The Role of Sulfur Species in Establishing the Corrosion Reactions in Refinery Metallurgies

  • Author / Creator
    Lepore, Justin N
  • This thesis is focused on the studying the role that model sulfur-containing molecules have in corrosion reactions on relevant metallurgies. This was done by using a design of experiments where a number of sulfur-based compounds were reacted with various metallurgies. The 8 model sulfur compounds were chosen to represent a broad set of structures: two mercaptans (M1 and M2) with M2 having a longer chain than M1, an aliphatic sulfide and disulfide (LS and LS), an aromatic sulfide and disulfide (RS and RD), and two cyclic thioethers (C1 and C2) with C2 containing more hydrogen than C1. The 5 metallurgies used were: 5 chrome alloy, 9 chrome alloy, 410 steel, 316 stainless steel, and carbon steel. In the first round of experiments, the compounds were tested by placing 5000 ppm by weight of sulfur of a respective sulfur compound into 9 mL of Paraflex white mineral oil along with a rectangular carbon steel coupon in a sealed reactor, pressurized to 40 psig, and held at a medium temperature for a fixed set of time. The next round of experiments replaced the rectangular coupons with 1-inch extruded wire sections 200 µm in diameter of the five metals. Each of the eight compounds were reacted with the carbon steel wires at two process temperatures, a medium temperature and a medium-high temperature, and two experiment times, a short experiment time and a long experiment time. The remaining four metallurgies (5Cr, 9Cr, 410 steel, and 316 stainless steel) were reacted with each of the eight sulfur compounds only at the most extreme conditions of the medium-high temperature and reacted for the long experiment time. Once again, for these experiments the compounds were measured to 5000 ppm by weight of sulfur and placed with 9 mL of Paraflex white mineral oil into the sealed and pressurized reactor along with the extruded metal wire. After reacting, these wires were mounted in nickel-infused epoxy and polished for SEM and EDXS analysis, or left unmounted and used for XRD analysis. Overall, in these corrosion experiments, the 316 stainless steel remained nearly pristine after reacting with any of the sulfur compounds, while the carbon steel samples were heavily corroded. To react the metals with pure H2S, a sealed tube furnace was sparged and filled with 5000 ppm H2S gas (5174 ppm H2S, 10.19% hydrogen, argon balance) and heated to either a medium or medium-high temperature with the extruded metal wires supported vertically inside in the tube. After reacting for either a quick, short, or long experiment time, these wires were then removed and mounted in nickel-infused epoxy and polished for SEM and EDXS analysis. The decomposition temperature of each sulfur compound was recorded as the lowest measured temperature that H2S was detected in the headspace gas of the sealed reactor after reacting for a long experiment time at the respective temperature in pure Paraflex mineral oil. This was determined by either increasing or decreasing the reaction temperature in 5 °C increments until the temperature was found such that H2S was first detected. As expected given their thermal stability, the cyclic thioethers, C1 and C2, did not decompose into H2S in any of our experiments, up to the limit of temperatures we were capable of reaching with our equipment. On the other hand, the aliphatic disulfide, LD, readily decomposed into H2S at temperatures lower than the medium corrosion experiment temperature, likely due to the overall structure and properties of the compound.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.