Ultrasonic testing of welds

For example:

• distance to the fault – through the propagation time of the ultrasonic wave in the tested material;
• relative size of the defect – through the amplitude of the reflected pulse.

There are five main methods of ultrasonic testing, which are used in the industry, and which differ only in the way of registration and evaluation of the data:

• shadow method (control of reducing the amplitude of the ultrasonic vibration of transmitted and reflected pulses);
• mirror-shadow method (detect defects in welds through the attenuation coefficient of the reflected vibrations);
• echo-mirror method or “tandem” (which means to use two machines which working together and from different directions detect the defects);
• delta method (control of ultrasonic energy, which is re-emitted from the defect);
• echo method (registration of the reflected signal from the defect).

The procedure of the inspection:

• Remove all the paint and rust from welding seams and of the area 50 – 70 mm on both sides.
• For more correct results of UFD, it is required to provide a good passing of ultrasonic vibrations. Therefore, the metal surface around the weld seam and also the weld seam itself should be treated with “couplant” or any other liquid like of that kind (transformer, turbine, machine oil or grease, glycerin, etc.).
• The device is to be pre-configured for the specific tasks:

– for thickness up to 20 mm – standard configuration (notches);

– for thickness over than 20 mm – configure DGS diagrams;

– for quality testing of the welds – configure AVG diagrams.

• The transducer is moved zigzag along the seam and at the same time trying to turn around its axis at 10-15 degrees.
• At occurrence of stable flaw signal move the transducer again and again. Find the position, where the flaw signal will show it’s maximum.
• Make sure that the welding steam itself does not cause such reflection of the oscillations. It is often the case during UFD.
• If not, then the position of the defect should be recorded.
• As usual, weld seam inspection is carried out in one or two approaches.
• T-joints (90 degrees weld seams) are checked by echo method.

Via ultrasonic inspection following defects can be detected:

• cracks in the weld zone;
• pores;
• lack of fusion in welded joints;
• stratification of weld metal;
• discontinuities and incomplete fusion of weld joints;
• slack metal in the lower zone of the weld;
• areas which are affected by corrosion;
• areas with the mismatch of chemical composition;
• areas with distortion geometric size.

All such tasks, can be solved with our ultrasonic flaw detectors – NOVOTEST UD-1 and NOVOTEST UD2301-mini.