Phased Array Ultrasonic Testing of Welds — D1.1:2025 Annex H
Phased array ultrasonic testing is governed by Annex H of AWS D1.1:2025 — a mandatory annex covering groove welds and heat-affected zones from 3/16 in to 8 in [5 mm to 200 mm] using encoded linear scanning. Personnel need NDT Level II or III plus 320 hours of PAUT experience.
What Phased Array Ultrasonic Testing Is
Phased array ultrasonic testing (PAUT) is an advanced UT technique that uses a multi-element probe instead of a single-element transducer. Each element is pulsed independently with controlled time delays, defined by a phased array operational file called a focal law. By varying the focal law, the system electronically steers the sound beam through a range of angles or focuses it at different depths without moving the probe.
This electronic beam control enables imaging views that single-element conventional UT cannot produce: A-scan amplitude vs. time, B-scan ultrasonic-axis vs. probe-movement axis, C-scan plan view, and S-scan sectorial cross-section. Each view is reconstructed from the encoded position of the probe along the weld, giving the inspector a stored, reviewable record of the entire scan.
For welding inspection, PAUT compresses scan time relative to multi-angle conventional UT and provides image-based interpretation that is easier to communicate to the engineer or owner. The trade-off is equipment cost, scan-plan complexity, and the additional 320-hour personnel experience requirement of Annex H4.1.
When PAUT Applies Under D1.1:2025
Annex H is a mandatory annex of AWS D1.1:2025 — when phased array ultrasonic testing is selected in place of conventional UT under Clause 8.15, all of Annex H applies: introduction (H1), scope (H2), definitions (H3), personnel (H4), equipment (H5), equipment qualification (H6), scan plans (H7), calibration (H8), examination (H9 through H10), and acceptance (H11 through H12).
D1.1 permits both conventional UT and phased array UT as alternative ultrasonic techniques on groove welds. Variations in testing procedures, equipment, or acceptance standards outside Part F of Clause 8 may be used only with the Engineer’s approval, and any such variation must be recorded in the inspection records. PAUT is not a substitute for conventional UT in every situation — the choice between them depends on weld geometry, thickness, joint accessibility, and contract requirements.
UT itself (conventional or phased array) is required only when specified in the contract documents per Clause 8.15. PAUT does not become applicable until the Engineer specifies UT for the weld and the contractor selects PAUT as the technique.
“Annex H is a mandatory annex — when PAUT is selected in place of conventional UT, every requirement in H1 through H14 applies. There is no ‘PAUT-lite’ under D1.1.”
Annex H1 Introduction, AWS D1.1/D1.1M:2025
PAUT Scope: Thickness and Joint Range
Per Annex H2, the procedures and standards in Annex H govern PAUT examinations of groove welds, including heat-affected zones (HAZ), for thicknesses between 3/16 in and 8 in [5 mm and 200 mm] using encoded linear scanning. The encoder is what tracks the probe’s position along the weld so that the scan data can be reconstructed and reviewed afterward — manual, unencoded PAUT is not within the scope of Annex H.
Annex H explicitly excludes the PAUT examination of tubular T, Y, and K connection welds. For those joint geometries, alternative techniques require separate qualification and Engineer approval.
For materials over 2 in [50 mm] in thickness, a mockup verification block per H5.7.2 may be required by the Engineer or used at the option of PAUT personnel. The mockup block contains representative weld geometries with planted reflectors at locations where it is difficult to direct sound beams — ensuring the scan plan covers the entire weld volume and HAZ.
PAUT Personnel Qualification (Annex H4)
Per Annex H4.1, NDT Level II and III PAUT personnel who collect or analyze PAUT data shall be qualified per Clause 8.14.6.1 and 8.20. In addition, the PAUT inspector shall have documented a minimum of 320 hours of work-time experience in PAUT applications. The practical examination required by Clause 8.20 shall consist of at least two flawed specimens representing the joint types to be examined, each containing a minimum of two flaws.
Individuals not meeting these requirements may assist in PAUT data collection only under the direct supervision of qualified PAUT personnel.
Per Annex H4.2, certification of NDT Level II and III PAUT personnel shall be performed by NDT Level III UT personnel who meet the requirements of H4.1. The certifying Level III therefore needs both general UT qualification and the additional 320 hours of PAUT-specific experience.
