Objective
The ICON project (CEC Project Number OG/0098/90/FR/UK/IT) has been set up to evaluate the performance of a range of NDT tool equipment when used for subsea inspection. The original project proposal included an evaluation of the influence of environment on NDT performance by comparing the results from trials conducted in laboratory tanks, near shore test facilities and culminating in trials offshore.
The ICON project was funded under the THERMIE initiative but with the sea trials excluded. This proposal is for the conduct of a series of trials, complementary to those already being carried out onshore within the ICON project schedule, in order to enable the ICON project results on equipment performance in tanks to be related directly to performance observed offshore. It will provide the Offshore Industry with complete information on the effect of representative subsea environment and providing the maximum benefit from the results of the ICON trials.
Manual Sea Trials have taken place in the Northern North Sea in 100 m waterdepth, with divers in saturation operating from semi-submersible "STADIVE".
Six pieces of equipment suitable for cracks detection and/or sizing were tested :
- TSC 11 Crack Microgauge (ACFM mode)
- Lizard Eddy Current system
- MPI Coils
- MPI Yoke
- British Gas ACPD
- TSC 11 (ACPD mode)
A seventh item (ACFM Array) was tested nearshore from an IFREMER R/V.
The specimens used for the tests were 3 nodes comprising 6 braces each.
All techniques had results consistent with tank trials, with a 100% detection for cracks greater than 31 mm long and 2 mm deep.
CAT Sea Trials have taken place in several phases :
- TV trackmeter was tested on FROY FIELD platform from a ROV operated by SONSUB.
- TSCII-ACFM, Lizard, MPI single leg, ACFM Array and G-Sean were tested in Stavanger and Haugesund fjords, from the ROV "REMO" operated by Stolt Comex Seaway.
Three successive periods were needed to complete the trial, between 14th September 1994 and 12th April 1995. The same 3 specimen modes were used.
Due to the stormy conditions and the geometry of the nodes, 100% converage was not achieved, and results obtained do not allow for a full statistical analysis.
Nevertheless they are fully coherent with CAT-trials results in the laboratory and tanks. More developments are needed to improve arm and probe holder motion control in order to reach results similar to manual deployments for Eddy current systems.
Other systems have been demonstrated to be fully operationnal at their nominal performance when deployed according to approval procedures.
This SEA TRIALS proposal is for a project to overlap with ICON, whereby equipment that has been satisfactorily evaluated in the laboratory would be subjected to trials both near shore and offshore to establish the degree, if any, of degradation in performance as the working environment is moved from a controlled tank to the uncontrolled environment of an offshore installation.
The principles adopted in ICON, of blind tests using a series of samples containing representative known defects will apply to the sea trials and it is proposed that both manual and CAT trials are conducted at sea. Two types of trial are foreseen.
These are:
* Manual diving trials.
* Offshore CAT trials.
The innovative part will be to provide quantitative information on performance, operational procedures and test procedures under Sea Trials conditions. A range of test samples has been manufactured. These have been used for NDT technique in air and underwater using divers and ROV/manipulators. The results will have been interpreted and incorporated into a database system, so that the capability of every NDT tool can be presented within well defined limits for any user specified purposes. The Sea Trials data will confirm and extend the database for real service conditions.
Another innovative part is to evaluate the capabilities of the Cybernetix Computer Aided Telemanipulator (CAT) connected to a Remote Operated Vehicle (ROV) that will substitute human diving operations. This kind of programme has not previously been performed. Blind tests procedures, which have been developed and internationally agreed during ICON, offer a guarantee of independent assessment and, therefore, of database value.
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DEM - Demonstration contractsCoordinator
92138 Issy les Moulineaux
France