Interpretation Definitions

Sensitivity – capacity of an NDT technique to detect discontinuities or alternatively the smallest recordable indication that can be located with a given NDT method. The main factors which control this are contrast and definition.

Example:

• Contrast when using black ink on a white background is 10:1 to 20:1.
• Contrast for fluorescent inks against a dark background is up to 100:1

Discontinuity – an interruption in the normal physical structure or configuration of a part or alternatively a detectable change in the material produced inherently or artificially.

Non-relevant – indications from something on the test piece, which is expected, i.e. brazed joints, sharp changes to cross sections, internal splines, bores, drilled holes near the surface or changes in the metallurgy.

Relevant – a genuine indication from a source which is unexpected.

Flaw – an imperfection not necessarily rejectable to the applicable specification or standard.

Defect – something that creates a substantial risk of failure during service and is therefore rejectable to an applicable specification or standard.

Indication – particles accumulated and held at a site by a leakage field.

Adequate reporting is essential for the transmission of relevant and correct information after the test. Any test report should include the information required by the relevant specification for the work being performed.

A typical report would require the following:

1. Name of the company;
2. Work location;
3. Description and identity of the part tested;
4. Stage of test (e.g. before or after heat treatment, before or after final machining);
5. Reference to the written test procedure and the technique sheets used;
6. Description of equipment used;
7. Magnetising technique, including (as appropriate) indicated current values, tangential field strengths, waveform, contact or pole spacing, coil dimensions etc.;
8. Detecting media used and contrast paint if used;
9. Surface preparation;
10. Viewing conditions;
11. Method of recording or marking of indications;
12. date of test;
13. Name, qualification and signature of the person performing the test.

The test report shall then contain the test results, including a detailed description of the indications and a statement as to whether they meet the acceptance criteria.

A common method of recording indications is to reproduce indications on a scaled diagram.
Indications should be drawn with references to a datum on the test piece. The diagram(s) should not be overloaded with too much information; use two diagrams if necessary. A separate diagram showing magnetising techniques should ideally be included where it is not obvious which technique has been applied.