New Handheld for Carbon, CE in Steels and Carbon in L-grade Stainless
Measuring Carbon as Part of Residuals in HF Alkylation Units
API Recommended Practice 578 (3rd Edition) now recognizes a new handheld technology, laser induced breakdown spectroscopy (LIBS), for the measurement of carbon and other alloying elements in steels and stainless.
Handheld LIBS, developed by U.S. instrumentation company SciAps, has found wide usage in refining and fabricating for its ability to measure carbon content in stainless at suitable levels to separate L and H grade stainless. Virtually every major pipeline owner/operator or their NDE provider now uses the device for carbon content and carbon equivalents (CE), thus weldability in pipeline steels (API 5L).
A growing application for the LIBS is residual element analysis in steels for HF alkylation units per API 751. The most common RE formula employed is Cr% + Ni% + Cu% < 0.15%. In fact, this RE formula only applies to steels where the carbon content is <= 0.18%. If carbon content is > 0.18%, the more easily achieved RE formula Ni% + Cu% < 0.15% may be used.
So why is the more stringent RE formula used? Historically, operators use handheld X-ray guns to perform PMI for HF alkylation units. Handheld X-ray cannot measure carbon content, so it is assumed that carbon is under 0.18% and the more conservative RE formula including Cr is utilized. Despite this limitation, X-ray has been preferred because it is much easier to use and far more portable than the carbon-capable spark OES technology. In short, operators prefer the more conservative RE (which is tougher to meet) so they can use handheld X-ray, instead of lugging around spark OES and the large tanks of accompanying argon gas.
LIBS technology offers a method to measure both C and Cr, Ni, and Cu simultaneously in a handheld device. If carbon is > 0.18%, then the device may use the more relaxed RE formula for only Ni and Cu. This means more incoming and in-service materials may meet the residual limit if Cr can be omitted. The LIBS carbon measurement is quite valuable because as more steel product originates from recycled material rather than virgin iron ore, residual levels especially of Cr and Cu have steadily increased over the years, making it more challenging to obtain steel product that meets the 0.15% requirement on RE.
Carbon testing pre-2017
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.
Spark OES is fraught with a number of challenges. An experienced, well-trained operator is a must. Analysis requires an inert gas environment, usually argon, so spark systems are equipped with a large (40+ lb.) metal container of high-pressure argon. Users must purge the spark system before using it. Before moving to the next location, they turn off the argon supply, then re-purge and recalibrate at the new location, reducing throughput. Argon runs continuously during testing, thus a large tank is required. Still, until recently, spark OES was the only choice for in-field carbon work.
What is LIBS?
Many of the people who launched SciAps in 2013 were the innovators 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). X-ray technology had become rock solid for PMI, including residual transition metals like Cr, Cu and Ni. Despite the advancements in X-ray, there remained a significant limitation to handheld X-ray: carbon. Due to the extremely low energy of carbon X-rays (and other low atomic number elements like lithium, beryllium and boron), there’s no practical way to measure carbon or similar “light elements” with a handheld X-ray gun. Yet carbon concentration is critical to measure in steels and stainless.
So the SciAps founders got to work analyzing carbon with a handheld. LIBS is an OES method like spark, but the bulky spark source is replaced by a very small high-powered pulse laser. SciAps miniaturized the laser and other key components into a 4.5 lb. handheld. This breakthrough required three major innovations:
- Replace the power-hungry high voltage sparking system with a miniature pulsed laser. The SciAps laser delivers a pulsed beam in a small spot (100 um), in a very short time scale (1 ns), powered by an on-board battery.
- Re-invent the purge process. The narrow laser requires a small purge volume (a few cc’s). Between tests the argon flow halts. The result is about a 1,000x reduction in argon consumption, allowing a tiny canister in the handle of the device to replace the 40+ lb. argon tank. The canister delivers 600 burns, thus 600 carbon tests. You can carry the Z anywhere without shutting off argon and re-purging.
- Miniaturize the spectrometer, while still delivering the needed spectral range and resolution for carbon and required transition and heavy metals.
The resulting device – the SciAps Z – now has nearly 600 installations worldwide into petrochemical, pipeline, and steel fabricators. It is recognized in RP 578 3rd edition. It has been evaluated favorably to spark OES in numerous independent studies by leading users and institutes for C and CE in pipeline steels, L-grade stainless, residuals, and even sulfidic corrosion applications.
The SciAps Z for carbon in steels and stainless: Proven handheld technology with nearly 600 installations globally.
The NACE paper “03651 Specification for Carbon Steel Materials for Hydrofluoric Acid Alkylation Units” originated test and corrosion rate measurement procedures for evaluating materials in HF environments and a carbon steel materials specification with respect to the levels of residual elements and carbon in steels for HF alkylation equipment.
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.