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Ultrasonic Testing of Welds — D1.1:2025 Requirements
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.
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.
Frequently Asked Questions
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.
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.
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.
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.