):
→ Portable prods with systematic overlap plan
Rationale: Unlimited area coverage, adjustable amperage for different thicknesses

Welds on structural steel:
→ AC yoke with dry visible particles
Rationale: Portable, fast, no arc burn risk, adequate sensitivity for most structural weld cracks

Welds on pressure vessels/piping:
→ AC or DC yoke (based on expected discontinuity depth) with wet or dry particles
Rationale: May need DC for subsurface HAZ cracking in alloy steels

Production aerospace parts:
→ Bench unit with wet fluorescent particles, darkroom examination station
Rationale: Maximum sensitivity required, controlled environment, traceable process

Field Measurement and Verification

The Level II uses measurement tools to verify that the calculated or specified amperage produces adequate field strength at the actual examination surface.

Gaussmeter (Hall-Effect Probe)

Measures the tangential field strength at the part surface in Gauss or A/m.

• Place the probe flat against the surface in the area of interest
• Read the peak value during the magnetization pulse
• Compare to the specification (typically 30-60 Gauss per ASTM E709)
• Take readings at multiple locations to verify uniformity

Pie Gauge (Flux Indicator)

A small disk with surface slots oriented in multiple directions. When placed on the examination surface and magnetized:

• Particles accumulate in the slots perpendicular to the field direction
• Confirms both field direction and adequate field strength
• Quick, qualitative verification - does not give numerical values
• Must be placed on the examination surface (not on the equipment)

Quantitative Quality Indicator (QQI)

An artificial flaw shim placed on the part surface:

• Contains grooves of known depth in specific orientations
• When magnetized and particles applied, visible grooves indicate adequate sensitivity
• Cross-pattern QQIs verify multi-directional coverage
• More quantitative than the pie gauge - specific groove depths correspond to sensitivity levels

When to Verify

• At the start of each shift or technique setup
• After any change in equipment, technique, or part geometry
• When results seem inconsistent with expectations
• During procedure qualification or demonstration

Coating Interference with MT Detection

Non-conductive coatings (paint, galvanizing, plating, thermal spray) between the examination surface and the particle application point reduce detection sensitivity by attenuating the leakage field.

Effect of Coating Thickness

• Each mil (0.001 inch) of coating increases the distance between the discontinuity and the particle accumulation surface
• Leakage field strength at the coating surface decreases as coating thickness increases
• Small, tight discontinuities are affected more than large, open ones
• The practical limit for MT through coatings is typically 2-3 mils (0.002-0.003 inch) maximum

Code Requirements

• ASME V Article 7: Coatings up to 1 mil (0.001 inch) generally accepted. Above 1 mil, demonstration is required.
• AWS D1.1: MT can be performed through coatings up to 2 mils with demonstration of adequate sensitivity
• Many client specifications require bare metal examination (all coatings removed)

Verification

When examining through coatings:
1. Measure the actual coating thickness with a DFT gauge
2. Verify it is within the procedure's allowable maximum
3. Demonstrate sensitivity using a QQI placed under the coating (or on the coating surface)
4. Document the coating type, measured thickness, and sensitivity demonstration results

Engineering-Based Media Selection

As a Level II, you specify the particle type and carrier in the written procedure. This selection directly affects sensitivity, and must be matched to the application.

Sensitivity Hierarchy (Highest to Lowest)

1. Wet fluorescent - Highest sensitivity. Fine particles (1-10 μm) suspended in a liquid carrier, examined under UV-A light. Detects the finest cracks on smooth surfaces.
2. Wet visible (non-fluorescent) - Moderate-high sensitivity. Colored particles in liquid carrier, examined under white light.
3. Dry visible - Standard sensitivity. Coarser particles (50-180 μm) applied as dry powder. Most common for field work.

Selection Matrix

Carrier Selection Factors

Choose petroleum-based (oil) carrier when:

• Indoor examination with ventilation
• Need maximum particle mobility and suspension
• Parts can tolerate oil residue
• No fire hazard in vicinity

Choose water-based carrier when:

• Fire hazard restrictions (welding/cutting nearby)
• Environmental requirements prohibit petroleum
• Outdoor work where fire risk exists
• Parts require water-compatible processing

Contrast Enhancement

For visible (non-fluorescent) methods, contrast between the indication and the background determines readability:

• Dark particles on white contrast paint: Highest contrast for visible methods
• Red particles on unpainted machined surfaces: Good contrast on light metals
• Gray particles on dark, oxidized surfaces: Adequate contrast on rusty or dark surfaces

Bath Maintenance Engineering

As a Level II, you are responsible for the quality and performance of the wet particle bath. This includes scheduled maintenance, contamination control, and concentration management.

