DNV GL has supported the safe construction, installation and operation of tension leg platforms (TLPs) since the technology’s inception. The company’s Noble Denton marine assurance and advisory service area provided marine warranty services for the first ever production TLP, installed in the North Sea’s Hutton Field in 1984.
DNV GL has since been involved in the transportation and installation of approximately 80% of the world’s TLPs: from the first, Hutton, to the most recently installed TLP in the Papa Terra field offshore Brazil.
Installed at a water depth of 1,180 metres, the P-61 tension leg wellhead platform (TLWP) was the first of its kind to be introduced to a field offshore South America. FloaTEC LLC, the joint venture company between McDermott and Keppel FELS, responsible for engineering, procurement, construction and installation of the TLWP, called for support from DNV GL’s Noble Denton marine assurance and advisory technical team, based upon the company’s experience across the design, construction, transportation and installation process of a TLP.
“TLPs are a widely adopted and trusted solution for projects in deep waters,” explains DNV GL's senior principal engineer Mike Roberts, “in particular, where there is an infrastructure already in place. They have a smaller footprint on the seabed, are not subject to swell or roll motions, and can be more suitable when it comes to surrounding infrastructure since the TLP does not require a large mooring spread.”
However, TLPs have their own challenges when it comes to construction, transportation and installation. “Various elements of a TLP are typically constructed in multiple locations and need to be transported safely to the final destination to be assembled and installed,” explains Mike. “Each aspect of that process has to be reviewed and assessed to identify and mitigate risk.”
This was the case with the P-61 TLWP. The topsides were constructed in Singapore, the tendon and piles in the US, and the hull in Brazil. The topsides were transported to Brazil where the hull and the topsides were mated using the floatover methodology.
DNV GL’s global team of experts provided end-to-end support for this process from construction to the installation of the TLWP, offshore Brazil. This involved reviewing: design and installation documents for the various components that made up the TLWP; heavy lift procedures for the site fabrication of the components; procedures for the dry transportation of the topsides from Singapore to Brazil; and procedures for the transportation of the piles, tendons and tendon buoyancy modules from the Gulf of Mexico to Brazil. The team also reviewed the procedures for the floatover of the topsides onto the hull at an inshore location in Brazil, and the asset’s subsequent tow and installation at the offshore location.
“Our global reach made it possible for us not just to provide tailored expertise, but also to be on the ground in the construction and assembly yards, as well as during the offshore installation. We used local DNV GL surveyors to attend these key construction, transportation and installation activities,” says Mike.
“Each project is different,” he adds, “but, all require specialist support. We have considerable experience working with operators across multiple sites, helping them to bring a project together by providing assurance that their designs are correct, their procedures are safe, and their schedules are accurate. We are able to share best practice based on our work on previous projects, helping our customers to identify potential pitfalls and to cope with any changes in project scope or timing, without compromising on safety.”