There have been a handful of truly revolutionary inventions throughout history.
Fire. The wheel. Electricity. Donuts. The handheld XRF. No, I’m not over-exaggerating!
In all reality, the handheld XRF really has done a lot for positive material identification (PMI). That’s why I feel it’s important for manufacturers to understand how it works and why we use it.
Olympus Vanta Element Handheld XRF
The big question I’m setting out to answer today is…
What is handheld XRF and why is it so popular for positive material identification (PMI)? Handheld X-ray fluorescence (XRF) is a widespread technique used to determine the elemental composition of a material, normally a metallic alloy. Compared to previously available techniques, the lower cost, speed, handheld design, and flexibility of testing led handheld XRF analysis to quick and widespread adoption for PMI testing.
There’s the “quick” answer. But, of course, there’s a little more to it.
In this article, we’re going to explore
- What, exactly, X-ray fluorescence (XRF) is
- Why XRF for PMI is important
- The pros and cons of using a handheld XRF analyzer for PMI
- The cost of owning a handheld XRF analyzer
- Common mistakes to avoid when using handheld XRF
Let’s get started, shall we?
Psst: This post is based on a podcast with co-host Chris Carolan. To hear this episode (and more like it), subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.
What is Handheld X-ray fluorescence (XRF)?
Handheld XRF, or X-ray fluorescence, is a popular technique used to determine the composition of a material (often a metal alloy). This process is called positive material identification (PMI). Handheld XRF analyzers use X-rays to excite atoms within an alloy and produce secondary X-rays that are characteristic of particular elements. The secondary X-rays are compiled and processed by the detector which, in turn, displays the results on a screen. The results will usually be the chemistry and/or alloy grade of the metal material being tested.
Handheld XRF is the most widely used technology for positive material identification.
There are literally thousands of grades that have been documented by the Unified Numbering System (UNS) for metals and alloys. Alloy grades are like recipes for each metal material.
Essentially, the base metal — like copper or steel — is alloyed with special elements to add or adjust properties of the metal. Take the following recipes for example:
- Chromium and nickel are added to stainless steel for corrosion resistance and oxidation prevention.
- Molybdenum ("Moly") is often added to steel and iron for its hardness and tensile strength.
- Copper is added to aluminum to increase strength.
- Beryllium is added to copper to increase hardness and strength.
In order to ensure alloy recipes like those above contain the right amount of elements, elemental analysis (PMI) can be done with handheld x-ray fluorescent technology.
SS 321 grade recipe seen on Olympus Vanta handheld XRF
How X-ray fluorescence works
XRF technology has been around for over 70 years. It’s proven to be a very reliable technique for elemental analysis and identifying materials of all types.
All XRF instruments, including handhelds, consist of two major components:
- the X-ray source
- the detector
How an XRF analyzer identifies materials:
- Primary X-rays are produced by the source and penetrate the surface of the sample. (Sometimes X-rays are passed through a filter to modify the beam.)
- The X-ray beam collides with atoms in the sample, resulting in secondary X-rays. This is because when the high-energy primary X-ray impacts an atom, the atom’s equilibrium is disturbed.
- An electron (a negatively-charged particle orbiting the atom) shoots out and creates a vacancy around the atom. This makes the atom unstable.
- To recover stability, an electron from a higher energy level takes the place of the ejected electron. The excess energy from the electron moving between two energy levels is emitted as a secondary X-ray.
- The secondary X-ray is distinctive to the particular element.
- The secondary X-rays are then compiled by the detector and processed by the analyzer. This produces a spectrum revealing each X-ray’s intensity peak compared to its energy.
- The peak energy identifies the element. The peak intensity uncovers the amount of the element present.
- The analyzer, then, calculates the elemental composition of the material.
An atomic view of XRF analysis in action
Phew! That’s quite the process.
Luckily, we have handheld XRF analyzers to help us through this process in a matter of seconds.
Why is XRF important?
X-ray fluorescence is one of the most widely used methods of testing metal alloys. It’s crucial that XRF is accurate because proper PMI prevents disasters and fatalities.
Positive material identification (PMI)
Positive material identification — or, PMI — is best done with proper training and technique. PMI verifies all the structures around us. Without proper PMI testing, things like
- oil drills,
- medical devices,
- and machinery
are at risk of containing faulty parts. PMI verifies that the metal parts making up our world won’t corrode, break, overheat, or poison the environment.
