(26a) Corrosion in Crudes, Myths and Reality

Corrosion problem is a very common and extensive conversation topic between process engineers and operators. HCl corrosion by hydrolysis of Ca, Mg salts is the most known form of corrosion; use of caustic to transform hydrolysable salts to non-hydrolysable NaCl is also widely used. As the refiners start to process more and more frequently crudes from the spot market ?sometimes meaning heavier crudes or for the same API less quality- many other factors play an important role in the corrosion: H2S, NH3, organic chlorides and light organic acids (LOA).

One of the Process engineer key roles is to study extensively the crude characteristics: i.e. salt content (Ca, Mg, Na), H2S presence and generation at process conditions, presence of LOA, water formation quality, etc. The process conditions: i.e. salt formation temperature, potential for shock condensation, water pH at overhead drum, metallurgy, etc. So, the process engineer is to work closely with chemical suppliers to define the right strategies to tackle down the corrosion.

Strategies may include caustic addition, combination of neutralizers, filmic amines, wash-water and/or combinations of all. The use and efficiency of desalters is also very important: proper adjustment of desalter is a key element to reduce as much as possible the Ca, Mg salts. Depending on refinery configuration, it might be necessary to add some caustic for further corrosion reduction. The addition of caustic will depend on Na balance to Cokers and/or Visbreakers to avoid fast coking, normally happening at levels above 20 ppm Na in the feed to those units.

There are no simple solutions anymore like 30 yrs ago, when using a combination of NaOH and NH3 was good enough for all crudes. General guidelines and examples are given for a variety of light, medium and heavy crudes for different operating conditions and different contaminants.