Correct stud/bolt torquing of engine parts is a critical feature of maintenance, as shown by The Nautical Institute’s latest Mars Report. In this report, a stud that was not tightened enough resulted in engine damage.
The Nautical Institute gathers reports of maritime accidents and near-misses. It then publishes these so-called Mars Reports (anonymously) to prevent other accidents from happening. A summary of this incident:
The engine crew started auxiliary engine No.1 for a routine operational test while at anchor. After about two minutes of warm up, the engine was connected to the electrical board.
A few minutes later, there was a loud noise followed by strong vibrations. Numerous alarms were activated, and the engineers immediately disconnected and stopped the affected engine.
A forensic examination of the damaged engine and reconstruction of the sequence of events suggested that one of the two studs of the cam shaft connecting rod for cylinder two had not been adequately tightened during maintenance. A gap developed due to stud B being under-torqued. This overstressed stud A, which consequently sheared and caused the subsequent damage sequence.
Following this hypothesis, the hydraulic stud tensioning pump used for tightening the con rod mechanism was thoroughly examined. The pressure gauge on this pump read 60 bar higher than actual supplied pressure. This could well have led to the less than adequate tensioning of the connecting rod nuts during maintenance, and could be the cause of premature failure. The company subsequently added periodic calibration of the hydraulic stud tensioning pump as a separate item within the planned maintenance system (PMS).
Advice from The Nautical Institute
- Correct stud/bolt torquing of engine parts is a critical feature of maintenance. Many incidents and accidents have occurred in the past due to incorrect torquing. Having a properly calibrated tensioning pump is vital to attain the required specifications.
- PMSs are a lynchpin of safety – use them rigorously and add value to them when the opportunity presents itself, as in this occurrence.
This accident was covered in the Mars Reports, originally published as Mars 202331, that are part of Report Number 369. A selection of the Mars Reports are also published in the SWZ|Maritime magazine. The Nautical Institute compiles these reports to help prevent maritime accidents. That is why they are also published (in full) on SWZ|Maritime’s website.
More reports are needed to keep the scheme interesting and informative. All reports are read only by the Mars coordinator and are treated in the strictest confidence. To submit a report, please use the Mars report form.