Erosion-corrosion of carbon steel and duplex stainless steel elbows in potash brine-sand slurry
Date
2020-04-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
Carbon and low alloy steel pipes are widely used to transport slurries in the mining and mineral processing industry because of their good mechanical properties and relative affordability. However, the exposed internal walls of these pipes are prone to erosion-corrosion damage, which can lead to product leakage and eventual failure of the piping system. The purpose of this research is to evaluate the performance of AISI 1018 carbon steel and AISI 2205 duplex stainless steel elbows to erosion-corrosion damage in a saturated potash brine-sand slurry.
Erosion-corrosion tests were conducted in a flow loop using a slurry consisting of saturated potash brine-sand slurry. Flow velocity and particle concentration were varied, but the slurry temperature was kept constant at 30 ± 1 °C. The synergistic effect of corrosion and erosion during erosion-corrosion was evaluated by conducting corrosion and erosion tests using particle-free saturated potash brine and deaerated slurry, respectively. The elbow surfaces before and after exposure to different test conditions were characterized using a scanning electron microscope, optical profilometer, Vickers micro-hardness tester, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and electron-backscattered diffraction.
The results of these study revealed that the synergy between corrosion and erosion accelerated erosion-corrosion rates for the exposed carbon steel elbows. Microstructural examination showed that mechanical wear, in conjunction with pitting corrosion, played a substantial role in removing materials from the exposed surfaces of carbon steel elbows, especially at low slurry flow velocity. Raman and X-ray spectroscopic studies indicated that the corrosion products found inside the pits of the exposed carbon steel elbow are FeOOH, Fe2O3 and Fe3O4. This confirms the oxidation of iron during erosion-corrosion in saturated potash brine slurry.
Furthermore, mechanical wear was the sole material removal mechanism for the duplex stainless steel elbows, which indicate that the combined effects of corrosion and erosion did not influence erosion-corrosion rates. X-ray and electron-backscattered diffraction techniques revealed that some austenite phase of the duplex stainless steel transformed to martensite after particle impacts at high velocity. The exceptionally high hardness and brittleness of martensite accelerated the removal of materials from the duplex stainless steel surface by brittle chipping. Plastic deformation due to particle impingement occurred up to about 4 μm below the exposed elbow surface.
Description
Keywords
Erosion-corrosion, Wear, Synergy, Surface roughness
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Mechanical Engineering
Program
Mechanical Engineering