The pH stabilization technique is a widely used corrosion protection method for multiphase gas pipelines with glycol as hydrate inhibitor. It implies to increase the pH by addition of  3 HCO in order to enhance the formation of protective iron carbonate films. The protection mechanism at ~20°C is of concern because the conditions for precipitating protective corrosion film are less favorable compared to higher temperatures due to the increasing solubility of FeCO 3 with decreasing temperature. The scope of the ongoing work is to investigate whether corrosion mitigation of pipelines at ~20°C relies on the formation of protective corrosion films or if the corrosion rate is sufficiently lowered by the elevated pH. This paper discusses the corrosion rate and corrosion potential observed on carbon steel exposed to varying concentrations of  3 HCO and Fe 2+ at 20°C in a 1wt% NaCl and 50wt% glycol solution purged with CO 2 at 1 atm partial pressure. The objective was to promote protective FeCO 3 films by high iron and bicarbonate concentrations and study the effect of supersaturation and variations in iron and bicarbonate concentration. Protective films did not form despite high supersaturation and long exposure times. The reason for this is discussed in light of exposed iron carbide (Fe 3 C) and prerequisites for iron carbonate growth.

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A formula is proposed to predict fatigue strength of corroded members and joints of steel structures. The concept of the formula is first studied from recently identified mechanism of corrosion fatigue. Hence, the corresponding fatigue strength curve (i.e. S‐N curve) of corroded steel is presented. It is further improved to derive linear, bilinear or trilinear S‐N curve for corroded constructional details of steel structures. The parameters of the corroded steel S‐N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water and seawater. Hence, the parameters for the derived S‐N curve of corroded constructional details are predicted based on the above parameters and tabulated for the detail categories given in the Eurocode and DNVGL code. The proposed S‐N curve formula is compared with full‐scale fatigue test results of several constructional details, and the validity of the formula is confirmed.

Several chemical problems can occur during the production of oil and gas through flow lines. This includes corrosion, scale deposition and gas hydrate plugging. Three separate chemicals may be needed to treat these issues. Kinetic hydrate inhibitors (KHIs) are used in cold oil or natural gas production flow lines to prevent the formation and plugging of the line with gas hydrates. They are often injected concomitantly with other production chemicals such as corrosion and scale inhibitors. KHIs are specific low molecular weight water-soluble polymers with amphiphilic groups formulated with synergists and solvents. However, many corrosion inhibitors (CIs) are antagonistic to the KHI polymer, severely reducing the KHI performance. It would be preferable and economic if the KHI also could act as a CI. We have explored the use of maleic-based copolymers as KHIs as well as their use as film-forming CIs. KHIs were tested using a natural gas mixture in high pressure rocking cells using the slow constant cooling test method. A terpolymer from reaction of vinyl acetate:maleic anhydride copolymer with cyclohexy lamine and 3,3-di-n-butylaminopropylamine (VA:MA-60% cHex-40% DBAPA), gave excellent performance as a KHI, better than the commercially available poly(N-vinyl caprolactam) (PVCap). CO2 corrosion inhibition was measured by Linear Polarization Resistance (LPR) in a 1 litre CO2 bubble test equipment using C1018 steel coupons. The new terpolymer gave good CO2 corrosion inhibition in 3.6 wt% brine, significantly better than PVCap, but not as good as a commercial imidazoline-based surfactant corrosion inhibitor. The terpolymer also showed good corrosion inhibition efficiency at high salinity conditions, (density 1.12 g/cm3). VA:MA-60% cHex-40% DBAPA shifted the open-circuit potential to more positive values and significantly decreased the corrosion rate.