Three Tips for Accurate Weld Analysis Using Handheld XRF
Handheld x-ray fluorescence (XRF) analyzers, more commonly called handheld XRF or HHXRF, are useful tools for installing new or replacement sections in a welding project. Here are three best practices to perform accurate weld analysis with HHXRF ...
Handheld x-ray fluorescence (XRF) analyzers, more commonly called handheld XRF or HHXRF, are useful tools for installing new or replacement sections in a welding project. Here are three best practices to perform accurate weld analysis with HHXRF analyzers.
Tip #1: Clean the Test Surface
Handheld XRF analyzers work best on surfaces that are free from welding residue, scale, or oxidation. Before testing with the analyzer, remove any weld spatter, scaling, or rust from the test area (Figure 1).
Figure 1: Example of a weld (stainless steel with argon). It is important to clean the weld before testing with HHXRF.
At a minimum, make a few strokes with a clean wire brush to expose the bright metal in the test area. Better yet, use a grinder (if available) to grind a swath across the weld or on the piece to be installed. This practice exposes fresh, bright metal for good HHXRF analysis (see lead photo).
Note that welding rods often have a coating of flux that improves the welding process but has a different material chemistry than the rest of the rod. So, to obtain a composition result for welding rods, you can either
-Test an uncoated end-of-the-weld material if available (the tested surface must not have any flux on it); or
-Weld a small test area with the rod and analyze the pooled weld material.
If you are taking tests before installing a part, another good practice is to sort materials before the welding process. Group the parts and sections to be installed into their respective material type, such as carbon, stainless, and chrome steels as well as nickel, aluminum, titanium, copper, and cobalt alloys.
Tip #2: Take Tests across the Weld Area
For each weld area, it is important to take several tests across the area. Depending on the size of the area available for testing and the weld’s width, operators should take 1–2 tests on each parent material side and on the weld. If your HHXRF analyzer has a weld mask faceplate, use it during tests to help focus the testing areas.
Olympus’s Vanta™ HHXRF analyzers have a weld mask faceplate that contains a narrow slot to focus analysis instead of the traditional oval window (Figure 2). This narrow opening enables the operator to take readings directly on top of the weld and minimize readings from the parent material.
Figure 2: Modern HHXRF devices like the Vanta analyzer offer grade matching for quick weld analysis.
During this test, the operator will ideally want to see similar grade match results for the base material tests and the weld area either to the base material specification or the welding grade.
Tip #3: Match the Grade
A nice benefit of modern HHXRF analyzers is that grade matching for alloys is a standard feature. However, weld material usually has enriched elements compared to the same element range for the base material.
Consider the Alloy ER316. The material specification requires chromium to be between 18 to 20% in composition. For 316 stainless base material, the specification requires between 16 to 18% chromium for compliance.
Why? For certain alloys, the welding process causes a localized depletion of particular elements, so those elements start at a higher concentration before being welded. If the weld material had the same element concentrations as the base material, these localized depletions could lead to corrosion issues in the vicinity of the weld when placed in service.
What does this mean for the welder who needs to identify their base material and weld material? They need both a specialty welding material grade library and a base material library on their HHXRF analyzer.
Even if a material has lost its identifying paperwork at the site, it can be quickly sorted into the correct group or type with an HHXRF analyzer. Just consider the time spent on repair work if the incorrect material is installed. A few seconds of XRF analysis before the start of a job helps ensure the right piece is in the right place the first time.
When a HHXRF analyzer does not match a grade, it indicates that a second look is needed. Sometimes this issue happens when the operator improperly positions the analyzer window on the sample.
A quick retest with the analyzer moved to the right location is a simple way to fix this. If, after retesting in the desired spot, a grade match does not display for the weld or base material, the operator must check the chemistry information on the instrument for further composition issues.
Modern HHXRF analyzers offer features like onboard cameras that capture an image of every test and user-edited notes for record keeping, improving the traceability of a welding project.
Developing a useful workflow with a HHXRF analyzer is ultimately up to the user. However, following these three basic tips before starting a welding project can help prevent many headaches after the work has begun.’’
This article was written by Alex Thurston (applications engineering manager, analytical instruments, at Olympus Scientific Solutions Americas Inc., Waltham, Mass.) for the American Welding Society.