A member has reported an incident which occurred while a diving support vessel was conducting subsea operations installing j-tube clamps on a jacket. In this particular case, divers had resumed installing a particular j-tube clamp where the angle of the clamp extension had not been correctly aligned on the original installation. The bracelet clamp had been loosely closed around the jacket tubular member and was being held in place by two winches on the platform. The clamp had to be rotated. The divers had confirmed that the clamp bolts were loose and that the clamp was free to rotate. Tension was being taken up on the outboard winch in 15cm increments and, as a result, the clamp started to rotate towards the correct angle, but then came to a stop.
Instruction was given to come up another 15cm. However, during this last movement, the 5 tonne round-sling between the platform winch wire and the clamp rigging master-link broke.
Following the event, the lifting equipment was inspected. Apart from the round-sling, all of the rigging appeared to be in good condition.
Although the cause of the snagging is not exactly known, it appears that the round-sling had been overloaded. Both winches on the platform could monitor the exact load being pulled, but this has not helped the company in identifying the cause.
The control method used to minimise overloading had been to use small incremental steps, but it seems that this failed to prevent overloading in this case. Such operations are fairly commonplace, thus the event is being reported to warn others intending to conduct remote pulling operations.
The company involved has recommended that if a load comes to a stop and does not move as previously observed when lifting/pulling force is applied, rather than applying further force, the lift/pull should be suspended and the route of the lifting/ pulling wire investigated first for any apparent snags. The load being applied should be continuously monitored where such systems are fitted. It has instructed its personnel to include such precautions in task plans and in toolbox talks conducted before such remote pulling/lifting operations commence.