Key issues related to modelling of internal corrosion of oil and gas pipelines - A review

Reactions of pipeline steels in carbon dioxide solutions

A review of surfactants as corrosion inhibitors and associated modeling

The influence of microstructure and chemical composition of carbon and low alloy steels in CO2 corrosion. A state-of-the-art appraisal

On the fundamentals of electrochemical corrosion of X65 steel in CO2-containing formation water in the presence of acetic acid in petroleum production

The relation between the corrosion rate of steel in carbonic acid and the CO2 partial pressure was determined by means of weight loss and polarization resistance measurements. This relation is compared with that expected for completely dissociated acids, and appears to be significantly different. A theoretical analysis of this effect shows that it can be quantitatively explained if the direct reduction of undissociated carbonic acid is the rate-determining step in the cathodic process. Both anodic and cathodic processes have been further studied by means of potentiodynamic polarization curves. The effect of temperature on the corrosion rate can be analyzed in terms of an activation energy for the overall corrosion process.

Carbonic Acid Corrosion of Steel

Starting from a “worst case” corrosion rate prediction with the deWaard-Milliams equation, correction factors can be applied to quantify the influence of environmental parameters and corrosion product scale formed under various conditions. Equations are proposed for each factor. A low-temperature scale formed in condensing water can cause a reduction in the top-of-the-line corrosion rate in pipelines. At higher temperatures, a more protective scale forms even under high liquid flow rates. The decrease of corrosion rates caused by dissolved Fe is accounted for with a pH correction factor. The effect of the presence of a liquid hydrocarbon phase is included. Equations are presented that enable the effect of glycol injection on corrosion to be calculated along the length of a pipeline. Combinations of effects in the model are discussed.

Predictive Model for CO2 Corrosion Engineering in Wet Natural Gas Pipelines

Internal CO2 corrosion in crude oil transport pipelines is always associated with the presence of “free” water, and the likelihood of corrosion generally increases with the volume fraction of the water phase. A recently developed method is applied here to predict the critical velocity for entraining the water by the flowing oil phase. Entrainment of the water eventually eliminates the corrosion problem. The effects of pipe diameter, surface tension, oil viscosity and density on the critical velocity for water entrainment are discussed in detail in this paper. On the other side, if all the water is not entrained by the flowing oil phase, it is important to predict the thickness of the water film, the in-situ: water cut, film velocity and wetted area. A new model is proposed here that can be used to calculate these parameters, which are crucial for corrosion prediction in multiphase flow. A comparison is carried out between this new model and experiments conducted in large diameter horizontal pipe flow.

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Modeling of water wetting in oil-water pipe flow

Es wird eine einfache und schnelle Methode zur Ermittlung des ochfraspotentials von nichtrostenden Stahlen beschrieben. Durch die Verwendung von Drahten als Meselektroden, an die eine festliegende gleichspannung angelegt wird, kann in einem einzigen Versuch ein beliebig groser Potentialbereich gepruft werden. Versuche mit 4 austenitischen Stahlen in 1 n NaCl zeigen, das Mo und Si das Lochfraspotential bei Raumtemperatur anheben; dieser Effekt geht jedoch bei hoherer Temperatur verloren. Zusate von NaBr und NaJ zur NaCl-Losung fuhren zu einer betrachtlichen Zunahme des Lochfraspotentials von molybdanfreien nichtrostenden Stahlen. Das Versuchsprinzip kann auch zur Unter suchung von Spannungskorrosion verwendet werden.



Simple method for the potentiostatic determination of teh pitting potential in one single experiment



A simple and fast method is described for the determination of the pitting potential of stainless steels. By using wire electrodes to which a constant DC-potential is applied one may scan potential ranges of any size in one single experiment. Tests with four autenitic steels in 1 N NaCl have shown that addition of Mo and Si displaces the pitting potential to higher values at room temperature; at higher temperature, however, this effect vanishes. Addition of NaBr and NaJ to the NaCl-solution produces a considerable increase of the pitting potential of Mo-free stainless steels. The experimental principle can be used also for the investigation of stress corroison cracking.

Einfache Methode zur potentiostatischen Bestimmung des Lochfraßpotentials in einem einzigen Versuch

Unless special protection is provided, pitting corrosion may occur at the upper side and the bottom of ballast tanks. Usually a partial coating (horizontal areas) is used in connection with cathodic protection by sacrifical anodes. More than two years' observation of coated and uncoated cathodically protected containers has shown that anode efficiency is generally better than 90% and in many cases as high as 100%. The current densities measured depend on where the measurements are performed. They are usually higher at the bottom, especially when the bottom is coated. Measurements of protective current density vs potential can be used to calculate the protective current requirements for horizontal and vertical surfaces.

C. De Waard

Papers

Carbonic Acid Corrosion of Steel

Predictive Model for CO2 Corrosion Engineering in Wet Natural Gas Pipelines

Modeling of water wetting in oil-water pipe flow

Einfache Methode zur potentiostatischen Bestimmung des Lochfraßpotentials in einem einzigen Versuch

Cathodic protection of cargo/ballast tanks of crude oil tankers