Cranes have traditionally been certified for their “fitness for purpose” by the application of a test load. Typically, the structure’s resilience to withstand the stresses imposed by the Proof Load (a load that surpasses the generally applied load) illustrates that all defects that are within the structure are sub-critical. By the periodic application of such load tests owners can content themselves that because the crane passed the previous test, then there must be some redundancy within the system that will permit the continued safe operation until the next scheduled test.
In other industries, such as in pressure systems this methodology has been enhanced by coupling the traditional “load test” other technologies. Imes in conjunction with Water Weights pioneered a process on cranes which listens to the structural behavior of the material while in the loaded condition. The technique utilizes highly sensitive instrumentation with the ability to “hear” localized yielding, which therefore allows identification of initiating and propagating defects. Such is the sensitivity that the technique boasts listening to even the active corrosion on the material under test.
Acoustic Emission is defined as excerpted from ASTM E610-82 as “The class of phenomena whereby transient elastic stress waves generated by the rapid release of energy from localized sources within a material.” The term AE is referred not only to the phenomena, but also to the non-destructive technique. Typical sources are cracking, plastic deformation, phase transformation and it is very sensitive to the initiation and propagation of discontinuities.
The technology of this non-destructive technique can be utilized for testing the integrity of crane structures (booms and slew rings) as part of a Condition Based Maintenance Program. Tried and tested, the application was pioneered by Imes Group.
The system utilizes the unique application of a load with Water Weights (a trading division of Imes) during the load application. In conjunction with the applied load, the method measures structural performance by “listening” for the telltale “creaks” and “groans” that emanate from the highly stressed regions during gradual application of the test load.
This activity can be located to a position on the crane structure and additionally ranked for its intensity such that a qualitative assessment of damage severity is made.
The operator can monitor in real time the acquired data and determine location of Acoustic Emission activity and how this varies with time and or load. Each wave has a unique signature composed of counts, amplitude, rise time, duration, energy and relative time of arrival. Full analysis of the emissions can be used to determine the characteristics of the source emissions and help characterize the flaws. The processed data can then be displayed as required by the operator. As the system has the capability of capturing the full waveform then the data file can be run as required and full post-test analysis can be undertaken either on or off site.
Periodic monitoring utilizing this method during load testing will give an indication of the condition of the crane detecting any growing discontinuities. The exercise would greatly enhance the load test and should be conducted in conjunction with future tests to verify the cranes integrity and develop a trend history.
for more info visit: www.waterweightsinc.com
About Imes:
Imes delivers knowledge-based solutions that, in partnership with its clients, produce radical improvement in the management of full life cycle costs, performance and safety of their assets. Imes provides inspection, in-service support, reliability, measurement and specialist engineering products, systems and services to construction, defense, heavy process, marine and shipping and the oil and gas industries in over 60 countries.
for more info: visit www.imes-group.com
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