Case Study

24" Caisson Liner 95m Long, Piper Bravo, North Sea, UK

Tool - Caisson Lifting Tools

Location - North Sea - UK

Operating Environment - Offshore Topsides, Offshore Subsea

Pipeline Medium - Produced Water

Activity - Maintenance, Pipeline Repair, Engineered Solutions

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Some repairs can't be solved by swapping out the failing part. At Piper Bravo in the North Sea, an existing 98 metre, 24 inch caisson needed a liner to accommodate water discharge - but height and deck level restrictions at the worksite ruled out replacing the caisson altogether. Whatever went in had to work with what was already there.

Fitting a 95 Metre Liner Into an Existing Caisson Without Replacing It

The liner also had to seal the annulus space between itself and the caisson, resist internal corrosion, pass through a bore restriction at the waterline, and accommodate thermal expansion along its length.

Highlights

95 metre liner installed into an existing 24 inch caisson at Piper Bravo without replacing it.
Liner spools internally clad with Inconel 625 for internal corrosion resistance.
Reduced 14 inch OD slip-on flanges let the lower spools clear the caisson's bore restriction at the waterline.
Sliding sleeve arrangement in the upper section accommodated thermal expansion along the liner's length.
Job completed safely and ahead of schedule.

A 95 Metre Liner Built in Sections to Fit the Deck

STATS manufactured the liner from carbon steel spools, sized to work within the space restrictions on the installation deck, and assembled them into a finished liner 95 metres long. Each spool was internally clad with Inconel 625 to address the corrosion requirement, and the base section carried a hydraulically operated dual seal and lock arrangement to seal the annulus space.

Reduced Flanges to Clear the Bore Restriction, a Sliding Sleeve for Thermal Movement

To pass the caisson's bore restriction at the waterline, the lower liner spools were fitted with reduced 14 inch OD slip-on flanges. The upper section of the liner used a sliding sleeve arrangement to accommodate thermal expansion along its length, and eight Inconel control, actuation and injection lines were incorporated into the assembly.

Assembled and Checked In-House Before Installation

The whole liner was assembled in-house to check its straightness and flexibility before being sent offshore for installation at Piper Bravo.

Installed Safely and Ahead of Schedule

The liner was installed successfully, with the job completed safely and ahead of schedule.

The project shows how a fully engineered liner solution can extend the working life of ageing platform infrastructure, without the cost, disruption or logistical challenge of a full caisson replacement.