Spark Source Atomic Emission Spectrometry (Spark OES) is an analytical technique that uses high-voltage electric sparks to excite the sample surface and cause atoms to emit light. The chemical composition of the material is determined by analyzing the wavelength and intensity of the emitted light. In simple terms: by striking a spark on metal and observing the color and brightness of the spark, we can identify the type of steel. It is the most common and fastest analytical method used in iron and steel metallurgy, machinery manufacturing, and raw material acceptance for pressure vessels.
1. Working Principle: From “Spark” to “Spectrum”
The whole process can be divided into four steps: ExcitationHigh-voltage capacitive discharge (spark) is generated between the electrode of the instrument and the metal sample surface.Instant high temperature (up to 10,000 K) vaporizes a small amount of metal on the sample surface, forming a plasma. Atomization & EmissionAtoms in the plasma are excited; outer electrons return from high energy levels to low energy levels, releasing photons (light) of specific wavelengths.Principle: Similar to unique human fingerprints, each element (such as Fe, C, Cr, Ni) emits light of a distinctive wavelength (color). DispersionThe composite light emitted passes through a grating (a precision optical component), which separates light of different wavelengths to form a spectrum. DetectionPhotomultiplier tubes (PMT) or CCD/CMOS detectors measure the intensity of light at specific wavelengths.Quantification: The intensity of light is proportional to the content of the element (higher content produces stronger light).
2. Why It Is the Industrial “First Choice”? (Advantages & Disadvantages)
Advantages
- Extremely fast: Results are typically available in 30 seconds to 1 minute, ideal for rapid composition adjustment during steelmaking.
- Simultaneous multi-element analysis: A single spark can measure dozens of elements, including C, Si, Mn, P, S, Cr, Ni, Mo, etc.
- Non-destructive testing: Only a tiny pit forms on the sample surface, without damaging the overall structure.
- Direct solid analysis: No sample dissolution is required as in chemical analysis; bulk samples can be tested directly.
- High precision: Excellent accuracy for major elements in metal matrices (content > 0.1%).
Disadvantages
- Poor performance for non-metallic gases: Difficult to accurately measure H, O, N and other gaseous elements (usually analyzed by ONH analyzers).
- Higher detection limits for trace elements: Less sensitive than ICP-MS for ultra-low content (ppm level) impurities.
- Strict surface requirements: The sample surface must be polished to a smooth, mirror-like finish; otherwise, conductivity and excitation efficiency will be affected.
3. Standard System
In China, spark OES analysis is mainly performed in accordance with the following standards:
- GB/T 4336-2016 Carbon steel, medium and low alloy steels — Determination of multi-element content — Spark discharge atomic emission spectrometric method (conventional method)The most commonly used standard for analysis of plain carbon steels and low-alloy steels (e.g., Q345R).
- GB/T 11170-2008 Stainless steels — Determination of multi-element content — Spark discharge atomic emission spectrometric method (conventional method)For analysis of stainless steels such as 304 and 316L.
- GB/T 14203 General rule for photoelectric emission spectrometric analysis of iron, steel and alloys
4. Application Scenarios
Ladle AnalysisDuring steelmaking, a sample is taken from molten steel for rapid analysis. If composition is out of specification, adjustments are made immediately by adding alloying materials. Incoming InspectionWhen pressure vessel manufacturers receive steel plates or pipes from steel mills, a spectrometer is used to verify that the material matches the quality certificate (preventing material mix-ups, such as using 20# steel instead of 304). PMI (Positive Material Identification)On-site installation uses handheld spectrometers (portable Spark OES or XRF) to scan pipe fittings and confirm compliance with material specifications on drawings.
5. Analysis Procedure
SamplingRepresentative samples are cut from molten steel or finished steel products. Sample Preparation (Critical Step)The sample surface must be ground flat and bright using a grinding wheel or milling machine to remove oxide scale, oil stains, and decarburized layers.Surface roughness is typically required to be Ra < 1.6 μm. ExcitationThe sample is placed in the instrument chamber, and the instrument automatically performs spark excitation. ReadingThe computer automatically calculates and displays the percentage content of each element. JudgmentResults are automatically compared with standard grade ranges (e.g., Q345R) to determine conformance.
