The Fabricator - December 2015

TECHNOLOGY SPOTLIGHT By Eric Lundin, Contributing Editor

If you need to sort through a small pile of metal scrap to separate steel items from aluminum, or if you need to figure out if a stray tube is carbon steel or stainless steel, a magnet is the way to go. However, if you need to identify an alloy and quantify its chemical composition (elemental content), you need something more sophisticated. This is where X-ray fluorescence (XRF) can be helpful.

The XRF process bombards the object under test with X-rays, imparting energy to a sample of atoms in the object. When that energy is released just milliseconds later, it gives off a series of distinctive signatures. The XRF detector evaluates these signatures and, in doing so, determines the specific elements and the relative quantities of each in the alloy.

This branch of science is XRF spectroscopy, which studies the interactions between matter and electromagnetic radiation, but you don’t need a science degree or a fancy title (“spectroscopist”) to use this technology. To analyze the spectrum given off by the object under test, you just pull the trigger and the tool does the rest.

Let’s say you have an alloy consisting of 80 per-
cent copper, 11. 5 percent lead, 6. 5 percent tin, and 1
percent each of zinc and nickel. That’s a tin bronze,
which goes by the Copper Development Association
(CDA) designation 936 copper. An iron-based alloy
that has 0.15 percent carbon, 0.60 percent manga-
nese, 0.040 percent phosphorus, and 0.050 percent
sulfur is a low-carbon steel, designated 1018 by the
American Iron and Steel Institute (AISI). A similar al-
loy that has a little less carbon, 0.10 percent, and
another element, silicon, at 0.10 percent, is an old
friend, 1010 carbon steel.

XRF analyzers have been available for decades, so they’re nothing new, but according to Mark Lessard, a market development manager for Thermo Fisher Scientific, industry needs them now more than ever.

Review, Repair, or Replace

It’s commonly known that manufacturers rely on XRF to identify incoming material and scrap dealers use the technology to segregate material, but these are just two of many applications.

“We see significant growth potential for mission-critical applications,” Lessard said, referring to catastrophic events. “In the petrochemical industry, using the wrong alloy can result in an explosion. The implications are much more severe if materials get mixed up in a nuclear power plant or at an aerospace component manufacturing facility,” he said.

Sometimes the hazard isn’t as abrupt, but it can be devastating nonetheless.

“Much of the pressure is regulatory in doing re-
pairs or in reviewing a construction project,” he
said. “Using the wrong material can lead to corro-
sion, and corrosion can lead to failure.”
Of course, some applications aren’t mission-criti-
cal, but mixups can have huge cost implications.

“For about 100 years, the automotive industry relied on steel,” Lessard said. “These days the industry is using aluminum, magnesium, and titanium.” Verifying that the right alloy showed up at the receiving dock is an ideal use for an XRF detector, as is keeping the incoming raw materials and the scrap from production segregated every time they’re handled. The pressure is on to improve fuel efficiency, and one of the tactics is to use the lightest-weight metals possible. As the material’s weight drops, the cost increases. Nobody wants to make thousands of parts from the wrong alloy.

An XRF analyzer also can
be used to check a coating
thickness, including pas-
sivation or conversion coatings, which is an impor-
tant step when preparing a steel surface for a bond-
ing agent, Lessard said.

“Auto manufacturers have been using adhesives for years and their use is only going to grow,” he said. “When using an adhesive, it’s critical that the coating thickness is correct to ensure the structural integrity of the bond.”

The Pace of Technology

Technologies are ever-changing—compare a digital camera or a computer or a cell phone of today with one from a decade ago—and this includes XRF analyzers. According to Lessard, the company’s latest unit, model XL5, is much more capable than its predecessors.

“The unit has about three times better the level of detection than previous units,” he said, stating that the latest unit can detect the presence of some elements down to single-digit parts per million. As recently as five years ago, this level of detection (LOD) was available only with laboratory-grade analyzers, not hand-held units, Lessard said. This has the potential to benefit any industry that relies on recycled metals.

“It’s often a matter of what is not supposed to be in the metal as what is supposed to be in it,” he said. The risk of contaminating known metals with tramp metals—so-named because they are as unwelcome as tramps, vagrants, and other ne’er-do-wells who tend to show up uninvited—is more prevalent than ever due to growing recycling efforts. A low LOD is necessary for any scrap dealer that guarantees the furnace melt chemistry content of the scrap, as the top-tier recyclers do.