How to Use a Handheld XRF for PMI

Emily Kingland
March 27, 2020
How to Use a Handheld XRF for PMI

There have been a handful of truly revolutionary inventions throughout history.

Fire. The wheel. Electricity. Donuts. The handheld XRF.  No, I’m not overexaggerating!

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. It's also essential to understand the risks and costs of using a handheld XRF.

via Metal Analysis Group

The big question I’m setting out to answer today is… 

How do you use a handheld XRF for positive material identification (PMI)? X-ray fluorescence (XRF) is a widespread technique used to determine the elemental composition of a material, normally a metallic alloy. A handheld XRF uses 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.

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 for PMI
  • The cost of owning a 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 X-ray fluorescence (XRF)?

XRF, or X-ray fluorescence, is a popular technique used to determine the composition of a material (normally a metal alloy). This process is called positive material identification (PMI).

"Handheld XRF is the most widely used technology for positive material identification."

Chris Carolan

Alloy recipes

There are literally thousands of recipes that have been documented by the Unified Numbering System (UNS) for metals and alloys. 

Essentially, the base metal — like copper or steel — is alloyed with special elements to add or adjust the 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 the ones above contain the right amount of elements, PMI can be done with XRF technology.

How X-ray fluorescence works

XRF technology has been around for over 70 years. It’s proven to be a very reliable technique for identifying materials. 

All XRF instruments, including handhelds, consist of two major components:

  1. the X-ray source
  2. the detector

How an XRF instrument tests for materials:

  1. 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.)
  2. 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.
  3. An electron (a negatively-charged particle orbiting the atom) shoots out and creates a vacancy around the atom. This makes the atom unstable.
  4. 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.
  5. The secondary X-ray is distinctive to the particular element.
  6. 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.
  7. The peak energy identifies the element. The peak intensity uncovers the amount of the element present.
  8. The analyzer, then, calculates the elemental composition of the material.

Phew! That’s quite the process.

Luckily, we have handheld XRF devices to help us through this process in a matter of minutes or even 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 carefully.

via Unsplash

PMI verifies all the structures around us. Without proper PMI testing, things like

  • oil drills,
  • medical devices,
  • engines,
  • airplanes,
  • vehicles,
  • bridges,
  • electronics,
  • 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.

XRF for positive material identification

With the help of accurate and accessible XRF technology, diligent PMI can be performed. In other words, XRF devices help to keep our world intact.

"XRF technology can be used for a variety of applications, such as for analyzing mineral content, plastics, lead, soil, precious metals, and PMI."

Chris Carolan

It’s an established method of PMI testing.

When to use a handheld XRF

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.

That includes

  • Scrap to foundry
  • Foundry to parts manufacturer
  • Parts manufacturer to refinery
  • Refinery to maintenance and inspection

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.

Plus, you probably want to be sure all the parts of an airplane have been tested before taking off, right?

How much does a handheld XRF 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 device can cost anywhere between $15k-$35k. It’s critical to note that you’ll get the quality you pay for; if you go less expensive, the quality of the XRF will likely be lacking.

Take into account the cost of ownership and maintenance as well. There are some very fragile parts on a handheld XRF. Furthermore, the X-rays tubes will need to be replaced every 5-10 years depending on usage.

Purchasing a used handheld XRF

Once you get into the used market for a handheld XRF, plan on spending anywhere from $5k-$15k.

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 total the device — you’d be better off buying a new handheld XRF.

The pros and cons of using a handheld XRF

It’s beneficial to weigh the pros and cons of using a handheld XRF device for PMI testing, especially if you’re considering purchasing one. Look over the benefits and drawbacks of using a handheld XRF below.

The pros of using a handheld XRF 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.

  • The XRF is non-destructive. That means it doesn’t destroy the sample whatsoever.
  • It’s one of the fastest methods of PMI testing. Tests can be conducted within seconds out in the field.
  • The handheld XRF is extremely portable. Compared to other PMI tools, the XRF is very easily moved and can reach what would be inaccessible spots for other devices.
  • It’s flexible when it comes to applications. The XRF is essentially point-and-shoot technology.
  • It has increased sensitivity. The XRF can test for lower concentrations of elements than other PMI tools.
  • The software is easy to use. The analyzer makes it easy to understand test results.

Basically, the handheld XRF is the iPhone of PMI devices. It’s portable, easy to use, and fast.

The cons of using a handheld XRF for PMI

Of course, there are a few drawbacks to using a handheld XRF for positive material identification, too.

  • XRF uses radiation to test. This can prove to be dangerous if the handler hasn’t had the proper training.
  • Most states regulate the use of XRF technology. Because it uses radiation, many states require XRF devices to be registered.
  • The handheld XRF can be fragile and expensive to repair. Expect to spend around $7k-$10k — oftentimes, more depending on the part — for a repair.
  • It has trouble testing for lighter elements. For elements like lithium, carbon, magnesium, and silicon, use technologies such as LIBS or OES for the best results.
via Unsplash

"OES is one of the only ways to yield carbon values in the field."

Chris Carolan

Although it’s easy to use, the handheld XRF cannot test for carbon in materials and usually has to be registered in order to use it in the U.S.

Suppliers of the handheld XRF

Today, brands supplying manufacturers with handheld XRF instruments include:

  • Thermo
  • Olympus
  • Hitachi
  • SciAps
  • Bruker

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.

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.

It’s also important to remember that sample preparation and clean surfaces are crucial 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?

XRF takeaways

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.

Now, go forth and master your metals!

For more information on positive material identification or XRF, subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.