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Full-scale testing of a ‘Rocksteady’ connector

Working alongside Industrial Member company Subsea Riser Products (SRP), TWI has demonstrated its capabilities in the development of a bespoke test programme to qualify a new position mooring system for offshore vessels (the ‘Rocksteady’ connector). The connector design includes pre-tensioned fingers which enhance its fatigue resistance.

The TWI project team produced test-specific risk assessments and agreed a test procedure. The qualification requirements set for the new connector were demanding and included applying static tensile loads of 9900 kN (1010 tonnes), fatigue loading at three different load levels and a test involving disconnecting the connector while under a tensile load. SRP also wished to measure the strain experienced by the fingers in the connector during the application of the pre-load, and during the external load tests.

TWI’s first task was to apply strain gauges to the fingers. Project engineers chose suitable gauges and applied these to the fingers at agreed locations. These were used to measure the strain experienced by the fingers during application of the pre-load and during the subsequent tests.

The team helped next by designing and assembling a test machine capable of applying a static load of up to 1010 tonnes, and fatigue loads of up to 500 tonnes, and working with SRP to design end fittings to fix the connector to the test machine. The following tests were carried out on the fully calibrated equipment:

Connector installed in the TWI-designed test machine
Connector installed in the TWI-designed test machine
Partially assembled connector with the strain gauges attached
Partially assembled connector with the strain gauges attached
Rendering of SRP's 'Rocksteady' concept
Rendering of SRP's 'Rocksteady' concept
  • static proof test
  • fatigue test
  • static minimum break load test
  • static disconnect under load test.

The strain experienced by the connector was recorded throughout and the project team analysed the data so that the measured strain values could be compared with the values predicted by SRP’s finite element models.

In conclusion, the test programme verified that the Rocksteady connector can withstand the applied loads without damage, and that it is fit for use.

For further information, please email contactus@twi.co.uk

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