Cape Town-based designer and supplier of hydraulic, pneumatic and control systems Optima Hydraulics recently awarded steel fabri- cating company Belmet Marine a contract to fabricate a cursor frame for the offshore diamond mining industry.

The cursor frame acts as a guide to the seabed for a drill and suction tower section that is hydraulically driven verti- cally by means of motors and gearboxes. To accommodate these moving parts, the frame had to be fabricated to extremely tight tolerances and specifications.

The cursor frame weighed about 37 t with overall dimensions of 6 870 mm in length × 6 870 mm in width × 6 800 mm in height. The structure was built from grade 350WA structural sections; grade 300WA plate and a primary structure of tubular square sections of 400 mm × 16 mm and 300 mm × 12 mm.

The full penetration welds were 100% ultrasonic tested and Belmet achieved a 0% weld defect rate.

The frame was completed in Belmet’s heavy fabrication workshop in seven weeks, was loaded out using two 25 t overhead cranes and delivered by abnormal road transport to Optima’s premises near the Cape Town harbour.

Belmet Marine reports that following the successful delivery of a 150 t multi- purpose elevated transport (MPET) unit, in January last year, for consulting engineering company Hampco, Belmet recently received an order for a multipurpose cart due for completion this month.

Belmet fabricated the MPET unit for Hampco in 12 weeks, which was chal- lenging, as the design of the unit took place simultaneously with the fabrication process and a tight delivery schedule.

Belmet Marine MD Pieter Kroon explains that, although also designed by Hampco, the order for the multipurpose cart was placed by Korea-based Samsung Shipyard for installation on board a newbuild drillship for South Africa-based offshore drilling company Pacific Drilling.

“It will be fabricated here, in South Africa, tested here and delivered to Samsung Shipyard,” he says adding that the 100 t unit will be load tested to 1 200 t before leaving Cape Town and must, therefore, adhere to stringent specifications, as well as quality parameters stipulated by autonomous and independent foundation Det Norske Veritas.

Fabrication of the unit is mainly in S355 grade steel that has been impact- tested to –40 ºC. While some of the steel was brought in already certified, a quantity had to undergo external testing at approved labs.

Final load testing of the unit will be undertaken in conjunction with South Africa-based consulting engineering company Origen and includes a training element that will provide practical expe- rience for students from Stellenbosch University.

Kroon explains that strain gauges on the multipurpose cart will simulate a 1 200 t load using 250 hydraulic jacks to ensure that the strains registered on the gauges correspond with the final ele- ment analysis specifications for the spe- cific load.

Meanwhile, Kroon says, the company is currently also in the process of building a second subsea crawler for diamond mining company De Beers Marine, adding that the first crawler was commissioned in December last year and is currently in use by the diamond mining company.

The second unit will be completed during June before being commissioned by De Beers.

Subsea crawlers are remotely operated, submersible vehicles designed to traverse the ocean floor. They are used for deep- sea diamond mining, exploration, exca- vation, and the laying of underwater pipes and cables.