1. Scope
This procedure covers manual contact ultrasonic examination (UT) of full-penetration butt welds in carbon-steel and low-alloy-steel pressure vessels constructed to ASME Boiler and Pressure Vessel Code (BPVC) Section VIII Division 1. The examination is performed in accordance with ASME BPVC Section V, Article 4 and qualified to the supplemental requirements of Section VIII Division 1 Mandatory Appendix 12 where the vessel is to be marked with UT in lieu of radiography under UW-11(a)(7).
Material thickness range: 6 mm (¼ in) to 200 mm (8 in). Geometry: longitudinal and circumferential butt welds, weld crown ground flush or contoured per code.
2. References
- ASME BPVC Section V, Article 4 — Ultrasonic Examination Methods for Welds (current edition)
- ASME BPVC Section VIII Division 1, UW-11, UW-51, UW-52, Mandatory Appendix 12
- ASNT SNT-TC-1A or CP-189 for personnel qualification
- Customer Written Practice (WP)
- ASME BPVC Section IX for welding-procedure context (informational)
3. Personnel Qualification
UT examination shall be performed by personnel certified to ASNT NDT Level II or higher in Ultrasonic Testing, qualified to the employer's Written Practice meeting SNT-TC-1A or CP-189. Procedure approval and interpretation of indications outside the straightforward limits of Table T-441.1 shall be referred to a Level III.
4. Equipment
- Pulse-echo flaw detector with calibrated A-scan display (e.g., Olympus EPOCH 650 / Sonatest Veo+ / Krautkrämer USM 100). Vertical linearity within ±5% of full screen height; horizontal linearity within ±5% per T-441.1.
- Single-element transducers:
- 0° longitudinal-wave, 5 MHz, 25 mm diameter — for thickness reference and lamination scan.
- Angle beams 45°, 60°, 70° shear-wave wedge — frequency 2.25 MHz or 5 MHz, element 9 × 9 mm or 12 × 13 mm — selected per material thickness per T-451.1.
- Couplant compatible with material — typically glycerin-based, water-based, or low-sulfur cellulose paste. Compatibility verified against the customer's service-fluid contact list (e.g., halide-free for austenitic stainless).
- Calibration block per Figure T-434.1: V1 / V2 (ISO 2400) or per Mandatory Appendix VIII customer-specific block reflecting the actual production material and thickness.
- Distance Amplitude Correction (DAC) reference block with side-drilled holes (SDH) sized per T-434.2.1 — typically 1.5 mm (0.060 in) diameter for thicknesses ≤ 25 mm.
5. Surface Preparation
The scanning surface shall be free of weld spatter, paint scale, mill scale, slag, oil, and surface irregularities that interfere with sound transmission. Acceptable surface roughness: 6.3 µm Ra or finer (250 µin). Scanning surface extends a minimum of 1.5 × material thickness on each side of the weld centerline.
Material temperature at the time of examination shall be between 0 °C (32 °F) and 52 °C (125 °F). For elevated-temperature contact UT, high-temperature couplant and probes shall be specified by the Level III.
6. Calibration
6.1 System Calibration
Range and sensitivity shall be set using the reference block of Figure T-434.1 or an approved customer block. The DAC curve shall be constructed from a minimum of three SDH responses spanning the metal-path range of interest. The reference level shall be set so that the peak response from the primary reference reflector reaches 80% ± 5% FSH.
6.2 Calibration Verification
System calibration shall be verified:
- At the start of each examination
- After any change of operator, probe, cable, or wedge
- At the end of each examination period
- At intervals not exceeding 4 hours during continuous use
If calibration verification shows DAC peak amplitude has changed by more than 20% or 2 dB, all examinations performed since the last valid calibration shall be repeated.
6.3 Couplant Verification
Couplant transmission loss shall be checked daily on the calibration block; loss greater than 6 dB from the as-procured baseline requires couplant replacement.
7. Examination Technique
7.1 Coverage
The complete weld and adjacent base metal (the heat-affected zone plus 25 mm) shall be examined from both sides of the weld where accessible, from both surfaces where accessible per T-471. Scanning shall be performed at a maximum index increment of (W − D × tan θ) / 1.5 where W is the transducer width, D is the metal path, and θ is the refracted angle.
7.2 Scanning Sensitivity
Scanning gain shall be set 6 dB above the reference DAC level. Evaluation of indications shall be at reference level.
7.3 Scanning Speed
Maximum scanning speed: 150 mm/s (6 in/s).
7.4 Coupling Verification
Continuous coupling shall be maintained throughout each scan. Loss of coupling for more than 25 mm of scan length requires re-scanning.
8. Evaluation and Recording
Indications producing a response equal to or greater than 20% of the DAC reference level shall be investigated to determine the shape, identity, and location of the reflector. All indications producing a response equal to or greater than the DAC reference level that cannot be classified as geometric shall be evaluated against Section VIII Division 1 Mandatory Appendix 12.
9. Acceptance Criteria (ASME Section VIII Div 1 App 12)
Indications shall be classified as:
- Cracks, lack of fusion, incomplete penetration — rejectable regardless of amplitude per App 12-3(a)
- Other linear indications: rejectable if amplitude exceeds reference level AND length exceeds the limits of App 12-3(b)(1) through (3):
- ≤ ¼ × t for ½ × t < ℓ for the depth zone in question
- Customer Written Practice may impose more stringent limits.
10. Reporting
The examination report shall include, as a minimum: customer and job identifier; component identification; drawing number and weld number; material and thickness; welding process; surface condition; equipment serial numbers (instrument, transducer, wedge); calibration block identifier and last-calibration date; couplant; scanning gain and reference level; date of examination; examiner name, certification level, and ID; Level III approval signature; and a sketch or weld map showing the location, length, depth, and amplitude (% DAC) of every recordable indication.
11. Safety
Standard plant safety rules apply. Specific NDT considerations: confined-space entry procedures for in-vessel examination; hot-surface PPE for above-ambient examinations; couplant compatibility with downstream service (e.g., halide content limits for stainless and high-nickel alloys); ergonomic management of continuous overhead scanning per ANSI Z365.
This procedure is a published reference. Production use requires Level III review and approval against the current code edition and the customer's Written Practice. For a tailored procedure including specific transducer selection, exact DAC block geometry, and customer-specific acceptance criteria, use the free AI Procedure Generator.