Confirm the material before specifying MPI

Magnetic particle inspection relies on magnetising a suitable ferromagnetic component. Aluminium is unsuitable, and many stainless steels are not suitable. A description such as 'metal bracket' or 'stainless assembly' does not establish the material response needed for a valid examination.

For magnetic particle inspection, share material specifications, component drawings and any mixed-material construction. Where identity is uncertain, resolve suitability before writing MPI into the inspection scope. Penetrant or another technique may be appropriate for a non-magnetic material, depending on the question.

Define the examination surface

MPI is commonly used to look for surface and near-surface discontinuities, but detectability depends on field strength, direction and the technique. It is not a volumetric examination of the entire component. Identify weld toes, heat-affected zones, machined transitions or other selected regions using a component map.

Cracks aligned unfavourably to the magnetic field can be difficult to reveal. Procedures may require magnetisation in more than one direction. Restricted access around a pin, corner or attachment may prevent the necessary positioning; report that coverage limit instead of labelling the whole assembly examined.

Agree cleaning and coating treatment

Loose scale, grease, dirt and heavy corrosion can interfere with particle movement and visibility. Coatings may reduce sensitivity or conceal surface features. Whether a coating can remain depends on its condition, thickness and the qualified technique; 'MPI through paint' should not be treated as a blanket allowance.

Discuss preparation with the inspector before grinding or stripping. Aggressive grinding can smear metal over a surface opening or change the feature being investigated. If a suspected indication already exists, photograph and locate it before preparation, and record what was removed or altered.

Provide suitable examination conditions

Visible and fluorescent techniques need their respective lighting and viewing conditions. Site glare, shadows, wet surfaces and wind can affect application or interpretation. Plan sheltered access where needed and confirm space for equipment, consumables and the required magnetisation arrangement.

The site's isolation and access controls apply independently of the NDT method. Agree whether residual magnetism needs assessment or demagnetisation for the component's subsequent use. Consumable removal and reinstatement of protective coatings should have an owner; completing the test does not automatically complete those maintenance tasks.

Interpret and preserve the evidence

Particle accumulations can arise at geometry changes or from other non-relevant responses, not just cracks. The report should distinguish relevant indications from interpretation limits and identify the applicable acceptance criteria. Where further confirmation is needed, retain location photographs and the original observation.

For a repaired weld, request traceability between the original indication, repair extent and follow-up examination. Do not assume a clear MPI result excludes internal flaws or settles the component's load capacity. Those questions may need other testing or engineering review under a separately agreed scope.