PCN NDT Radiographic Testing Level 2 Exam cheat sheet

Inverse square law: I1/I2 = (d2/d1)², so doubling the source-to-detector distance reduces the exposure rate at the detector to one quarter.

Attenuation follows I = I0·e^(−μx); half value layer HVL = ln2/μ = 0.693/μ and ten value layer TVL = 2.303/μ.

Photoelectric absorption varies approximately with Z³/E³ and dominates at low kilovoltage; Compton scattering depends on electron density and dominates at higher energies in steel.

Subject contrast arises from differential attenuation between the discontinuity and the surrounding material; lowering kV raises contrast but narrows exposure latitude and usable thickness range.

Geometric unsharpness Ug = F·t/d, where F is the effective source size, t is the object-to-detector distance and d is the source-to-object distance.

Bremsstrahlung is the continuous spectrum from deceleration of electrons in the target; characteristic radiation comes from electron shell transitions and produces sharp energy peaks.

Photon energy and wavelength are related by E(keV) = 12.4/λ(Å); shorter wavelength means higher energy and greater penetrating power.

Units used in radiography: 1 Bq = 1 decay per second, 1 Ci = 3.7×10¹⁰ Bq, 1 Gy = 1 J/kg absorbed dose, and equivalent dose in Sv = absorbed dose × wR, with wR = 1 for X and gamma rays.

ICRP and IRR17 dose limits: occupational effective dose 20 mSv per year averaged over five years (maximum 50 mSv in any single year), public 1 mSv per year, lens of eye 20 mSv per year, extremities 500 mSv per year.

The three ICRP principles are justification, optimisation (ALARA) and dose limitation; ALARA requires doses kept as low as reasonably achievable with economic and social factors taken into account.

Distance is the most effective control: dose rate follows the inverse square law, so doubling the distance from the source reduces the dose rate by a factor of four.

Shielding calculation: I = I0·e^(−μx); the number of half value layers needed is n = log2(I0/I), and the total thickness is n × HVL.

In UK practice, areas where dose rates exceed 7.5 µSv/h are designated as controlled or supervised according to the annual dose that could be received; boundaries are marked and access is restricted.

Personal dosimetry: a whole-body TLD or film badge is worn on the trunk, with extremity and neutron dosimeters where required; dosimeters are exchanged at defined intervals and results are recorded.

Sealed sources are leak tested by wipe test at intervals not exceeding six months and after any incident, with results entered in the source log and compared with the exemption limit.

Emergency response: evacuate and cordon the area, use remote handling tongs, minimise time, do not touch an unshielded source, and notify the RPS, RPA and the regulator immediately.

X-ray tube: the heated filament cathode emits electrons which are accelerated by the kilovoltage onto the anode; less than about 1% of the energy becomes X-rays, so anode cooling and duty cycle limit continuous operation.

Kilovoltage controls photon energy and penetration; tube current and time (mA·s or mA·min) control the quantity of photons and therefore film density.

Focal spot size controls geometric unsharpness: smaller focal spots give sharper images but carry lower tube current ratings.

Ir-192 has a half-life of 73.8 days, principal energies of about 0.3 to 0.47 MeV and an HVL in steel near 12 to 13 mm, making it suitable for steel roughly 10 to 40 mm thick.

Co-60 has a half-life of 5.27 years, gamma energies of 1.17 and 1.33 MeV and an HVL in steel of about 20 mm, so it suits thick sections above roughly 50 mm of steel.

Se-75 has a half-life near 120 days with energies of 0.2 to 0.4 MeV for thinner sections; Yb-169 has lower energies suited to thin light-alloy components.

Decay correction: A = A0·e^(−0.693t/T½); the exposure time must be multiplied by the ratio A0/A to maintain the required film density.

Exposure devices: crank-out or wind-out types drive the source from the shield through a guide tube to the collimator; source travel and cable position must be verified at each exposure.

Beam limitation uses a diaphragm or collimator sized to the area of interest; a panoramic collimator gives 360° coverage for circumferential weld inspection.

Film construction: a polyester base coated on one or both sides with emulsion of gelatin and silver halide grains, plus a subbing layer and a protective supercoat.

Density D = log10(I0/It); density 2.0 transmits 1% of incident light and density 3.0 transmits 0.1%.

The characteristic curve plots density against log relative exposure, showing fog and toe, a linear region with maximum gradient G, a shoulder and Dmax.

ISO 11699-1 film system classes C1 to C6 rank films by gradient and graininess; finer grain gives better detail but needs more exposure.

Lead intensifying screens reduce exposure time and filter low-energy scatter; front screens are typically 0.02 to 0.15 mm and back screens are thicker to absorb forward scatter.

Manual processing: developer at 20 °C for about 5 minutes, stop bath, fixer, final wash and drying; automatic processors run at roughly 28 to 30 °C with short cycles.

