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CO2 and The Partial Pressure Bandit


By James McDonald, Hempel USA

Presented at SSPC 2016; Session: Mini Session: Tank Linings; Session chair: Ernst Toussaint

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Pressurized Atlas Cell Testing is commonly understood to be the most aggressive accelerated test for tank lining systems due to The Cold Wall Effect. This is especially true when CO2 is added to the gas phase, as CO2 is miscible with oil and soluble in water. A familiar gas mix of 5% CO2, 5% H2S, and 90% CH4 is added to test protocols to simulate head space conditions of tanks and pressure vessels in oil and gas production conditions. The temperature and pressure conditions in these protocols are adjusted to match field conditions as closely as possible. Results are often inconsistent between tests when the same gas mixtures are used but changes are made to temperature and pressure only.

This author believes that there is a connection between the test pressure and the percentage of CO2, also described as partial pressure, and the failure of coatings by blistering. Often understood as Cold Wall Effect blistering it is the aim of this paper to describe additional failure considerations when testing with CO2.

This research will describe testing methodology and key findings for using the partial pressure of CO2 rather than current 5% calculations to determine the effect of Carbon Dioxide in Cold Wall Effect type failures.

Testing was centered around NACE TM 0174 Laboratory Methods for the Evaluation of Protective Coatings and Lining Materials on Metallic Substrates in Immersion Service - Modified, otherwise known as Pressurized Atlas Cell Testing. Multiple frequently used tank linings were tested in conditions with the primary consideration given to partial pressure of CO2 and Cold Wall Effect blister type failures.

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