Repair solution reinstates caissons to full operation, saving almost 50% and avoiding full replacement

Project Summary

The majority of caissons are now exceeding their expected design life. As a result, they can develop perforations, cracks and other anomalies, increasing the risk of failure. This impacts production performance and can be a in a major accident hazard. Oil and gas operators with aging assets are working tirelessly from both an integrity and HSE perspective, to ensure caissons are in a safe and operable condition.

Stork developed a swaging solution which reinstates structural integrity, eliminates the dropped-object potential and returns the caisson back to full service without the need to replace the entire caisson.

The Stork swage solution uses prefabricated liners which are fixed to the caisson by applying annular volume via the swage tool, which in turn causes the liner to plastically deform and make contact with the caisson. A secondary swaging operation is then performed below the corroded area, which reduces the load on the damaged area and transfers it to the newly installed string of liners, reducing the risk of failure for the existing caisson.

Supported by NZTC, a field trial was undertaken on one of CNR’s assets. Repairs were undertaken on an upper liner, middle liner and lower liner in a live environment.

Industry value:
A typical caisson repair solution would be in the region of £240,000. Using this new approach would realise a cost saving of £110,000, against full replacement, alongside broader benefits such ease of installation and deployment.

Key results:
A swage repair was completed using the 26″ tool. The scope was successfully completed and on time. The results were captured and verified during the trial with camera visual inspections verifying that the liner assembly and the swage connection were at the correct elevation and there was a clear swage geometry.

Lessons learned:
During the trial procedural improvements identified during the scope which could further drive efficiency of the swaging operations offshore. The team implemented a more accurate means of measuring the internal diameter of the liners which provide greater control over the dimensional tolerances of the liners.

Next steps for this technology is to fully commercialise the tool and develop a total of four swage tools, which would provide the full range for typical caisson sizes ranging from 18” through to 40”. Stork is working with the supply chain to develop a 38” swage tool with the capabilities of covering the range 36” through to 40”.