Bath Degradation Mechanisms

Particle degradation: Particles lose their magnetic coating and fluorescent dye over time due to mechanical action (pumping, recirculation), chemical exposure (pH changes, contaminant reactions), and UV degradation (for fluorescent particles).

Contamination sources:

• Parts carrying machining oil, coolant, or rust into the bath
• Grinding swarf and metallic debris from parts being examined
• Fluorescent leak detection dyes from nearby testing operations
• Dust and airborne contaminants in the work environment
• Bacterial growth in water-based baths

Concentration drift:

• Particles settle in low-flow areas of the system and are not recirculated
• Particles are carried off on examined parts (drag-out)
• Carrier fluid evaporates (especially water-based baths and petroleum baths in warm environments)

Maintenance Schedule

Each shift:

• Settling test (concentration check)
• Visual check for contamination (discoloration, debris, odor)
• Agitate the bath for minimum 30 minutes before use

Weekly:

• Full contamination assessment (settling test with UV and white light examination of settled particles)
• Carrier fluid quality check (flash point for petroleum, pH for water)
• System cleanliness check (pump screens, hoses, nozzles)

As needed (typically every 3-6 months or per manufacturer):

• Complete bath replacement with system flush
• Filter element replacement
• System cleaning and sanitization (especially water-based systems)

Settling Test - The Critical Bath Quality Check

The settling test measures the concentration of magnetic particles in the bath. It is the most important daily quality check for wet method MT.

Procedure

1. Agitate the bath by recirculating for at least 30 minutes
2. Draw a 100-ml sample from the hose nozzle (where particles are applied to parts)
3. Allow to settle undisturbed for 30 minutes (petroleum carrier) or 60 minutes (water carrier)
4. Read the volume of settled particles in the graduated bottom of the tube

Acceptance Ranges

• Fluorescent particles: 0.1 to 0.4 ml per 100 ml of carrier
• Non-fluorescent (visible) particles: 1.2 to 2.4 ml per 100 ml of carrier

Interpretation

Below range: Insufficient particles - indications may be faint or missed entirely. Add concentrated particle suspension.
Above range: Too many particles - background noise increases, small indications masked by excess particles. Add carrier fluid.
Contamination: If the settled column shows distinct layers (particles + debris), or if the supernatant liquid is discolored, the bath is contaminated and may need replacement.

Aerosol Particle Application

Aerosol cans provide a convenient, portable method for applying wet visible particles in field applications. The Level II must understand proper aerosol technique to ensure consistent results.

Application Technique

• Hold the can 8-12 inches from the surface
• Apply with a sweeping motion, maintaining uniform coverage
• Avoid excessive application - too thick a coat obscures indications
• Allow the carrier to flow for a few seconds before inspecting
• For vertical surfaces, apply from the top and let gravity assist particle migration

Limitations

• Aerosol particles have a limited shelf life - check expiration dates
• Performance degrades in extreme temperatures (cold: poor spray pattern; hot: rapid evaporation)
• Cannot perform settling tests on aerosol particles - rely on manufacturer QC and system performance verification
• More expensive per examination than bulk bath systems
• Wind can deflect the spray pattern - use wind shields in exposed locations

System Performance Verification

Per ASTM E1444, the complete MT system (equipment + particles + technique + operator) must be verified to demonstrate that it can detect discontinuities. This verification is separate from field adequacy checks and focuses on the system as a whole.

Reference Standards

Ketos Ring (Tool Steel Ring Standard):
A ring-shaped test specimen with drilled holes at various depths and orientations. When magnetized with a central conductor, the holes produce flux leakage that attracts particles, forming indications of predictable size and location. The number of visible hole indications indicates system sensitivity.

Test Specimens with Known Defects:
Actual parts with confirmed natural or artificial discontinuities. Used to verify the system under realistic conditions. The known defects must be reproducibly detectable.

Pie Gauges:
Used for field direction and strength indication (qualitative only). Not a sensitivity standard, but verifies that the system produces adequate field and particles respond to flux leakage.

