Collaborative Research on Grouted Pile-Leg Sleeve Connections Enabled Life Extension of Aged Platforms

Abstract

Background For an older fleet of the bottom founded steel jacket type platforms which has been operating in Abu Dhabi offshore oil & gas fields, each of the platforms is secured by pile-leg grouted connections with shear keys provided on the outside of the pile only. · As the leg diameter was about 800mm, this precluded the provision of shear keys· on the inside of the leg. This connection design pre-dated the API or ISO recommended practice, which specifies the provision of shear keys on the pile and leg to offer a more direct load transfer mechanism. Majority of existing fixed offshore platforms in offshore Abu Dhabi have non-conventional grouted connection between pile and jacket where grout is the only medium for load transfer between the two components. Due to their confinement these connections are not inspectable. Moreover, grout parameters associated with these structures do not comply with codal provisions. Hence the applicability of codal formulations to fixed jacket structures in offshore Abu Dhabi is a major uncertainty. Many Fields in offshore Abu Dhabi have significant life extension necessitating many structures in operation beyond their original design life. Quantification of grout performance considering ageing effect plays vital role in life extension of these structures and is currently beyond industry knowledge. In addition to this, continuous requirements of significant load additions make this problem more intense. This has raised a major concern for ensuring integrity of these structures while allowing life extension of these aged structures. To address the above, ADNOC Offshore entered into a collaborative research program with one of the leading offshore Institutions at Centre for Offshore Research & Engineering, National University of Singapore (NUS) aimed at conducting experimental investigations supported by analytical simulations to develop ADNOC Offshore specific grout strength design equations which will be helpful in assessment of strength of aged grouted connections.