Carbon steel piping with silicon content less than 0.1% has been shown to have accelerated corrosion rates when exposed to hydrogen-free conditions where sulfur compounds are present at elevated temperatures (>450 degrees C). Accelerated corrosion related failures can easily result in major accidents that cause worker injury or unplanned outages.
Examples of such parts of the process are hydro processing and hydrocracking units in the feed and distillation sections. The process conditions under which this will happen are a bit difficult to predict and continuous monitoring is thus required.
A common monitoring technique uses an ultrasonic (UT) thickness gauge to measure thinning in the pipe wall thickness. Even with prediction models, this can be considered a reactive analysis. However, Positive Material Identification (PMI) can be used to proactively identify those low silicon parts in the process, which are most susceptible to sulfidic corrosion. Best practice indicates that these critical parts should be 100% PMI inspected. Handheld XRF (HHXRF) analyzers such as Bruker’s S1 TITAN can easily perform the PMI analysis to identify the low alloy steel containing relatively low Si levels (< 0.1%). Modern HHXRF analyzers, using SDD detectors, can measure these low levels of Si with no need for vacuum or gas purge. Silicon’s low X-ray energy makes it necessary for any XRF analysis to use a relatively long measurement time (>30 sec). This long measurement time, when combined with elevated pipe temperatures (> 450°C), can potentially cause analyzer damage when performing PMI inspection during “hot” process conditions. Rather, it is recommended that PMI be performed during scheduled maintenance breaks if possible. In addition, the analysis location is best performed on clean, bare metal. This can be easily accomplished with a handheld grinder and properly selected abrasive material (no Si in the abrasive material).
Bruker’s S1 TITAN 600 / 800 can reliably measure low concentrations of Si in low alloy steel. In addition to the S1 TITAN’s SMART Grade™ timing and patented SharpBeam™ tube and detector geometry, the S1 TITAN includes a secure results file which maintains the integrity of the data, and fast and efficient in-situ naming of samples.
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