Boots are best for working outside. Tennis shoes are best for the gym. Sandals are best for the beach.
Sometimes, though, footwear styles overlap each other. Maybe you need tennis shoes for working outside or sandals in the gym’s locker room. It all depends on the application.
The same can be said about positive material identification (PMI) testing techniques. There are three primary technologies you can use to carry out PMI testing. Test methods for PMI include:
LIBS, OES, and XRF all have their pros and cons. But, when you get down to it, it all depends on the scenario. The application.
When should you use LIBS vs. OES vs. XRF for PMI testing? To choose the correct PMI testing technique (LIBS vs. OES vs. XRF), ask yourself these 4 questions:
We’ll unpack these questions so you can better identify which PMI testing technique to use. But first, let’s review how LIBS, OES, and XRF work.
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X-ray fluorescence, or XRF, is a widely used PMI technique. XRF technology has been around for over 70 years and is more recently available in a handheld format.
Olympus Vanta Element Handheld XRF
All XRF instruments, including handheld and benchtop, consist of an X-ray source and a detector.
XRF technology uses X-ray beams to excite the atoms in a metal sample. A secondary X-ray is generated from the unstable atoms. The secondary X-ray is specific to the elemental composition of the metal.
The detector, then, recognizes the secondary X-ray beam and is processed by the analyzer.
Next, the analyzer’s results are compared to a metal grade library and an alloy grade ID is provided based on the chemistry.
Like anything else, the cost of a handheld XRF depends on the industry, urgency, and critical nature of the application.
Purchasing a new handheld XRF analyzer can cost anywhere between $15,000-$35,000. It’s critical to note that you’ll get the quality and functionality you pay for; if you go less expensive, the performance of the handheld XRF might not meet all of your needs.
Take into account the cost of ownership and maintenance as well. There are some very fragile parts on a handheld XRF. If they do not fail or break, the X-ray tubes will need to be replaced every 5-10 years depending on usage.
Fragile parts like X-ray tubes and detectors can often cost $7,000-$10,000 a piece not including labor and associated fixes.
The benefits of using XRF technology for positive material identification include:
There are also drawbacks when using XRF analyzers for PMI. These include:
The more you understand the ins and outs of the technology, and how it's used for your application, the better prepared you'll be to make the right decision for you, your team, and your customers.
QuantoLux QLX1 Portable LIBS Laser OES
OES, or optical emission spectroscopy, comes in two forms:
In the 1960s, metal production labs had evolved from using a flame to using a spark for PMI testing. And, although it’s not widely adopted yet, advances in technology have made it possible for the spark to be replaced by a maintenance-free laser.
The traditional spark OES system uses an electrical source to charge the atoms in a sample. This causes the sample to emit light corresponding to its elemental makeup.
Purchasing a portable spark OES will put you out anywhere from $40-$60K, sometimes more. You may be able to budget in the initial cost; however, spark-based portable optical emission spectrometers require more maintenance than most other machines.
Maintenance costs
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.
Repair costs
Depending on the repair, plan on spending $7-$20K for the maintenance of spark OES analyzers. A few more factors you should prepare for include
To keep costs down and increase convenience, consider renting your spark-based portable OES (or, switch to a laser-based system).
The pros of using spark OES include:
The disadvantages of using spark OES for PMI are:
Honestly, we could go on. You may think this list of cons is being a little harsh. This is the sacrifice the industry has been making to handle strict testing requirements out in the field or on the shop floor. So, yes, it is harsh. A harsh reality.
LIBS laser OES uses high-energy laser pulses to charge the atoms within a sample. The plasma light that is subsequently emitted shows spectral signatures of the present elements.
Similarly to spark OES, laser OES provides a computer software system with light intensity data. The system, then, makes it easier for the user to understand the elemental composition of the sample.
Purchasing a portable LIBS laser OES will cost roughly $40-$60K, sometimes more. Unlike spark spectrometers, there is little ongoing maintenance or expensive repairs. Also, with proactive component monitoring and remote troubleshooting, you avoid the costs of surprise downtime and service technician travel.
