Well thought out - managing corrosion offshore
The UK offshore oil and gas industry comprises around 300 installations ranging from unmanned gas platforms, large oil and gas production facilities, to floating production installations and drilling rigs. The industry is a major contributor to the UK economy and currently employs some 30,000 offshore workers. The mature nature of the sector presents particular challenges, including maintaining an infrastructure to maximise the exploitation of reserves and extending intended design lives in response to rising oil prices.
The North Sea is one of the most hostile working locations for oil and gas extraction in the world. Offshore structures are subject to severe environmental and operational conditions such as corrosive effects from the reservoir, accidental loading conditions, for example fire and blast, and severe weather in an exposed marine environment. This places stringent performance requirements on engineering materials.
Corrosion can detrimentally affect any part of the installation, from the hydrocarbon (HC) containment system to walkways and gratings. The Health and Safety Executive (HSE), in its role as the UK regulator for offshore heath and safety (H&S), regards corrosion as a significant and persistent threat to installation integrity and hence to the H&S of those on board. It seeks to ensure that operators manage corrosion such that risks to H&S are as low as reasonably practical.
The UK offshore industry has set itself the target of being ‘the safest place to work in the worldwide oil and gas industry’ by 2010. Key to this is lowering the risks from major accident hazards. One area where corrosion is a significant factor is primary containment of the HC system. To address this, the sector is committed to reducing HC leaks by 10% year on year. The graph (top, right) based on industry HC release data, indicates an encouraging downward trend in reported leaks from corrosion over the last three years – particularly for internal corrosion.
However, this measure focuses on a single, safety critical system – namely HC containment. Consequently, from 2004 to 2007, HSE undertook an industry wide inspection programme of about 40% of offshore installations. The investigation identified concerns for the widespread condition of safety related and safety critical parts. The HSE has subsequently challenged the industry to improve its corrosion performance.
Design to dismantling
The Health and Safety at Work Act 1974 requires employers to manage the hazards from their business enterprise such that the risks to the H&S of persons are as low as reasonably practicable. The duty holder must have in place an appropriate system for corrosion management (see also p30 this issue). It should encompass the lifecycle of the installation, from design to dismantling. The design should be complementary and feed into the operation, and experience from operation should feed into the design. The diagram (bottom, right), from the HSE publication Successful Health and Safety Management, illustrates a generic model for such a management system.
The HSE has recently worked with Oil & Gas UK, based in London and Aberdeen and the Energy Institute in London to produce the Energy Institute publication Guidance for Corrosion Management in Oil and Gas Production and Processing. It is based on the model described above and provides good industry practice.
In support of its challenge to the industry, the HSE is undertaking a third inspection focused on production installation duty holders. The programme targets the management of external corrosion and includes, fabric maintenance and secondary structures. In addition to fundamental equipment integrity, the scheme specifically examines –
• Senior management leadership – managers should give necessary priority to maintenance of safety critical and safety related plant and equipment.
• Performance indicators – effective measures should exist to give managers a clear understanding of the status of maintenance activities in order to take appropriate action.
• Performance standards – quantified acceptance criteria, based on sound engineering and recognised industry standards, should be in place to define when a corroded component must be repaired or replaced.
• Maintenance plans – appropriate plans should be drawn up and adhered to so that safety critical and safety related plant and equipment remains in an efficient state and working order, and is repaired with regard to external corrosion.
• Safety culture – the offshore workforce should be knowledgeable and active in identifying corrosion.
The inspection is less than half way through and will continue for another 18 months. The assessment template is available on the HSE website and as the project progresses, HSE will add further information on its findings.