Power cables, flexibles pipes and umbilicals (but also climbing ropes, sewing threads, gardening hoses etc.) may display torsion-related motion under handling.
As an example, while a cable is routed from an onshore turntable to an installation vessel, longitudinal markings can be observed to roll, torsion starts building up, until either the cable is damaged (with the tensile armor showing a "bird cage" related behavior), or takes the shape of a cork-screw which is difficult to manage.
Since 2009, SINTEF has been invited to discuss or investigate torsion-related failures that have occurred during production, loadout (to installation vessels), installation, and even during operation. Several lessons are learnt from this:
- The costs of some of these failures are considerable. Expensive products are damaged, deliveries significantly delayed, installation of vessels remain on stand-by, and so forth. SINTEF are aware of several events where the costs are of the order of 100 million NOK (10 million Euros).
- Failures are unacknowledged. Luckily, the failures we know about have not caused death, injury or pollution. Therefore, they tend not to be reported to the authorities, and the problem remains unmapped and largely unacknowledged. Yet, SINTEF has seen documentation of dozens of events. Further, our understanding of the underlying mechanisms suggests that there are many incidents we have not yet heard about.
- It's complicated. A glossary of all the terms needed to describe torsion-related concepts, just to make it possible to discuss a mishap, a failure or an improved design, takes several pages. The mathematics applied to model the relevant processes includes advanced concepts (rotations in 3D, material vs. spatial derivatives etc.). A variety of torsion-generating mechanisms, including several instability phenomena, have been identified.
Services
Failure investigations
SINTEF has investigated several failures, some of them extremely costly events. SINTEF's role is to gather all relevant data from all parties involved in the failure, review and analyze the data and conclude on the mechanism (or the possible mechanisms) of the failure, and where relevant propose solutions to avoid future problems.
SINTEF has also provided less comprehensive services for other torsion related events and have studied information from dozens of incidents.
Our work has put us in contact with multiple incidents during loadout operations, problems in the factory when spooling the product, installation on the sea floor, beach pull-in and torsion-related failure during the operation phase. We have studied documentation for a surprising variety of torque-induced failure modes, some of which had been wrongly attributed to excessive compression or curvature. Our failure investigations have helped us develop a unique competence into the physical processes underlying torsion.
While we learn about generic aspects of torsion through failure investigation, and put that knowledge to use to serve other customers, all data we receive about cross section design, factory, quay or deck layout, including the fact that there has been an incident, will be handled by SINTEF as confidential, unless agreed otherwise.
Torsion JIP
In September 2019, SINTEF initiated a 3-year Joint Industry Project (JIP). The JIP is sponsored by Ørsted, Equinor, Hellenic Cables, NKT HV Cables, Aker Solutions, Hengtong and Petrobras.
Main objectives of the project:
- To provide comprehensive documentation and training to the industry of how torsion arises.
- To provide a guideline for the conservative evaluation of the torques to be expected in an operation.
- To provide means to evaluate the capacity of a cable, flexible pipe or umbilical to withstand torque
Design-related torsion analysis services
SINTEF can use in-house software to assess a customer's design for a routing (in factory, loadout or deck layout), thus providing indications on how to improve the routing. It must be emphasized that we do not yet have the ability to compute all the processes that we have identified.
Future services
We are working to widen the scope of services we can provide. We will soon be able to provide:
- Torsion capacity rig: A rig to test the capacity of electric cables and umbilicals to withstand torsion. We are currently working on a concept. The planned rig will provide conservative results at a moderate cost.
- Numerical analysis: We are developing our ability to run numerical models of all recognized torsion-related physical processes. Currently we can only model some aspects.
- Troubleshooting during operations: Today, we understand the cause of most torsion related incidents. Unfortunately, because friction plays a major role, "rewinding" the operation will generally not resolve issues. SINTEF will develop generic strategies that might help to get an operation back under control.
- Monitoring of torsion during operation: We plan to collaborate with an industrial partner to create equipment for the real time assessment of torsion during complex operations.
- Training: In the Torsion JIP we are developing training material for both engineers and operators.In 2023, the restriction of the JIP deliverable to the JIP participants will be lifted, and we will be able to provide training to other companies as well using the comprehensive "Torsion Handbook".
Expressions of interest for the above services are important for us to prioritize our capability development.