Stainless steel analysis is challenging due to the wide variability in elemental concentrations when compared to the low alloy family of steels. Low alloy steels have at least 90% iron and are alloyed with 10% other elements, such as carbon, chromium, nickel, molybdenum, silicon and aluminum. By comparison, stainless steel compositions vary broadly, with iron compositions of as little as 50% and alloying elements such as chromium and nickel (for example) ranging from nearly zero to about 30%.
Carbon is the most important alloy ingredient in all families of stainless steels. Carbon in steels controls many physical properties, including hardness, strength, weldability and brittleness. Correct identification of stainless steels in the field can indicate the appropriate grade to be used for your specific application or for design remediation. Of great importance in stainless steel analysis is the ability to differentiate between L and H grades. Low grade stainless steels contain < 0.03% carbon, while those with concentrations above this are considered High grade stainless steels.
Quality Control (QC) and Positive Material Identification (PMI) instruments have become indispensable tools for robust material verification programs. These tools help ensure that the correct grade of stainless steel is used in the right place at the right time. The wrong grade can have consequences as simple as economic loss, or as crucial as loss of life. Explosions in chemical and petrochemical plants are vivid reminders of the dangers of using incorrect alloys. Therefore, most industries strive to ensure product quality by verifying raw materials used during the production process.
New portable handheld analyzers have been designed to accommodate the demanding needs for stainless steel analysis with excellent accuracy and precision (variability) at low and high concentrations of alloying elements. These analyzers are based on Laser Induced Breakdown Spectroscopy (LIBS), the analytical technique using a high-focused laser to determine the chemical composition of materials. LIBS utilizes a highly-focused laser that ablates the surface of a material, it then forms plasma in which the material is broken down into single elements. Compared to portable OES, the amount of material ablated on the sample by the handheld LIBS analyzer is a fraction of the total amount. LIBS is capable of measuring elements, including carbon, in the field for material identification.
Handheld LIBS analyzers rapidly and accurately determine major and minor alloy elements in stainless steel across a wide range of concentrations. Handheld LIBS analyzers are even capable of accurately differentiating between L and H grade stainless steels, critical to safety and material compatibility considerations in manufacturing environments. Field users can safely and easily analyze pipes in situ without heavy equipment, using the real-time data display for accurate decision making.
To see data and analysis demonstrating the accuracy and high reproducibility of a handheld LIBS analyzer for elements of interest in stainless steels using a multiple instrument comparison method (average of six (6) readings from sixteen (16) instruments), download the application note, Stainless Steel Performance Characteristics Using the Niton Apollo Handheld LIBS Analyzer.
Further recommended reading:
- How Carbon Affects the Quality of Steel Weldability and Hardness
- The 4 Methods for Analyzing Carbon in Steel: Which is Best?
- Webinar: Why is Analyzing Carbon Important?