| name | radiographic-testing |
| description | Radiographic testing (RT) — Beer-Lambert attenuation (I=I₀exp(−μx)), X-ray and gamma ray sources (Ir-192, Se-75, Co-60, X-ray kV), image quality indicators (IQI/penetrameter), geometric unsharpness U_g = F×d/D, film vs. digital (CR/DR), source-to-film distance, density requirements, sensitivity %, scatter control (lead screens, collimation), ASME Section V Article 2, ASTM E1742, weld discontinuity interpretation, real-time radioscopy. |
| metadata | {"priority":7,"promptSignals":{"phrases":["radiographic testing","RT inspection","X-ray inspection","gamma ray","ASTM E1742"],"minScore":3}} |
Radiographic Testing — Complete Skill
Physics of Radiation and Attenuation
Beer-Lambert Law
Radiation attenuation through material:
I = I₀ × exp(−μ × x) [I = transmitted intensity; I₀ = incident intensity; μ = linear attenuation coefficient [cm⁻¹]; x = material thickness [cm]]
Mass attenuation coefficient:
μ/ρ = f(Z, E) [depends on atomic number Z and photon energy E; from NIST XCOM tables]
μ = (μ/ρ) × ρ [ρ = material density kg/m³]
Half-value layer (HVL):
HVL = ln(2)/μ = 0.693/μ [thickness reducing intensity by half]
Steel HVL at Ir-192 (avg 340 keV): ≈ 12 mm; at Co-60 (1.25 MeV): ≈ 21 mm
Interaction mechanisms:
Photoelectric effect: dominant at low E; complete absorption; E_photon = E_binding → image detail
Compton scatter: dominant at medium E (100 keV – 10 MeV); photon scattered → degrades image (noise)
Pair production: E > 1.02 MeV; minor; positron emission
Radiation Sources
X-Ray Machines
X-ray tube: electrons accelerated by voltage V → Bremsstrahlung + characteristic X-rays
Max photon energy E_max = eV [eV; V in kV × 1000]
kV selection: higher kV → more penetrating → use for thicker material; lower kV → more contrast (differential attenuation)
kV guidelines for steel:
0–25 mm: 150–250 kV (industrial X-ray)
25–75 mm: 250–400 kV (high-energy X-ray)
75–200 mm: 1–2 MV (linear accelerator, LINAC) or gamma sources
Gamma Ray Sources
| Isotope | Energy (MeV) | HVL Steel (mm) | Steel Range (mm) | Activity (Ci range) |
|---|
| Tm-170 | 0.084 | 3 | 2–13 | 30–120 |
| Yb-169 | 0.063–0.308 | 6 | 2–15 | 10–100 |
| Se-75 | 0.066–0.401 | 8 | 10–40 | 10–100 |
| Ir-192 | 0.206–0.612 | 12 | 13–75 | 10–100 |
| Co-60 | 1.17, 1.33 | 21 | 50–200 | 10–50 |
| Cs-137 | 0.662 | 17 | 30–150 | 1–50 |
Activity and half-life:
Activity A(t) = A₀ × exp(−λt) = A₀ × 2^(−t/T½) [A in Curie or Becquerel; T½ from table]
Ir-192 T½ = 73.8 days; Se-75 T½ = 119.8 days; Co-60 T½ = 5.27 years
Dose rate at distance:
Ḣ = Γ × A / r² [mSv/h; Γ = exposure rate constant [mSv·m²/(h·GBq)]; A = activity [GBq]; r = distance [m]]
Ir-192: Γ = 0.118 mSv·m²/(h·GBq) [for shielding/exclusion zone calculation]
Geometric Factors
Geometric Unsharpness
Geometric unsharpness (U_g):
U_g = F × d / (D − d) [mm; F = source focal spot size [mm]; d = object-to-film distance [mm]; D = source-to-film distance (SFD) [mm]]
Approximate for d << D: U_g ≈ F × d / D
ASME Section V requirement:
U_g ≤ values per Table T-276.1 based on material thickness t:
t ≤ 50 mm: U_g ≤ 0.51 mm (0.020 in)
t = 50–75 mm: U_g ≤ 0.76 mm (0.030 in)
t > 150 mm: U_g ≤ 1.78 mm (0.070 in)
Source-to-film distance (SFD) — ASME minimum:
SFD_min = F × d / U_g_max [from above rearranged]
Or per ASME: minimum SFD from Table T-276.2 (depends on f, t)
Sensitivity:
Radiographic sensitivity [%] = (smallest detectable wire or hole diameter [mm]) / (specimen thickness [mm]) × 100%
Target per ASME: 2% sensitivity for critical welds
Image Quality Indicators (IQI / Penetrameter)
Wire IQI (ASTM/ISO Wire Type)
ASME wire IQI (ASTM E747):
Set of wires of known diameters; placed on source side of specimen
Essential wire: smallest wire visible on radiograph → determines sensitivity
Wire designation: 1 through 21 (ASTM E747); diameter doubles every 6 steps
Required essential wire per ASME Section V (Table T-283.2):
Thickness 6–10 mm: essential wire diameter 0.40 mm (Wire #10)
Thickness 25–51 mm: essential wire diameter 0.81 mm (Wire #13)
Thickness 51–76 mm: essential wire diameter 1.02 mm (Wire #14)
Hole IQI (ASTM E1025 — plaque type):
Circular holes of specific diameters in metallic plaque
Essential hole: must be visible; 2T hole (diameter = 2× plaque thickness) must be visible for 2% sensitivity
