Characterization of Corrosion Products in Saudi Aramco’s Oil and Gas Facilities Using the X-ray Powder Diffraction MethodAuthors: Dr. Syed Rehan Zaidi, Dr. Husin Sitepu and Ahmed A. Al-Shehry ABSTRACT Boiler tubes have occasionally failed in refineries and gas plants. The Research and Development Center (R&DC) has helped plant engineers overcome problems by identifying the nature and source of compounds leading to failure (e.g., corrosion products, formation materials and scale deposits). The boiler consists of a furnace, boiler tubes, steam drum, mud drum and boiler. The furnace provides heat to the boiler, changing water into steam. The presence of certain compounds in sample deposits from boiler tubes can indicate why they fail. The presence of vanadium and sodium compounds in the sample indicates the quality of burning fuels is poor. If large quantities (>15%) of hematite, Fe2O3, appear in the deposits, it indicates the presence of dissolved oxygen in the boiler feed water. If iron carbonate appears in the samples, it indicates the presence of dissolved carbon dioxide (CO2) in the system. If the metallic copper is present in the deposits, it indicates erosion in the boiler. In the last case, special precautions to prevent the plating out of copper during cleaning operations are required. The procedures used to identity corrosion products, formation materials and scale deposit materials will be described. ADVANTAGES OF THE XRD TECHNIQUE XRD is an excellent analytical technique used for the phase identification of a crystalline material in the form of a solid or powder, such as a catalyst, scale deposit, chemical, core, shell, clay mineral and cement1-10. XRD identifies compounds, whereas XRF, induced coupled plasma and atomic absorption techniques only identify elements. A sample XRD and XRF analysis is given in Table 1. The XRD method1-10 differentiates between different forms of a compound with the same chemical formula. If the sample is calcium carbonate (CaCO3) either it is calcite (scale formation materials), aragonite (scale), or vaterite. Additionally, XRD identifies the forms of a compound, such as the iron sulfides (FeS), that have different chemical formulae; e.g., pyrite (FeS2), marcasite (FeS2), mackinawite (FeS0.9), pyrrhotite (Fe7S8) and greigite (Fe3S4). It is very important to know the form of (FeS), because some of these iron sulfides are pyrophoric. Furthermore, the XRD technique can differentiate the hydration state of compounds, e.g., gypsum (CaSO4.2H2O), bassanite (CaSO4.0.5H2O) and anhydrite (CaSO4). XRD APPLICATIONS IN SAUDI ARAMCO The X-ray Group of the Analytical Service Division fully supports the R&DC Downstream and Strategic and Upstream research projects, on topics such as scale mitigation, oil to hydrogen, pipeline integrity, black powder and catalysts. We support the Engineering Service Agreement projects, including mineralogical determination for the Qusaiba shale in the northwest region (ERAD), analytical services support for the Operation Service Division of the EXPEC ARC, and hydrajetting impacts in the filtration system. We support the Technical Service Projects (TSPs) in facilities, such as the Weight Percentage XRF Wt% Element Wt% 60.4 Ca 0.2 28.8 Si 0.1 0.5 P 0.1 0.2 (Wt%) XRD Compound Wt% Magnetite-Fe304 44 Hematite-Fe2O3 28 Pyrite-FeS2 7 Sulfur-S 21 INTRODUCTION The furnace, boiler tubes, steam drum, mud drum and boiler are all parts of the boiler. When the furnace provides heat to the boiler, the water changes into steam. The failure of boiler tubes has been observed in refineries and gas plants for several years. The failures occurred mainly due to corrosion erosion, deposition and scale formation. Due to the failure of boiler tubes, the refinery and gas plants were shut down, ultimately causing a financial loss. Therefore, the Research and Development Center (R&DC) provides support to plant engineers in identifying the nature and source of compounds leading to failure (e.g., corrosion products, formation materials and scale deposits), using X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) techniques. The findings will help engineers to take proper action to prevent future occurrences, avoiding plant slowdowns that result in loss of production. 