The benefits of using LIBS laser OES technology are:
Sounds too good to be true?
Get a sneak peak of the QLX1 Portable LIBS Laser OES here!
There are a few drawbacks of deciding to use laser OES for PMI:
LIBS (aka, laser-induced breakdown spectroscopy) was established 50 years ago, but LIBS handheld technology has only been around for 7 or 8 years.
Advancements in technology have made it possible to miniaturize the laser while maintaining quality performance. So, instead of a benchtop LIBS system, manufacturers now have access to the more handheld LIBS device.
Rigaku KT-100S Handheld LIBS
Handheld LIBS technology uses a laser source to vaporize the sample, thus exciting the atoms within it. Just like LIBS laser OES describe above.
This results in a signature light source given off by the elements in the material. The detector recognizes the light signatures and transfers the data to the analyzer. The analyzer determines the chemistry and makeup of the metal.
Lastly, the analyzer compares the elemental percentages, chemistry, and composition against a grade library to provide an alloy ID. The handheld format is better for sorting and alloy ID rather than for the full chemistry results provided by its portable counterpart.
Buying an analyzer will run you between $20,000 and $40,000. The reason for the wide range is that there are a group of LIBS analyzers that can test for carbon and sometimes even non-metals.
They are more expensive and closer to $40,000. The metals only group that does not analyze carbon will run in the $20,000 to $30,000 range.
Master Tip: If you don't need Carbon values, don't pay the premium for it.
Beyond the purchase price, the cost of maintenance and ownership is very minimal compared to handheld XRF and OES.
The advantages of using handheld LIBS for PMI include:
If you're looking to sort aluminum, handheld LIBS is the way to go.
The disadvantages of using handheld LIBS are:
Now that we’ve covered the backgrounds of these three PMI techniques, let’s explore the questions that need to be asked before picking one.
If the answer is NO…
Choose XRF. Because it uses X-rays, it’s the only truly non-destructive PMI technique.
Keep in mind, however, that if the sample has any plating or coating applied, it will affect your results. Shop around for a handheld XRF device that allows you to see the outer layer as well as the base layer.
If the answer is YES…
Consider using a laser-based analyzer so you can avoid the radiation and expensive repairs of XRF.
For measuring carbon above 800 ppm, you’ll want…
If you need to positively identify based on carbon, you have to have a carbon number, and you can't use XRF.
For L-grade and H-grade steel at <800 ppm carbon, you’ll want…
For measuring boron, phosphorus, sulfur, and nitrogen, you’ll want…
For measuring tungsten, you’ll want…
To sort aluminum in the yard, you’ll want…
We could go on for a while here but these are the most common examples where we see that choosing the right technology can make a big impact on results.
For many PMI testing applications, all three technologies are a viable solutions and we make recommendations based on the pros and cons previously discussed.
As quickly as possible, choose…
LIBS. Its speed is unmatched in the applications it’s able to do. Plus, since it doesn’t use x-ray radiation, you can simply hold the sample in your hand to test. This can lead to greater efficiency and productivity.
PMI techniques from fastest to slowest (with a clean sample and direct contact):
Handheld LIBS > LIBS Laser OES > Handheld XRF >>> Spark OES
Choose LIBS. You’ll have minimal government paperwork if any.
Nonetheless, make sure your employees are properly trained in using LIBS. Although LIBS doesn’t use any dangerous radiation like XRF, it’s still important that users have a complete understanding of how the tool works.
Refer to this table for a bird’s eye view of LIBS, OES, and XRF:
The main takeaway I hope you walk away from this article with is to do your homework when it comes to choosing the best PMI testing technique for you and your organization.
There are negative and positive stories about each of these three PMI techniques. It’s up to you to understand the ins and outs of your application and to determine the features you need in a PMI system.
And, as always, never stop testing your metals!
To learn more about PMI techniques, subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.