Darkroom control: safelight filtration and distance must be verified by a safelight test, and cassettes are loaded and unloaded under safelight only with no white light leaks.

Common film faults: static marks, frilling, water spots, dichroic fog, pressure marks, roller marks and screen marks from dirty or damaged screens.

Source-to-film distance is selected from the standard table using source size and object-to-detector distance so that geometric unsharpness stays within the allowed value; ISO 17636-1 gives minimum SFD values.

Technique class A (basic) and class B (improved) differ in source size, minimum SFD, film system class, density range and required IQI value; class B is required where the specification demands higher sensitivity.

Single wall single image is used where the inside of the component is accessible; double wall single image or double wall double image is used where only one side is accessible.

The central beam must be perpendicular to the object surface at the centre of the area of interest; offset or angled beams cause distortion and can miss planar discontinuities.

The IQI is placed on the source side wherever accessible; when it must be placed on the film side, a lead letter F is used and the technique is adjusted accordingly.

Exposure charts relating kilovoltage or source activity to thickness are starting points only; actual exposures are confirmed by test shots and density measurement.

Elliptical and double wall exposures require verification of weld coverage; where the standard demands it, a second exposure at 90° is made to cover the full circumference.

Typical kilovoltages for steel are about 100 to 150 kV for 5 to 15 mm and 200 to 300 kV for 25 to 50 mm; gamma sources are selected by activity, energy and required exposure time.

Image quality indicators: wire IQI to ISO 19232-1, step-hole IQI to ISO 19232-2 and duplex wire IQI to ISO 19232-5, the last being used for unsharpness measurement.

IQI sensitivity in percent = (diameter of the smallest visible wire / material thickness) × 100; a lower percentage means better sensitivity.

The required IQI wire number depends on technique class and material thickness and is taken directly from the standard tables for the applicable class.

Film density is measured with a calibrated densitometer; ISO 17636-1 sets minimum and maximum densities that differ between class A and class B and between X-ray and gamma techniques.

Geometric unsharpness limits are tabulated in the technique standard; smaller focal spot, larger SFD and smaller object-to-detector distance all reduce Ug.

Total unsharpness combines geometric, film and screen contributions and is approximated by Ut = (Ug³ + Ui³)^(1/3), so the largest single component dominates.

Scatter lowers contrast and is controlled by collimation, low kilovoltage, lead masking of the object, lead screens and a lead backing sheet behind the cassette.

Interpretation conditions: a viewing box with adjustable brightness, low ambient light, masking of the film, and a densitometer for density checks; optical magnification is used for fine detail.

Gas porosity appears as dark rounded spots, which may be isolated, clustered or linearly aligned; the size and distribution are compared with the reference quality level.

Slag inclusions appear as irregular, often elongated dark indications lying along the weld, caused by non-metallic material trapped during solidification.

Lack of fusion is a planar dark indication with fairly straight edges at a weld interface; detection is strongly dependent on beam orientation relative to the fusion face.

Lack of penetration appears at the root as a dark, essentially straight line of near-uniform width and must be distinguished from root concavity and root undercut.

Cracks are fine, sharp, often branching dark lines; they may only be visible over a limited range of beam angles, so multiple exposure directions are used.

Tungsten inclusions appear as bright, sharply defined spots because tungsten attenuates more than steel; they occur in TIG welds when the electrode touches the weld pool.

Acceptance levels: ISO 5817 quality levels B, C and D for fusion welded joints, ASME Section VIII Division 1 UW-51 and Appendix 4 for pressure vessels, and API 1104 for pipeline girth welds.

A discontinuity becomes a defect only when it exceeds the acceptance criteria of the applicable code; evaluation compares the recorded indication with the code limits, not with appearance alone.

A written procedure states scope, reference standards, personnel qualification, equipment and materials, technique parameters, IQI and density requirements, acceptance criteria and reporting arrangements.

Technique sheets record material, thickness, source or kilovoltage, SFD, exposure in mA·min or Ci·min, film and screens, IQI identity, density and the exposure geometry for each weld or area.

Traceability links each radiograph to the source serial number and current activity, film type and batch, screen set, IQI number, densitometer and survey meter calibration dates.

The report includes client and project, component identification, date, applicable standard, acceptance criteria, results, and the signature and certification number of the Level 2 interpreter.

Certification to ISO 9712 at PCN Level 2 is valid for five years, with revalidation at the mid-term point and re-certification by examination before expiry.

Non-conformances trigger documented corrective action and, where required, retest or repair using the same technique or an approved alternative; all results are recorded and retained.

Calibration intervals: survey meters annually, densitometers annually or as specified, and X-ray kilovoltage, current and timer checks carried out periodically with certificates retained.

Quality management follows ISO 9001 or ISO 17025 principles, with document control, authorised signatories and secure retention of radiographs, films and reports.