Global non-destructive testing leader Applus RTD UK Ltd is unveiling a world-first subsea inspection system at this week's largest European oil and gas exhibition, Offshore Europe 09.
Designed to ensure operational suitability and prolong the life of vital assets, specialists at Applus RTD have developed the first fully customisable NDT phased array solution by combining and integrating three technologies synonymous with subsea oil and gas exploration and production.
Charlie Lawther, advanced NDT manager at Applus RTD, says the amalgamation of ultrasonic phased array and time of flight diffraction (TOFD) techniques with alternating current field measurement (ACFM) is an industry first.
Pooling vast knowledge of subsea exploration techniques, Applus RTD tested the system in 130 metres of water offshore Australia and the entire project was completed by ROV using custom-designed tools.
The test focussed on detailed site preparation, coating removal, inspection and coating reinstatement take place at a number of locations where inspection for intergranular stress corrosion cracking (IGSCC) of 12-inch 13 Chrome (13Cr) butt-welded joints was required.
"First and foremost, our focus was on ensuring that the test was safe and incident-free - particularly as it called for the use of new equipment and procedures, people and a considerable volume of surface deployment systems and deck operations," says Charlie Lawther.
"The test was passed with flying colours - the fact we recorded no incidents or accidents is testament to our commitment to quality, health, safety and the environment throughout all of Applus RTD's research and development operations.
"Close collaboration was at the core of the test, and the commitment shown by all involved could clearly be seen by the fact the inspection was completed in half the time planned - resulting in a significant cost-saving to the client."
Applus RTD's international team, including specialists from its Aberdeen base, handled all tool works, including design and manufacture, as well as trial operations and final inspection of the butt-welded joints under scrutiny.
Prior to the inspection itself, Applus RTD carried out numerous trials to determine the best way to detect IGSCC in 13Cr material. The highest detection probability for the critical internal weld root area was found to be with a combination of Phased Array and TOFD technologies.
"Due to the variety of disciplines involved, my colleague Andy Garswood was tasked with designing and manufacturing a remote inspection tool capable of deploying the two technologies via ROV.
"Later in the project a request was made to include ACFM, to assist in detection of external surface discontinuities and, as scope of work increased, an ACFM probe was specially adapted to become part of the tool array."
The tool has been designed for deployment by virtually any make of work-class ROV, with the concept using the vessel to position the tool as closely as possible to the weld under inspection.
"Once in position, the ROV moves away and all further positioning and movement of the probe is carried out remotely from the support vessel - making the technique hugely flexible and applicable in virtually any situation if conditions permit," says Charlie Lawther.
"The tooling worked perfectly, first time and the employment of ROV-deployed tooling enabled twice as many welds to be inspected for the same cost compared with a diver-led inspection campaign.
"As far as performance was concerned, the test delivered across every key area - schedule, cost and inspection integrity. Persons on board constraints did limit the ability to carry out resource capacity offshore, the fact that all involved were able to maintain equipment up-time was a considerable achievement."