CORROSION CONTROL BY pH STABILISER, MATERIALS AND CORROSION MONITORING IN A 160 KM MULTIPHASE OFFSHORE PIPELINE

摘要

Three gas condensate fields are planned as subsea development. They will be connected to a subsea pipeline end module, PLEM, via flowlines and a 160 km multiphase pipeline from the PLEM to an onshore liquid natural gas plant. The gas has a high content of carbon dioxide and condensed water will be present, which makes the fluid corrosive to carbon steel. The temperature and pressure is moderate, the formation water contains approximate 160 g/l of salt, but the probability for production of formation water is low. Ethylene glycol will be used as hydrate inhibitor and will be injected on each wellhead and on the PLEM. The glycol will contain sodium hydroxide and when necessary corrosion inhibitor. The glycol will be regenerated onshore. Carbon dioxide will be separated and reinjected offshore. Corrosion resistant alloys will be used for well equipment, manifolds and piping and for the flowlines. Based on test programs evaluations and experience from other fields, carbon steel is selected for the main pipeline in combination with pH stabilisation and high focus on corrosion monitoring. Backup solutions if formation water should be produced, are injection of scale inhibitor or film forming corrosion inhibitor.