QQI (Quantitative Quality Indicator) Shims:
Artificial flaw shims with precision-machined grooves. Provide a quantitative sensitivity check when placed on the part surface. Different groove depths test different sensitivity levels.

What System Performance Verification Proves

1. The equipment is producing adequate magnetizing force
2. The particles have acceptable magnetic and physical properties
3. The particles are at the correct concentration (for wet methods)
4. The UV light is producing adequate intensity (for fluorescent methods)
5. The examination environment (lighting, temperature) is suitable
6. The operator can detect and recognize indications

The system verification must be performed:

• At the start of each shift or examination period
• Whenever any component of the system changes (equipment, particles, carrier, UV light)
• When the system performance is questioned
• After any equipment maintenance or repair

Reference Standards for MT Performance

Ketos Ring (Tool Steel Ring Standard)

The Ketos ring is a ring-shaped test specimen machined from tool steel with a series of holes drilled at various depths and orientations. When magnetized using a central conductor:

• Holes near the surface produce strong, clear indications
• Deeper holes produce progressively weaker indications
• The number of detectable holes indicates the system's sensitivity level

Typical use: Verify that the complete MT system (equipment + particles + technique) can detect discontinuities at the required sensitivity level. A properly functioning system should detect a minimum number of holes (specified in the procedure).

Test Specimens with Known Defects

Maintaining a library of reference specimens with documented, confirmed discontinuities is invaluable for:

• System performance verification (can we detect this known flaw today?)
• Operator proficiency testing (round-robin among technicians)
• Procedure qualification (does this new procedure detect the representative flaws?)
• Training (showing new technicians what real MT indications look like)

Reference specimens must be handled carefully - they can become contaminated, mechanically damaged, or corroded, which alters their MT response. Store in a protected, clean environment and handle with clean hands or gloves.

Ketos Ring Testing

The Ketos ring (ASTM ring standard) is the primary quantitative benchmark for MT system sensitivity.

The Standard

The Ketos ring is a cylindrical ring of tool steel approximately 5 inches OD × 3 inches ID × 7/8 inch thick with 12 holes of identical diameter drilled at varying depths and orientations from the outer surface.

How It Works

When the ring is magnetized using a central conductor with a specific amperage:

• Holes near the outer surface create detectable flux leakage
• Deeper holes create weaker flux leakage
• The number of holes detectable measures the system's overall sensitivity

Using the Ketos Ring

1. Place the ring on a central conductor in the bench unit
2. Apply the procedure's standard amperage
3. Apply particles using the production technique
4. Count the number of detectable hole indications
5. Compare to the acceptance criterion (typically 4-6 holes minimum detectable)

When Sensitivity Is Low

If fewer holes are detected than expected:

• Check bath concentration (settling test)
• Check particle condition (age, contamination)
• Check ammeter accuracy
• Check UV-A intensity (fluorescent method)
• Investigate each variable systematically until the root cause is identified

Advanced Demagnetization

As a Level II, you specify demagnetization requirements, select the appropriate method, and troubleshoot failures. This goes beyond the Level I scope of simply performing the procedure.

Method Selection

AC Coil (Through-Coil) Demagnetization:
Most common and most effective for the majority of steels. The part is slowly withdrawn from an energized AC coil, experiencing a progressively weaker alternating field that randomizes domain orientation.

• Best for: Carbon steels, low-alloy steels, ferritic stainless steels
• Speed: Withdraw at ≤1 foot/second
• Distance: Continue at least 3 feet (1 meter) past the coil
• Multiple passes may be needed for high-coercivity materials
• Always keep the coil energized until the part is fully clear

AC Yoke Demagnetization:
For field applications where a demagnetizing coil is not available, an AC yoke can be used as a local demagnetizer. Move the energized yoke slowly across the surface and gradually lift it away from the surface while maintaining contact.

• Less effective than a coil - covers only local areas
• Useful for removing residual magnetism from a specific zone (weld prep area)
• Must be performed systematically across the entire area

DC Step-Down (Reversing DC) Demagnetization:
Apply DC field, reverse polarity, and reduce amplitude by approximately 10-20% per step. Repeat until the field is below specification.

• Used for very high-coercivity materials where AC demagnetization is ineffective
• Time-consuming but effective
• Requires a DC power source with polarity reversal and variable output
• Typical sequence: Start at the last magnetization level, reverse and reduce 10%, reverse and reduce 10%, continue...

