Tuesday, July 26, 2011

Lloyds Register Develops New Ice Fatigue Tool for Shipping Lines and Owners

'ShipRight FDA ICE' Standard to Help Manage Risks
Shipping News Feature

ARCTIC – In response to anticipated demand for ships for use in the Arctic region in the near future, Lloyd's Register has given ship owners and shipping lines a new tool to help assess designs and reduce the risk of fatigue damage in the hull structures of ice-strengthened vessels.

The development of new procedures under the notation, ShipRight FDA ICE, comes as changes in the exploitation of natural resources, the climate, world trade and marine infrastructure are increasing marine activity in cold-climate areas, with Lloyd’s stating that greater trade through the Arctic is driving demand for larger ice-class vessels, particularly oil tankers and LNG carriers.

According to Dr Shenming Zhang, the project leader and a Lead Specialist in Lloyd’s Register’s Marine Product Development department, it is increasingly important that the industry develops a better understanding of the risks involved, including the potential for fatigue to affect the strength of ships' hull structures.

“Designers and owners need to have confidence in the structural performance of the latest generation of large ships. The fatigue performance of these hull structures as the ships navigate in ice-covered waters is a key component in their operational capability and reliability," said Dr Zhang.

"This assessment will give operators and owners the confidence to operate in these demanding and challenging environmental conditions."

With the Arctic estimated to hold about 20% of the world’s remaining recoverable hydrocarbon reserves greater exploration and transportation is expected off the coasts of Alaska, Canada, Greenland and Russia. In addition to hydrocarbons, large quantities of minerals may need to be shipped from the Arctic to ports in Europe and Asia.

The ShipRight FDA ICE assessment procedure examines ship-ice interaction loads, ice-load impact frequency, ice-load distribution, structural responses and the fatigue behaviour of hull structures in cold temperatures including associated fatigue responses. The fatigue-response assessment is determined for different winter conditions and ice thicknesses on typical routes for winter trade.

The procedure provides the measure to identify high-stress locations and to help reduce the risk of structural failure caused by increased fatigue. It was developed from Lloyd’s Register’s extensive experience with ships operating in ice and uses full-scale measurements conducted on ships navigating in ice and is further validated by experimental testing.

“The needs of the industry are changing and the development of larger, ice-strengthened vessels is just one example of this. This new procedure extends the boundaries of current fatigue-calculation methods,” said Dr Zhang.

“We are committed to reducing the risks to ships, to crews and to the environment. By helping to improve the fatigue performance of the hull, we can increase confidence that vessels will be suitable for trade in cold climates.”

By using a developed methodology on ice-load spectrum, structural stress responses to these loads and the associated 'S-N curves' (which define the number of stress cycles that are needed to produce a fatigue crack in a structural detail) fatigue damage can be determined for the typical structural details of larger, ice-strengthened ships. The results will identify the fatigue accumulation for different winter conditions and trading routes.

Ships complying with the requirements of the procedure will be eligible to be assigned the notation ShipRight FDA ICE.

(pic: Steel fatigue failure after experimental testing at low temperature)