FPSO Held Firm by Back-Up Lines Made with DYNEEMA® (The Netherlands)

Ropes made with Dyneema®, ultra-high molecular weight polyethylene (UHMWPE), are being successfully used to secure rigs, Mobile Offshore Drilling Units (MODUs), Buoyant Turret Mooring (BTM) systems and similar constructions in the offshore oil and gas industry.

Users are finding them invaluable when original equipment steel wire rope (SWR) and chains that secure mooring legs break or suffer damage. The back-up lines made with Dyneema® are installed as a safety feature until regular maintenance can be carried out.

Dyneema® manufacturer DSM Dyneema cites the example of the Chinese Floating Production, Storage and Offloading vessel (FPSO), the NanHai KaiTuo. The vessel operated in the Xijiang Oil Field at the mouth of Pearl River about 130km from Hong Kong in the South China Sea. The oil field is operated by ConocoPhillips and the China National Offshore Oil Corporation, CNOOC.

An inspection of the NanHai KaiTuo by an ROV (Remotely Operated Vehicle) found broken wires on two of the SWR mooring legs of its BTM system. SBM Services, a service provider to the offshore industry, was requested by ConocoPhillips to design and supply a back-up system consisting of a special connector to fit a positively buoyant back-up line made with Dyneema®. Installation of this back-up system was required in case of a SWR failure in one of the damaged composite anchor legs.

The back-up system is designed to be capable of retaining the FPSO in position and maintaining production, gaining time for ConocoPhillips to mobilize the required vessels and equipment to replace the broken wire leg, in case one of the wires fails due to its reduced strength.

SBM Services verified that the connector and the back-up line in its new configuration could withstand a load of 580 tonnes, the maximum likely in the event of a broken leg.

Bexco nv, a Belgium-based rope manufacturer, designed and manufactured the back-up line with Dyneema®. Lines made with Dyneema® were selected in preference to SWR and other synthetic materials because of its high strength and low weight. The 1000-tonne MBL (Maximum Break Load) line consists of parallel laid cores of Dyneema® SK78 yarn protected by a polyester cover. It was designed for a minimum of one year under full load. Performance is not affected by sea water, nor does it rot.

For ConocoPhillips, the main reasons for choosing lines with Dyneema® were its low weight, neutral buoyancy and high durability and strength compared to alternative synthetic materials. Furthermore, the ability to do the installation job quickly played a role in the decision making process. Installation of the back-up lines was carried out by divers, because an ROV would not have been able to get close enough to the wires to perform the action. The buoyancy of the lines meant the divers could do their job in a fast and safe manner.

ConocoPhillips used the lines for 15 months to its complete satisfaction, before the FPSO NanHai KaiTuo was decommissioned during 2010. The lines are now in storage, ready for further use if necessary.

About DSM Dyneema

DSM Dyneema is the inventor and manufacturer of Dyneema®, the world’s strongest fiber™. Dyneema® is an Ultra High Molecular Weight PolyEthylene (UHMWPE) fiber that offers maximum strength combined with minimum weight. It is up to 15 times stronger than quality steel and up to 40% stronger than aramid fibers, both on weight for weight basis. Dyneema® fiber floats on water and is extremely durable and resistant to moisture, UV light and chemicals. The applications are therefore more or less unlimited. Dyneema® is an important component in ropes, cables and nets in the fishing, shipping and offshore industries. Dyneema® is also used in safety gloves for the metalworking industry and in fine yarns for applications in sporting goods and the medical sector. In addition, Dyneema® is also used in bullet resistant armor and clothing for police and military personnel.

UHMWPE fiber from DSM Dyneema is produced in Heerlen (The Netherlands) and in Greenville, North Carolina (U.S.A.). DSM Dyneema is also a partner in a high modulus polyethylene (HMPE) manufacturing joint venture in Japan.

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Source: DSM Dyneema, February  24, 2011;