Sanders, Laura (University of Leeds) | Hu, Xinming (University of Leeds) | Mavredaki, Eleftheria (U. of Leeds) | Eroini, Violette (U. of Leeds) | Barker, Richard (University of Leeds) | Neville, Anne (U. of Leeds)
The formation of calcium carbonate scale and the occurrence of corrosion in CO2-saturated environments in different parts of oil and gas facilities are both phenomena that have been extensively studied. However, to date, very limited work has been carried out on evaluating combined products in a combined scale/corrosion methodology. This paper presents the results from a new combined bulk jar scaling/bubble cell corrosion test. The aim of this project is to investigate the effect of two combined chemicals in a new experimental setup; to study the corrosion and scale interactions which occur simultaneously. Two combined products were assessed at 5 ppm concentration at two temperatures (60ºC and 80ºC) in a CO2-saturated brine. Bulk scale precipitation was monitored using a turbidity meter and the corrosion rate measurements were made using the linear polarisation resistance (LPR) technique. Scale deposition and corrosion mechanisms have been studied using surface analyses. The performance of the two combined products has also been tested to measure: (i) the increase in the induction time of the calcium carbonate formation in the bulk, (ii) the change of the morphology of the crystals and (iii) the formation of a partial protective layer on the sample.
According to this study, the new experimental method has enabled the corrosion and scale deposition on pipeline steel (X65) and the bulk precipitation process to be studied simultaneously. Detailed scale deposition mechanisms on the material surface in the presence of corrosion processes and combined products are addressed from this study.
Keywords: calcium carbonate, scale, corrosion, combined inhibitors
Lean Duplex stainless steels are becoming attractive for applications in oilfield and marine environments due to their economic advantages, very good mechanical properties and relatively good corrosion resistance. However, there is little information about the pitting behaviour of lean Duplex stainless steels in oilfield and marine environments. This paper discusses the tendency for pitting corrosion to initiate through an evaluation of breakdown potentials of lean Duplex stainless steels UNS S32101, UNS S32304, LDX2404, standard Duplex stainless steel UNS S32205 and Austenitic stainless steels, 304L and 316L in aerated 3.5% NaCl and a CO2-saturated oilfield brine solution. Electrochemical measurements were made using a three-electrode electrochemical set up using an Ag/AgCl reference electrode and a platinum counter electrode. The results showed that breakdown potentials are generally higher in aerated 3.5% NaCl than the CO2-saturated oilfield brine solution for all the alloys tested. Lean Duplex stainless steel UNS S32101 and Austenitic stainless steel 304L showed comparable breakdown potentials in both environments while lean Duplex stainless steel UNS S32304 and Austenitic stainless steel 316L also have comparable breakdown potentials. There does not seem to be a universal relationship between Pitting Resistant Equivalent number and breakdown potential for the lean Duplex and Austenitic stainless steels.
Key words: Lean Duplex stainless steels, breakdown potential, aerated 3.5% NaCl, CO2 saturated oilfield brine.
Corrosion and scale deposition are well known problems in pipelines. Corrosion control of carbon steel pipelines requires an understanding of the simultaneous occurrence of both processes. To date there have been few studies demonstrating the interactions between surface scale deposition and corrosion processes. Common methods of controlling corrosion and scale are deploying corrosion and scale inhibitors. However, combined (ComI) are receiving increased attention from industry as their application can significantly reduce chemical costs. Many factors influence the performance of corrosion and scale inhibitors and the influence of supersaturated brines on the surface scale deposition and subsequent effects on corrosion processes are generally not well understood. The work presented describes a range of laboratory tests conducted to assess the influence of different supersaturated brines on corrosion and scale on both inhibited (ComI) and uninhibited systems. Corrosion is measured by conventional electrochemical techniques and surface deposition is assessed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX). Bulk precipitation is measured by turbidity.
Akbar, Abdulmuhsen (Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds) | Hu, Xinming (Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds) | Wang, Chun (Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds) | Neville, Anne (Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds)
Barker, Richard (Institute of Engineering Thermofluids, Surfaces and Interfaces School of Mechanical Engineering University of Leeds) | Hu, Xinming (Institute of Engineering Thermofluids, Surfaces and Interfaces School of Mechanical Engineering University of Leeds) | Neville, Anne (Institute of Engineering Thermofluids, Surfaces and Interfaces School of Mechanical Engineering University of Leeds) | Cushnaghan, Susan (Shell U.K. Limited)