NDE · D1.1:2025 · Clause 8 · Table 8.2

Ultrasonic Testing of Welds — D1.1:2025 Requirements

This ultrasonic-testing guide explains where UT fits in weld inspection, how it differs from visual and radiographic review, and what information a project team should confirm before accepting results. Use it as a navigation page for UT scope, setup, reporting, and related NDE terminology.

D1.1:2025 Clause 8.15 requires UT only when specified in contract documents — it is not automatic for all welds. When required for CJP groove welds, discontinuities are classified by four classes in Table 8.2 or Table 8.3 depending on connection loading type.

When Is UT Required Under D1.1:2025

UT is not required for all structural welds. Per Clause 8.15, UT is required only when specified in the contract documents. The engineer specifies UT when radiographic testing is impractical (thick sections), when higher sensitivity for planar defects is needed, or when the joint geometry does not allow RT. When RT is specified, both RT and UT criteria may apply to the same weld.

Planar discontinuities such as cracks and lack of fusion are oriented parallel to the radiation beam in RT, making them difficult to detect radiographically. UT uses an angled sound beam that intersects planar defects more effectively. For this reason, UT is often specified for joints where fatigue life or fracture toughness is critical and planar defect detection is the priority.

When the contract documents specify UT, the testing shall be performed in accordance with Clause 8.13 through Clause 8.15. The contractor is responsible for ensuring UT is performed by a qualified operator using calibrated equipment before the work is accepted.

`Table 8.2` — Discontinuity Classes for Static Connections

When UT is performed on CJP groove welds in statically loaded connections (and cyclically loaded connections in compression), Table 8.2 applies. Discontinuities are classified into four classes based on the indication rating and the db values from the calibration procedure:

Class	Acceptance Rule	Length Limit
Class A	Reject regardless of length	Always unacceptable
Class B	Reject if length exceeds limit	3/4 in [20 mm]
Class C	Reject if length exceeds limit	2 in [50 mm]
Class D	Accept regardless of length	Always acceptable

Classification depends on the indication rating relative to the reference level established during calibration. A higher indication rating (closer to or above the reference level) places a discontinuity in a more restrictive class. The exact db thresholds defining each class boundary are set by Table 8.2 based on weld thickness.

Inspector note: Table 8.2 applies to statically loaded nontubular connections and cyclically loaded nontubular connections in compression. For cyclically loaded connections subject to tension, use Table 8.3 — the acceptance limits for Classes B and C are tighter. Misapplying the wrong table is a common source of acceptance errors on mixed-loading structures.

`Table 8.3` — Cyclic-Tension Connections

For CJP groove welds in cyclically loaded connections subject to tension, Table 8.3 applies stricter limits than Table 8.2. The Class B and Class C thresholds are tighter, reflecting the higher fatigue sensitivity of cyclically loaded connections in tension.

Fatigue cracks typically initiate at stress concentrations. A discontinuity that would be acceptable in a statically loaded connection may act as a fatigue crack initiator when the connection is subject to repeated tensile loading. Table 8.3 accounts for this by requiring smaller discontinuities to be rejected, reducing the probability of fatigue initiation at UT-detectable flaws.

The engineer determines whether a connection is cyclically loaded in tension based on the structural analysis. When loading type is ambiguous or the connection is subject to both tension and compression cycles, the more restrictive Table 8.3 criteria should be applied unless the engineer specifies otherwise in the contract documents.

Testing Procedure Requirements

Table 8.7 specifies the testing angle or angles required based on material thickness range and joint type. Testing from the correct angle is essential for detecting planar discontinuities (lack of fusion, cracks) that may be missed at other angles. The sound beam must intersect potential planar defects at a favorable angle to produce a detectable reflection.

Table 8.8 specifies calibration frequency requirements. Horizontal linearity and gain (sensitivity) calibration must be verified at least every 2 months. Operators must also perform calibration checks at the start of each examination day, when the operator or equipment changes, when equipment malfunction is suspected, and at the conclusion of any series of examinations. Calibration records must be maintained and available for review.

The scanning pattern and search unit movement shall be systematic and overlap to ensure complete coverage of the weld and heat-affected zone. The operator records the indication rating, location, and depth for any indication that meets or exceeds the applicable reference level for each class boundary in the applicable table.

Inspector Qualification

Per Clause 8.14.6, UT inspectors must hold qualification per the American Society for Nondestructive Testing (ASNT) Recommended Practice No. SNT-TC-1A or a national standard. This requires documented training, examination, and work experience specific to the UT method and material application.

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Qualification under SNT-TC-1A has three levels. Level I personnel perform examinations under supervision. Level II personnel interpret and evaluate results. Level III personnel establish techniques and administer the program. D1.1 does not specify which level is required but requires qualification under the practice — the employer’s written practice (as required by SNT-TC-1A) defines the applicable level for each task.

The contractor is responsible for maintaining qualification records and making them available to the engineer or inspector on request. An inspector who cannot produce qualification documentation shall not be permitted to perform UT under D1.1:2025.

Phased Array Ultrasonic Testing (PAUT) — `Annex H`

For the full Annex H reference — scope, personnel, equipment, calibration, scan plans, and the comparison table for choosing PAUT vs conventional UT — see our dedicated Phased Array Ultrasonic Testing guide.