64 SPRING 2011 SAUDI ARAMCO JOURNAL OF TECHNOLOGY Element Fe S Na Al Table 1. XRD phase identification and XRF elemental analysis of corrosion products we identified the compounds of deposits formed in the boilers of refineries and gas plants by using the XRD technique. This spectrometry simultaneously detects the element from sodium (Na) to uranium (U). the RTR boiler #8 tubes. XRD Phase Identification For the qualitative analysis (i.Rabigh refinery.. The fine powder was then mounted into the XRD sample holder by back pressing. The deposits were considered to be excellent canidates for this study because these deposit materials caused the failure of the refineries’ and gas plants’ boiler tubes. The energies of the X-rays emitted by the sample were measured using a silicon semiconductor and were processed by a multichannel analyzer. knowing the approximate crystal structure of each phase of interest in a mixture is necessary. with irradiated and specimen lengths of 1 mm and 10 mm. Analysis of synthetic mixtures has yielded high-precision results. and homogenized. combined with the International Center for Diffraction Data (ICDD) and powder diffraction file (PDF) database of the standard reference materials.11° to 0.e. This QPA method does not require measurement of calibration data or the use of an internal standard. respectively. however. XRD Data Measurements EXPERIMENTAL PROCEDURE Sample The starting powders were collected from boiler tubes F-3001 in the Jiddah refinery. Subsequently. This grinding was conducted to achieve adequate intensity reproducibility7-8. PSD length in 2θ was 2. The pellet samples were then irradiated with X-ray photons from a molybdenum X-ray tube. the elements with high atomic numbers provide better accuracy than the lighter elements. The concentration range goes from the part per million level to 100%.e. A position sensitive detector (PSD) X′Celerator was used with a scanning step time of 10 seconds. X-rays emitted by these elements. the software package PANalytical HighScore Plus. then the quantitative phase analysis. source and formation mechanism of the deposits. was completed using the Rietveld method7-9. Elemental composition data obtained from the EDXRF analysis was used as additional information for the phase identification.01 was employed to provide adequate sampling of the peaks (full width at the half maximum (FWHM) approximately 0. XRF Spectra Measurements Step-scanned patterns were measured with a PANalytical X′PERT XRD diffractometer. 5 grams of the homogenized deposit sample were further manually ground for several minutes to achieve a fine particle size. In the present study.34°). Ju’aymah gas plant and Abqaiq gas plant. The use of an internal standard10 will allow the determination of total amorphous phase content in a mixture.12°. Berri gas plant (BGP). weight percentage (Wt%) for each phase. Once all the phases for each of the deposits in the XRD data had been identified using HighScore Plus software. In this study. as requested by the TSP Program Director. The XRD data were measured from 4° to 90° in a 2θ Bragg angle. Quantitative Phase Analysis (QPA) Using the Rietveld Method Quantitative Phase Analysis (QPA) of multicomponent mixtures10-14 using XRD data10 has been used worldwide to determine the Wt% for a given phase. Figure 1 shows the goniometer of the XRD instrument used in this study. with XRF is one of the powerful analytical tools used to determine the elemental composition of all kinds of materials. The findings will help refinery and gas plant employees to take proper action to prevent future occurrences. Due to the X-ray interaction with electrons. The homogenized mixtures were pressed at a pressure of 20 tons to form pellet samples with a diameter of 31 mm. Jiddah refinery and Ras Tanura refinery (RTR).9 grams of Licowax C micropowder PM binder (Hoechstwax). The intensity of the rays was processed by the instrument’s software to determine the elemental concentrations. All of the samples were spun during the data collection to improve particle counting statistics. screen tubes of a boiler at the Yanbu’ gas plant and at boilers at the Berri gas plant. SAUDI ARAMCO JOURNAL OF TECHNOLOGY SPRING 2011 65 . i. Four grams of the fine powder were mixed well and homogenized with 0. and determined the nature. and the Consulting Services Department (CSD). so the intensities are not dominated by a small number of crystallites. ensuring reasonable intensity counting statistics. 