Load Testing for Modular Offshore Cranes

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Thunder Cranes offshore load test

By Fauzy Khamis (Head of Technical Support)


What is a load test?


In the offshore lifting industry, a load test is a type of test that proves the fitness of a crane. It involves the application of a static, dynamic, or functional load for a period of time. It is conducted after completing the visual crane inspection. A load test is usually expressed as a percentage of the working load limit or safe working load (WLL or SWL) that the equipment is designed to withstand at the specific working radius.


When is it required?


A load test is to be carried out under the following conditions:
1) When a new crane is put into service.
2) When a crane is permanently relocated.
3) When deploying a temporary crane after each rig up and relocation.


The exact requirements of load testing and the extent of each test can vary depending on the standards and requirements applied. In our case the standard applied is the API standard. API is the American Petroleum Institute, the leading standards organisation in the oil and gas industry. API provides standards for the design (API spec 2C), operation and maintenance (API RP2D), of offshore cranes.


What are the requirements of the Load Test?


Load Cell
A load cell is required to verify the load applied to the crane during the load test. A load cell is a transducer that converts the mechanical force into readable electrical units. Using a load cell ensures that accurate test loads are recorded and that no overload occurs during the test. In the offshore lifting environment it is critical for audit reasons to keep a record of tests of lifting equipment. The load cell plays an important role, so must be calibrated and certified accordingly. This load cell will also be used to calibrate the existing load indicator on the crane to ensure the accuracy of the weight lifted.


Water Bags
Prior to the development of water bags, and until the 1970’s, solid weights were used to load test offshore cranes. Water bags are now the preferred alternative as they are safer, and when empty they are easy to ship, handle and store. Using pumps we can quickly fill the water bag to the desired weight with sea water (less than an hour for a 20 ton weight).


Witness
Load testing should always be witnessed and certified by 3rd Party inspection company.


What is the difference between Pull Test Vs Load Test?


Pull Test
The pull test is load that is applied to the crane on a predetermined fixed point (engineered pad eye or structural hard point) for a determined period of time – usually 5 to 10 minutes – and not exceeding 100% onboard SWL at the specific radius. Upon the completion of the pull test, a pre-use inspection will be performed on the crane to ensure that no damage occurred during the test.


Load Test
Offshore load testing typically is performed by the lifting of a “test load” (e.g. water bag). The test load for all lifts shall be based on crane rating chart, wire rope strength, available hoist line pull, and number of parts of line. The onboard test load and the test radius should be calculated to load the crane as shown below.


During a load test the “test load” is raised and lowered, and swung in all directions where applicable, to demonstrate the function of the crane and to test the brake.


Table 1 – Static/Onboard Test Load and Radius

Did you know?


Our cranes undergo the equivalent of an annual API check-list inspection and static load test each time they are rigged up. A Thunder Crane typically will be rigged up between 6 and 20 times per year depending on utilization rate. That means our cranes are typically inspected and load tested 6 to 20x more often than the typical fixed platform crane.


Would you like to learn more? Contact us if you have any questions or would like to learn more about Thunder Cranes’ offshore temporary rental crane services, lifting solutions, or lift planning services.