Pipe dope is slang for anaerobic chemical sealant that is used to make a pipe thread joint leak proof and pressure tight. Although common pipe threads are tapered and therefore will achieve an interference fit during proper assembly, machining and finishing variances usually result in a fit that does not result in 100 per cent contact between the mating components. The application of pipe dope prior to assembly will fill the minute voids between the threads, thus making the joint pressure tight. Various types of pipe dope formulation exist, the appropriate type being determined by the application, e.g., pneumatic, hydraulic, caustic, etc., as well as the expected pressure. Improper selection of the type of pipe dope may result in leakage despite best assembly practices.
A specially formulated blend of lubricating grease and fine metallic particles that prevents thread galling (a particular form of metal-to-metal damage) and seals the roots of threads. The American Petroleum Institute (API)* specifies properties of pipe dope, including its coefficient of friction. The rig crew applies sufficient amounts of pipe dope to the drillpipe tool joints every time a connection is made.
In my earlier days "pipe dope" (drilling) was distinguished from “thread compounds” (workovers & completion) where basically pipe dope is used for “dynamic” situations under an applied stress field (pressure & temperature under drill pipe /BHA make-up & rotary torque) that is usually much greater than that experienced by thread compounds in "static" situations (casing, tubing,storage, etc)
In either case the categories of interest are usually regulatory approval, environmental, health, and performance arising from the interaction of the chemistry of the dope or compound and the metallurgy of the threads.
See
*API Recommended Practice 5A3, 01-Jul-2003 Recommended Practice on Thread Compounds for Casing, Tubing and Line Pipe, Second Edition ($121.00) / ISO 13678:2000 Petroleum and natural gas industries - Evaluation and testing of thread compounds for use with casing, tubing and line pipe
DP dope as per API RP 7G: Calculations for recommended tool joint make-up torque are based on the use of a thread compound containing 40 to 60 percent by weight of finely powdered metallic zinc applied to all threads and shoulders, and containing not more than 0.3 percent total active sulfur (reference the caution regarding the use of hazardous materials in Specification 7, Appendix G).
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