Breakthrough Technology for Measuring Carbon and Carbon Equivalents
For those who need to measure carbon in steels, there’s now a handheld analyzer for the job. Where operators previously either used spark OES technology—which required substantial operator expertise—or hired a third-party testing company to bring the OES with them, there’s now a better option.
Two years ago, SciAps debuted the world’s first LIBS unit that differentiates steels by carbon content in steels and stainless, and verifies carbon equivalents for weldability of metals. SciAps has put carbon analysis in the palm of the hand for the first time. In addition, SciAps is committed to free training, including re-training, for more and better-trained operators. Already, nearly 600 units are being used in the field for virtually every major industry globally.
Many of the people who launched SciAps in 2013 were veterans of the handheld X-ray industry, having been founders and/or employees at the two leading handheld alloy analyzer companies, Niton and InnovX (now Thermo Fisher Scientific and Olympus).
At that time, X-ray technology was rock solid with transition metals and heavy metals, even Mg, Al, Si, P and S. X-ray worked great on stainless, high-temperature alloys, brasses/bronzes, aluminums, etc., greatly improving alloy analysis and handling specialty applications like low silicon in steels for sulfidic corrosion, P and S content in steels and stainless.
Despite all this innovation, there remained a significant limitation to handheld X-ray: carbon. The extremely low energy of carbon X-rays would get completely absorbed in the window material covering the detector and the air in the pathway. The same is true of other low atomic number elements like oxygen, nitrogen, boron, lithium and beryllium. Without an enclosed system under high vacuum where you’d have to remove a piece of the metal, there’s no practical way to measure carbon or similar “light elements” with a handheld X-ray gun.
Yet carbon concentration is critical to verify in steels and stainless. For steel weldability, it is essential to determine carbon equivalents. CE measurement requires C, plus common alloying elements like Mn, V, Cr, Ni, Cu, Mo and Si. You can measure these other elements with X-ray, but without carbon, there’s no CE.
Users of stainless face a similar challenge. Many specifically call for a low or high carbon grade of stainless, such as 316 or 316L. L-grades require the carbon content to be <0.03%, whereas H-grades require carbon content to be >0.04%. Given the sheer volume of steel and stainless that is produced, used, and recycled globally, a handheld device to distinguish L from straight and H-grades is a major breakthrough.
The carbon old guard: spark OES
Until 2017, spark OES had been the only technique for in-field carbon analysis. Spark OES works by generating a high frequency electric spark that heats and burns into the metal and creates an electron plasma by stripping the valence electrons off the various atoms (carbon, chromium, iron, manganese, etc.) that comprise the alloy. As the plasma instantly cools, the electrons recombine with the atoms, emitting light in the ultraviolet, visible and infra-red spectrum. An onboard spectrometer collects the light, analyzes the intensity at various wavelengths, and applies a calibration to determine elemental chemistry.
Spark OES has been the only technique for in-field carbon analysis until SciAps invented a handheld LIBS for the same purpose. But spark OES has a number of challenges. To obtain reliable data, an experienced, well-trained operator is a must. Analysis requires an inert gas environment, usually argon, so spark systems are paired with a heavy (40+ lb.) metal tank of high-pressure argon. Users must purge the spark system before using it, then run the argon continuously during testing (thus the large tank). For safety purposes, the argon gas is generally shut off before the OES is moved, which then requires repurging and often recalibration when the device is at its next location. The spectrometer is sizable as well. All of these components rest on a dolly cart for moving around to various testing locations. For “in ditch” pipeline testing, a crane is required to move the OES from location to location.
The mobility limitations are significant. Typical complaints are difficulty in getting into pipeline ditches, up towers, or on or over racks of material. Moving and re-purging reduces throughput. Cost and availability of argon, especially in more rural or isolated areas, is a problem. Still, until recently, spark OES was the only choice for in-field carbon work, and the technique yields reliable data provided operators are well-trained and follow the SOP.
What is LIBS and how does it work?