Heat Demagnetization:
Heating above the Curie temperature (~770°C for steel) completely destroys magnetic order.

• Used only when the part is undergoing heat treatment as part of manufacturing
• Impractical solely for demagnetization purposes

Residual Field Measurement

After demagnetization, measure residual field with a Gaussmeter:

• Measure at the part ends (where residual fields concentrate)
• Measure at geometric transitions (section changes, holes, notches)
• Measure at the center of the part
• Rotate the part 90° and re-measure (field may be oriented differently than expected)
• Record all measurements and compare to specification limit

Advanced Demagnetization - Level II Perspective

Demagnetization Sequence Planning

When multiple magnetization directions have been applied (circular + longitudinal), the demagnetization sequence matters:

1. Demagnetize the last-applied direction first - This removes the most recent domain alignment
2. Then demagnetize the earlier direction - This addresses any residual from the first magnetization
3. Verify with a Gaussmeter after completing all demagnetization

Troubleshooting Demagnetization Failures

Residual field still exceeds limit after standard procedure:
1. Make additional slow passes through the AC coil
2. If still above limit, try DC step-down (reversing polarity with decreasing amplitude)
3. If still above limit, check the demagnetizing coil's output - it may be degraded
4. For very high-coercivity materials, consider heat demagnetization if the part is going to heat treatment anyway

Residual field is zero at the center but high at the ends:
This is normal - demagnetizing fields from the coil are weakest at part extremities. Orient the part so that the ends pass through the strongest part of the coil. For long parts, make multiple passes with different orientations.

Residual field returns after demagnetization:
Some materials exhibit magnetic aftereffect - domain walls slowly creep to new equilibrium positions after the demagnetization process. Wait 15-30 minutes and re-measure. If the field has increased, perform an additional demagnetization pass.

Demagnetization - Level II Depth

Why Demagnetize?

Residual magnetization can:

• Interfere with subsequent welding (arc blow)
• Attract metallic debris during service
• Interfere with subsequent machining operations (chip adhesion)
• Affect compass readings on marine vessels
• Interfere with electronic instruments near the part

Demagnetization Methods

AC coil (most common): Pass the part through an energized AC coil or move the coil over the part, then withdraw slowly. The alternating field progressively randomizes domain orientation as intensity decreases with distance.

DC step-down: Apply DC in one direction, then reverse at slightly lower amplitude. Continue reversing with decreasing amplitude until the field is effectively zero. Used for high-coercivity materials where AC methods are insufficient.

Heat demagnetization: Heating above the Curie temperature destroys all magnetic ordering. Used only when the part is going to heat treatment anyway - never applied solely for demagnetization purposes.

Verification

Use a calibrated Gaussmeter to measure residual field:

• Take readings at multiple locations (ends, center, critical surfaces)
• Typical acceptance: ≤3 Gauss residual field
• Some specifications require ≤2 Gauss
• Measure in at least two orthogonal directions at each point
• Document the readings and locations

Level II Indication Evaluation

The fundamental distinction between a Level I and Level II technician is the ability to evaluate indications - to determine whether they are relevant, classify their severity, and apply acceptance criteria to make accept/reject decisions.

The Evaluation Process

Step 1: Classification
Is the indication relevant, non-relevant, or false?

• Relevant: Caused by a discontinuity that may affect part integrity
• Non-relevant: Caused by a geometric, metallurgical, or magnetic feature that is not a discontinuity
• False: Not caused by flux leakage at all (mechanical entrapment, gravity, contamination)

Step 2: Characterization (for relevant indications)

• Linear or rounded (3:1 length-to-width ratio)
• Surface-breaking or subsurface (based on indication sharpness, definition, and depth of the leakage field)
• Location relative to the weld or part feature
• Single or clustered

Step 3: Measurement

• Length (major dimension for rounded indications)
• Width if required by the acceptance criteria
• Spacing between adjacent indications
• Cumulative length in a given span

Step 4: Acceptance Criteria Application
Compare measured indication dimensions to the acceptance criteria specified in the applicable code. This may involve:

• Maximum individual indication size
• Maximum cumulative size in a given length
• Minimum spacing between indications
• Maximum number of indications in a given area
• Specific restrictions for linear vs. rounded