1. Subsequent processing of the data provided spectral information that identified the elements present in the sample and the intensities of the Fig. phase identification). was used. we used the SPECTRO energy dispersive X-ray fluorescence (EDXRF) spectrometry to analyze the elemental compositions of the corrosion product samples. The parts of the XRD goniometer and optics. A detector step size of 0. The untreated deposit samples were manually ground with an agate mortar and a pestle.. and (2) The potential for the correction of preferred orientation6-9 and microabsorption effects15. It is noted that the Rietveld method for quantification of a mixture of 20 phases using the HighScore Plus software (with a total of 6. as derived in a multicomponent Rietveld analysis of the powder diffraction pattern. respectively. The presence of sodium oxide and vanadium oxide in ash deposits suggests the occurrence of fuel ash corrosion. 3.2 Table 2. it is less susceptible to primary extinction effects and minor amounts of preferred orientation6-9. The weight of a phase in a mixture is proportional to the product of the scale factor. Identification of Scale Removed from RTR Boiler Tubes RESULTS AND DISCUSSIONS Analysis of External Deposits from Boiler Tubes in the Jiddah Refinery Scale deposits were observed in the high-pressure boiler tubes at RTR. such as sodium vanadate. to take corrective measures. H2O Na 4. 2a and 2b. the mass of the formula unit and the unit-cell volume (in Å3). Scale deposits accumulated in high-pressure boiler tubes at RTR. If all phases are identified and crystalline. This equation is the basis of a method providing accurate phase analyses without the need for standards or for laborious experimental calibration procedures. The engineers asked the R&DC TSP Program Director to identify the deposits to determine the source and formation mechanism.000 times more powerful than the reference intensity ratio method1-5 for the quantification of just two phases of the mixture.V2O5 70 S 5. To mitigate this corrosion. a fuel additive treatment can be adopted to prevent the formation of a low melting point phase of the sodium vanadate complexes.6 Mackinawite . Additives containing magnesium and aluminum oxide have been successful in controlling fuel ash corrosion. 2a. the number of formula units per unit cell. When fuel oil is burned. and (2) A large tube. 2a 2b The Jiddah refinery boiler is an oil-fired boiler. vanadium and sodium compounds — present in the fuel in high quantities — react with oxygen to form V2O5 and Na2O in the furnace.9 Ca 0. For the tube in Fig. preventing scale buildup and avoiding future tube failure.3 Calcite . exposing the underlying metal to oxidation.9 Sodium vanadium oxide 15 NaV2O5 Ni 5. the weight fraction W of phase p is given by: where s. these ash deposits pose potential corrosion problems.Na(SO4)2.CaCO3 Trace Fe 1.000 reflections) is 30. fuel oils that contain low quantities of vanadium. A huge accumulation of ash deposit was observed on the external surface of the tubes.0% absolute. M and V are the Rietveld scale factor.FeS 2 Si 1.2 Al 0. with the mass and volume of the unit cell. Under optimum conditions. sodium and sulfur are used. Z. Fig. sulfur and sodium are present in fuel oil. so they could use the results Weight Percentage (Wt%) XRF Elemental XRD Chemical Composition Composition V 31. XRD histogram of deposits from boiler tubes at RTR (inside screen tube) along with the reference patterns of identified phases. Figure 2 shows two samples of the affected tube sections submitted to the R&DC TSP Program Director: (1) A section cutout from wall and screen.5 Vanadium oxide . an analysis was required to identify the deposits. If the above option is not possible. Since this technique fits the complete diffraction pattern. The identification of the deposits led to a procedure to chemically clean the boiler tubes without damaging them.errors generally less than 1. The V2O5 and Na2O react on the metal surface to form a low melting point phase of the conpound. 66 SPRING 2011 SAUDI ARAMCO JOURNAL OF TECHNOLOGY . Additional benefits of this technique — over traditional quantitative analysis methods1-5 — include: (1) The determination of precise cell parameters and approximate chemical compositions. Therefore. Vanadium. Table 2 shows the elemental composition obtained from the EDXRF spectrometry and the chemical compounds obtained from the XRD technique. and they stick to the metal surface. they can form a liquid that fluxes the protective oxide scale.4 Sodium vanadium sulfate 13 hydrate . Summary of elemental and chemical compositions of the Jiddah boiler deposits Figs. If this was the case. Table 5 and Figs. it meant that the mesh holding the catalyst has a pinhole.CaSO4 Talc . which indicates the presence of dissolved oxygen in the boiler feed water and also erosion in the boiler tubes. showed a high percentage of hematite and metallic copper. Identification of Scale Deposits Removed from BGP The XRD results. The formation of