Lab Case Study of Microbiologically Influenced Corrosion and Rietveld Quantitative Phase Analysis of X-ray Powder Diffraction Data of Deposits from a Refinery.

Abstract

This paper reports a laboratory-based case study for the characterization of deposits from a crude cooler and reboilers in a Saudi Aramco refinery by microbiologically influenced corrosion (MIC) using microbial, metallurgic, and special analyses and correlates the Rietveld quantitative phase analysis of high-resolution X-ray powder diffraction (XRD) data of scale deposits with microbe compositions. Therefore, rapid in-field microbiological assays could be carried out to assess the potential of MIC. Based on the results, it can be highlighted that the MIC investigation showed that total bacteria and sulfate-reducing bacteria (SRB) were detected in all sampling locations. Methanogens, acid-producing bacteria, and sulfate-reducing archaea were not detected in all samples. Iron-oxidizing bacteria (IOB) were detected in the solid samples from reboilers C and D. Low loads of general bacteria and low levels of microbes with MIC potential were detected in both C and D samples. The trace amount of corrosion products in one sample and the low level of MIC microbes cannot justify the contribution of MIC microbes in the formation of accumulated solids in the system. The findings recommend conducting frequent sampling and analysis including water, oil, and solid from upstream locations to have more decisive evidence of the likelihood of the scale formation and possible contribution of MIC in the formation of deposits in the plant. Subsequently, quantitative phase analysis of XRD data of scale deposits by the Rietveld method revealed that the major phase is calcium sulfate in the form of anhydrate and the minor phases are calcium carbonate in the form of calcite and aragonite, silicon oxide in the form of quartz, and iron oxide corrosion product in the form of magnetite. The results are supported by high-resolution wavelength-dispersive X-ray fluorescence (WDXRF) results. These accurate and reproducible X-ray crystallography findings obtained from Rietveld quantitative phase analysis can guide the field engineers at the refineries and gas plants to overcome the problems of the affected equipment by drawing up the right procedures and taking preventive actions to stop the generation of these particular deposits.