Serious nonconformities from the regulations, which had significance for safety, were identified by the investigation into this incident on the North Sea field The gas leak, which happened on 26 May, was one of the largest on the NCS for a number of years.
The incident occurred ahead of testing two emergency shutdown valves (ESDVs) on the Heimdal main platform (HMP), which is an integrated production, drilling and quarters facility.
To prepare for the job, a bleed-off pipeline was to be blown down to the flare. This line incorporated a shut-off valve with a 16-bar pressure rating as the final pre-flare barrier.
The valve was closed instead of open, and failed when subjected to a pressure of 129 bar. A total of 3 500 kilograms of gas escaped at an initial rate of 16.9 kg per second, and was detected over much of the platform.
According to the PSA’s investigation report,his incident had a clear potential to become a major accident.
The nonconformities found indicated that important improvement measures identified and initiated by Statoil after earlier events – such as the Gullfaks B hydrocarbon leak on 4 December 2010 – have not had the expected effect on Heimdal.
Nonconformities were established in such areas as the design solution and recognition of its deficiencies, and the description of how the work was to be done. Others included Statoil’s document management, risk assessment in planning, experience transfer and learning from earlier incidents, and expertise and risk understanding.
The report also highlighted inadequate capacity in the firewater system and the firewalls between the production and drilling areas on the HMP.
Several of the nonconformities also exposed weaknesses in management followup to ensure that work is being pursued in an acceptable manner.
On the basis of these findings, the PSA ordered Statoil in January 2013 to identify why its improvement efforts have failed to achieve the necessary results on Heimdal. The company was then required to ensure that these measures do take effect on the field, and to confirm that similar conditions are not present on any of the other installations it operates.