AWS D1.1 UT Acceptance Criteria, Explained Table by Table

Table of Content

• Introduction
• Which edition, and where things live
• Scope and setup
• The indication rating
• Scanning levels
• Table 8.2: statically loaded nontubular connections
• Table 8.3: cyclically loaded nontubular connections
• Severity classes and the rules under the tables
• Scanning patterns
• Worked examples
• Calibration checks, reporting and personnel
• Conclusion

Introduction

AWS D1.1 doesn't size ultrasonic indications. It rates them. Each signal on a structural groove weld is converted into a single number in decibels, which, when combined with the probe angle and weld thickness, determines whether the weld passes. If you perform the math correctly, the tables will take care of the rest. You can reject a good weld or pass a bad one if you are off by two decibels.

The indication rating, the scanning levels, the two acceptance tables, the severity classes and the rules printed beneath them, the scanning patterns, and four worked examples are all covered in this guide in the manner that an inspector would utilize it.

Which edition, and where things live

The 2020 edition was superseded by the current version, AWS D1.1/D1.1M:2025. The ultrasonic acceptability tables are Table 8.2 for statically loaded nontubular connections and Table 8.3 for cyclically loaded nontubular connections. Inspection is located in Clause 8. Procedures written to 2015 or earlier editions still reference Tables 6.2 and 6.3 for the same criteria because the 2020 edition shifted inspection from the previous Clause 6 to Clause 8.

Subclause numbers have shifted between editions. Always check the clause and table numbers against the edition named in your contract documents before you quote them on a report.

The contract documents also decide which table applies. Cyclically loaded criteria are stricter, but they are not the default. They apply only where the Engineer has designated the connection as cyclically loaded.

D1.1 is only one of several codes that decide how a weld gets judged, and clause numbers change between editions. See how the major UT standards and codes compare before you write a procedure to one of them.

→ Read: Ultrasonic Testing Standards and Codes

Scope and setup

The D1.1 UT procedures cover groove welds and their heat-affected zones from 5/16 in. (8 mm) to 8 in. (200 mm) thick. Outside that range, or for other techniques, the code points to its alternative-techniques annex, which needs the Engineer's approval. The standard procedures are not used for tubular T-, Y- and K-connections, which have their own criteria.

A few setup rules matter for everything that follows:

• Angle-beam probes must produce a beam within ±2° of 70°, 60° or 45°.
• Calibration for distance and sensitivity uses the IIW-type block, or another block shown to give equivalent sensitivity. A corner reflector may not be used for calibration.
• The reject (clipping or suppression) control stays off. Once you've calibrated, the only adjustment you make during testing is gain.
• Laminations first. Before angle-beam testing, scan the base metal the sound will pass through with a straight-beam probe, with the first back reflection set at 50% to 75% of full screen height.

The indication rating

Everything in the acceptance tables keys off the indication rating, d:

d = a − b − c

• a, indication level: the gain, in dB, needed to bring the peak of the indication to the reference line.
• b, reference level: the gain, in dB, needed to bring the reference reflector (the hole in the calibration block) to the same reference line.
• c, attenuation factor: a correction for sound path. Subtract 1 in. (25 mm) from the sound path and multiply what's left by 2. So c = 2 × (sound path in inches − 1).

The formula above is for instruments that read gain in dB. On older instruments that read attenuation, the order flips to d = b − a − c.

Two things trip people up here. First, c uses sound path, not depth and not plate thickness. On an angle beam, the sound path is always longer than depth, so using depth understates c, overstates d, and makes the indication look less severe than it really is. Second, the sign. A higher (more positive) rating means a weaker reflector. A rating of +8 is less serious than −2.

Earlier editions rounded c to the nearest whole dB. The 2020 edition updated the attenuation factor method because modern instruments report fractional dB values. Check how your edition handles rounding before you build it into a procedure or a spreadsheet.

Scanning levels

You search for indications at a sensitivity above the reference level, then evaluate at the reference level. The increase depends on sound path, not thickness:

Cyclically loaded welds are scanned 6 dB more sensitively at every sound path. They're searched harder and, as the next tables show, judged harder too.

Table 8.2: statically loaded nontubular connections

Each table is entered with three values: the indication rating d, the weld thickness band and the probe angle. Weld thickness is the nominal thickness of the thinner of the two parts being joined. The two thinnest bands use the 70° probe only.

The values below are the long-standing published values of this table. Confirm them against your own copy of the 2025 edition before using them to accept or reject.

Notice how the boundaries move. In thin welds, even a fairly weak reflector (a positive rating) can be Class A. In thick welds, where c is large and the sound has traveled further, the same rating may be minor. That's the code compensating for distance and section size.

Table 8.3: cyclically loaded nontubular connections

The cyclically loaded table has the same layout, but every boundary is shifted so that a given rating falls into a more severe class. Confirm these values against your copy too.

There is a significant practical impact. When a weld is cyclically loaded, an indication that is a length-limited Class C on a statically loaded weld may be an outright Class A reject. The loading condition should therefore be on the report header rather than in the inspector's head.

Severity classes and the rules under the tables

The class tells you what to do with the indication:

The notes under the tables are just as binding as the numbers:

1. Spacing. Class B and C discontinuities must be separated by at least 2L, where L is the length of the longer one. If they're closer, but their combined length plus the gap is still within the allowable length for that class, they're treated as a single acceptable discontinuity.
2. Weld ends. Class B and C discontinuities must not begin closer than 2L to the ends of welds carrying primary tensile stress.
3. Root face of double-groove tension welds. Discontinuities found at scanning level in the root face area of complete joint penetration double-groove welds that are designated as tension welds are evaluated 4 dB more sensitively: subtract 4 dB from d before you enter the table.
4. Electroslag and electrogas welds. Discontinuities found at scanning level that are longer than 2 in. (50 mm) are suspected to be piping porosity and are evaluated further with radiography.

