How to Get Accurate Silicon Readings when Analyzing Silicon in Steel

Typical metal alloys that are at risk of sulfidation corrosion are carbon steels. At high temperature, these alloys will corrode leading to metal wall thinning when exposed to sulfur compounds present in crude oil and can cause failures. Those failures can result in leaks, early replacements, unplanned outages, and incidents potentially resulting in loss of property and injury to workers.

To help prevent these incidents from occurring, silicon analysis of carbon steel is done. Handheld XRF instruments are used in as Positive Material Identification (PMI) programs to analyze carbon steel and verify elements where sulfidic corrosion, is a concern. X-ray Fluorescence (XRF) technology is a non-destructive analytical technique used to determine the elemental composition of materials.

Data quality objectives dictate the sample preparation requirements and the minimum analysis time used when analyzing the steel. Surface oxidation can affect the accuracy of the reading when performing an XRF analysis. As the chromium concentration in the metal gets lower, the oxidation will get worse. It is imperative to remove any corrosion in order to ensure an accurate reading.

In addition to oxidation, there can often be paint or oil or grease on the surface. Paint typically contains metals, such as titanium, zinc or calcium, that can impact the results of analysis. Grease can contain molybdenum and other additives.

In order to get the accurate silicon readings, all surface contamination must be removed in the area to be analyzed.

The fastest way to prepare an oxidized surface is to use a right angle die grinder equipped with the proper abrasive media, such as a zirconia/alumina grinding disc.

Since data quality objectives dictate the sample preparation requirements and the minimum analysis time used, we analyzed samples against certified reference standards after ensuring the surface was clean and clear of any contaminants that could introduce silicon or other elements to our analysis.

Depending on the concentration of silicon and the desired precision, the samples were analyzed for 9 to 33 seconds using both the main filter (3 seconds) and light filter (between 6 and 30 seconds) after thorough surface preparation. We were able to identify both pipe material that passed inspection as it was not susceptible to sulfidic corrosion, and pipe material that failed and would be susceptible to sulfidic corrosion because it did not reach the recommended threshold of 0.1% Si in carbon steel.

For additional details, including methods and instruments used, correlation curves, measurement repeatability data, results and conclusion, read the application note: Analysis of Silicon in Steel to Prevent Sulfidic Corrosion Using the Niton XL5 Plus XRF Analyzer

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