Naphthenic acids corrosion

Naphthenic acid corrosion Naphthenic acid pertains to a group of organic acids present in crude oil with the general chemical formula R (CH2) COOH, where R is one or more cyclopentane rings, and n is typically greater than 12. The ring structure can be tricyclic, tricyclic, or polycyclic. In addition, crude oil contains various other organic acids that contribute to acidity. These are often... 

Naphthenic acid corrosion has been a problem ia petroleum-refining operations siace the early 1900s. Naphthenic acid corrosion data have been reported for various materials of constmction (16), and correlations have been found relating corrosion rates to temperature and total acid number (17). Refineries processing highly naphthenic cmdes must use steel alloys 316 stainless steel [11107-04-3] is the material of choice. Conversely, naphthenic acid derivatives find use as corrosion inhibitors ia oil-weU and petroleum refinery appHcations. 

Where is naphthenic acid corrosion found Naphthenic acid corrosion occurs primarily in crude and vacuum distillation units, and less frequently in thermal and catalytic cracking operations. It usually occurs in furnace coils, transfer lines, vacuum columns and their overhead condensers, sidestream coolers, and pumps. 

E. Babaian-Kibala. Naphthenic acid corrosion inhibitor. Patent US 5252254, 1993. 

Naphthenic acid corrosion is quite severe in vacuum and visbreaker towers. Crudes with total acid numbers over 2.0 mg KOH/g have corroded type 316 SS in the inlet areas. At times, type 317 (UNS S31700) SS, 904L (UNS N08904), or other corrosion resistant alloys are needed. Matching weld filler metal must be used. In one case, a type 310 (UNS S31000) SS weld filler metal was used on type 316 SS lining. While the strip lining was not attacked, the weld dissolved in one year. 

Reprinted from Naphthenic Acid Corrosion—An Old Enemy of the Petroleum Industry," Corrosion, December 1956.)... 

NAPHTHENIC ACID or NAPHTHENIC ACIDS (1338-24-5) Combustible liquid (flash point 300°F/149°C oc). Incompatible with sulfuric acid, caustics, ammonia, aliphatic amines, alkanolamines, isocyanates, alkylene oxides, epichlorohydrin, strong oxidizers. Generally corrosive to metals. 

Corrosion-related issues regarding processing are handling organic acids [also referred to as naphthenic acid corrosion (NAC)] and sulfur species at high temperatures as well as water containing corrosives such as H2S, CO2, chlorides, and high levels of dissolved solids. 

Blending may be used to reduce the naphthenic acid content of the feed, thereby reducing the corrosion to an acceptable level. Blending of heavy and light crudes can change shear stress parameters and might also reduce corrosion. Blending is also used to increase the sulfur content of the feed and inhibit, to some extent, naphthenic acid corrosion. 

The application of the FSM-IT system has since been developed by iicorr Ltd (formerly CorrOcean Ltd) within over 20 refineries worldwide, for monitoring the effects of high temperature Naphthenic acid corrosion, which is an increasing concern with the processing of high acid - opportunity crudes. 

Severe naphthenic acid corrosion occurs primarily in vacuum distillation towers at temperatures in the range of 550°F to 650°F. In piping, there will be an increase in general corrosion in direct proportion to an increase in neutralization number. 

Absence of scale and severe pitting of the steel, as if it were caused by erosion, often is evidence of naphthenic acid corrosion. It should be noted, however, that this type of damage also is produced by droplet impingement at high velocities in the absence of naphthenic acids. 

A crude unit which has metallurgical protection for running high-sulfur crudes is not protected against naphthenic acid attack. For example, naphthenic acids attack 12-Cr stainless steel and carbon steel with equal vigor. Type 316 or, preferably. Type 317 is required to resist naphthenic acid corrosion, but even these alloys will pit in severe cases. Other materials effective against naphthenic acid corrosion are aluminum or alonized steel. 

---