Length is measured with the code's discontinuity length procedure, by moving the probe until the indication drops 6 dB from its peak at each end.

The class limits only work if the length you measure is right, and the 6 dB drop method has known weak spots. Find out where it over- or under-sizes an indication and what to watch for in the field.

→ Read: 6 dB Drop Method for Ultrasonic Flaw Length Sizing: Drawbacks

Scanning patterns

The code's goal is simple: wherever practical, pass sound through the entire weld and heat-affected zone in two crossing directions. Butt welds are tested from both sides of the weld axis. Corner and T-joints are mainly tested from one side.

The testing angle and scanning pattern for each weld are taken from the code's testing-angle table, which assigns them by weld type and material thickness. The basic movements are:

• Longitudinal discontinuities: rotate the probe about 10° either side of the scan dadirection, move it far enough to cover the weld section being tested, and advance about half the transducer width on each pass. Advancing further than that leaves gaps that won't show on the report.
• Transverse discontinuities, weld ground flush: scan along the weld axis on top of the weld.
• Transverse discontinuities, reinforcement not ground flush: scan from the base metal at a scanning angle of 15° maximum to the weld axis.
• Electroslag and electrogas welds: an additional pattern with the probe rotated 45° to 60°.

Where laminations block a beam path, the code allows other ways to get full coverage, such as grinding the weld flush, testing from the other face, or using a different probe angle.

Worked examples

In each example the instrument reads gain in dB, so d = a − b − c. Sound paths are chosen to give whole-number values of c.

Example 1: same indication, two tables. A 2 in. weld is tested with a 60° probe. The reference level is b = 45 dB. An indication peaks at the reference line at a = 54 dB, with a sound path of 3.5 in.

- c = 2 × (3.5 − 1) = 5 dB

- d = 54 − 45 − 5 = +4

• Statically loaded (Table 8.2): the 60° column for over 1-1/2 to 2-1/2 in. puts +4 in Class C. It's accepted if it's no longer than 2 in. (50 mm).
• Cyclically loaded (Table 8.3): the same column puts +7 and lower in Class A. At +4, it's rejected regardless of length.

Example 2: a thin weld. A 5/8 in. weld, statically loaded, tested with a 70° probe. b = 48 dB, and the sound path to the indication is 2.0 in., so c = 2 dB.

• If a = 55 dB, d = 55 − 48 − 2 = +5. In the 5/16 to 3/4 in. band, +5 and lower is Class A: rejected.
• If a = 58 dB, d = +8. That's Class D: accepted, regardless of length.

A 3 dB difference in signal separates an automatic reject from an automatic accept. In thin welds the margins are that tight.

Example 3: a thick weld, Class B. A 3 in. weld, statically loaded, tested with a 70° probe. b = 40 dB, the sound path is 4.5 in., so c = 7 dB, and a = 44 dB.

• d = 44 − 40 − 7 = −3
• In the over 2-1/2 to 4 in. band, 70° column, −4 and −3 are Class B.
• The indication is 1/2 in. long, under the 3/4 in. Class B limit, so it's accepted, provided it's at least 2L (1 in.) from any other Class B or C discontinuity and, on a weld carrying primary tensile stress, at least 2L from the weld end.

Example 4: the root face rule. A 1-3/4 in. complete joint penetration double-groove weld, designated as a tension weld and statically loaded, is tested with a 60° probe. An indication found at scanning level in the root face area rates d = +5.

• Without the root face rule, +5 in the 60° column for over 1-1/2 to 2-1/2 in. is Class C.
• Because it's in the root face of a double-groove tension weld, subtract 4 dB: +5 − 4 = +1.
• At +1, it's Class A: rejected, regardless of length.

Calibration checks, reporting and personnel

Recalibration. The instrument must be recalibrated after any change of operator, at intervals of no more than 30 minutes, and whenever the electrical circuitry is disturbed, such as by a transducer, battery, cable or power change.

What goes on the report. The probe angle, sound path, depth, length, and location of each assessed indication, as well as the class and decision, are all recorded in the UT report along with a, b, c, and d. With the exception of welds that the contract identifies as fracture critical, where acceptable indications within 6 dB of the minimum rejectable rating must also be documented, only rejectable discontinuities must be recorded. The entire length of the rejected discontinuities is noted on the weld.

Who can test? UT personnel are qualified in accordance with ASNT SNT-TC-1A. The testing is carried out by Level II individuals or Level I personnel working under a Level II. A practical test based on the D1.1 UT requirements must also be part of the UT operator's qualification. A Certified Welding Inspector credential is not a replacement for UT certification, nor is a generic Level II certificate sufficient on its own.

Conclusion

You are not asked to size flaws in AWS D1.1. You are asked to rate them consistently. The tables become easy to use once you realize that every decision is based on a single number, the indication rating.

In reality, your calls' durability is determined by three factors: the table that corresponds to the loading situation specified in the contract documents, an attenuation factor based on sound path rather than depth, and an appropriately established reference level. Apply the length limitations and the notes under the table, such as the 2L spacing rule and the 4 dB root face adjustment, after rating each indication using d = a − b − c and reading the severity class from the thickness band and probe angle.

Make sure your procedure and report forms are linked to the edition you are working with, document enough information on each report so that another person can verify the math, and cross-reference the table values with your own copy of the code. If you do that, your D1.1 UT results will be reliable when challenged and consistent from weld to weld.