Subsea NDT system passes test offshore Australia

Applus RTD UK will introduce what it claims is the world’s first subsea non-destructive testing (NDT) inspection system this week at Offshore Europe.

Offshore staff

ABERDEEN, UK -- Applus RTD UK will introduce what it claims is the world’s first subsea non-destructive testing (NDT) inspection system this week at Offshore Europe.

The customizable system combines ultrasonic phased array and time of flight diffraction (TOFD) techniques with alternating current field measurement (ACFM). Applus RTD tested the equipment in an application in 130 m (426 ft) of water offshore Australia, with the project being completed by an ROV using custom-designed tools.

The test focused on detailed site preparation, coating removal, inspection, and coating reinstatement at a numerous locations requiring inspection for inter-granular stress corrosion cracking (IGSCC) of 12-in. (30.5-cm) 13 Chrome (13Cr) butt-welded joints.

“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, advanced NDT manager at Applus RTD.

Prior to the inspection, the company performed various 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 via a combination of Phased Array and TOFD technologies.

Applus RTD’s 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. As the scope of work increased, an ACFM probe was specially adapted to become part of the tool array.

The tooling can be deployed by virtually any make of work-class ROV, with the concept using the vessel to position the tooling 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 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. 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, but the fact that all involved were able to maintain equipment up-time was a considerable achievement.”

9/8/2009

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