The crude oil extracted from the well is typically containing inorganic salts, and most of them are chloride. And the main components are Nacl, Mgcl2 and Cacl2. These salts are hydrolyzed into HCL during the process of refining the crude oil at the refinery and they will corrode the equipment. The hydrolysis of HCI and water near dew point temperature will cause serious corrosion and damage to the refinery equipment. The sodium salts usually do not hydrolyze under distillation, but when the crude oil in the presence of naphthenic acid and some metal elements, it could be hydrolyzed into HCI above 300 ℃. Sometimes the actual precipitation of crude oil exceeds the HCl produced by the hydrolysis of all inorganic salts, which is caused by the hydrolysis of the oil in the process of extraction. Because paraffin waxes contain about 20% of chlorinated alkanes, they can be hydrolyzed to HCI at temperatures above 100 DEG C when water is present.
Crude oil processing is the method of using water injection to dissolve the salts in it. Then the oil and water can be separated from the electric desalination tank and the salt water will be discharged to achieve the effect of desalting. However, after treatment, they still contain small amounts of NaCI, CaCI2 and other salts. The hydrochloric acid is formed after the solution of saltwater, which is corrosive to the equipment. This kind of corrosion occurs mainly in the gas liquid phase change, so it is called "dew point corrosion". They exist mainly in the constant vacuum distillation unit, the tower top circulation system and corresponding process pipelines and heat transfer equipment. Generally, the corrosion of the gas phase is lighter, the liquid phase is more corrosive, and the gas liquid phase is the most serious.
The corrosion results of various steel corrosion: the carbon steel is uniform corrosion, the 0Cr13 steel is the pitting corrosion, the austenitic stainless steel is the chloride stress corrosion cracking.