Step 5: Disposition

• Accept: Indication is within acceptance criteria
• Reject: Indication exceeds one or more criteria
• Investigate further: Grind to explore depth, use another NDT method for additional characterization, or request engineering evaluation

Evaluating Non-Relevant Indications

Per ASTM E1444, any indication with a major dimension exceeding 1/16 inch (1.6mm) that is initially interpreted as non-relevant must be re-examined to confirm. Methods include:

• Cleaning the surface and re-examining
• Examining from a different magnetization direction
• Light grinding to remove surface features and re-examining
• Comparison with part geometry (confirming the indication coincides with a known feature)

Applying Acceptance Criteria

Different codes have different acceptance criteria for MT indications. As a Level II, you must know which criteria apply and how to apply them correctly.

ASME Section VIII (Pressure Vessels) - UW-51/UW-52

ASME acceptance criteria for welds examined by MT typically include:

• Linear indications exceeding 1/16 inch (1.6mm) are unacceptable (for certain joint categories)
• Rounded indications have maximum individual and cumulative size limits based on the governing weld joint category and thickness
• Aligned indications (rounded indications in a line) are evaluated as a single indication

AWS D1.1 (Structural Steel Welding)

AWS D1.1 Table 6.1 acceptance criteria for MT:

• No cracks regardless of size or location
• Incomplete fusion not acceptable when examination reveals the defect
• Specific dimensional limits for undercut, porosity, and other indications based on the joint type (complete joint penetration, partial joint penetration, fillet)

AWS D1.5 (Bridge Welding Code)

More restrictive than D1.1, reflecting the fatigue-critical nature of bridge structures:

• No cracks of any size
• More restrictive limits on rounded and clustered indications
• Fracture Critical Members (FCMs) have the most stringent criteria

API 1104 (Pipeline Welding)

Pipeline weld acceptance criteria based on workmanship or fitness-for-service evaluation options.

Key Principle

Never apply acceptance criteria from memory alone. Always have the actual code section and table open when evaluating indications. Codes are revised periodically, and criteria change between editions. Using the wrong criteria (or the right criteria from the wrong edition) can result in incorrectly accepting a rejectable defect or rejecting an acceptable one.

Subsurface Indication Characteristics

Subsurface discontinuities (those below the surface but within MT detection range) produce characteristically different indications from surface-breaking defects. As a Level II, you must recognize these differences.

Surface-Breaking vs. Subsurface Indications

Surface-breaking indications:

• Sharp, well-defined edges
• Tight, dense particle accumulation
• Strong holding force - resist removal by gentle air
• Located precisely at the surface crack opening

Subsurface indications:

• Diffuse, fuzzy edges (particles spread over a broader area)
• Less dense particle accumulation
• Weaker holding force - easier to blow away
• May be displaced from the actual discontinuity location (particles accumulate where the leakage field reaches the surface, which may be offset from the subsurface flaw)

Depth Estimation

The width and intensity of the indication provide rough depth information:

• Narrow, intense indication → shallow (near surface)
• Broad, diffuse indication → deeper subsurface
• Very broad, very faint → at the limit of detection depth

Accurate depth determination requires supplementary examination (UT) - MT cannot quantitatively measure depth.

Level II Evaluation

When you encounter a subsurface-type indication:
1. Document its characteristics (diffuse, broad, weak holding force)
2. Note the magnetization technique used (AC vs. DC - subsurface indications should only appear with DC/HWDC)
3. If the indication appeared with AC magnetization, it is likely surface-breaking despite its diffuse appearance (possibly a very tight crack with a smeared-over surface)
4. Recommend UT follow-up for depth characterization if the indication's size or location makes it potentially rejectable

Applying Acceptance Criteria - Level II Skill

The Level II must correctly apply acceptance criteria from the governing code. This requires understanding the criteria structure, the terminology, and the measurement methods.