PAUT Equipment Requirements (Annex H5)
Per Annex H5.1, inspections shall be performed using phased array pulse-echo equipment that meets the requirements of Clause 8.21 for conventional UT equipment, qualified in accordance with H8. In addition, phased array instruments shall meet several PAUT-specific requirements:
H5.1.1 — Number of Pulsers
The instrument shall be equipped with a minimum of 16 pulsers and 16 channels (16:16). A minimum of 16:64 is required if electronic scans are to be used. The pulser/channel ratio dictates how many elements within a phased array probe may be applied within a given focal law.
H5.1.2 — Imaging Views
The phased array instrument shall be equipped with sufficient display options to include A-scan, B-scan, C-scan, and S-scan views, and encoded scans to provide thorough data analysis through the entire scan length and through all beams.
H5.3 — Angle-Beam Search Units
Per H5.3.1, the angle-beam phased array probe shall be a linear array type with a minimum of 16 elements and shall produce frequencies between 1 and 6 MHz. Probe pitch dimensions shall be small enough that standing wave signals do not appear on the display.
Per H5.3.2, the wedge shall be of a sufficient incident angle to produce shear waves in the material between 40° and 70°. Wedges shall be used within the angular range specified by the manufacturer.
H5.4 and H5.5 — Encoder and Scanner
The encoder shall be digital and capable of line scanning. Encoding shall be performed using a semi-automated or automated scanner as defined in H3.22. Automated scanners are mechanized devices in which the PAUT probe movement is computerized or driven by remote control; semi-automated scanners are manually driven along welds while the encoder records position.
PAUT Calibration: SSL and Reference Blocks (H5.7)
Per Annex H5.7, the standard reflector used to establish the Standard Sensitivity Level (SSL) shall be the 0.060 in [1.5 mm] diameter side-drilled hole in an IIW-type block in conformance with ASTM E164. The temperature of the calibration standard shall be within ±25°F [±14°C] of the temperature of the part or component to be examined — a substantial temperature differential changes wedge geometry and refraction angles enough to invalidate the SSL.
Per H5.7.1, a supplemental reference block shall be used that allows a minimum 3-point time-corrected gain (TCG) establishment throughout the angular range specified in the scan plan. The block shall be of sufficient thickness and length to allow calibration of reflectors throughout the entire examination volume. Each block shall have at least three side-drilled holes at depths covering the entire material range to be tested. NAVSHIP and custom machined blocks meeting these requirements may be used.
Per H5.7.2, for materials over 2 in [50 mm] in thickness, when required by the Engineer or at PAUT-personnel option, the detectability of the standard reflector shall be verified in a mockup or production part. When this verification block is used, the standard sensitivity reflector shall be detectable above DRL established in H8.2.4.2; if not detectable, the scan plan shall be adjusted until adequate detectability is achieved.
PAUT Imaging Views Explained
Per Annex H3.12, imaging views are images defined by different plane views between the ultrasonic path (ultrasonic axis), beam movement (index axis), and probe movement (scan axis). The five primary views recognized by Annex H are:
- A-scan — the received pulse amplitude versus time of flight in the ultrasonic path. Same waveform produced by conventional UT.
- B-scan — a 2-D view of A-scan data along the probe-movement (scan) axis, color-coded for amplitude.
- C-scan — a 2-D plan view of beam movement (index axis) versus probe movement (scan axis), using the maximum A-scan amplitude at each transverse location.
- D-scan — similar to S-scan but less commonly used for weld inspection; shows the ultrasonic axis versus the index axis.
- S-scan — a 2-D cross-sectional view of all A-scans corrected for delay and refracted angle, presented as a single slice of focal laws (one focal law sequence) along the probe-movement axis.
Scan Plans (Annex H7)
Per Annex H7.1, a scan plan as defined in H3.21 shall be developed for the welds to be examined. The scan plan must specify the attributes necessary to achieve examination coverage, including the essential variables listed in Table H.1.
Per H7.1.2, the scan plan shall demonstrate by plotting or computer simulation the appropriate refracted angles to be used during examination for the groove weld geometry and areas of concern. The scan plan must demonstrate and document coverage of the required examination volume. Performance shall be verified through the initial calibration: beam index point and beam angle verifications.
