NDT Services from TWI

Automated Ultrasonic Testing (AUT) of Pipeline Girth Welds

TWI's PipeWIZARD crawler mounted on a pipe for laboratory trials
TWI's PipeWIZARD crawler mounted on a pipe for laboratory trials

Description

In AUT of pipeline girth welds a series of probes or a phased array probe is mounted on a band strapped around the pipe adjacent to the weld and is driven around the pipe's circumference. As the probe(s) travel around the pipe, ultrasonic data are collected from the weld and the software enables flaw sizes and positions to be displayed. Very fast scanning speeds (~100mm/s) are called for, since, to keep pace with construction, it is necessary to complete a weld inspection every 2-4 minutes. AUT is replacing radiography for pipeline girth weld inspections worldwide. The advantages of conventional AUT over radiography are:

  • No radiation hazard.
  • Better process control of welding, giving lower reject rates.
  • Larger defect acceptance using Engineering Critical Assessment (ECA), also giving lower reject rates.
  • Faster inspections.
  • Rapid and reliable data interpretation from special output display.
  • Overall, onshore mechanized ultrasonics offer a better inspection solution with lower reject rates than radiography.
PipeWIZARD in the field (courtesy of Olympus NDT) PipeWIZARD in the field (courtesy of Olympus NDT)

TWI's AUT system is the PipeWIZARD® supplied by Olympus NDT. This has the further advantage over conventional AUT systems that it utilises phased arrays. Phased arrays offer major advantages over conventional AUT.

PipeWIZARD computer screen
PipeWIZARD computer screen
  • Smaller probe pans, reducing the length of pipe coating that has to be cut back.
  • One PipeWIZARD can scan pipes ranging in diameter from 2 in. to 56 in.
  • The standard PipeWIZARD can scan pipe walls from 6 mm to 50 mm.
  • Increased number of zones for better detection and vertical sizing.
  • Scan time is reduced by several seconds due to the narrower probe pan.
  • Any weld profile, pipe diameter, or wall thickness can be accommodated by recalling the appropriate setup files.
  • Arrays can be programmed to check the coupling automatically using the back wall.

In the PipeWIZARD computer screen shown, the vertical plots are the signals associated with specific zones of the weld (cap, body and root) on the upstream and downstream sides of the weld. Each zone is approximately 2mm deep and is scanned by selecting an appropriate focal law that controls the phasing of the array. The screen display essentially 'opens out' the weld from the root. Flaw lengths are estimated from circumferential position markers and depths from the number of zones affected. The red zones are above threshold. The central grey area is a TOFD plot.

For more information on the services offered, contact:

NDT Technology Group

TWI Ltd, Granta Park, Great Abington,
Cambridge, CB21 6AL, UK
Tel: +44 (0)1223 899000 Fax: +44 (0)1223 892588

TWI NDT Validation Centre (Wales), ECM2,
Hoel Cefn Gwrgan, Margam, Port Talbot, SA13 2EZ, UK
Tel: +44 (0)1639 873100 Fax: +44 (0)1639 864679

E-mail: ndt@twi.co.uk