Spectroscopic tools like XRF, OES, and LIBS make material verification faster, smarter, and more reliable, proving essential for preventing alloy failures in oil and gas infrastructure.
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Material reliability is critical in the oil and gas industry. Infrastructure ranging from pipelines to pressure vessels operates under extreme conditions where even a minor failure can lead to catastrophic consequences. Positive Material Identification (PMI) is a key safeguard against failures, ensuring that alloys and steels used in these operations conform to strict specifications.1
Traditionally, PMI is carried out through chemical assays and laboratory testing, but such methods are slow and impractical for use in the field.
While still essential in high-assurance settings, these methods are increasingly supplemented by advanced spectroscopic techniques, particularly X-Ray Fluorescence (XRF), Optical Emission Spectroscopy (OES), and Laser-Induced Breakdown Spectroscopy (LIBS). These techniques have significantly improved the PMI process, making it fast and field-portable.1
Each technique has unique strengths: XRF excels in identifying stainless steels, OES is indispensable for carbon steels, and LIBS represents a fast, versatile, and increasingly popular technology. This article explores the principles of each, their application in the oil and gas sector, and case studies proving their effectiveness.
X-Ray Fluorescence (XRF)
XRF relies on the emission of secondary X-rays from a material when irradiated with primary X-rays. Each element emits characteristic energy lines, allowing analysts to identify and quantify its presence. Modern handheld XRF analyzers are compact, battery-powered, and capable of providing results in seconds.2
A key advantage of X-ray fluorescence is its non-destructive nature, which allows materials to be tested without any damage. It offers high accuracy in detecting heavier elements such as chromium, nickel, and molybdenum, which are critical for stainless steels. Its accuracy is influenced by factors such as calibration quality, surface condition, and matrix effects, especially at lower concentrations.2
The technique is also convenient in field applications and suitable for use in demanding environments such as offshore rigs and refineries. But XRF is less able to detect lighter elements (e.g., carbon, boron), making it less applicable to carbon steels, where carbon concentration is critical.2
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Optical Emission Spectroscopy (OES)
OES involves creating a spark or arc discharge on the sample surface. This excites atoms within the material, causing them to emit light at characteristic wavelengths. By analyzing this emission, OES can detect a wide range of elements, including lighter ones like carbon, sulfur, and phosphorus.3
OES is particularly important for the oil and gas sector because carbon content determines whether a steel is classified as low-, medium-, or high-carbon. This directly influences mechanical properties such as hardness and weldability.3
In a case study by Fahad et al., Optical Emission Spectroscopy was applied alongside XRF, XRD, and SEM-EDS for manganese ore analysis. Plasma diagnostics provided electron temperatures (~7500 K) and electron densities (~8.18 × 107 cm-3) providing precise elemental quantification of Mn, Fe, Ca, and Ti.3
These results, in particular, refer to a type of OES known as LIBS-induced plasma within geological materials, not traditional spark OES used for metal alloys. So, the findings reflect broader spectroscopic capabilities rather than direct application to PMI in steels.
OES is the industry standard for verifying carbon steel compositions. For example, confirming that a pressure vessel is built with SA-516 Grade 70 (carbon steel), not a lower-grade alternative, can prevent premature failure under high-pressure operations. While portable OES exists, laboratory-grade spark OES remains more common for certified testing in critical infrastructure projects.4
Laser-Induced Breakdown Spectroscopy
The afore-mentioned technique, LIBS, is a relatively new but expanding optical emission spectroscopy. It uses high-energy laser pulses to ablate microscopic amounts of material from the surface, creating a plasma. As the plasma cools, it emits light that can be spectrally analyzed to identify elemental composition.5
The main advantage of LIBS is its ability to detect light elements such as carbon, lithium, and boron, which are often beyond the capabilities of XRF. It generally requires little to no sample preparation and can be effectively applied even to rough or unpolished surfaces. The method is portable, with handheld analyzers now available for field use, making it practical for on-site inspections.5,6
Additionally, LIBS can provide rapid, multi-element analysis within seconds, a fast, multi-functioning solution for material identification. However, with its advantages come some setbacks. It is more sensitive to surface contamination, requires careful calibration, and typically shows greater variability and lower repeatability than XRF.
Calibration-Free LIBS (CF-LIBS) methods attempt to address some of these limitations, though research is ongoing.5
Case Studies:
Stainless Steel Verification in Scrap Recycling
In a study by L. Brooks and G. Gaustad, handheld XRF units were tested in the metals secondary industry under “scrap yard conditions,” where samples were unpolished, painted, or coated. XRF analyzers consistently provided reliable identification of stainless steels and aluminum alloys, even under rough conditions.1
While specific numerical comparisons were not always disclosed, the study found that handheld XRF outperformed handheld LIBS in consistency under challenging surface conditions.