AWS D1.1 Acceptance Criteria (Structural Welding - Steel)

Statically loaded structures:

• No cracks (any size)
• No linear indications exceeding 1/8 inch
• No rounded indications exceeding 3/16 inch

Cyclically loaded structures (fatigue-critical):

• No cracks (any size)
• No linear indications exceeding 1/16 inch
• No rounded indications exceeding 1/8 inch
• More restrictive because fatigue cracks grow from smaller initiators

ASME Section VIII (Pressure Vessels)

Relevant indications: Any indication ≥1/16 inch is considered relevant (must be evaluated)

Rejectable conditions:

• Any linear indication
• Any rounded indication exceeding 3/16 inch
• Four or more rounded indications in a line separated by 1/16 inch or less (edge to edge)

The Evaluation Process

1. Is the indication relevant? (≥1/16 inch → yes)
2. Is it linear or rounded? (L ≥ 3W → linear; L < 3W → rounded)
3. Measure the indication dimensions accurately
4. Apply the specific acceptance criteria from the governing code
5. Accept or reject - document the basis for the decision

MT Procedure Development

At Level II, you develop and qualify MT procedures. A procedure is the formal document that specifies every parameter of the examination. It must be complete enough that a qualified Level I can perform the examination with consistent, reproducible results.

Essential vs. Nonessential Variables (ASME V, Article 7)

ASME classifies procedure variables as essential (changes require re-qualification) or nonessential (changes documented but no re-qualification needed).

Essential Variables - changes require procedure re-qualification:

• Magnetization technique (e.g., yoke → prods)
• Current type (AC → DC → HWDC)
• Particle type (fluorescent → visible, wet → dry)
• Examination method (continuous → residual)
• Direction of magnetization
• Surface preparation (as-welded → ground)
• Minimum light intensity (UV-A or visible)

Nonessential Variables - changes documented but OK:

• Part configuration or size (within the procedure's scope)
• Specific amperage value (if within the established range and field adequacy is verified)
• Specific brand of particles (if same type and specification)
• Post-examination cleaning method

Procedure Content Requirements (ASME V, T-753)

A written MT procedure must include:

1. Scope (materials, joint types, thickness ranges covered)
2. Surface preparation requirements
3. Magnetization technique(s)
4. Current type and amperage range (or field strength range)
5. Particle type and application method
6. Continuous or residual technique
7. Minimum field strength or amperage verification method
8. Examination coverage requirements (two-directional, overlap)
9. Environmental requirements (lighting, temperature)
10. Personnel qualification requirements
11. Acceptance criteria reference
12. Post-examination requirements (demagnetization, cleaning)
13. Documentation and reporting requirements

Procedure Qualification

For ASME applications, the procedure must be demonstrated (qualified) by performing an examination on a representative test specimen under the specified conditions and verifying that known discontinuities are detected. The qualification records become part of the procedure package.

Examination Reporting

As a Level II, you are responsible for the completeness and accuracy of the examination report. Beyond the Level I recording requirements, you add evaluation, disposition, and supervisory review.

Level II Report Additions (Beyond Level I)

1. Indication evaluation: Each indication classified as relevant (linear/rounded), non-relevant, or false, with supporting rationale
2. Acceptance criteria application: Specific code section and table cited, with a clear statement of how each indication compares to the criteria
3. Disposition: Accept, reject, repair, or additional examination required - for each indication
4. Technical adequacy statement: Confirmation that the examination technique, equipment, and environmental conditions met all procedure requirements
5. Personnel supervisory role: If you supervised a Level I performing the examination, your report covers your evaluation of their work quality

Traceability Requirements

Every element of the examination must be traceable:

• Equipment → calibration records: Yoke lifting force verification, ammeter calibration, UV light intensity measurement - traceable to calibrated instruments
• Particles → batch records: Particle batch number, expiration date, settling test results - traceable to manufacturer certification
• Personnel → certification records: Examiner and evaluator certification levels, certificate numbers, employer - traceable to the employer's Written Practice
• Part → manufacturing records: Material heat number, weld procedure used, welding operator - traceable to fabrication documentation
• Acceptance criteria → code edition: Specific code, edition year, section, and table number - not just "per code"

Report Retention

Examination reports must be retained per the applicable code and contract requirements. For ASME vessels, reports are typically retained for the life of the equipment. For structural steel, retention periods vary by jurisdiction and project specification. As a Level II, ensure your reports are complete and clear enough to stand alone years or decades later.

Report Quality Standards

The Level II's examination report is a legal quality record. Its quality reflects the quality of the examination itself. As a Level II, you both produce reports and review reports from Level I technicians.

