Objectives/Scope

During decommissioning of an offshore platform jacket the removal of the structure will entail cutting and recovery of the piles driven into the seabed. Uncertainty on the effectiveness of the cutting process can lead to non-productive time and increase in operating cost. The scope of this paper is to present work undertaken to identify a suitable technology that provides near real time cut performance monitoring of single wall piles and conductors.

Methods, Procedures, Process

Abrasive Water Jet cutting is commonly used during pile cutting and remote monitoring of parameters gives valuable information of the cutting process. However, the decision to pull the pile is often based on the know-how or skill of the cutting operators to interpret what the gauges are showing them. Uncertainty leads to increased risk and project costs and can result in disputes between heavy lift vessel contractors and cutting service providers. Several techniques are claimed to be effective in verifying cutting performance but there are none that provide near real-time mapping of cut performance at the cut location.

Results, Observations, Conclusions

Two optical technologies namely laser scanning and photogrammetry were identified as having potential and extensively tested to detect cuts in representative mock-up conditions on varying pile wall thicknesses from 30mm up to 90mm. This paper will present the results of the testing and how each technique performed when asked to identify partial circumferential cuts and incomplete through-wall cuts. The results are compared with physical measurements and evaluated to meet the requirements set out by the project objectives. Field application of each technique was assessed and how the optical method can be integrated into existing equipment is described. Seawater turbidity in the pile which would render optical techniques ineffective has been considered and novel techniques are proposed to overcome this. Limitations and application of each technique in the real world are presented and the paper provides description on how the technique selected may be implemented into existing pile cutting tools.

Novel/Additive Information

This paper will be of benefit to those planning decommissioning of platform jackets and wind turbine piles due to the provision of new techniques resulting in reduction of project uncertainty and cost when employing heavy lift vessels.

You can access this article if you purchase or spend a download.