Non destructive inspection: which NDT method finds which defect, and who may sign the results in South Africa

Visual and penetrant testing find defects open to the surface, magnetic particle and eddy current testing also find them just below it, and ultrasonic and radiographic testing find internal ones.^{[2][3][4][5][6][7]}

Sources:^{[2][3][4][5][9][6][7][16][17]}

Both do. Choose magnetic particle testing where the material can be magnetised, because it also shows cracks just below the surface that penetrant cannot; choose penetrant testing for every part a magnetic field cannot be passed through, provided the crack is open to the surface.^[4][3]

If parts will be tested hot or cold, say so: SAIW notes that heat and cold change the penetrant liquids' viscosity and evaporation, and the penetrant standard has separate parts for testing above 50 °C and below 10 °C (ISO 3452-5 and ISO 3452-6).^[3]

Either finds internal weld defects, so the choice turns on the site and on what you need back: radiography uses ionising radiation and needs a barricaded, cleared area, while ultrasonic testing works with probes on the part.^[5][6][16]

Ultrasonic testing also gives each discontinuity's size, orientation and position; radiography records an image of the weld, on film or with electromagnetic sensors.^[5][6]

Phased array ultrasonic testing (UT 2.10), time-of-flight diffraction (UT 2.11) and digital radiography (RT 2.9) are separate SAQCC NDT certificates, each requiring Level 2 certification in the basic method and at least nine months' experience in it first.^[10][11][12]

Industrial radiography needs SAHPRA's authority: the radioactive sources it uses are controlled under article 3A of the Hazardous Substances Act 15 of 1973 and the Group IV hazardous substances regulations, and industrial X-ray equipment under article 3(1) of the same Act, both administered by SAHPRA's Radiation Control.^[16][17]

SAHPRA's codes of practice say industrial radiography "may only be performed by" a qualified radiographer granted a personal authority by SAHPRA, a trainee under that radiographer's direct supervision, or an operator inside an enclosed exposure facility (gamma guideline 8.1, X-ray guideline 7.1.1).^[16][17]

On an open site, the barriers go at a distance calculated before the exposure, so that the dose rate at the barrier is as low as reasonably achievable and does not exceed 10 µSv/h, checked with a monitor once the source is exposed. Warning signs, and at night warning lights, go on the barrier, and nobody may be inside the demarcated area when an exposure starts (gamma guideline 8.2.4, 8.2.6 and 8.2.7; X-ray guideline 7.2.4, 7.2.6 and 7.2.7).^[16][17]

During the work, no worker without a personal dosimeter may receive more than 20 µSv, and no member of the public more than 4 µSv, in any one day (gamma guideline 8.2.5); a gamma radiography team operating one unit is one radiographer and at least one assistant (8.2.15).^[16]

The radiography company applies to SAHPRA for its authority, showing that it has the equipment, facilities and trained personnel to work safely, and nominates a radiation protection officer, who must pass an approved examination and hold an approved Level II industrial radiography qualification with two years' experience (gamma guideline 3.1 and 3.2).^[16]

Under the SAQCC NDT scheme, a certified Level 1 performs the tests under supervision and a certified Level 2 interprets the results and signs the report; for radiography, the radiographer also needs SAHPRA's personal authority. SAIW Certification, accredited by SANAS to ISO 17024, runs the scheme and keeps a national register of everyone it has certified. For welders, see coded welders.^{[14][8][9][16][17]}

The scheme follows ISO 9712. SAIW Certification is moving certificate holders from ISO 9712:2012 to ISO 9712:2021 at renewal or recertification, with a December 2026 deadline, and existing certificates stay valid until they expire. The SABS catalogue lists the national adoption as SANS 9712:2009, edition 2.^[13][20][19]

Under the scheme, a certificate covers one method, one level and named product sectors (for ultrasonic testing, the four in the table) and is valid for five years, with an eyesight test every year.^[9]

On pressure equipment, the inspection authority's side needs its own certificate: SAIW notes that SANS 10227 requires an inspection authority's personnel responsible for inspection, testing and verification of NDT to hold certification meeting the minimum requirements of SAQCC-IPE, and that scheme requires each applicant to hold current certification in radiographic interpretation.^[15]

What each level may be authorised to do, in SAIW Certification's scheme documents:^[8][9]

• Level 1 sets up the equipment, performs the tests, records and classifies results against written criteria and reports them, under Level 2 or Level 3 supervision; a Level 1 is responsible neither for choosing the method or technique nor for interpreting results.^[8]
• Level 2 selects the technique, turns the code into a written instruction, sets up and checks the equipment, interprets and evaluates results against the applicable standard (accept or reject), supervises Level 1 and reports the results: "compile and sign report", in the scheme's words.^[9]
• Level 3 compiles and approves the NDT procedures that the Level 2 instructions are based on.^[8]

The Pressure Equipment Regulations name crack detection outright for one item: every fire-tube steam generator needs a witnessed hydraulic test and "crack detection of critical welds every 36 months" by an in-service approved inspection authority (regulation 11(1)(c)). For the other inspection intervals, see AIA inspection.^[18]

The Department of Labour's guidance notes define critical welds as tube-sheet-to-shell welds not made as full penetration welds and other welds whose failure can cause a catastrophic incident, which "shall be surface crack and ultrasonically tested". In fire-tube boilers these are the shell-to-endplate, furnace-to-endplate and access-tube-to-endplate welds and the ash drop-out chutes to furnace and shell (note (d) to regulation 11).^[18]

A manufacturing AIA may grant permanent dispensation from the in-service hydraulic test only if the equipment gets at least a visual inspection and "appropriate non-destructive testing to detect the expected deterioration", or an appropriate non-intrusive inspection (note (g) to regulation 11).^[18]

The user keeps NDT reports in the regulation 14 record for the operating life of the equipment (note (a) to regulation 14), and regulation 15 requires access to every manhole and inspection opening to be "safe and unobstructed".^[18]