Sonomatic, a market leader in the provision of advanced automated ultrasonic inspection services, has developed a brand-new tool for the internal inspection of caissons. The integrity of caissons is critical to safe and efficient operation of offshore structures. As offshore facilities age there is a growing need for inspection of caissons, with knowledge of their condition providing a basis for justification of ongoing operation or highlighting the need for repairs or replacements before in-service failures occur. The development was carried out internally by Sonomatic’s Research and Development group and brings together their considerable skills and experience in Mechanical Engineering, Automation, Electronics, Software and Signal Processing.
In the first field application of the new Internal Caisson Tool (ICT), Sonomatic were recently tasked to perform critical inspections on three caissons for a North Sea operator. The work was completed in collaboration with Cape Specialist Services in a single campaign with a combined offshore team. Cape Specialist Services deployed their environmentally safe caisson cleaning system capable of operating below sea level to remove all scale and marine growth from the caisson interior back to deck level for disposal. This prevents debris from dropping to the seabed or being sucked into the lift pumps on adjacent caissons.
In response to Operators wishing to reduce POB where possible, Sonomatic and Cape Specialist Services have assembled a team where cross training of the disciplines has been undertaken. This multi skilling of personnel has led to a three or four member team to conduct HP water jet cleaning, digital image surveying and NDT inspection from a single mobilisation.
The ICT performed reliably throughout, allowing Sonomatic to deliver industry leading inspection results.
Recognising the needs of industry, the focus of Sonomatic’s inspection service is on providing accurate and consistent data, this allowing client’s to make effective integrity decisions that contribute to operational safety and efficiency. The ICT was developed with this objective in mind and it provides rapid and reliable deployment of Sonomatic’s industry leading ultrasonic inspection techniques.
The inspection was performed from the internal surface of the caissons, using 0° Corrosion Mapping. Data scan files were collected at 500 mm axial intervals, with the data collected in a helical scan pattern. All of the ultrasonic data was processed in making several million thickness measurements for each caisson. This data was used to create corrosion maps that provide a colourgraphic representation of areas of wall loss.
Caissons often have internal corrosion, this means the inspection is from the corroded side which represents a challenge to maintaining accuracy of corrosion mapping. Sonomatic has optimised its approach to the inspection set up and has developed a range of new signal processing algorithms specifically to enhance the accuracy and reliability of measurements made from the corroded surfaces. Sonomatic’s approach means they can provide accurate measurements, to support fitness for service and remaining life assessments, in situations where the measurements made by competing systems have considerable uncertainty. Sonomatic’s results provide the basis for sound integrity decisions, proving significant cost benefits to clients.
“Obtaining reliable inspection data from the inside of caissons has long been recognised as a challenge in the industry”, says Sonomatic’s Topside Project Manager, Scott Bulloch. “This was one of the main drivers for development of the internal caisson inspection tool. In addition to massively improved data quality, Sonomatic is also advancing the methods of data presentation to ensure clients get the most from the data. This includes 3D presentation of corrosion maps, statistical summaries and comprehensive datasets for efficient creation of finite element models used in fitness for service assessments.
Feedback on the results obtained has been very positive, with comments from clients indicating that they see Sonomatic’s measurement capability as offering a step change in the value of internal inspections.”