A one-of-a-kind testing machine designed and built by TWI is being used to research the fatigue performance of high-strength steel mooring chains used on large floating structures offshore.
Tests are being carried out in seawater to simulate the typical corrosion conditions and cyclic loading experienced offshore.
The machine, which has a load capacity of 6000kN, is currently being used to carry out fatigue tests on chain composed of grade R5 steel. With a link diameter of 127mm, the chain steel has a proof strength of around 1000MPa.
Fatigue data for mooring chain in seawater has been obtained before, but for lower strength, smaller diameter samples. Fatigue data for this relatively new specification of mooring chain is not widely available, so a joint industry project has been established to obtain an S-N curve for this chain type - thereby providing valuable data for industry.
Project leader Yan-hui Zhang said: 'The data will be analysed and compared with current �design curves. We will see whether, for such a high steel grade and a larger diameter, the existing design curves are applicable or not. If not, how can we modify them? This is the main purpose of the project.'
The first test now underway is being conducted in air to check that all systems on the machine are working satisfactorily. This will be followed by a total of 23 tests in seawater at the relevant temperature, on chain of two different grades and two diameters. The programme is scheduled to be completed in 2016.
Specified and assembled in-house, the rig demonstrates how TWI can construct bespoke equipment to carry out highly specialised tests to benefit its Industrial Members.
Watch the video.
For more information please contact us.