AWS D1.1 “Structural Welding Code – Steel” is the American reference standard for welding carbon and low-alloy steel structures. Published by the American Welding Society, it is adopted worldwide in civil engineering, offshore construction, bridges, tanks and heavy industrial steelwork. The part covering ultrasonic weld inspection sets specific instrumentation requirements, which the Dakota NDT FX70-DL, FX71-DL and FX81-DL flaw detectors are declared to meet.
Structure of AWS D1.1 and the place of UT inspection
AWS D1.1 is organised into clauses covering the entire life cycle of a structural weld: procedure qualification (WPS), welder qualification, fabrication, inspection, in-service verification. Clause 6 “Inspection” defines the permitted non-destructive testing methods:
- VT (Visual Testing) — mandatory visual inspection
- PT (Penetrant Testing) — liquid penetrant testing
- MT (Magnetic Testing) — magnetic particle testing
- UT (Ultrasonic Testing) — ultrasonic testing
- RT (Radiographic Testing) — radiographic testing
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UT is particularly important for butt welds on thicknesses greater than 8 mm and for welds in joints that do not lend themselves to radiography (T-joints, cruciform joints, corner joints). AWS D1.1 devotes Clause 6 Part F to UT, with specific procedures.
UT instrumentation requirements in AWS D1.1
The technical requirements that UT inspection to AWS D1.1 places on the instrument and the probes are:
- Frequency range typically 2 – 5 MHz (although AWS D1.1 allows an extended range in specific cases)
- Angle probes: 45°, 60°, 70° (shear wave transducers)
- Ability to perform calibration on the IIW block or other reference blocks defined by AWS
- Gain system with steps of 1 dB or less
- Verifiable vertical and horizontal linearity
- Adequate signal-to-noise ratio
- Clear, readable A-Scan display
- Ability to set a reference level and evaluate echoes in relative dB
The AWS toolkit built into the Dakota FX
The Dakota FX70-DL, FX71-DL and FX81-DL flaw detectors natively include — according to the official data sheet — an AWS toolkit for automatic flaw sizing using the AWS D1.1 method. This means the operator does not have to carry out the indication rating calculations (indication level d) by hand:
- The reference level b is set on the echo from a reference reflector
- The echo of the actual indication is measured (indication level a)
- The instrument automatically calculates the attenuation factor (c) based on the sound path
- The indication rating d = a − b − c is calculated automatically
- The value d can be compared directly with the acceptance criteria of Table 6.2 of AWS D1.1
Other built-in toolkits
The Dakota FX include other toolkits that are also useful for standards other than AWS D1.1:
- DAC (Distance Amplitude Correction): amplitude correction curve as a function of distance, useful for inspections to EN ISO 17640 and ASME V
- TCG (Time Corrected Gain): automatic software compensation for attenuation
- DGS (Distance Gain Size) / AVG: European flaw sizing method based on theoretical curves
- Z-Cross, Flank, Peak detection: three selectable methods for the measurement point on the echo
Qualification of UT personnel to AWS D1.1
AWS D1.1 requires the UT operator to be qualified under a recognised scheme, typically:
- AWS CWI (Certified Welding Inspector) with UT endorsement
- ASNT Level II UT (SNT-TC-1A or CP-189)
- EN ISO 9712 Level 2 UT, commonly accepted in Europe and recognised in many international specifications
Documentation and reporting
AWS D1.1 requires a formal UT report to be produced for every inspection, including the instrument parameters, the reference calibration, the position of the indications, the flaw sizes and their classification against the acceptance criteria. The Dakota FX, with a data logger of up to 4 GB and DakMaster™ integration, make it possible to store the A-Scan of each indication, simplifying the preparation of professional reports compliant with AWS requirements.
For advice on configuring a Dakota flaw detector for AWS D1.1 inspections and for hands-on training services, contact our technical department.