Phased array ultrasonic testing is an advanced UT technique governed by Annex H of D1.1:2025, separate from the conventional UT requirements of Clause 8.15. Annex H is a mandatory annex — when PAUT is used in place of conventional UT, all of Annex H applies. PAUT uses multi-element probes and focal laws to electronically steer and focus the sound beam, enabling imaging views (A-scan, B-scan, C-scan, and S-scan) not available with single-element conventional UT.

PAUT, conventional UT, and any variations in testing procedures, equipment, or acceptance standards outside Part F of Clause 8 require written procedures and the Engineer’s approval, with variations recorded in the inspection records. Per Clause 8, Annex N and Annex H specify alternative ultrasonic techniques for conventional UT and phased array UT on groove welds; Annex H is the mandatory annex governing PAUT specifically.

PAUT Scope and Thickness Range (H2)

Annex H governs PAUT examination 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 tracks probe position along the weld so the scan data can be reconstructed and reviewed afterward — manual, unencoded PAUT is not within the scope of Annex H.

Annex H explicitly excludes PAUT examination of tubular T, Y, and K connection welds. For those geometries, alternative techniques require separate qualification and Engineer approval.

PAUT Personnel Requirements (H4)

Per Annex H4.1, PAUT inspectors must hold NDT Level II or III qualification per 8.14.6.1 and 8.20 — that is, they must first meet the UT inspector requirements of Clause 8 — and in addition must have documented a minimum of 320 hours of work-time experience in PAUT applications. The practical examination required by 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. 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 (H4.2).

PAUT Equipment (H5)

Phased array instruments shall meet the requirements of Clause 8.21 for conventional UT equipment, and additionally: a minimum of 16 pulsers and channels (16:16), or 16:64 if electronic scans are used (H5.1.1). The instrument display shall support A-scan, B-scan, C-scan, and S-scan views together with encoded scans sufficient for full data analysis (H5.1.2).

Angle-beam phased array probes shall be linear-array type with a minimum of 16 elements, producing frequencies between 1 and 6 MHz (H5.3.1). The wedge shall generate shear waves in the material between 40° and 70°, used within the manufacturer’s specified angular range (H5.3.2). Encoding shall use a digital encoder capable of line scanning, driven by a semi-automated or automated scanner (H5.4, H5.5).

The Standard Sensitivity Level (SSL) reference reflector is the 0.060 in [1.5 mm] diameter side-drilled hole in an IIW-type block conforming to ASTM E164 (H5.7). Calibration-block temperature must be within ±25°F [±14°C] of the part or component under examination.

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Frequently Asked Questions

When is ultrasonic testing required for structural welds under D1.1:2025?

Per D1.1:2025 Clause 8.15, ultrasonic testing (UT) is required only when specified in the contract documents — it is not automatic for all structural welds. The engineer specifies UT when it is required for the project. UT is commonly specified for CJP groove welds in critical connections, for thick sections where radiographic testing is impractical, or when higher sensitivity to planar discontinuities (cracks, lack of fusion) is needed.

What are the four discontinuity classes in D1.1:2025 Table 8.2?

D1.1:2025 Table 8.2 classifies UT discontinuities in statically loaded connections into four classes: Class A — reject at any length (always unacceptable); Class B — reject if length exceeds 3/4 in [20 mm]; Class C — reject if length exceeds 2 in [50 mm]; Class D — accept at any length (always acceptable). The classification is determined by the indication rating from the UT calibration procedure. Table 8.3 applies stricter Class B and Class C limits for cyclically loaded connections in tension.

What does D1.1:2025 Table 8.2 cover?

D1.1:2025 Table 8.2 provides acceptance criteria for ultrasonic testing of CJP groove welds in statically loaded nontubular connections and cyclically loaded nontubular connections in compression. The table defines four discontinuity classes (A through D) based on the indication rating from the UT examination. Class A discontinuities are always rejected. Class D discontinuities are always accepted. Classes B and C have length-based acceptance limits of 3/4 in and 2 in respectively.

How often must UT equipment be calibrated under D1.1:2025?

Per D1.1:2025 Table 8.8, ultrasonic testing equipment must be calibrated at specified intervals. Horizontal linearity calibration and gain (sensitivity) calibration must be verified at least every 2 months. Additional calibration checks are required at the start of each day of testing, when the operator changes, when the equipment is suspected of being off calibration, and at the conclusion of any series of examinations. Calibration records must be maintained.

What is phased array ultrasonic testing (PAUT) under D1.1:2025?

Per Annex H of D1.1:2025, phased array ultrasonic testing (PAUT) is a mandatory annex governing advanced UT examination of groove welds and heat-affected zones using multi-element probes with electronic beam steering. Annex H applies 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 excluded from Annex H scope. PAUT produces A-scan, B-scan, C-scan, and S-scan imaging views that conventional single-element UT cannot provide.

What qualification is required for PAUT inspectors under D1.1:2025 Annex H?

Per Annex H4.1, PAUT inspectors must hold NDT Level II or III qualification per Clause 8.14.6.1 and 8.20, and in addition must document a minimum of 320 hours of PAUT work experience. 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 at least two flaws. Certification per H4.2 must be performed by NDT Level III UT personnel meeting the same H4.1 requirements.