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Floating Production Storage and Offloading (FPSO) - Mooring Inspection

  • Safety notice: 3/2005
  • Issue date: Apr 2005

Introduction

1. This notice is for operators of monohull weather vaning FPSO's and FSU's. It explains why they need to ensure that the top sections of their mooring chains are not subject to excessive wear that can affect the integrity of the mooring system.

Background

2. It has come to the attention of HSE that premature and unexpected mooring chain wear has been experienced on one UKCS FPSO inside the trumpet connected to the turret's chain table (spider). Essentially, the mooring chain is directed through a carefully designed trumpet that has the ability to rotate about a horizontal axis and thus accommodate the vertical motions of the FPSO without transferring significant bending or twist into the mooring chain.

3. Damage to chain links at the trumpet bell mouth, within the trumpet body itself, and around the chain stopper suggests that unexpected wear is occurring. The exact cause of the wear has as yet not been ascertained. Causes might include inaccurate offshore installation, defective design of the trumpet and/or unforeseen load conditions at the trumpet.

4. The wear experienced is generally manifested as a loss of cross-sectional area. In some chain links the loss of material has been such that retained strength would be insufficient to achieve design factors of safety. Furthermore, the deterioration in the chain links has occurred after just 4 years into a 20-year design life.

5. The principal concern to HSE is that similar wear mechanisms may be taking place on other floating installations that have mooring chains passing through a trumpet. Defects that affect more than one mooring chain can increase the risk of multiple mooring line or system failure.

Action required

6. Operators of FPSO and FSU installation need to be aware of such occurrences, and to ensure that they have suitable inspection routines in place.

7. Operators should inspect the mooring chains around and inside the mooring trumpet during 2005, and take any necessary remedial action to ensure the continuing integrity of the mooring system.

8. Periodic inspection of the chain around and inside the trumpet should be carried out based upon the findings of the initial inspection.

Further information

Any queries relating to this notice should be addressed to:

Health and Safety Executive
Hazardous Installations Directorate
Offshore Division
Lord Cullen House
Fraser Place
Aberdeen
AB25 3UB

Tel: 01224 252500
Fax: 01224 252615

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice

Updated 2009-09-06