Chevron Refinery Fire
From the CSB: "On August 6, 2012, the Chevron U.S.A. Inc. Refinery in Richmond, California (“the Chevron Richmond Refinery”) experienced a catastrophic pipe rupture in the #4 Crude Unit. The incident occurred from piping referred to as the “4-sidecut” stream, one of several process streams exiting the refinery’s C-1100 Crude Unit Atmospheric Column.
The pipe rupture occurred on a 52-inch long component of the 4-sidecut 8-inch line (the 52-inch component). At the time of the incident, light gas oil was flowing through the 8-inch line at a rate of approximately 10,800 barrels per day (bpd).
The ruptured pipe released flammable, high temperature light gas oil, which then partially vaporized into
a large, opaque vapor cloud that engulfed 19 Chevron U.S.A. Inc. (Chevron) employees. At 6:33 p.m.,
approximately two minutes following the release, the released process fluid ignited.
Eighteen of the employees safely escaped from the vapor cloud just before ignition; one employee, a Chevron refinery firefighter, was inside a fire engine that was caught within the fireball when the process fluid ignited. Because he was wearing full-body fire-fighting protective equipment, he was able to make his way through the flames to safety. Six Chevron employees suffered minor injuries during the incident and subsequent emergency response efforts.
The release, ignition, and subsequent burning of the hydrocarbon process fluid resulted in a large plume
of vapor, particulates, and black smoke, which traveled across the surrounding area. In the weeks following the incident, approximately 15,000 people from the surrounding communities sought medical treatment at nearby medical facilities for ailments including breathing problems, chest pain, shortness of breath, sore throat, and headaches. Approximately 20 of these people were admitted to local hospitals as inpatients for treatment."
Another preventable accident that could have been avoided with proper PMI inspection of the failing system components.
XRF for positive material identification
With the help of accurate and accessible XRF technology, diligent PMI can be performed. In other words, XRF analyzers help to keep our world intact.
It’s an established method of PMI testing.
When to use a handheld XRF analyzer
Like I mentioned before, careful PMI testing is absolutely crucial. That means whenever metal is changing hands down the supply chain, it needs to be tested.
Points of the metal supply chain can include
- scrap to foundry,
- foundry to parts fabricator,
- fabricator to refinery or airplane,
- and inspection of in-service parts during maintenance or safety audits.
Check out our API 578 Supply Chain Diagram
PMI testing at each of these checkpoints should be done with the utmost care and attention to detail.
The other important thing to remember is that 100 percent of the batches need to be tested. In previous years, only 10-20 percent needed inspecting. This was in part due to less regulation and laborious testing methods.
Now, with tools like the handheld XRF, it’s easier and faster to test metals and get real time results.
Plus, you probably want to be sure all the parts of an airplane have been tested before taking off, right?
The pros and cons of using a handheld XRF analyzer
It’s beneficial to weigh the pros and cons of using a handheld XRF analyzer for PMI testing, especially if you’re considering purchasing one. Here are the advantages and disadvantages of using a handheld XRF analyzer.
The pros of using a handheld XRF analyzer for PMI
Using a handheld XRF for positive material identification is accompanied by several benefits. It is the most widely used form of PMI testing, after all.
- A handheld XRF is non-destructive. That means it doesn’t destroy the sample whatsoever. No marks at all on the metal.
- It’s one of the fastest methods of PMI testing. Tests can be conducted within seconds out in the field.
- A handheld XRF is extremely portable. The device is very easily moved and can reach what would be inaccessible spots for other devices.
- It’s flexible when it comes to applications. A handheld XRF is essentially point-and-shoot technology that can analyze a variety of different material types.
- It has increased sensitivity. A handheld XRF can test for lower concentrations of elements than other PMI tools.
- Depending on the manufacturer, the software can be easy to use. The analyzer makes it easy to obtain test results.
Using a handheld XRF to identify metal in seconds definitely serves as a reminder that we are in a new era of technology. It’s portable, easy to use, and fast.
The cons of using a handheld XRF analyzer for PMI
Of course, there are a few drawbacks to using a handheld XRF for positive material identification, too.
- A handheld XRF uses ionizing radiation to analyze a sample. This can prove to be dangerous if the user hasn’t had the proper training.
