Tower bracing instrumented with


strain gauges and FDS (marked yellow)


DCV Balder instrumented for lifetime extension


Heerema Marine Contractors (HMC)


contracted MARIN to design, install and maintain a Fatigue Monitoring System


for the J-Lay Tower of the Deepwater Construction Vessel (DCV) Balder.


One of the many capabilities of DCV Balder is deepwater pipeline installation. As offshore oil and gas production has spread around the globe, the deepwater work vessel oper- ated by HMC is exposed to a great variety of oceanic conditions and indeed, wave- induced motions. This response could be the source of fatigue loading and therefore, HMC decided to monitor and verify the design calculation of fatigue loading in the J-Lay Tower as a pilot case, in order to con- tinue to operate its vessels and equipment in a safe and economic manner.


HMC initiated the LIFetime EXtension (LIFEX) project and contracted MARIN and AMARCON. As well as installing the Fatique Monitoring System (FMS) MARIN should analyse the measured data over a three-year period in order to verify numerical models and to determine the fatigue lifetime consumption. AMARCON should develop the advisory part of the FMS that visualises and advises on fatigue lifetime consumption of fatigue critical joints.


Pieter Aalberts p.aalberts@marin.nl


Successful installation In October 2009 in the Gulf of Mexico, MARIN installed the FMS successfully onboard the Balder. The FMS


comprises strain gauges, accelerometers and Fatigue Damage Sensors (FDS). In total, 25 strain gauges were installed in the tower bracings at seven different locations. In addition, 14 accelerometers were installed to monitor the rigid body motions of the Balder and the accelerations in the tower.


FDS were installed at seven locations. The fatigue consumption where they were attached could then be directly determined. A connection of the monitoring system with the Balder network system was made in order to relate the environmental conditions, the vessel’s heading and loading condition and the tower parameters to the measured responses. All responses are measured continuously with 25 Hz. Daily emails showing the status of the monitoring system are automatically sent from the Balder to MARIN. Monthly backups of the monitoring data are made by the crew and sent to MARIN for analysis.


Three backups have already been received. The first analyses have shown that the monitoring data is consistent and of high quality. Validation of the fatigue design calculations will be the next step.


report 21


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