Exposure of Various Polymer-lined Carbon Steel Pipe Sections to a Sour Hydrocarbon Fluid at a Maximum Service Temperature: Methodology and Observations

• Published in: NACE International Corrosion Conference Proceedings pp. 1 - 16
• Main Authors: Craster, Bernadette, King, Barnaby, Mitzithra, Maria-Eleni, Taylor, James, Parvez, Anwar, Asiri, Abdulaziz, Jones, Colin
• Format: Conference Proceeding
• Language: English
• Published: Houston NACE International 01.07.2020
• Subjects: Additives; Antioxidants; Carbon dioxide; Carbon steel; Carbon steels; Connectors; Corrosion; Corrosion mechanisms; Corrosion rate; Corrosion tests; Diffusion layers; Evaluation; Extrusion; Fluids; Fluorides; Gases; High temperature; Hydrocarbons; Hydrogen sulfide; Linings; Low carbon steels; Partial pressure; Pigments; Pipelines; Polyamide resins; Polyethylene; Polymers; Polyvinylidene fluorides; Pressure ratio; Species diffusion; Steel pipes; Water flooding; Water injection

Key words: polymer-lined-carbon steel pipe, polyamide, raised temperature polyethylene, polyvinylidene fluoride, sour hydrocarbon fluid, hydrogen sulfide, scale, rapid gas decompression INTRODUCTION Polymer lined pipe Carbon steel host pipes lined with thermoplastic polymers have been used in surface and operations for the transport of water injection fluids for oil and gas for 30 years and in water injection subsea for 25 years. 1-5 In order to produce a polymer lined pipeline, there are a few key elements: lining method, connectors, terminations and potentially venting systems depending on the operating environment. In order to determine the corrosion mechanism and evaluate the corrosion rate of mild steel in the presence of both gases, the CO2 to H2S partial pressure ratio, p(CO2)/p(H2S) was introduced. 7-8 For p(CO2)/p(H2S)>200, i.e. a mixed CO2 to H2S environment, H2S aqueous concentration >>50ppm is reported to reduce the corrosion rate at temperatures between 60°C and 120°C, due to the formation of stable iron sulfide scale. The material suppliers may have added antioxidants, stabilizers, plasticizers and pigments to the capsules prior to melting during the liner extrusion process and the generic chemistry of such molecules, as well as the diffusion of these species through some polymer layers at elevated temperature has been raised as an issue in the published literature. 28 During testing and evaluation of polymer liners, which involves 180days of exposure to the sour hydrocarbon fluids, some of these organic and inorganic additives may be displaced to the surface of the carbon steel and so alter the corrosion rate and the structure of scales formed. There are also documented field studies on the corrosion of carbon steel host pipe lined with polyamide and, subsequently, high density polyethylene. 32 The aim of the study documented here, was to assess the barrier behavior of different polymer lined -carbon steel pipe sections using a flow loop test set up.