For petroleum and petrochemical refining facilities, the emphasis on safety and accident prevention has never been greater — increased public scrutiny, stepped-up industrial safety regulations, and more stringent OSHA oversight and fines. Our last article outlined how carbon steels with low silicon (<0.10%) content have been shown to corrode at an accelerated rate when exposed to sulfidation corrosion conditions. And that corrosion has led to leaks, outages, fires, and loss of property and injury to workers.
Examples of equipment where H2-free sulfidation occurs include crude/vacuum, fluid catalytic cracker, coker, and visbreaker units. Hydroprocessing and hydrocracking units experience H2-free sulfidation corrosion in their feed and distillation sections. To help prevent these incidents from occurring, elemental analysis of such piping and equipment with portable x-ray fluorescence (XRF) should be part of your best practices. A handheld XRF analyzer in the field can help rapidly verify alloys in seconds, recover lost material traceability, and isolate finished welds to validate filler material composition and dilution rates, as well as confirm the integrity of process piping, valves, and reaction vessels.
Using Piping and Instrumentation Diagram (P&ID) software, a safety team can determine the best areas from which to take readings to check the silicon content of various components of the piping system. Most of these piping systems are exposed to the atmosphere and typically have some amount of surface corrosion and contamination that can interfere with the analysis. For this reason, surface preparation is required before any analysis can be made. Typically a small area is treated with a portable grinding tool equipped with an abrasive disk to provide a clean area for analysis.
When exposed to external x-rays of a sufficient energy, each individual element present in a sample will produce a unique set of characteristic fluorescent x-rays that essentially serve as a “fingerprint” for that specific element. These characteristic x-rays can then be categorized and counted when they contact an x-ray detector within the XRF instrument. The x-ray detector, a small semiconductor, receives the emitted x-ray, and passes it to the instrument processor as an electronic signal. By counting the individual emission events from each element over a period of time, this information can be modeled to produce a chemical composition of the sample being analyzed.
Testing has been done to ensure that given appropriate sample preparation and no introduction of contamination, a handheld XRF analyzer can consistently detect silicon levels in steel at a level of 0.03% or less. Results achieved from the handheld instrument demonstrate excellent agreement with the lab results.
Read about the testing methods and results used in the analysis of silicon content in steel and sulfidic corrosion, including surface preparation, correlation curve to lab certified results, and repeatability testing.