Swivel ring flange failures
- Safety Flash
- Published on 1 January 2000
- Generated on 9 December 2025
- IMCA SF 01/00
- 1 minute read
We have recently received the following information from one of our Members.
All diving personnel should exercise extreme caution when tightening a leaking swivel ring flange. Application of additional bolt load to certain lightweight swivel ring flanges can cause leakage to worsen. In extreme cases, these flanges have failed catastrophically, causing a hazard to personnel and the environment.
There have been several recent failures of lightweight swivel ring flanges. In these cases the rotating ring and/or the hub portions of these flanges did not comply with the appropriate strength requirements. The failures occurred either during the bolt tightening sequence or at a later date, when additional external loads (thermal or mechanical) were applied to the pipeline.
The contractor has issued the following advice to its divers. A swivel ring flange is unlikely to comply with appropriate standard specifications if the thickness of the rotating ring is identical to that of a standard weld neck flange. In general, the rotating ring should be about twice the thickness of the mating weld neck flange to provide sufficient strength.
IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of the entire offshore industry.
The effectiveness of the IMCA Safety Flash system depends on the industry sharing information and so avoiding repeat incidents. Incidents are classified according to IOGP's Life Saving Rules.
All information is anonymised or sanitised, as appropriate, and warnings for graphic content included where possible.
IMCA makes every effort to ensure both the accuracy and reliability of the information shared, but is not be liable for any guidance and/or recommendation and/or statement herein contained.
The information contained in this document does not fulfil or replace any individual's or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.
Share your safety incidents with IMCA online. Sign-up to receive Safety Flashes straight to your email.