In 1987, the IADC adopted an improved Rock Bit Dull Grading System. Although it was modeled after the previously used T-B-G System, it was expanded to provide a much clearer "mental picture" of a dull bit. This paper documents the changes from the 1987 version to the 1992 IADC Dull Grading System. Since the changes are minor, they are listed at the beginning of the paper. Additionally, for those needing more detail, the entire 1992 IADC Dull Grading System is presented. CHANGES FROM 1987 * Outer Cutting Structure: Definition will change to "All cutting elements that touch the side of the hole".*Reasons Pulled Add: "LIH" - for "Left in Hole"*Bearing Grade Add: "N" - for "Not Able to Grade"*Location: "G" represents gage area, replacing "H".*IADC bit topics also updated in 1992 include IADC Classification and Fixed Cutter Dull Grading. Introduction The use of dull bit evaluation methods represents a key step in the advance of rock bit technology. Historically, a driller would learn through experience how to examine a "dull" to determine what type of bit to run next, and how it should be run (WOB, RPM, etc.). This was part of the art that separated the best drillers from the rest. An industry wide effort began years ago to teach the art of bit wear analysis to a broader range of personnel so that dull bit evaluation would become an integral part of daily drilling practice. General guidelines were established in the mid-1950's for relating typical bit wear patterns to the possible causes and remedies. This approach was helpful but limited by the lack of a common vocabulary for describing bit wear and documenting the dull condition in drilling reports. Meanwhile, basic bit performance studies produced a greater appreciation for the economic impact of bit wear and its close relationship to bit selection and operating practices. An industry standard for reporting bit wear was clearly needed. The Weight/Speed/Penetration Sub-Committee of the American Association of Drilling Contractors (AAODC) established the first dull grading standard in 1961. P. 819^

The IADC (International Association of Drilling Contractors) roller bit classification system provides a convenient method for categorizing rock bitsaccording to their design features and intended applications. The system has been used worldwide since 1972. The 1992 version includes improvements which reflect the latest design trends in roller cone bits. This paper explains the IADC roller bit classification code. Current classification charts are shown for major bit manufacturers. The relationship between the IADC code, bit design factors, and operating guidelines is discussed. Examples depict the major design features included in the code. Since this version contains only minor changes from the 1987 Roller Bit Classification System, these changes will be listed at the beginning of the paper. Those experienced with the code need only read the changes. Subsequent paragraphs present a complete discussion of the classification system for the benefit of the readers who may not be familiar with the system or who wish more detail. IADC bit topics also updated in 1992 include Fixed Cutter Classification and Dull Bit Grading. CLASSIFICATION CHANGES In 1987, the Classification System was changed to include a fourth character to denote features available. The 1992 revision made the following changes to list of "Features Available". B - Special Bearing Seal - Added H - Horizontal/Steering Application - Added L - Lug Pads - Added M - Motor Application - Added T - Two Cone Bits - Added W - Enhanced Cutting Structure - Added R - Reinforced Welds - Deleted Introduction Hundreds of roller cone bit designs are commercially available for oilfield use. Four major manufacturers market competitive product lines of 1000 or more distinctly different bits. Five or more smaller manufacturers produce at least 100 additional bits. Why are there so many roller bit designs? P. 801