The manufacturing industry has little to no tolerance for error. That means suppliers often need to know the exact composition of the metallic alloys they’re dealing with.
Portable optical emission spectrometers (OES) have gained popularity in PMI testing. This is likely due to their portability and ability to provide the full chemistry of a metal including true carbon measurement.
QLX1 Portable LIBS Laser OES from QuantoLux
In this post, we’ll cover questions around portable OES including:
What is an optical emission spectrometer (OES)? An optical emission spectrometer, or OES, is a spark- or laser-based system designed to accurately determine the elemental composition of metals by burning the metal surface and measuring the light wave emissions coming from the plasma created.
And specifically for portable OES:
Let’s dive in!
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First thing’s first: If you’re unfamiliar with positive material identification (PMI), take a gander at this post. Then come right back! Reviewing PMI testing will help you better understand optical emission spectroscopy.
Now, what exactly is optical emission spectroscopy (OES)?
OES starts with an electrical or laser-based source to charge atoms within a metallic sample. When the atoms within a particular metal get excited, they emit a trademark light.
This light, or optical emission, requires a small piece of the sample to be heated up to thousands of degrees Celsius. What’s good at heating stuff up? Lightning and lasers!
Essentially, OES uses electricity or lasers to vaporize the sample’s surface, charging up its atoms and creating a plasma. Then, the metallic sample shows its true colors. The light a sample emits is consistent with its chemical composition.
So, you’ve seen the colors that the metallic sample produces when heated. Now, it’s time to measure the intensity of each of those colors.
Fun fact: Iron emits over 8,000 different wavelengths!
The emitted light passes into the spectrometer. The OES spectrometer is then able to grade each separate light into element-specific wavelengths. A corresponding detector measures the intensity of each wavelength (aka, each light’s intensity).
Subsequently, the intensity of each wavelength is proportional to the concentration of their respective elements.
In other words, the nickel wavelength measures at a high intensity? There’s a lot of nickel in the sample. The wavelength corresponding with copper is weak? There’s not much copper in there.
Thirdly in OES testing, a computer system processes the intensity data. Through a predefined calibration, the system is able to generate elemental concentration levels.
Ta-da! You now know the overall composition of the sample. That means you can accurately compare it to a metal alloy grade library or database to make sure it’s the right stuff. (Ex. Stainless Steel 316)
As the knowledge around positive material identification began to expand, so did OES methods. Here’s a quick history of where the portable OES got its start.
In the early 20th century, manufacturers used a flame as the light source for OES testing. The flame would heat up the sample’s atoms, producing a light consistent with its components.
Burning Copper
Ever heated up a penny before? You probably saw a greenish-blue light emitting from it due to the copper. Using a flame for OES testing is the same concept.
Of course, there had to be a more accurate way of measuring the composition of metals.
Enter, arc spark OES (or, spark OES). This metal testing method came about in the 1950s and 60s because of its increased excitation capabilities.
Gotta keep those atoms excited, right?
In its early days, spark OES was primarily used in metal production labs where they needed to know the full chemistry and composition. The only spark OES spectrometer available was rather stationary. But, it got the job done.
As PMI testing became prevalent outside of the lab, portable OES was developed to support the need for testing materials on the shop floor or out in the field.
A laser can replace the spark as the source that's vaporizing the metal.
Recently, the advancement of laser technology has allowed lasers to take the place of sparks in the vaporizing process.
Considering a portable optical emission spectrometer for your business? Take note of the following pros and cons we've collected through our experience serving the metals supply.
With a portable optical emission spectrometer, you can…
The analytical performance makes it the go-to technology to acquire full metal chemistry outside of the lab.
Sounds pretty great, huh? Well, there are also a few drawbacks to think about when using a traditional, portable spark OES analyzer.
Drawbacks of using a traditional, spark-based portable OES include…
Pro tip: Laser-based OES provides all the chemistry and sensitivity you need with almost none of the cons of traditional, spark-based OES.
Get a sneak peak of the QLX1 Portable LIBS Laser OES here!
Next, we’ll discuss the costs of using a portable OES for positive material identification.
It’s safe to say purchasing your business’s own portable optical emission spectrometer isn’t going to be cheap. Even so, the consequences of failing to conduct positive material identification are even costlier.
From the CSB: "On the evening of January 12, 2009, 2 refinery operators and 2 contractors suffered serious burns resulting from a flash fire at the Silver Eagle Refinery in Woods Cross, Utah. The accident occurred when a large flammable vapor cloud was released from an atmospheric storage tank, known as tank 105, which contained an estimated 440,000 gallons of light naphtha. The vapor cloud found an ignition source and the ensuing flash fire spread up to 230 feet west of the tank farm. On November 4, 2009, a second accident occurred at the Silver Eagle Refinery in Woods Cross, Utah, when a powerful blast wave - - caused by the failure of a 10 inch pipe - damaged nearby homes."
A pipe failure that could have been avoided with proper PMI testing.
It’s a necessary evil, some would say, to gain access to a portable OES and conduct proper PMI testing. The reliable analysis and quality control is always worth it.
Purchasing a portable OES will put you out anywhere from $35-$60K, sometimes more. You may be able to budget in the initial cost; however, traditional, spark-based portable optical emission spectrometers require more maintenance than most other machines.
On-going maintenance costs of traditional, spark OES will put a big dent in any operating budget. With constant Argon gas usage, electrode cleaning and sharpening, and other consumables that need to be maintained, maintenance costs can easily reach thousands of dollars per year.
Beyond the actual dollars, the time and effort it takes to constantly maintain and operate these analyzers should also not be overlooked or underestimated.
Depending on the repair, plan on spending $7-$20K for the maintenance of spark OES analyzers. A few more factors you should plan on include
To keep costs down and increase convenience, consider renting your spark-based portable optical emission spectrometer (or, switch to a laser-based system).
A one-month rental of a portable spark OES system usually runs between $7,000 and $10,000.
To attain the best PMI results with your OES metal analyzer, avoid these mistakes during testing:
If you don't have strong enough light signals, you're not going to be able to read the elements.
Avoid making these mistakes when using a portable OES and there should be smooth sailing.
Brands that supply portable optical emission spectrometers include
In addition to these listed brands, there are more European OES providers entering the market.
Choosing the right tool for PMI testing is crucial for numerous reasons. OES is a cornerstone technique for determining the complete chemistry of a metallic alloy.
In an industry that requires little to no margin of error, it’s worth it to fully understand all the PMI tools at your disposal and remember to...
Never stop testing your metals.
For more expert insights on PMI testing, subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.