The "Innovative solution" award during the "International Business Excellence Awards" ceremony was received by Drydocks World and Maritime World, which is the leading provider of maritime and offshore services to the shipping, oil, gas and energy sectors. The prize was awarded for the building of the subsea oil storage tank Solan.

Drydocks World started the project of constructing the subsea oil storage tank in 2013 and finished the works in 2014. The underwater tank has the capacity to accommodate over 400,000 barrels of oil below the sea surface.

The main reason such kind of storage tank to be built is the reduction of the extended pipelines under the sea, which transfer oil. The huge tank does not use a pipeline for oil export, instead it collects and stores the oil extracted from the fields, which afterwards is directly transferred from the tank to the oil tanker.

Drydocks World constructed the largest and deepest subsea oil storage tank in a collaboration with the Premier Oil. The structure, which has weight nearly 10,150 tonnes and measures 45m x 45m x 25m, is built in eight mega blocks, linked with pile sleeves and mud mats.

For the successful Solan tank installation in a 130m-depth under the sea, first it was necessary the tank to be floated over by a heavy lift transportation vessel, which transferred the construction at the location, doing a challenging towing operation at sea.

The tank is currently situated below the sea waters of the Scottish Shetland Islands.

Drydocks World wins

Image: Lerwick Harbour

Among the challenges that the company faced during the facility’s installation works occurred are: the lifting of a 7,170-tonne structure; skidding the facility from the General Assembly Area to the dry docking area for its loading out and finally the 895-tonne block installation on the tank completed by the shipyard’s floating crane.

The underwater oil storage facility was built in a way to cover special standard requirements. All weld joints, included in the construction, were recorded and documented with details of the welder, the date and used weld method. The total 120,000 meters welding except recorded is also NDT tested. More than the half of the welded joints were ultrasonically scanned, which ensures the highest possible quality standards in this type of work.

The subsea tank Solan includes four quadrants with watertight bulkheads and eight pile sleeves with mud mats.

The construction works and the whole setup of the facility was highly challenging for the engineers, following extremely complex procedures and processes covering meanwhile high quality requirements.

Image: DNVGL

The piping installation, which is part of the facility, has weight of 171 tonnes, which includes oil inlet and outlet, ballast and displacement piping systems made by various piping materials like super duplex and carbon steel.

Other Solan systems, which are integral parts of the facility are the Temporary Level Monitoring (TLMS), Permanent Level Measurement (PMS) and Corrosion Protection Monitoring (CPMS) systems.

The project achieved successfully 2.5 million LTI free man hours, because of the covered high standards in HSE and the implementation of the “Zero Harm” initiative.