Monitoring of tendons on modern tension leg platforms

Paul Boughton

In order to ensure safe and economic operation of tension leg platforms (TLPs), a tendon tension monitoring system (TTMS) is required to provide reliable measurement of the tensions in the tendons. A record of these loads along with user-friendly displays of all the data are available in real-time and in various formats.

To measure the tensions in the tendons three load sensors are installed into the tendon top connector assembly. The data from these sensors is then used to calculate the maximum, minimum and mean tensions and standard deviation in the tendon, together with the bending movement angle.

The Strainstall Tendon Load Cells, ranging from 1000 to 3000Kips, have been designed to provide such reliability, and have been approved by Certifying Authorities, eg ABS, DNV, LRS.

The load cell element is a specially heat treated high grade marine stainless steel with straingauges matched to the material. The straingauges are installed onto the machined element as two fully independent straingauge bridge networks, a primary and secondary, and then a stainless steel cover is welded over the billet to provide hermetic sealing and full protection for the straingauges. The wires from each bridge are brought through glass-to-metal seals to separate underwater mateable connectors.

The load cell is then coated with a marine grade finish and supplied with a top cover to allow for any misalignment within the tendon connector rings. The underwater connectors and signal cables are chosen to provide the same long-term reliability as the load cells.

In the control room the logging and display system comprises two PCs to provide mirror logging, so in the event of a failure in one machine the other takes over to provide seamless monitoring. 

Strainstall UK Ltd is based in Cowes, Isle of Wight, UK. www.strainstall.com

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