Corrosion fouling during crude oil flow on a heated surface: Effects of temperature, shear and material of construction.

Fouling in refinery equipment occurs predominantly by corrosion, chemical reaction, asphaltene precipitation or coke formation depending on prevalent operating conditions. Iron sulphide formation via a corrosion mechanism on metallic surfaces has been identified via past studies to precede coke formation. These studies however have been carried out at temperatures where coke formation blankets the sulphide layer (>350 °C). The present study reports results from experimental investigations conducted to understand crude oil corrosion fouling on a heated surface in a temperature range where this fouling mechanism is expected to be largely prevalent and not blanketed by other mechanisms (<300 °C). Experiments were conducted using a High Temperature Variable Shear (HTVS) coupon test rig. The test runs covered a wide range of fluid bulk temperatures and stirrer speeds (which incorporated a shear effect), ranging from 250 to 300 °C and 100 to 600 RPM respectively. Parts of the foulant deposits collected were found to strongly (hard) and weakly (soft) adhere to a coupon surface. These deposits were subsequently characterized using Thermogravimetry (TGA), Elemental analysis, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The nature of soft deposits was found to be distinct from the nature of crude oil used. The formation of hard and soft deposits on a Carbon Steel (CS) and Stainless-steel (SS) surface was investigated. Based on the data obtained, a mechanism is proposed to explain the underlying fouling phenomena. [ABSTRACT FROM AUTHOR]