03314 FLOW ASSURANCE OF pH STABILIZED WET GAS PIPELINES

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Product Number: 51300-03314-SG

ISBN: 03314 2003 CP

Author: Arne Dugstad, Rolf Nyborg and Marion Seiersten

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The pH-stabilization method is a cost effective and reliable way to control bottom of line corrosion in gas/condensate pipelines where glycol is used as hydrate preventer. Increasing the pH to 6.5-7.5 facilitates the formation of a protective iron carbonate film on the steel surface and reduces corrosion of the steel. pH stabilization will also affect top-of-line corrosion, but to a less extent than in the bottom of the line. In order to reduce top-of-the-line corrosion significantly, pH stabilized glycol must be transported from the liquid water/glycol phase in the bottom of the pipeline to the gas phase in droplets and then hit the wall. The likelihood for this is discussed and it is also discussed how the pH stabilizer can reduce the detrimental effect of HAc in the gas. The carry-over of formation water will put limits on the use of the pH stabilization technique as carbonate scale may form. Scale formation in glycol carrying pipelines is not easy to predict, as solubility data for CO2 and scale forming compounds in glycol solutions are very scarce. Glycol affects scale formation by changing the solubility and the precipitation kinetics, and the solubility of for instance calcium carbonate is markedly reduced. If the periods with formation water carry-over into a pH-stabilized pipeline are short, scale inhibitors can probably be applied without adverse effects on corrosion. Long-term use of scale inhibitors in a pH stabilized pipeline is probably not feasible. Keywords: CO2 corrosion, pH stabilization, formation water, glycol