- Most states and countries regulate the use of XRF technology. Because it uses ionizing radiation, all states and many countries require XRF devices to be registered. Rigorous required training and monitoring of staff handheld XRF use can also create headaches and liabilities.
- A handheld XRF can be fragile and expensive to repair. Expect to spend around $7,000-$10,000 for a repair. X-ray tubes and silicon drift detectors are not cheap.
- It has trouble testing for light elements. For elements like lithium (Li), carbon (C), magnesium (Mg), aluminum (Al), and silicon (Si), use technologies such as LIBS or OES for the best results.
- The ease of point-and-shoot results can lead to misidentified material. Improper training and technique does not prevent a result showing up on the screen. Just because you see a result doesn't mean its the correct result.
- Variable test times can lead to misidentified material. Adding another variable like test time allows the operator to decide when to stop the test leading to inconsistent results between tests and operators. An XRF gun capable of testing light elements, often needs time to switch modes in order to see elements like Al and Si. If you don't wait for that, you will get an incorrect result.
Say it with me now. Just because you see a result on the screen, doesn't mean it is the correct result.
Although it’s easy to use, the handheld XRF cannot test for carbon in materials and has to be registered in order to use it.
How much does a handheld XRF analyzer cost?
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
Purchasing a new handheld XRF analyzer can cost anywhere between $15,000-$40,000. 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.
Purchasing a used handheld XRF
Once you get into the used market for a handheld XRF, plan on spending anywhere from $5,000-$15,000.
Just like with a used car, make sure you obtain the necessary paperwork, any service records, and a summary of the analyzer’s capabilities. You want to make sure you’re getting what you’re paying for and don’t want any surprises.
One surprise repair will likely double the cost so be sure to do your due diligence when buying a used handheld XRF.
Common mistakes to avoid when using handheld XRF for PMI testing
- False positives. Just because you obtained a result on the screen doesn't make it the right result. Understand the technique and each of the variables below that can affect your testing.
- No sample preparation. Handheld XRF is a surface technique so if your metal is dirty, rusted, or coated the device will read the dirt, rust, or coating as well as the base metal. It is always best to shoot a clean base metal whenever possible.
- Changing test times. Holding the trigger until you see the result that you expect is a recipe for disaster. Some elements, especially lighter elements like Mg and Si, take much longer for handheld XRF to read. Testing the same sample for 5, 15, and 30 seconds may yield 3 different results. Whichever material you are testing, it is always best to use the same exact test times within a matrix group to ensure consistent test results.
- No maintenance. Just like a dirty sample can affect results...so can a dirty handheld XRF window. Ensure you have a clean window when testing your metal samples.
- Unsafe use. As you have heard from me many times, handheld XRF uses ionizing radiation to provide test results. If you decide to shoot a sample in your hand or on your knee, know that ~12 shots (depending on the brand/model) may take you over the recommended exposure limit of 5 rems per year.
Top brands for handheld XRF
There are many brands to choose from and each brand offers a number of different models. I've listed the most well-known brands below:
- Thermo Niton - (Ex. XL2, XL3 GOLDD+)
- Olympus IMS (Purchased Innov-X) - (Ex. Delta, Vanta)
- Hitachi (Purchased Oxford) - (Ex. X-MET8000 Smart)
- SciAps - (Ex. X-200, X-250)
- Bruker - (Ex. S1 Titan 800)
The knowledge and skills gap
While the ease of use is definitely a benefit of the handheld XRF, it can be a drawback in some situations.
Let me explain.
Handheld XRF tech is relatively easy to use and it doesn’t require much knowledge to populate a result on its screen. Unfortunately, that means handlers of this potentially harmful technology don’t always receive adequate training.
This lack of understanding and experience leads to false positives and material mix-ups: the things we’re trying to avoid in the first place. Oops...
It’s also important to remember that sample preparation and clean surfaces are critical for getting the best results with a handheld XRF.
Make sure the handlers of any type of PMI technology have sufficient training and knowledge of the tools they’re using. Otherwise, why even test your materials in the first place?
Kudos to you for taking the time to learn a little bit more about X-ray fluorescence!
Here are the points I hope you take away from this article:
- The handheld XRF is a very reliable tool that’s been around for 25+ years.
- Although it’s very easy to use, inadequate training can lead to false positives and mistakes.
- Take into account the cost of ownership and maintenance before purchasing a handheld XRF.
Until next time, Never Stop Testing Your Metals!