Non-Destructive Testing (NDT), Ultrasonic Shear-Wave Weld Flaw Sizing & ASME Sec V
Ultrasonic NDT Weld Skip Distance & Flaw Depth Formula
Calculate V-Path Full Skip Surface Distance S = 2*T*TAN(theta) (mm), Horizontal Probe-to-Flaw Surface Projection (mm), Leg-1 vs Leg-2 True Flaw Depth Below Top Surface (mm), and Inspection Leg Number.
After an ultrasonic shear wave bounces off the back wall into Leg 2, deeper sound path means SHALLOWER flaw depth!
Inspecting butt-weld fusion faces without grinding off the weld crown uses an Acrylic Wedge Angle-Beam Transducer launching refracted shear waves at angle theta (typically 45°, 60°, or 70° measured from plate normal!) through plate thickness T (mm). A beam bouncing off the bottom root surface returns to the top plate surface at Full Skip Distance S = 2 * T * TAN(theta_rad) (Half-Skip = T * TAN(theta_rad))! When the flaw detector screen measures total slant Sound Path SP (mm) to a crack or slag echo, Horizontal Surface Distance from probe index point is PA = SP * SIN(theta_rad), while Unfolded Vertical Projection is V_raw = SP * COS(theta_rad): on Direct Leg 1 (`V_raw <= T`), True Flaw Depth from top surface is simply d_1 = V_raw; on Bounce-Back Leg 2 (`T < V_raw <= 2*T`), the beam is traveling UPWARD from the back wall, so True Flaw Depth is d_2 = 2 * T - V_raw!
Try this 25.0 mm Pressure-Vessel Butt-Weld 60° Shear-Wave Scan—Plate_Thickness T = 25.00 mm (B2), Probe_Refracted_Angle theta = 60.0° (B3 -> Full V-Path Skip Distance S = 86.60 mm in E2), and Echo_Sound_Path SP = 36.00 mm (B4): Horizontal Surface Projection PA equals 36 * SIN(60°) = 31.18 mm (E3), Unfolded Vertical V_raw = 36 * 0.5 = 18.00 mm <= 25 mm places the reflector in Leg 1 (E5 = 1) at True Depth = 18.00 mm below the top plate surface (E4)!
| ASME Sec V Ultrasonic Weld KPI (T=25.0 mm Plate, 60° Shear Probe, SP=36.0 mm) | Formula | Verified Output |
|---|---|---|
| Full V-Path Skip Distance S (mm) | 2 * Plate_T * TAN(Angle * PI()/180) | 86.60 mm |
| Surface Projection Distance PA | Sound_Path_SP * SIN(Angle * PI()/180) | 31.18 mm (58.89 mm @ SP = 68 mm) |
| True Flaw Depth Below Top (mm) | IF(Leg=1, SP*COS(th), 2*T - SP*COS(th)) | 18.00 mm (16.00 mm @ Leg-2 SP=68!) |
| Active Ultrasonic Beam Leg (1/2) | IF(SP * COS(th) <= T, 1, 2) | Leg 1 (Leg 2 bounce @ SP = 68 mm) |
Angle-Beam Ultrasonic V-Skip & Two-Leg Folded Flaw Depth Formula
Validate Plate_Thickness T > 2 mm, Refracted_Angle theta in [35°, 75°], and Sound_Path SP in (0, 2 * T / COS(theta)] (within first two inspection legs)!
=LET(th_t, B2, an_d, B3, sp_m, B4, IF(OR(th_t <= 2, an_d < 35, an_d > 75, sp_m <= 0), "Invalid UT Input", LET(rd_a, an_d * (PI() / 180), vr_w, sp_m * COS(rd_a), IF(vr_w > 2 * th_t, "BEYOND LEG 2 FULL SKIP", IF(vr_w <= th_t, 1, 2)))))Second-Leg Back-Wall Bounce Upper-Fusion-Face Crack Check (Set Sound Path SP = 68.0 mm)
Pull the transducer back to inspect the upper weld bevel via back-wall reflection at Sound_Path B4 = 68.00 mm: Surface Distance E3 extends to 58.89 mm, E5 switches to Leg 2 (`68 * COS(60°) = 34.0 mm > 25.0 mm`), and True Flaw Depth E4 folds cleanly to `2 * 25.0 - 34.0 = 16.00` mm below the top surface!
=IF(ISTEXT(E5), E5, LET(vr_w, B4 * COS(B3 * (PI() / 180)), ROUND(IF(vr_w <= B2, vr_w, 2 * B2 - vr_w), 2)))Try the example
Use the original values or change them to test your understanding.