Per H7.4, the base metal through which ultrasound must travel to test the weld shall be tested for laminar reflectors using a straight-beam scan unit conforming to H5.2. If any area of base metal exhibits total loss of back reflection or an indication equal to or greater than the original back reflection, refer to 9.2.2.
Per H7.4.1, the scan plan shall demonstrate full ultrasonic coverage in two crossing directions to cover the heat-affected zone (HAZ) with beam angles between 40 and 60 degrees and full weld volume including weld fusion face coverage within ±10° of perpendicular (90° to the weld fusion face) for azimuthal scans or ±5° of perpendicular for supplemental electronic scans where possible. The weld and HAZ shall be tested using a PAUT probe conforming to H5.3.
PAUT vs Conventional UT — When to Use Which
Both techniques are recognized by D1.1 for groove-weld examination. Choosing between them is an engineering judgment based on weld characteristics and project economics:
| Factor | Conventional UT | PAUT (Annex H) |
|---|---|---|
| Governing reference | Clause 8.15, Tables 8.2 / 8.3 / 8.7 / 8.8 | Annex H1 through H14 |
| Inspector experience | NDT Level II UT per Clause 8.14.6 | NDT Level II/III + 320 hours PAUT (H4.1) |
| Equipment | Single-element transducer, pulser/receiver | 16:16 minimum channels, 1–6 MHz linear array, encoded scanner (H5.1.1, H5.3.1, H5.4) |
| Imaging | A-scan only | A-, B-, C-, D-, S-scan (H5.1.2, H3.12) |
| Data record | Inspector log entries | Encoded electronic record, reviewable post-scan |
| Coverage method | Manual scan with multiple probe angles | Encoded linear scan, 40–60° per H7.4.1 |
| Scope limit | All groove welds + tubular T/Y/K | Groove welds only, 3/16–8 in; T/Y/K excluded (H2) |
| Best fit | Field repair, single-pass coverage, low equipment budget | Production fabrication, thicker sections, where image record adds value |
For tubular T, Y, and K connections, PAUT under Annex H is not permitted — conventional UT under Clause 8.15 with the procedures of Clause 8 Part F applies.
Related Standards Guides
Frequently Asked Questions
Per Annex H of D1.1:2025, phased array ultrasonic testing is permitted as an alternative to conventional UT when the contract specifies UT and PAUT is approved by the Engineer. Annex H is a mandatory annex — when PAUT is selected in place of conventional UT under Clause 8.15, all of Annex H (personnel qualification H4, equipment H5, scan plans H7, calibration H8, examination H9–H10, acceptance H11–H12) applies. Variations from Part F of Clause 8 require written procedures and Engineer approval, with the variation recorded in the inspection records.
Annex H2 governs PAUT examination of groove welds and heat-affected zones for thicknesses between 3/16 in and 8 in [5 mm and 200 mm] using encoded linear scanning. Tubular T, Y, and K connection welds are explicitly excluded from Annex H scope. For materials over 2 in [50 mm] in thickness, a mockup verification block per H5.7.2 may be required by the Engineer or used at the option of PAUT personnel.
Per Annex H4.1, PAUT inspectors must hold NDT Level II or III qualification per Clause 8.14.6.1 and 8.20, and must additionally have documented a minimum of 320 hours of work-time experience in PAUT applications. The required practical examination (per Clause 8.20) shall consist of at least two flawed specimens representing the joint types to be examined, each containing a minimum of two flaws.
Per Annex H5.1.1, the phased array instrument shall be equipped with a minimum of 16 pulsers and 16 channels (16:16). A minimum of 16:64 is required if electronic scans are to be used. Per H5.1.2, the instrument display shall support A-scan, B-scan, C-scan, and S-scan views together with encoded scans sufficient for thorough data analysis through the entire scan length and through all beams.
Per Annex H5.7, the standard reflector used to establish the Standard Sensitivity Level (SSL) is a 0.060 in [1.5 mm] diameter side-drilled hole in an IIW-type block conforming to ASTM E164. Calibration-block temperature must be within ±25°F [±14°C] of the part or component under examination. A supplemental reference block per H5.7.1 with at least three side-drilled holes at varied depths is also required to support a 3-point TCG (time-corrected gain) calibration.