Technique Development and Field Execution

Outcomes

After this chapter, the learner should be able to:

• turn a scope into a controlled MT technique;
• justify equipment, waveform, media and field directions;
• calculate and then verify starting settings;
• write a usable work instruction;
• troubleshoot weak or excessive indications; and
• demonstrate Level 2 competence through practical evidence.

14.1 Start with the examination objective

Technique development begins with a question, not a favourite instrument. Define:

• component identity, drawing and test boundary;
• material, product form and heat-treatment condition;
• manufacturing or service stage;
• expected discontinuity types, orientations and locations;
• required surface and near-surface sensitivity;
• coating, roughness, temperature and access;
• acceptance criteria and reporting threshold; and
• restrictions on current flow, arcing, chemicals, UV-A and residual field.

14.2 Select the field method

Use a simple decision sequence:

1. Is a portable local surface examination required? Consider an AC yoke.
2. Is near-surface response required? Consider a qualified DC/HWR technique and suitable media.
3. Must current through the component be avoided? Use magnetic flow, yoke, coil or central conductor as geometry permits.
4. Is the target a bore or ring surface? Consider a centred or offset conductor.
5. Is the target transverse on a long part? Consider a coil or magnetic flow.
6. Is the target longitudinal on a solid part? Consider axial current flow.
7. Can the second field direction be created and verified without leaving gaps?

Document why the selected method is suitable and what it cannot cover.

14.3 Select waveform and media

Match waveform to depth and particle mobility:

• fine surface condition: AC with wet fluorescent media is a high-sensitivity baseline where viewing can be controlled;
• rough hot surface: qualified dry visible media with a permitted waveform;
• favourable near-surface condition: HWR/DC with dry or otherwise qualified media;
• high-throughput small parts: fixed wet bench with controlled bath; and
• field colour-contrast work: AC yoke, visible wet media and qualified contrast coating where appropriate.

These are starting concepts, not automatic prescriptions. Product temperature, fire risk, coating and client restrictions may change the choice.

14.4 Calculate, demonstrate, adjust

Where the approved method provides a formula:

1. sketch geometry and identify the target surface;
2. write the formula and units before substituting values;
3. confirm waveform and meter basis;
4. calculate without premature rounding;
5. check equipment capacity and duty cycle;
6. set the starting value;
7. demonstrate field direction and performance at least-favourable locations; and
8. adjust only within the approved development rules.

Record both the calculated value and the verified production setting. If they differ, document why.

14.5 Work instruction structure

A Level 2 work instruction should be short enough to use at the job and complete enough to reproduce the technique. Its opening section identifies the title, scope, component, examination area, controlling procedure, product standard, acceptance criteria and personnel qualification. It also identifies the equipment, meters, reference pieces and consumables that form the controlled system.

The execution section states the safety and environmental controls, surface preparation, temperature range, pre-use checks, field method, waveform, current basis and starting setting. It defines pole, contact or coil geometry, placement sequence, media-application timing, viewing conditions, overlap and the two-direction coverage plan. A sketch is usually clearer than a paragraph when placement and coverage are geometric.

The closing section states how indications are interpreted, measured and evaluated; what records and report fields are required; how demagnetisation and residual-field verification are performed; and what post-cleaning and release condition is required. Do not paste whole standards into a work instruction. Convert controlling requirements into unambiguous actions and retain exact references for traceability.

14.6 Troubleshooting matrix

14.7 Practical assessment stations

Station 1 - Yoke weld scan: Prepare a plate weld, verify the AC yoke and visible or fluorescent system, create a two-direction grid, locate known indications and submit a coverage sketch.

Station 2 - Coil calculation: Calculate fill factor, L/D, ampere-turns and current for a supplied shaft, identify formula assumptions and demonstrate the field on an approved indicator.

Station 3 - Central conductor: Select ID or OD perimeter, calculate starting current, plan placements for a large ring and explain the favoured discontinuity direction.

Station 4 - Media control: Inspect a wet bath, perform the required reference-block comparison, measure viewing conditions and decide whether production may proceed.

Station 5 - Interpretation: Classify a set of repeatable and non-repeatable patterns, document confirmation steps and apply supplied acceptance criteria.

Station 6 - Demagnetisation: Select a method based on the original waveform and geometry, perform the controlled sequence and map final residual field readings.

14.8 Level 2 evidence standard

A satisfactory practical result includes more than finding seeded conditions. The candidate should demonstrate:

• correct document and safety controls;
• justified technique selection;
• accurate calculations and units;
• stable equipment and media checks;
• complete two-direction coverage;
• disciplined particle application;
• correct viewing measurements;
• defensible interpretation;
• traceable records and limitations; and
• compliant final component condition.

14.9 Common traps

• Starting with equipment and trying to make the scope fit it.
• Writing a work instruction that says "as per standard" instead of specifying actions.
• Recording only the final dial setting and losing the calculation basis.
• Changing several variables at once during development.
• Passing a practical because the known crack was found while missing coverage, safety or reporting failures.
• Treating a clean-looking report as evidence that the test itself was controlled.

Chapter summary

Technique development connects product risk to magnetic physics and then proves the connection on the real setup. A Level 2 work instruction converts that proof into repeatable actions. Competence is shown through justified selection, verified performance, complete coverage, sound interpretation and a traceable final record.

Closing professional practice statement

Magnetic particle testing is simple to demonstrate and demanding to control. The visible result depends on a chain of material response, field direction, waveform, media mobility, surface condition, viewing and human judgement. A Level 2 technician earns confidence by making every link visible in the technique and record.

This Draft 02 manuscript requires formal technical review and approval before issue as controlled training material.