Integrity management has become a vital aspect of all oil and gas facilities design and operation. Dr Tim Illson explains.
Although corrosion resistant alloys have been increasingly used the majority of existing and future production will come from facilities constructed of carbon steel. The corrosion of carbon steel is mainly controlled by the use of chemical corrosion inhibitors and considering the significant costs of inhibition it is vital that it provides effective protection.
Many companies ask their EPC contractor to select the initial corrosion inhibitor for a development but unfortunately few design/construction companies have in-house expertise in selection of chemical corrosion inhibitors. This means that they are reliant on vendor information and recommendations. Equally, in existing operations it is rare for companies to change their chemicals during the life of a field unless they become ineffective. The consequence is that the field does not employ newer more efficient treatments which could provide lower treatment costs.
Correct corrosion inhibitor selection is actually a complex process that needs to balance a number of competing demands. The inhibitor must both reduce corrosion rates to an acceptable level and be compatible with system materials and other production chemicals such as hydrate inhibitors and biocides. The selected inhibitor must also not adversely affect hydrocarbon production processes such as separation or dehydration by formation of foams or emulsions. Finally, the selected chemical must meet both regulatory and company environmental requirements.
Germanischer Lloyd (GL) offers an independent corrosion inhibitor selection and testing service. It covers all stages of corrosion inhibitor evaluation from the production of functional specifications, performance and compatibility testing, and ranking of the inhibitors and deployment systems.
The production of the inhibitor functional specification is a vital first stage of corrosion inhibitor selection. The specification must give the inhibitor vendor sufficient information for them to select their best candidate chemical based upon the field conditions and the performance required. The specification will include a description of the facilities, process parameters relevant to corrosion (eg fluid compositions, pressures, temperatures and flow velocities) and the target corrosion rate. Additional requirements such as compatibility and environmental aspects are also normally included.
Once candidate inhibitors and supporting information have been submitted then they are ranked according to weighted criteria such as performance, safety, cost, environmental rating, compatibility, storage, availability in country and physical properties. This then allows the selection of the highest ranked inhibitors for laboratory testing or field trials.
Laboratory corrosion inhibitor testing will consist of a series of tests designed to address the particular development conditions and concerns. Generally, this will include static and dynamic performance testing, emulsion testing, storage stability testing at the maximum and minimum ambient temperatures and compatibility testing with other production chemicals.
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Dr Tim Illson, Senior Corrosion Consultant, is with GL, Loughborough, Leicestershire, UK. www.gl-group.com