Hydroprocessing consists of hydrotreating and hydrocracking processes.

Hydrotreating is used to remove undesirable contents in the feedstock such as sulfur, nitrogen and other metal contaminants. Meanwhile hydrocracking cracks long chain hydrocarbons feedstock into lighter components.

Both processes require hydrogen at high temperature and pressure with the presence of catalysts for a reaction to take place. The effluent at the reactor outlet contains a combination of trapped, dissolved gases, like unreacted hydrogen, light hydrocarbons and Hydrogen Sulfide. The effluent will later let down pressure to a stripper or distillation column. When the high pressure is being let down in this application, the fluid will undergo outgassing, flashing and cavitation with entrained catalyst, therefore special attention is necessary for selecting the right valve to address erosion, corrosion and vibration. The most common service names found in both the hydrotreating and cracking units are hot high and cold high pressure separators.