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Audit of follow-up of fatigue cracks on Bideford Dolphin

The Petroleum Safety Authority has carried out an audit of Dolphin AS. The audit was aimed at documentation of welding of the implemented repairs, quality assurance of fatigue analyses and scheduling of inspections of load-bearing structures on Bideford Dolphin.

The audit was carried out at offices of the consultancy firm AGR Field Operations Holdings AS on Straume outside Bergen on 28 and 29 October 2010 and at Dolphin AS in Tananger 15 November 2010.

The background for the audit is that in the past ten years, three instances of crack formations have been discovered in load-bearing structures on the mobile drilling installation Bideford Dolphin. In a meeting with Dolphin in May 2009, the PSA was informed about how Dolphin plans to prevent future crack formations. We decided to carry out an audit with the purpose of achieving a more detailed review, especially of the implemented analyses, by means of questions and spot checks.

Dolphin received the PSA's Acknowledgement of Compliance (AoC) for Bideford Dolphin on 30 September 2004.

The purpose of the audit was to ensure that the documentation for repairs and the analyses complied with the regulatory requirements. The audit was planned as spot checks of documentation related to quality assurance, the welding work that had been done, as well as fatigue analyses and the use of reliability methods.

The performed analyses are comprehensive and complicated. In order for these to satisfactorily establish that the crack formations have been safely repaired, there is a lot that must be done correctly and sufficient safety margins used. The audit concluded with some deficiencies in this area.

One nonconformity from the regulatory requirements was identified as regards Dolphin's follow-up of service providers.

Furthermore, some improvement items were identified, related to

• Overview and accessibility of documentation
• Simplification of the fatigue analyses
• Application of parameters in the fatigue analyses
• Facilitation for own inspection activities
• Application of parameters in the reliability analyses
• Quality assurance of calculation tools (spreadsheets)
• Documentation of welding repair work
• Job descriptions 

Thor Gunnar Dahle, Principal engineer
Email: thor.dahle@ptil.no | +47 51 87 61 96