API · ASME · ISO · NIST · UKAS
Ultrasonic testing for detecting internal flaws, measuring thickness, and evaluating weld integrity in pipelines, tanks, and industrial structures.
Ultrasonic Testing (UT) uses pulses of high-frequency sound — typically 0.5–20 MHz — launched into the material by a probe. The sound reflects from the back wall and from any internal discontinuity; measuring the time-of-flight and amplitude of those echoes locates, sizes and characterises the flaw and measures remaining thickness.
As a volumetric method UT sees deep into the part, so we use it for weld flaw detection and sizing, corrosion and erosion thickness surveys, lamination checks and corrosion mapping across a wide range of components.
A piezoelectric transducer converts an electrical pulse into a short burst of ultrasound that travels into the material through a couplant. Whenever the beam meets an interface — the back wall or a discontinuity — part of the energy reflects back to the probe as an echo.
The instrument plots echo amplitude against time (an A-scan). The time to the echo, calibrated to the material's sound velocity, gives depth or thickness; the echo height and a distance-amplitude-correction (DAC or DGS) curve give flaw size. Angle-beam probes are used for welds so the beam strikes vertical fusion faces.
UT detects and sizes planar and volumetric internal flaws — cracks, lack of fusion, lack of penetration, slag, porosity, laminations and inclusions — as well as measuring wall thickness for corrosion and erosion assessment. It is particularly strong on planar, crack-like defects that radiography can miss.
Thickness gauging monitors corrosion-under-insulation, tank shells, pipe walls and vessel plate remaining life, while corrosion mapping builds a thickness grid over an area to reveal localised wall loss.
We use digital flaw detectors and thickness gauges with straight-beam and angle-beam single or twin-crystal probes, a couplant, and reference blocks (IIW V1/V2, step wedges and DAC/DGS blocks) for calibration. Frequency and probe angle are chosen for the material, thickness and expected defect.
Instruments are calibrated for range and sensitivity on certified reference blocks before and during the work, so echo positions convert accurately to depth and echo heights to flaw size.
For weld UT, each recordable indication is reported with its location, depth, length and amplitude relative to the reference level, then judged against the code's acceptance criteria (for example ASME BPVC Section V Article 4 with Section VIII, ASME B31.3 or API 1104). Thickness surveys report measured minima against the required minimum wall.
Reports include the technique sheet, calibration record and results. Personnel are certified to ASNT SNT-TC-1A or ISO 9712 at the level appropriate to interpret and report.
UT is more sensitive to planar, crack-like flaws and lack of fusion, gives instant results, needs access to only one side and involves no radiation or exclusion zone. Radiography images volumetric flaws such as porosity and slag well and leaves a permanent picture. The methods are complementary; the choice depends on the flaw type of concern, material thickness and code requirements.
Ultrasound is almost completely reflected by even a thin film of air, so a liquid or gel couplant (water, glycerine or a proprietary gel) is applied between probe and surface to expel the air and let the sound energy cross into the part. Without it, virtually no signal enters the material.
With the right high-frequency probe and a calibrated gauge, UT routinely measures thickness down to about 1 mm, and less on thin-wall tubing with dual-element or delay-line probes. Accuracy depends on surface condition, correct sound-velocity calibration for the material and probe selection.
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