Measurement of Crude Oil
Corrosivity Using Radioactive
Inclusive Dates: 07/01/01 - 09/30/02
Background - Technology is needed to accurately and quickly determine the corrosivity of crude oils and many of their derivatives. Current methods lack timeliness, reliability and accuracy, leading to inconsistencies between projected and actual corrosion experiences in refining and processing operations. No robust models exist for predicting crude oil corrosivity. Traditional estimators, based on sulfur and total acid concentration (TAN) measurements, are inadequate for assessing the true corrosivity of specific crudes. This has proven problematic for crude oil buyers, sellers and refiners, and will be more so as it becomes necessary to process poorer crudes.
Approach and Accomplishments - SwRI's radioactive tracer technology (RATT®) for measuring real-time wear in operating engines, pumps and other mechanical components was adapted to measure real-time corrosion in the laboratory at elevated temperature (600°F) under flows simulating refinery operations. Protocols were developed for standardized and experimental laboratory testing. Bulk neutron RATT was applied because of its high sensitivity. Iron coupons were irradiated to develop suitable tracers λ-rays from Fe-59 radionuclides) for detection using online gamma ray spectroscopy. Corrosion was measured by monitoring the buildup of radioactivity in a closed loop system as a function of test time. Activity was converted to corrosion mass using specially made calibrating solutions. The time-resolved data (10-minute) provided historical trending for each test (typically 4 to 5 hours). Testing was accomplished on several crude oils and crude oil derivatives, and on simulated crudes developed by adding specific amounts of cyclopentylacetic acid to 30-wt mineral oil. Results showed the onset of corrosion and corrosion during temperature transitioning to 600°F, and at steady state temperature. This method improves upon others by providing real-time corrosion data with much greater sensitivity, resulting in information that is not available using other means. The short test time avoids sample degradation that is common with other methods.
The test loop design and testing protocols were developed to simulate certain refinery conditions. Prospective designs and protocols were guided by CFD simulations and by an extensive literature search, which was initiated to gain a better understanding of corrosion detection and measurement. In addition to simulating specific refining conditions, high shear stresses during experimentation were intended to avoid corrosive film build-up (which could interfere with the corrosion measurements) and to add relevance to the results. Experimentation was accomplished using activated coupons inserted into a specially designed housing, providing confined tangential flows under controlled shear stress conditions.
Benefits - Expected crude oil corrosion is a major factor in determining the true economic value for a particular crude oil. Accurate knowledge of potential crude oil corrosivity can provide significant technical and financial advantages to a buyer or seller, and can prevent costly surprises to refiners and other downstream processors. The real-time corrosion data obtained by the radioactive tracer test method provides a means for obtaining absolute and relative corrosivity information for specific crudes of interest. Absolute corrosivity data can be used to develop databases for specific crude oils and derivatives, while relative corrosion indices can be developed to compare corrosion trends for a given crude with similarly measured trends for "benchmark crudes" whose characteristics are known to producers, buyers, and refiners. This method can be used as a screening tool to rapidly determine which oils are more corrosive than others for specific refinery materials, and as a research tool for further investigations of corrosion and other material related issues. The technology can be applied to many areas of study across several industries to obtain data at levels not generally available by other currently used means.