Surface examination should follow the material and the defect concern. Magnetic particle testing and liquid penetrant testing are both widely used, but they do not operate on the same principle or apply to every material in the same way. Choosing a method by habit can leave a requirement poorly defined.

For a ferromagnetic steel casting, the selection should consider the target discontinuity, surface condition, geometry and governing specification. The final report must identify the technique and acceptance basis rather than use the broad statement crack tested.

Confirm that the material suits the method

Magnetic particle testing depends on magnetizing a suitable material and observing particle indications associated with leakage fields. ASNT describes its application to surface and near-surface discontinuities in ferromagnetic materials. It is not a universal method for all stainless steels or all metals.

Penetrant testing addresses discontinuities open to a suitable surface. The component’s cleanliness and surface condition are therefore central to the examination. Neither method should be described as a complete volumetric inspection of the casting.

Compare the examination conditions

The method selected by the applicable specification governs. A supplier should not replace it solely because another method is cheaper or already available in the shop.

Review surface preparation before scheduling

Scale, coating, contamination or unsuitable roughness can affect examination. The procedure should identify the required condition and any preparation limits. Removing material to improve inspectability must not violate the drawing or conceal the original indication.

Inspection timing should also match the risk. If a later operation can introduce or expose a relevant condition, an earlier examination may not answer the final requirement. The route should state whether testing occurs before machining, after machining or at another specified stage.

Do not confuse an indication with its final disposition

An indication requires evaluation under the specified criteria. The inspector’s report should preserve location, extent and relevant examination details. The acceptance decision is not simply whether the operator noticed a mark.

For magnetic testing, geometry and field arrangement require qualified interpretation. For penetrant testing, surface condition and process control also influence what is observed. A photograph can support the report but should not replace the required examination record.

Include post-test condition in the plan

A finished casting may need cleaning after examination, and some applications require control of residual magnetism. These requirements should be identified before testing so the supplier can plan the final condition and verification.

For a TripleAce Castings enquiry, provide the ordered material, examination zones and governing acceptance requirement. If a customer simply requests both methods, clarify the intended purpose of each with the responsible NDT authority. Additional testing is useful when it closes a defined gap, not merely when it produces another certificate.

Method references

ASNT: Magnetic Particle Testing explains the magnetic method. ASNT: NDT Methods provides context for complementary techniques. This comparison does not replace a qualified procedure or a contractual acceptance standard.