The standard “ASTM G205-16 Standard guide for determining emulsifying properties, wetting behavior, and corrosion inhibiting properties of crude oils” developed by the American Society for Testing and Materials (ASTM) describes several generally accepted laboratory methodologies used to determine the emulsifying tendency, wetting behavior, and corrosion inhibiting properties of crude oils.
This guide does not cover detailed calculations and methods, but rather a range of approaches that have application in evaluating emulsions, wettability and corrosion rate of steel in crude oil/water mixtures. Only methodologies that have gained wide industry acceptance are discussed in this guide.
This guide is intended to assist in selecting methodologies used to determine the corrosivity of crude oil under conditions where water is present in liquid form (typically up to 100 degrees Celsius). These conditions normally occur during oil and gas production, storage and transportation in pipelines.
This guideline does not apply to the higher temperatures (typically above 300 degrees) that occur during the refining of crude oil in refineries.
This manual involves the use of electrical currents in the presence of flammable liquids. Fire safety awareness is critical to the safe use of this manual.
For the purposes of this standard,
This guideline includes methodologies for determining three properties of crude oil that are relevant to corrosion processes resulting from the presence of water in hydrocarbon transportation and handling:
The conductivity of the emulsion can be used to determine the type of emulsion: oil-in-water (O/W) or water-in-oil (W/O). An oil-in-water emulsion (where water is the continuous phase) has a high conductivity. A water-in-oil emulsion (where oil is the continuous phase) has a low conductivity.
The wettability of a steel surface is determined by the contact angle methodology or the diffusion methodology. The corrosivity of the water phase in the presence of crude oil can be determined using various methodologies.
Crude oil is not corrosive in the absence of water. However, trace amounts of water and sediment have the potential to create corrosive conditions if such substances accumulate and remain on steel surfaces during the handling or transportation of the crude oil. ASTM D96-88, ASTM D473-22, ASTM D4006-22, and ASTM D4377-00 standards provide methods for determining the water and sediment content of crude oil.
The potential for the development of a corrosive condition during the handling and transportation of water-containing crude oil can be determined by a combination of three properties: the type of emulsion formed between the oil and water, the wettability of the steel surface, and the corrosiveness of the water phase in the presence of oil.
Water and oil do not mix, but under certain conditions they can form emulsions. There are two types of emulsions: oil-water and water-oil. A water-oil emulsion has low conductivity and is therefore less corrosive, whereas a water-oil emulsion has high conductivity and is therefore corrosive. The percentage of water at which a water-oil emulsion changes to an oil-water emulsion is known as the emulsion inversion point. This point is determined by measuring the conductivity of the emulsion. At and above the emulsion inversion point, a continuous water or free water phase is present. Therefore, there is potential for corrosion.
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