In oil and gas contexts, this portability ensures that stainless steel pipes and flanges can be verified on-site before installation, preventing costly mix-ups of alloys with differing corrosion resistance. Field conditions, such as surface scale or weld beads, may impact accuracy and require operator expertise.1
Trace Element Detection in Cement and Alloys
Baig et al. (2024) reviewed LIBS applications in analyzing cement samples, geological ores, and molybdenum alloys. Their findings included reported Ca concentrations in cement ranging from 71-76 wt%, drawn from prior studies.
LIBS spectra also identified trace elements such as Sr, Ti, and Li that were missed by complementary methods. These results highlight LIBS’s rapid response time and its ability to detect a broad range of elements, even at low concentrations.6
Real-Time Analysis of Phosphate Ores Using LIBS
In a study by Rosenwasser et al., quantitative analysis was performed on phosphate ores using a commercial LIBS instrument. Elements such as phosphorus (P), calcium (Ca), magnesium (Mg), silicon (Si), and aluminum (Al) were detected with relative standard deviations (RSD) of only 2-4 % for most elements, confirming the method’s reliability.7
In a complementary study, Asimellis et al. applied single-pulse LIBS for in situ quality assessment of phosphate ore rocks based on the ratio of phosphorus to silica emission lines. This method enabled clear separation between “rich ore” samples (P/Si > 1) and high-silica ores (P/Si < 0.5).
While not directly applicable to alloy PMI, these examples demonstrate LIBS's flexibility across a range of materials.8
Comparative Discussion
Together, these methods form a complementary toolkit. XRF is typically the first choice for stainless steels, OES remains indispensable for carbon steels, and LIBS is a flexible newcomer filling gaps in light element detection. In critical applications, these methods are often used in conjunction with certified laboratory testing for final validation.
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Technique
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Strengths
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Limitations
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Oil & Gas Use Case
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XRF
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Fast, non-destructive, excellent for Cr, Ni, Mo in stainless steels
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Poor detection of light elements (C, B); surface coatings may affect accuracy
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Verifying stainless steel pipes, valves, and flanges
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OES
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Detects carbon and sulfur; accurate bulk analysis
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Requires surface prep (grinding); less portable
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Verification of carbon steels and welds
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LIBS
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Portable, detects light elements, minimal prep, rapid
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Sensitive to surface contamination; less repeatable than XRF; requires careful calibration
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On-site analysis of carbon steels, aluminum alloys, and exotic alloys
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Conclusion and Future Perspective
PMI is not just a compliance exercise. It is a frontline defense against potentially catastrophic material failures in oil and gas infrastructure. Modern spectroscopic techniques have reshaped the process, making it faster, more portable, and more comprehensive.
The integration of these technologies ensures robust PMI strategies, reduces the risk of alloy mix-ups, extends equipment lifetimes, and ultimately enhances the safety and efficiency of oil and gas operations. However, reliability depends on proper calibration, surface preparation, operator training, and awareness of each method’s limitations.
Looking ahead, the future of material identification lies in advancing efficiency through better sorting and detection technologies, including the development of more automated, in-line systems for in the moment verification.
References and Further Studies
- Brooks, L.; Gaustad, G., Positive Material Identification (Pmi) Capabilities in the Metals Secondary Industry: An Analysis of Xrf and Libs Handheld Analyzers. In Light Metals 2019, Springer: 2019; pp 1375-1380.
- Oyedotun, T. D. T., X-Ray Fluorescence (Xrf) in the Investigation of the Composition of Earth Materials: A Review and an Overview. Geology, Ecology, and Landscapes 2018, 2, 148-154.
- Fahad, M.; Sajad, A.; Iqbal, Y., Plasma Diagnostics by Optical Emission Spectroscopy on Manganese Ore in Conjunction with Xrd, Xrf and Sem-Eds. Plasma Science and Technology 2019, 21, 085507.
- Puspita, W. R. et al., Comparative Analysis between SA-516 Gr 70 Material with SA-537 Class 2 Material in Shell Pressure Vessel Fabrication Process. Jurnal Integrasi 2024, 16, 104-110.
- Mal, E. et al., Optimization of Temporal Window for Application of Calibration Free-Laser Induced Breakdown Spectroscopy (Cf-Libs) on Copper Alloys in Air Employing a Single Line. J. Anal. At. Spectrom. 2019, 34, 319-330.
- Baig, M. A. et al., Analytical Techniques for Elemental Analysis: Libs, La-Tof-Ms, Edx, Pixe, and Xrf: A Review. Proceedings of the Pakistan Academy of Sciences: A. Physical and Computational Sciences 2024, 61, 99-112.
- Rosenwasser, S. et al., Development of a Method for Automated Quantitative Analysis of Ores Using Libs. Spectrochimica Acta Part B 2001, 56, 707-714.
- Asimellis, G. et al., Phosphate Ore Beneficiation Via Determination of Phosphorus-to-Silica Ratios by Laser Induced Breakdown Spectroscopy. Spectrochimica Acta Part B 2006, 61, 1253-1259.
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