Level II Report Review Checklist

When reviewing a Level I technician's MT report:

1. Completeness: Are all required fields filled in? (Date, examiner, part ID, procedure, equipment, technique, results, signature)
2. Traceability: Can every element be traced back to its source? (Equipment to calibration, examiner to certification, part to material records)
3. Accuracy: Do the recorded parameters match the procedure requirements? (Correct amperage range, correct particle type, correct coverage)
4. Indication documentation: Are indications documented with sufficient detail for relocation and re-evaluation? (Location referenced to datum, measured dimensions, orientation, type)
5. Consistency: Do the results make sense? (No indications on a weld known to have defects? Indications in areas with no weld?)
6. Environmental documentation: Were UV-A intensity, ambient light, and surface temperature recorded as required?

Common Report Deficiencies

• Missing equipment serial numbers
• Incomplete coverage documentation (no map showing which areas were examined)
• Indication location references that cannot be replicated
• Missing or incorrect acceptance criteria reference
• Unsigned or undated pages
• No statement about demagnetization status

Writing MT Examination Procedures - Level II Skills

While the Level III approves procedures, experienced Level IIs often draft application-specific procedures under Level III supervision.

Essential Variables (Must Be Specified)

• Magnetization technique (yoke, prod, coil, head shot, central conductor, multidirectional)
• Current type (AC, DC, HWDC)
• Field direction(s)
• Amperage or field strength requirements
• Particle type (dry/wet, fluorescent/visible)
• Surface preparation requirements
• Examination sequence (continuous/residual)
• Acceptance criteria with specific code reference

Procedure Clarity Test

A properly written procedure should allow a qualified Level I technician who has never seen the specific application to perform the examination correctly and consistently by following the procedure step by step. If the procedure relies on assumptions, tribal knowledge, or verbal instructions to supplement the written steps, it is incomplete.

Audit Preparation - Level II Perspective

As a Level II, you will participate in quality audits as the technical subject matter expert. Proper preparation demonstrates program competence and prevents audit findings.

What Auditors Look For

1. Personnel files: Current certifications, training records, vision test results, all within dates
2. Procedures: Current revision, approved signatures, all code requirements addressed
3. Equipment records: Calibration certificates current, lifting force verification documented
4. Examination records: Complete, legible, traceable to personnel and equipment used
5. Consumables: Particle batch documentation, settling test records, shelf life compliance
6. Corrective actions: All findings from previous audits addressed and closed

Common Audit Findings

• Expired vision tests (most common personnel finding)
• Missing daily settling test records
• Examination reports missing equipment serial numbers
• Procedures referencing superseded code editions
• No documented lifting force verification for the current period

Maintaining these records in real-time prevents the audit-preparation scramble and demonstrates a mature, well-managed MT program.

Level II Troubleshooting

Field MT rarely goes exactly as planned. As a Level II, you must diagnose problems, determine root causes, and implement solutions - all while maintaining examination validity.

Systematic Troubleshooting Approach

When MT results are unexpected (missed known defects, excessive background, inconsistent indications), work through this diagnostic sequence:

1. Verify the equipment:

• Check ammeter reading against expected value
• Verify yoke lifting force at the actual spacing used
• Check UV-A intensity (for fluorescent methods)
• Inspect cables, connections, and prod tips for damage
• Run a system performance check on a known reference standard

2. Verify the particles:

• Check bath concentration (settling test)
• Examine particle condition (color, fluorescence, contamination)
• Verify particle type matches the procedure
• Check expiration dates

3. Verify the technique:

• Confirm correct magnetization direction for the expected discontinuity orientation
• Verify amperage or field strength is within specification
• Confirm correct spacing (prods, yoke poles)
• Verify two-directional coverage was performed

4. Verify the surface:

• Measure coating thickness
• Check for contamination (oil, moisture, condensation)
• Assess surface roughness
• Check part temperature

5. Verify environmental conditions:

• Ambient light level (for fluorescent)
• Wind (for dry particles)
• Temperature and humidity
• Electromagnetic interference from nearby equipment

Common Field Problems and Solutions

Particles won't stay on vertical surfaces:
→ Switch from dry to wet particles; use spray application with wet particles that adhere to the surface; work sections from bottom up

Yoke won't reach examination area:
→ Use prods instead; use a smaller yoke with articulating legs; use a cable wrap if the geometry allows

High ambient light washing out fluorescent indications:
→ Erect light-blocking enclosures (welding curtains, tarps); schedule examination for nighttime; switch to visible particles with contrast paint

Arc burns occurring despite contact pads:
→ Check pad condition (worn, contaminated, inadequate size); increase contact pressure; clean both the pad surface and the part surface; verify cables are properly connected

Handling Non-Standard Situations

Field work frequently presents situations not explicitly covered by the written procedure. As a Level II, you have the technical authority to make judgments within the framework of the applicable code and your employer's Written Practice.

