Failed nipple on bolt tensioning jack
- Safety Flash
- Published on 6 May 2009
- Generated on 23 February 2026
- IMCA SF 06/09
- 1 minute read
A Member has reported an incident in which a nipple failed on a bolt tensioning jack.
What happened?
A diver was carrying out bolt tensioning on a 24″ pipeline being connected to a pipeline end manifold (PLEM) flange when the nipple flew out of the jack whilst the system was pressurised and hit the diver. There were no injuries.
nipple shown loose
correct adapter
What were the causes?
On investigation it was noted that an incorrect bolt tensioning jack assembly had taken place when a nipple intended for the interconnecting whips had been installed instead of the recommended correct one. The difference in thread size is quite minimal but can be easily identified visually by the different size orifice. Whenever the incorrect nipple comes loose through constant utilisation, this difference is sufficient for it to be forced out when hydraulic pressure is applied to the system.
Lessons learnt
It is recommended that all nipples on used bolt tensioning jacks / interconnecting whips should be removed and visually checked to ensure that the correct fitting is in place, and replaced as necessary, followed by a maximum system pressure test.
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