The second of the American Bureau of Shipping (ABS) tests, the ‘Bend & Friction Test’, follows passing in August of the first test for ABS Class Approval, the ‘High-Pressure Test’.
Third test underway
A third test, the ‘Cyclic Fatigue Test’ is underway with completion expected this month.
The proprietary CNG Optimum is a world-leading CNG ship design and the result of two decades in the development of marine CNG solutions.
GEV chairman and CEO Maurice Brand said, “We are approaching the end of the ABS Full Class approvals process with outstanding results being achieved.
“Importantly GEV can now confidently move forward with the only remaining testing phase required before the CNG Optimum Ship design has been proved.”
GEV chairman and CEO Maurice Brand.
Testing has been carried out at the CFER Technologies testing facilities in Edmonton, Alberta, Canada.
The aim of the ‘Bend & Friction Test’ was to verify that the CNG containment pipes in the hold of the ship can be forced together in such a way that the pipes will not move relative to each other, or relative to the ship, even in extreme seas.
This required applying a downwards force on the pipes to reflect what would occur in an Optimum ship’s hold in order to mobilise sufficient friction to prevent relative movement.
The bend test was to determine if the pipes, when forced together in the ship’s hull will prevent any movement of the pipes relative to each other and thus stiffen the ship.
A rig was jacked up at either end and the deflections precisely measured.
The predicted deflection at the midpoint was 5 millimetres and the actual deflection measured was 5.45 millimetres which GEV said was a perfect result.
If the pipes did not prevent movement the defection would have been about four times more and the test, therefore, proves that the Optimum concept works as designed.
The friction component of the test showed that the required friction was achieved between each pipe.
This required applying a downwards force on the pipes, reflecting what would be done in the hold, to a pressure of 10 tonnes per square metre, then pulling on the pipe in the middle of the bundle and trying to extract it.
The force needed to move the pipe relative to the surrounding pipe was the critical measurement. This test confirmed that the required friction was achieved and that the system works as designed.
The ‘Cyclic Fatigue Test’ in progress comprises three individual sub-tests required by the ABS Rules and Guidelines.
Long-term fatigue test: This requires cycling a representative pressure vessel for 10 times the design life of the ship from minimum pressure to the operating pressure.
For GEV's 30-year ship life this means that the test must recreate 300 years or 20,000 cycles.
This extremely rigorous test began in September with 8,310 cycles, or 42%, now completed.
Notched burst test after fatigue: This requires fatiguing a specimen through three times the design life, or 6,000 cycles, and then bursting the pipe with a machined notch embedded to prove the pipes’ ductility.
The test will run after the 20,000-cycle test is complete.
Cooled burst test after fatigue: This also requires fatiguing the specimen through three times the design life and then bursting the pipe after it has been cooled to simulate temperatures that would result from the Joule-Thompson cooling effect of gas escaping through a crack.
The specimen has been made and this test will be run after the cycling of the notched burst test is complete.
ABS completes two key reports
In addition to the testing, two key reports have been completed by the ABS with final drafts issued for review.
The first of these, to assess the structural analysis of the ship focusing on the novel mid-body section, is complete and concludes that the design meets ABS Rule requirements.
ABS carried out an extensive analysis over the past seven months, including both 2D and 3D finite element models, resulting in a 200-page report.
GEV said this was the most critical analysis work from an approval perspective.
The risk assessment final draft report has been submitted and concluded that there were no hazards identified that cause serious concern.
This report supports the ABS approval process, which remains within the original budget set down by GEV.