Ultrasonic Testing of Pipe Weld Joints

www.ndt-ed.org for self study

or mail me hannes.barnard@andtc.com

The UT process is very good for use on any full penetrant welds. For pipe the transducers shoes should be machined to the approximate contour of the pipe. If the pipe is 2" or greater in diameter, mini transducers may be utilized without machining.

This is not a good process for socket welds or fillet welds except for referee use.

The "pro" is that extremely minute defects may be located within tens of thousanths of an inch. Radiography will reveal a flaw but not the depth of the flaw.

The "con" is that there is no film to review and the operator must be highly skilled. Also some codes prefer radiography because there is not a picture type of the test. Some instruments have "print-out" capabilities, but only a few inspectors are familiar with the determination of flaw detection.

You should clarify that most pulse-echo instrument and transducer combinations are reliable to about .010 inches. Shear wave shoes should always be ground to outside diameter of inspected pipe for consistant contact and angle. The smaller the transducer, and / or the higher the frequency the more beam spread and surface attenuation losses.

There was an article published in Materials Evaluation by Noel Proctor back in the 80's that extensively covered the topic.

Thanks Prof and Jerry. I hope I can trace Jerry's reference article.

I understand that problems do occur when there is an angle bend or a return bend on one side of the weld. Is this true?

Are there any particular types of defects that UT would be unable to detect? Are there references of projects where UT of pipe welds have been extensively and successfully used?

Actually I am thinking to propose one of our clients to replace process piping radiography with UT.

There are very few flaws that will be overlooked with UT. As far as beam spread or "bending", if the technician is really competent with the instrument it will not ocurr with any frequency. I have an old Kraut-Kramer unit that will shoot up to 120" with pretty fair accuracy. Most of the companies which do API 650 work use UT for the tank and the piping which may be process piping or pressure piping. The area around Houston TX is very familiar with this process.

Beam spread is a function of transducer frequency and diameter.

Any "bending" would be confined to surface waves following slight changes in contour.

UT is far more sensitive than radiography given that you have at least 2, and usually 3 angles to examine from, and a plethora of frequencies to choose from. Limit of detection is 1/2 wavelength in therory, 1 wavelength in typical field conditions.

Hi bm, if you are looking to replace RT with UT. Take view on ASME V Appendix N- Time Of Flight Difraction TOFD. Very good experience with this NDT.