"Blowdown" to reduce risk and raise decommissioning progress
The “blowdown” of a massive North Sea structure has been successfully accomplished at Lerwick Harbour to facilitate its ongoing decommissioning at the port’s Dale Voe Base.
The complex operation on the Ninian Northern platform topside was carried out by the principal decommissioning contractor, international partnership, Veolia/Peterson, supported by a demolition specialist.
Believed to be the first time that the industry has used explosives in the UK to lower such a structure, it was nine months in detailed planning, involving stakeholders including the Health & Safety Executive, NatureScot and SEPA.
The concrete decommissioning pad was protected by a berm, using approximately 30,000 tonnes of rock materials placed under the topside. The berm also acted as protection to the skid shoes used in bringing it ashore which will be reused.
Using a digital firing sequence, over 200kg of explosives were used in numerous sequential charges milliseconds apart to reduce the height of the remaining steel legs and diagonal bracing which previously attached the topside to the section of steel support jacket offshore.
The meticulous planning and execution meets HSE requirements to minimise significant risk from working at height, reducing the need for personnel at higher levels and use of high capacity cranes, and lessening exposure for personnel and plant during inclement weather conditions.
Port Authority Chief Executive, Captain Calum Grains, said: “Veolia/Peterson and the team involved are to be congratulated on the successful operation which has added another dimension to Lerwick’s extensive capabilities as an established leader in the demanding decommissioning market. We continue to evolve our resources to meet changing requirements and new opportunities.”
The 14,200 tonne topside arrived at Dales Voe in August, 2020, with decommissioning progressing well and expected to speed up following the blowdown.
