Caisson Securing & Recovery, North Sea, UK

STATS Group has developed a proven approach to caisson securing and recovery, deploying proprietary Internal Lifting Tools (ILT) and External Lifting Tools (ELT) to control, stabilise, and remove damaged or redundant caissons from North Sea platforms - all without forcing a production shutdown.

STATS' Internal Lifting Tools (ILT) and External Lifting Tools (ELT) are purpose-engineered for caisson recovery on offshore platforms where access is restricted, lead times are tight, and the stakes are high.

The ELT is designed for situations where internal access is compromised - by pump strings, installed liners, or prior repairs. Its split-section design allows each half to be installed independently, even in areas where overhead height or lateral clearance is severely restricted. Once positioned, eight hydraulic gripping locks clamp against the external caisson wall. Two independently actuated hydraulic circuits provide a critical contingency: if one circuit is compromised, the remaining four locks hold their position and the tool continues to carry its full 55-tonne design load. The taper-lock mechanism is fail-safe by design - once pre-tension is applied, the tool holds without any reliance on continued hydraulic pressure.

The ILT uses a twin-module design, with each module independently controlled, to bridge damaged or weakened sections of caisson and prevent separation during the recovery operation. When unset, the ILT offers generous bore clearance, allowing it to pass through swaged liners and other bore restrictions to reach the required deployment depth. Where there is a risk of the caisson separating during extraction, pigging discs and hydraulically activated centralising panels can be added to keep it aligned and guide it safely through support structures.

The modular design of the ILT also allows the distance between lock modules to be customised simply by adding linking rods - meaning the tool can be configured to the exact specification of each caisson without bespoke fabrication.

STATS' ILT and ELT tools have been deployed across multiple North Sea caisson recovery programmes, each presenting its own access constraints, structural complexities, and operational timescales.

Project 1: Twin 42" Caissons, 90 Metres Each - Bridging Bore Restrictions

Both 42" caissons were badly damaged and had previously been repaired with swaged liners, which presented a bore restriction that ruled out straightforward internal access. STATS deployed an ILT with sufficient clearance to pass through the liner restrictions and bridge the most vulnerable sections of each caisson, maintaining structural integrity throughout the recovery. Two ELTs were used simultaneously to lift each caisson in stages, cutting it into manageable sections until the full caisson had been recovered to the platform. The same method was then applied to the second caisson.

Project 2: 24" Fire Water Pump Caisson - Delivered Against a Tight Deadline

An engineering contractor approached STATS to recover and replace a 20-metre fire water pump caisson before the onset of winter. The operator was concerned that worsening North Sea conditions would cause the caisson to become fully detached from the platform. Despite a short lead time, STATS engineered an ILT to the client's exact specification, completed a full factory acceptance test, and mobilised offshore. The ILT was installed to straddle the damaged section, securing the caisson in position and preventing detachment throughout the recovery operation.

Project 3: 41" Caisson After 20+ Years in Service - Combined ILT and ELT Recovery

Following extensive internal and external repairs spanning more than two decades, a 41" caisson was finally scheduled for removal. The risk of the caisson severing and falling during recovery demanded a combined approach: an ILT bridged the most weakened sections, while ELTs secured and controlled the caisson throughout extraction. STATS also supplied clamshell cutting machines to section the caisson into manageable lengths during removal. Once the old caisson was recovered, the ELTs were redeployed to assist with installation of the replacement - mechanically attaching and lowering each new section safely into position.

Before any ILT or ELT is mobilised offshore, it undergoes a client or third-party witnessed Factory Acceptance Test (FAT). The FAT confirms the full functionality, serviceability, structural integrity, and safe working load of the tool under controlled conditions - removing uncertainty before the crew ever reaches the platform.

All STATS mechanical lifting tools are designed in accordance with the DNV Standard for Certification of Lifting Appliances, the internationally recognised benchmark for offshore lifting equipment. Operators can mobilise with confidence that every tool has been independently verified to perform at its rated capacity.