A structural inspection was carried out on all five seawater lift caissons and the upper sections of three of them were recommended for removal and replacement.
Scope & Deliverables
The engineering scope was based on a SOR supplied by the client. All caissons had suffered galvanic corrosion at the pump elevation, a common problem in caissons throughout the North Sea. As a result, caissons required to be replaced above the subsea DWS locations (LAT -15m)
Deliverables consisted of 2D/3D CAD drawings and construction workpacks for all three caissons. An animation was produced to assist during the HAZID forum and the construction phase.
Caissons were cut above the subsea DWS location using abrasive water jet cutting technology.
A stab in detail using hard wearing engineering fabric was adopted. This reduced installation risk.
A new bolted dead weight support arrangement for the replacement upper section was installed at cellar deck level. Caissons were installed in 3m sections using mechanical connectors.
The contract was delivered on a lump sum basis. All three caisson required destruct and construct workpacks which were successfully delivered in 16 weeks