IQI Placement
Placement rules (ASME V):
Source side (preferred): IQI placed on source side of specimen (image shows true material sensitivity)
Film side: when source side impossible; add 'F' designation to radiograph
Location markers (lead letters): weld ID, part number, date, shot number placed on source side
Film Radiography
Film Density
Optical density (OD):
OD = log₁₀(I_incident / I_transmitted) [measured by densitometer]
ASME V requirement: OD 1.8–4.0 in area of interest (for single film); OD 2.0–4.5 for composite
Film speed and contrast:
Fine-grain (D4, D5): slow speed, high contrast, high resolution → thin specimens, weld roots
Fast (D7, D8): fast, lower contrast → thick specimens, short exposure times
Screens:
Pb lead screens (0.1–0.25 mm): filter scatter, intensify high-energy radiation; improve contrast
Fluorescent screens: intensify by visible light emission; higher speed, lower resolution
No screen: fine detail; very low scatter
Exposure chart:
Milliampere-minutes (mA·min) for X-ray: mA·min = exposure × time
For gamma: Curie-hours (Ci·h) or Becquerel-seconds
Inverse square law: mA·min ∝ SFD²; adjust for SFD changes
Digital Radiography (CR and DR)
Computed Radiography (CR)
CR process: phosphor imaging plate (IP) stores latent image → laser scan releases light (photostimulated luminescence) → digitized
Spatial resolution: 50–200 μm pixel pitch; less than film (film ≈ 20–50 μm)
ASME Code Case 2439 (CR) and 2605 (DR): CR/DR equivalent to film if system qualification per ASTM E2007
Digital Detector Array (DR/FPD)
DR: flat panel detector with amorphous Si + CsI scintillator (indirect) or amorphous Se (direct)
Real-time imaging at ≥ 30 fps → radioscopy for moving parts, production line
Spatial resolution: 100–400 μm pixel pitch; dynamic range > 12 bits (4096 gray levels)
SNR and DQE (detective quantum efficiency): metric for DR panel quality; DQE ≥ 0.4 at 0 lp/mm
Scatter and Image Quality
Scatter degradation:
Compton scatter creates noise → reduces contrast → use:
Lead collimators to limit beam to area of interest
Back scatter shield: 1 mm Pb behind film; verify with 'B' marker (letter B in Pb)
ASME V: if 'B' appears as light image on darker background → unacceptable back scatter
Grid: lead strips at fixed spacing to absorb off-axis scatter; improve contrast at cost of dose increase
Grid ratio = height/spacing; 6:1 to 12:1 typical; primary transmission 60–75%
Standards and References
| Standard | Scope |
|---|
| ASTM E1742 | Standard practice for RT of welds |
| ASTM E747 | Wire IQI design and material grouping |
| ASTM E1025 | Hole IQI (penetrameter) design |
| ASTM E2007 | Standard practice for CR |
| ASME Section V Article 2 | RT for ASME code components |
| ASME Section VIII Div. 1 | RT acceptance criteria (UW-51, UW-52) |
| AWS D1.1 | Structural weld RT requirements |
| 10 CFR Part 34 | NRC regulations for industrial radiography |
| ISO 17636-1/2 | RT of fusion welds (X-ray/gamma) |
| EN ISO 11699 | Industrial radiographic films |
Output
Provide: part description (material; density ρ [g/cm³]; thickness t [mm]; weld type if applicable), source selection (X-ray kV or isotope; energy [MeV]; HVL [mm]; confirm t within recommended range), exposure geometry (SFD [mm]; d [mm]; F [mm focal spot]; U_g = F×d/(D−d) [mm]; U_g ≤ limit per ASME Table T-276.1?), IQI selection (wire type per ASTM E747 or hole type; essential wire/hole designation; placed source side: yes/no), exposure calculation (X-ray: mA·min; or gamma: Ci·h; adjusted for SFD²; target density OD 1.8–4.0), film/digital system (film class per EN ISO 11699 or CR/DR system qualified per Code Case; screens: Pb front + back), scatter control (Pb collimation; 'B' marker placed?; back scatter acceptable?), film density verification (OD measured at IQI area [value]; OD in range?; essential wire/hole visible?), sensitivity achieved (visible essential wire diameter [mm] / t [mm] × 100% = [%]; ≤ 2%?), discontinuities found (location; type: porosity/slag/LF/crack/UT; length [mm]; height [mm] estimated; location in weld: root/fill/cap), acceptance (ASME VIII UW-51 linear/rounded; AWS D1.1 Table 6.1; accept or reject with code reference), and applicable standard (ASME V Article 2; ASTM E1742; AWS D1.1 as applicable).
