Hydrocracking and other refinery hydroprocessing units have a common goal to convert organic sulfur compounds to hydrogen sulfide (H2S) that can be removed, thereby producing low-sulfur refinery products. Corrosion and equipment degradation risks range from high-temperature hydrogen attacks (HTHA) to ammonium bisulfide and ammonium chloride corrosion in the downstream heat recovery and fluid separation equipment.
This paper provides an overview of corrosion management principles that can be applied to reduce operating risks in new and existing units, focusing equipment susceptible to ammonium bisulfide (NH4HS) and ammonium chloride (NH4Cl) corrosion. Best practices for materials selection, as well as designing for corrosion management through adequate provision of corrosion management related instrumentation and sampling points are covered.

Stabilized austenitic stainless steel (SS) grade 347 is used extensively in high-temperature processes in the petroleum refining industry, while duplex SS (DSS) grade 2205 is a relatively newer material in the industry. Though these grades of SSs perform well in refinery process streams, there are incidents of failure of process equipment attributable to stress corrosion cracking (SCC).  The paper deals with a study on the cracking susceptibility of SS grade 347 and DSS grade 2205 in refinery simulated process environments containing hydrogen sulfide and chloride.  The paper also reports the electrochemical behavior of these SSs in the medium containing hydrogen sulfide and chloride.  The electrochemical behavior of the alloys was assessed by cyclic polarization experiments.  Slow strain rate test (SSRT) was used to evaluate the susceptibility of the alloys to SCC. The cyclic polarization studies indicate that the H2S – chloride synergism had a pronounced effect on the localized corrosion susceptibility of 347 SS, while the effect was marginal on the alloy DSS 2205. The SCC susceptibility of 347 SS and DSS 2205 is strongly influenced by hydrogen sulfide-chloride synergism.  Initiation of corrosion pits and the sulfidation of active pits due to the synergism were the important steps in the initiation of SCC.   

The application of corrosion inhibitors (CI) to producing oil and gas field systems is one of the most common practices of corrosion control. Acid stimulation fluids such as hydrochloric acid (HCl) and organic acids has high calcite and dolomite dissolving power; however, pumping HCl downhole during acid stimulation process particularly at elevated temperatures can cause severe corrosion. Therefore, the addition of corrosion inhibitors is indispensable to protect the metal from corrosion. More inhibitors that are efficacious are still needed to provide better protection against the corrosion.
Two new bisquaternary ammonium salts; 1,4-Benzenedimethanaminium, N,N'-didodecyl-N,N,N',N'-tetramethyl-, dichloride (CI-1) and 1,4-Benzenedimethanaminium, N,N'-dihexadecyl-N,N,N',N'-tetramethyl-, dichloride (CI-2) as corrosion inhibitors were successfully synthesized, characterized and electrochemically evaluated for their corrosion inhibition efficiency in 1 M hydrochloric acid (HCl) solution on API 5L X60 low carbon steel. Potentiodynamic polarization measurement revealed mixed type inhibition mechanisms of the synthesized inhibitors. Inhibition efficiency of CI-1 increase with increase in concentration 2.0 to 20.0 ppm while CI-2 efficiency does not go beyond 2 ppm. Adsorption isotherm of CI-1 was found to deviate from Langmuir isotherm due to its interaction on low carbon steel and the interaction was approximated by Temkin isotherm. Analysis of the adsorption of CI-1 on API 5L X60 involve both physisorption and chemisorption.