A member has reported an incident which a chain link parted when a shock load was introduced to the chains. The inappropriate use of chains was a major failing in a series of events which resulted in a high potential near miss incident. The incident serves to communicate the safe and appropriate use of chains in rigging operations.
The incident occurred during pipelay operations onboard a vessel. A constant tension winch was being used to transfer the first end of the pipe from the reel to the pipelay system. Because of earlier winch and sheave failures, a temporary rigging solution using chains, shackle and snatch-block was used to control the winch wire’s position. The chains in question were of the grommet type, grade 80 lifting chains. They had the required certification and had been inspected by a third party during the six monthly lifting inspections. Although the chains were rated for the loads involved in this operation, the complete assembly was not rated accordingly. This did not have a direct impact on the incident in question, although it was seen as bad practice.
During the operation, a shock load was introduced to the chains, leading to a chain link parting and in turn to a catastrophic series of events.
Our member’s investigation established that the use of chains in this manner was hazardous because:
- The chain was exposed to a shock load;
- The chains were wrapped around edges which were the incorrect radius for the chain diameter;
- As the chains overlapped each other within the shackle they had no chance of equalising the load when it was applied.
Our member drew the following lessons:
- Never wrap a chain around a diameter which is less than twice the diameter of the chain link;
- Never twist, knot or trap chain slings;
- It is recommended to use packing on edges to reduce the side loading on chain links;
- When attaching more than one chain to a shackle/hook always avoid overcrowding or use a master link;
- Never use a chain where there is potential for it to be exposed to dynamic or shock loads.
Members may wish to refer to the following similar incidents (key words: chain, link, failure):
(Failures of very large mooring chains for floating offshore structures have been excluded, as being a slightly separate issue.)
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