Situations Requiring Level II Judgment

Material not covered by the procedure:
The procedure may specify "carbon steel" but you encounter an alloy steel or stainless steel component. Before proceeding, verify the material is ferromagnetic and that the technique parameters are appropriate for its permeability characteristics.

Geometry not addressed by the procedure:
Complex nozzle configurations, multi-layer build-ups, or unusual joint designs may require modified coverage plans not explicitly described in the procedure.

Environmental conditions outside procedure limits:
Temperature, wind, humidity, or lighting conditions that exceed procedure-specified limits. Document the conditions and determine if examination validity is affected.

Equipment availability changes:
The procedure specifies one technique but the specified equipment is unavailable. Determine if an alternative technique can meet the same sensitivity requirements.

Level II Authority Boundaries

You CAN:

• Modify nonessential variables and document the changes
• Select amperage within the specified range based on field conditions
• Determine if environmental conditions are acceptable for valid examination
• Evaluate indications and make accept/reject decisions per the specified criteria
• Supervise and review Level I technicians' work

You CANNOT:

• Change essential variables without procedure re-qualification
• Create or modify acceptance criteria
• Override engineering disposition decisions
• Certify other technicians (Level III function)
• Approve new procedures (Level III function in most Written Practices)

Documentation of Non-Standard Actions

Any deviation from the written procedure must be:
1. Documented with the specific deviation described
2. Justified with technical rationale
3. Authorized by the appropriate authority (Level III, engineer, or client)
4. Recorded in the examination report
5. Assessed for impact on examination validity

Special Environment MT - Level II Considerations

Confined Space MT

Performing MT inside vessels, tanks, manholes, and other confined spaces introduces additional hazards and technical challenges:

Safety requirements:

• Confined space entry permit required per OSHA 29 CFR 1910.146
• Atmospheric monitoring (oxygen, combustible gases, toxic gases) before and during entry
• Attendant stationed at the entry point at all times
• Rescue plan and equipment available
• Communication between entrant and attendant

Technical considerations:

• Limited space for equipment positioning - smaller yokes or specialized probes may be needed
• Ventilation required for petroleum-based particle carriers - vapors accumulate rapidly in enclosed spaces
• Water-based carriers preferred for safety (no flammable vapors)
• Electrical equipment must be appropriate for the classified area (if applicable)
• Lighting limitations - portable UV-A lamps for fluorescent MT in confined spaces must be rated for the environment

Elevated Location MT

MT at height (scaffolding, aerial lifts, on top of tanks/vessels) requires:

• Fall protection per OSHA 29 CFR 1926.502
• Secured equipment - tools and particles must be tethered or contained to prevent falls
• Limitation on heavy equipment - some bench units and power packs may be too heavy for scaffolding load ratings
• Wind protection for dry particles at height (often more windy at elevation)

Underwater MT

Specialized application using permanent magnet yokes and specially formulated particles:

• Equipment must be waterproof and rated for the dive depth
• Particles formulated for underwater use (visible in turbid water)
• Performed by trained diver-NDT technicians
• Documentation challenges - indication recording must be adapted for underwater conditions

Special Application MT - Elevated Temperature

High-temperature MT is performed on components that cannot be cooled to ambient temperature for examination, such as:

• In-process weld examination during multi-pass welding
• Post-weld heat treatment hold temperature examinations
• Components in service that cannot be taken offline for cooling

High-Temperature Dry Particle MT

• Standard dry particles rated to approximately 600°F (316°C)
• Special high-temperature particles rated to 800°F (427°C) or higher
• No contrast paint above approximately 500°F - paint degrades
• Dark-colored particles on the bare metal surface provide adequate contrast
• Equipment modifications: extended-handle prods or yokes to protect the operator from heat

Underwater MT

• Used for offshore structure inspection, dam gates, ship hulls, and submerged piping
• Permanent magnet yokes (no electrical hazard in water)
• Specially formulated visible particles that work in seawater and turbid conditions
• Performed by qualified diver-NDT technicians with dual certifications
• Documentation challenges: indication recording uses underwater cameras and sketches on slates