ammonium hydrogen sulfate can be avoided by increasing the furnace temperature to burn the ammonia. the high percentage of hematite might indicate the presence of dissolved oxygen in the boiler water. as expected by the BGP engineers. causing a catalyst leak. XRD histogram of deposits from boiler tubes at RTR (inside large tube) along with the reference patterns of identified phases. The XRD results.Mg3Si4O10(OH)2 Weight Percentage (Wt%) Screen Side Large Large Tube Wall Tube Tube Inside Inside Inside Outside 41 46 60 47 34 28 14 12 13 13 11 - 12 - 13 - 15 - 13 8 Fig. Summary of chemical compositions of deposits from boiler tubes at RTR Compound Magnetite . Fig. Summary of results of deposits from a boiler at Yanbu’ gas plant Fig. The XRD results. Identification of Deposits from Screen Tubes of a Boiler at Yanbu’ Gas Plant Scale deposits were observed in a high-pressure boiler at the Yanbu’ gas plant. showed that the scale deposits scraped from the insides of the tubes mainly consisted of iron oxide corrosion products with calcium phosphate hydroxide (apatite) and magnesium phosphate hydroxide. Additionally. XRD histogram of deposits from a boiler at Yanbu’ gas plant along with the reference patterns of identified phases.Fe3O4 Hematite . 5. 6. XRD histogram of deposits from boiler tubes at RTR (outside large tube) along with the reference patterns of identified phases. The deposits removed from the outside of the large tube consisted of calcium sulfate and iron oxide corrosion products. Table 3 and Figs. 7.Cu Weight Percentage (Wt%) 39 35 26 Table 4. 7. which would require total plant shutdown and catalyst removal to repair or replace the mesh. The plant engineers’ concern was that the unknown material might be from the super claus catalyst (alumina and silica). An unknown material — produced with a sulfur product — was found in a condenser at a plant in the BGP sulfur recovery unit. SAUDI ARAMCO JOURNAL OF TECHNOLOGY SPRING 2011 67 . The deposits were removed from the boiler tube and submitted by the CSD to R&DC to support failure analysis work. 8 to 10. which contains ammonia. Ammonium hydrogen sulfate can be formed in the boiler feed water due to treatment with the chemical compound. The boiler tube failed due to these deposits. XRD histogram of deposits from boiler tubes at RTR (inside wall tube) along with the reference patterns of identified phases. 4.Compounds Magnetite-Fe304 Hematite-Fe2O3 Hydroxylapatite Ca5(PO4)3(OH) Magnesium phosphate hydroxide Mg2(PO4)OH Anhydrite . Table 3. showed no alumina or silica. 3 to 6. Fig. Table 4 and Fig. It meant that the mesh holding the catalyst is good.Fe2O3 Copper . 7. 38.: X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials. February 14-17. if hematite is present in the boiler deposits.S Weight Percentage (Wt%) Plant Plant Plant Deposit as White Yellow Received Part Part 84. Chung. presented at the 13th Middle East Corrosion Conference. pp. 158-167.” Journal of Applied Crystallography.R. 34. 9. B. F.H. H. The XRD results can guide the engineers at the affected refinery and gas plant to overcome the problems by devising the right corrective procedures. D. it means that the boiler feed water contains dissolved oxygen. 1974a..L. 7. 2005. Vol.H. Vol. S. Al-Mofleh.H. 3. and Sitepu. source and formation mechanism of deposits formed by the processes in the various units of refineries and gas plants. 1991. 5. Adiabatic Principle of X-ray Diffraction Analysis of Mixtures. Chung.. R. ACKNOWLEDGMENTS The authors would like to thank the management of Saudi Aramco for permission to publish the results in this article. 409-415.H. Vol. 7.” Journal of Applied Crystallography. it indicates erosion in the boiler tubes. Summary of chemical compositions of deposits from BGP REFERENCES 1.2 100 92. pp.P.: “Comparative Evaluation of Cobalt and Copper Tubes using X-ray Diffraction Data for Black Powder in Sales Gas Transport System. 10.8 15.: “Strategies for Preferred Orientation Corrections in X-ray Powder Diffraction Using Line Intensity Ratios.. Special precautions must then be taken to prevent the plating out of copper during cleaning operations. 8.: “Quantitative Interpretation of X-ray Diffraction Patterns of Mixtures II. Sitepu. Sitepu.H. 519-525.” Advances in X-ray Analysis. 17-19. XRD histogram of deposits (yellow part) from BGP along with the reference patterns of identified phases. Vol. Jenkins. S. L. For example. and Snyder. Table 5. H. and Li. 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Australia. pp. T. 3. Synthetic Bauxite. He has authored and coauthored 32 papers in several peer-reviewed journals. Vol. DSC and ICP instruments. 