Drill pipe corrosion control

Murray, A. S., and W. E. Holman, How to detect and control drill pipe corrosion, World Oil, January 1969. 

Many wells have to be redrilled due to drill pipe and casing failures caused by corrosion. All drilling fluid corrosion problems cannot be eliminated, but most can be controlled with proper diagnosis and treatment. Because the tubular goods are mostly iron and most muds are water-based, corrosion is inevitable. Four conditions must be met, however, before corrosion can occur ... 

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. 

Organic inhibitors used to protect drill pipe in weighted, as well as in low-sohds muds are effective when proper attention is given to the application method. Every effort should be made to apply the inhibitor to the drill pipe rather than to mix into the drilling fluids. This permits better control of drilling fluid properties and avoids excessive corrosion inhibitor costs. 

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. 

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