LIBS (laser induced breakdown spectroscopy) is an OES method like spark OES, but the power-hungry high-voltage sparking system is replaced by a very small, high-powered pulsed laser. SciAps miniaturized the laser and other key components into a 4.5 lb. handheld. This breakthrough required three major innovations:
- We replaced the spark system with a miniature pulsed laser to vaporize a small portion of the material and create the plasma from the valence electrons. The SciAps laser itself is a feat of innovation. Roughly a 1″ cube in size, it delivers very low average power (6mJ pulse of energy), but incredibly high instantaneous power (50 times per second). The average power is not enough to vaporize steel or high temperature alloys. But the laser beam is focused down to a small spot (100 um), in a very short time scale (1 ns). Compare this to a laser pointer, where you press and hold the ON button and the laser illuminates a spot continuously. In the case of LIBS, the laser illuminates the spot for a billionth of a second, rests and reloads for about 1/50th of a second, then
repeats. Do the math and the instantaneous power delivered to that location on the steel is in the gigawatt/cm 2 range, easily enough energy to vaporize the alloy in that location. So the first critical development was obtaining a laser that could deliver a pulsed beam of good quality, in a small spot (100um), in a very short time scale (1 ns), powered by a very small battery that also runs the processor and display.
- We-invented the purge process. The narrow laser requires a small purge volume (a few cubic centimeters). Between tests, the argon flow halts. The result is about a 1,000x reduction in argon consumption, allowing a tiny canister (3 inches long, 1 inch diameter, less than 100g/4oz.) in the handle of the device to replace the 40+ lb. argon tank. The canister delivers 600 burns, thus 600 carbon tests, or 125-150 site samples, and costs $7 to replace. You can carry the Z anywhere without shutting off the argon and re-purging.
- We miniaturized the spectrometer, while still delivering the needed spectral range and resolution, especially for the carbon line, and for the various transition and heavy metals. For example, the carbon line measurement at 191.3 nm requires a resolution of < 0.1 nm full width half max (FWHM) because of nearby interfering iron lines from the base metal excitation.
Who’s using and approved it?
As SciAps closes in a third year of commercial shipments of nearly 600 carbon units, handheld LIBS is now included in API Recommended Practice 578 (3rd edition) for carbon testing.
Most major pipeline owner/operators use a SciAps Z for their materials. In fact, SciAps Pipeline App was born when the largest owner/operator tested and accepted the Z for carbon and CE in pipeline materials, with a specific testing protocol. Four independent studies, including the Gas Technology Institute and ASTM, have proven that the SciAps Z performs equivalently or superior to spark OES technology. These studies usually include in-field testing with both spark OES and handheld LIBS, with samples removed for outside laboratory testing. In every study, handheld LIBS precision and accuracy has been on par with spark OES.
Major refineries are deploying them for carbon testing, as are the inspection companies that support their NDT/PMI programs. The most common applications for carbon analysis are pipeline steels for carbon content and carbon equivalents, verifying L and H grade stainless, and more recently, residual element analysis (API 751).
There’s increasing use of handheld LIBS for sulfidic corrosion studies, to verify silicon content is < 0.1% in carbon steels. The power industry uses the technology extensively for flow accelerated corrosion studies to verify chromium content in steel in the 0.03% range. Regulatory burdens on handheld X-ray make the handheld LIBS an attractive alternative.
In the scrap and recycling industry, there’s also an increasing interest to use LIBS analyzers to measure so-called contaminant elements, including lithium, in aluminum scrap and carbon content in steel. While XRF is the best analyzer for aluminum alloy sorting, SciAps recommends using the LIBS in niche applications, including to measure carbon, boron, beryllium and lithium, which are elements the XRF can’t measure.
The SciAps Z for carbon in steels and stainless: Proven handheld technology with nearly 600 installations globally.
True Demo Stories from the Field
2 days spark OES vs. just 3 hours with LIBS
They had budgeted two days for testing, since they had to get up a 100-foot tower with OES. Instead, they finished the work in just three hours with our handheld LIBS analyzer.
Z-200 solves the mystery in the stainless
Location: Texas. We were called out to do some testing of some real world materials with a big inspection company…
Testing in a tight spot
Here’s a great story from the front lines of stainless testing in Japan, courtesy of our Applications Manager in Asia Pacific.
The day LIBS beat OES
Here’s another carbon story and learning opportunity, courtesy of our EMEA manager Jeroen.
Does the handheld LIBS work in the wind?
We get this question all the time, and couldn’t understand why wind is a problem. Then a breezy round of golf got us thinking about some demo stories we’ve been hearing from the road.
Demos Down Under
For each test we automatically calculate and display the Carbon Equivalence, C.E. = C% + Mn%/6 + (Cr% + Mo% + V%)/5 + (Cu% + Ni%)/15. The results here were very repeatable and matched the customer’s certified pieces perfectly.