Although the tools are very useful in underwater construction because they can be used in any orientation, there have been many failures, underwater and above, the UK-based offshore contractor body says.
“The offshore environment can be particularly harsh, with its combination of temperature extremes, wind- blown dust or grit, atmosphere, silt, washing out of lubricants and general corrosion from seawater,” it says.
It says that hoists have failed in subsea because they were overloaded; underloaded; not built to a reasonable spec; used where the load varies (as the load is lifted out of water); because the mechanism was contaminated or corroded.
IMCA recommends that users separate hoists used for subsea work and is greased more frequently. It also suggests they are proof-load tested to over the working load limit every time the hoist is reassembled. It suggests that users avoid using it upside down because of risk that the chain will not run smoothly through the unit and get hung up.
The document goes on to discuss transport – the equipment needs to be protected from the elements during transport – and planning. It advises that users should consider back-up rigging so that the load will not drop if the hoist fails.
The 15-page guidance document also includes a thorough examination checklist. It costs GBP 5 (USD 10) for non-members from www.imca-int.com