315-326. Germany. H. and Lwin.M. 10. His specialized area of research is the mineralogical characterization of geological samples (clay and bulk rock) by using the XRD technique.D. S. which is an analytical procedure for the qualitative and quantitative determination of chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state. Husin Sitepu joined Saudi Aramco’s Research and Development Center (R&DC). SEM.V. Natural Granodiorite and Pharmaceuticals. L. which is an analytical technique used for the detection of trace metals. pp. pp.M.L. in 1989. He started his career working in the Chemistry Analysis Unit of the Laboratory Department. 467-474.30 Alloy. and XRD and XRF used to determine the chemical compositions of corrosion products. Virginia Tech University in Blacksburg.: “Quantitative Phase Analysis Using the Rietveld Method. Madsen.J. and Howard. India. Before joining Saudi Aramco. respectively. 2001. A43. TGA. the International Union of Crystallography (IUCr).. Ahmed is a Senior Digital System Technician and an expert in several analytical techniques. Aligarh. Neutrons for Science.” Journal of Applied Crystallography. 2009. Cranswick. N. Scarlett. 3. Hermann. 4. 20. including the International Union of Crystallography’s Journal of Applied Crystallography.Y. and the Curtin University of Technology in Perth. 24.” Journal of Applied Crystallography. MD. M. pp.” Powder Diffraction Journal. April 1988. Syed is also responsible for the XRD method development and research work. and Howard. 35. degrees in Chemistry from Aligarh Muslim University. and Upstream R&DC programs by providing chemical compositions of scale mitigation and catalysts projects. Syed Rehan Zaidi has been with Saudi Aramco since 1992. Vol. pp. J.S. et al.S. degrees in Physics from the Curtin University of Technology.H. including atomic absorption spectromery (AAS).A. He is a member of the American Chemical Society (ACS) and the Society of Petroleum Engineers (SPE). 1991 and 1998.V. Husin has extensive experience in Rietveld refinement of polycrystalline structures using X-ray. He now works in the Elemental Analytical Unit. I.J.” Journal of Applied Crystallography. FTIR. France. part of the Analytical Services Division of R&DC. M.C. degree in Inorganic Chemistry from Aligarh Muslim University. respectively. in Grenoble. India. He has successfully conducted a series of Technical Service Projects (TSPs) to support refineries and gas plants. Husin is a member of the International Center for Diffraction Data (ICDD). No. such as: XRF. Part 2. 15. BIOGRAPHIES Dr. and Ph. and Ermrich. Madsen.: “Microabsorption of X-ray Intensity in Randomly Packed Powder Specimens. he is contributing to several research projects under both the Downstream and Strategic and Upstream R&DC programs.: “Application of the Rietveld Refinement Procedure in Assaying Powdered Mixtures. R. Al-Shehry has worked at Saudi Aramco since 1981. 1988. 1987. Perth. the Institute LaueLangevin.7Ti49.S. inductively coupled plasma optical emission spectrometry (ICP-OES). Aligarh. in 2008. 2002.: “Outcomes of the International Union of Crystallography Commission on Powder Diffraction Round Robin on Quantitative Phase Analysis: Samples 1a to 1h.: “Outcomes of the International Union of Crystallography Commission on Powder Diffraction Round Robin on Quantitative Phase Analysis: Samples 2. L.D. SAUDI ARAMCO JOURNAL OF TECHNOLOGY SPRING 2011 69 . (Honors) and M. Vol. Cranswick. He is also familiar with the other analytical techniques. Syed has published more than 20 papers in peer review journals. 4.. Vol. the University of British Columbia in Vancouver. No. No. 401-405. synchrotron and neutron powder diffraction data. Vol. In 1986.(CaCO3) Powders and Ni50.” Powder Diffraction Journal.D. 4. 11. D. in 1977 and 1980.” Acta Crystallographica Section A. 13.. B. N. and Raven. 2-6. Vol.” Journal of Applied Crystallography. Bish. 3. Canada. VA.: “Quantitative Phase Analysis from Neutron Powder Diffraction Data Using the Rietveld Method. cements and catalysts.D. he received his Ph. Ruhr University Bochum Universität in Bochum. He received his Postgraduate Diploma. M. pp. Vol. O’Connor. which is a very common technique for detecting metals and metalloids in environmental samples. Western Australia. Dr.Y..C. Husin worked at NIST Center for Neutron Research in Gaithersburg.. 21.D. 12. 409-426. 1987. and the Neutron Scattering Society of America (NSSA). pp. Ahmed A. Ahmed has contributed to the Downstream and Strategic. Scarlett. 34. C. carbonate rocks. Currently. 14.