Drilling equipment corrosion control

Corrosion Theory 1259. Forms of Corrosion Attack 1268. Factors Influencing Corrosion Rate 1292. Corrodents in Drilling Fluids 1300. Corrosion Monitoring and Equipment Inspections 1312. Corrosion Control 1323. Recommended Practices 1340. 

Corrosion due to mechanical and metallurgical problems also exist. Metal tools used in drilling wells are often softer than the formation being penetrated. The abrasiveness of formation solids can easily erode protective films from drilling equipment, leaving metal exposed to corrosion-erosion attack. Mechanical and chemical separation of abrasive solids helps control this attack. It is difficult, however, to control stress concentrations in a string of driU pipe that may reach many kilometers into the earth. 

Time is always an important factor in corrosion control. The current trend in oil-well drilling that requires probing deeper strata of the earth increases equipment exposure time under the critical conditions. 

Stress increases corrosion attack and must be controlled through proper design and use of equipment, as well as by reduction of enviromnental corrosives. For example, corrosion pits concentrate stress and are prime initiation points for corrosion fatigue cracks, which are the major cause of drill pipe failure. It is easily understood that corrosion problems become more critical as well depth increases, because among other things, high temperature becomes one of the more critical problems faced in many deep drilling projects. 

Sand blasting has been used to clean drill pipe and remove barriers and scale from the metal. Control methods most often used on operating equipment include frequent treatments with oil-soluble, organic amine inhibitors apphed directly to the affected metal surface. These must penetrate and cover either the anodic or the cathodic area (or both) of the corrosion cell in order to stifle the cell. 

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