Fracture Toughness Criteria for High-Strength Drillpipe

Abstract

ABSTRACT Higher fracture toughness materials are more resistant to fracture than lower toughness materials under the same loading conditions. This fact is particularly important when considering potential drill pipe failures because there exists no industry standard which specifies fracture toughness for drill pipe. How fracture tough should your pipe be? This question is discussed through a comparison of recent fracture toughness criteria for high strength drill pipe. A Chevron Corp. criterion based on field observations has suggested 40 ft-lbf (54 J) at room temperature from 3/4 size Charpy impacts. Shell Canada Limited has developed fracture toughness criteria based on a fracture mechanics, leak before break concept for a pipe body containing fatigue cracking and on field observations of parted pipe and washouts in pipe. This has allowed the application of a room temperature, 80 J (59 ft-lbf), 3/4 size Charpy criterion in Shell Canada drilling contracts. A single, impact-type criterion has ease of application but flexible, fracture mechanics criteria may allow for better operational use of drill pipe in specific situations. An empirical relationship between fracture and impact properties was determined which allows the use of required toughness curves and leak before break curves based on operating conditions and drill pipe impact properties. Examples are given with respect to tested properties of new, high quality drill pipe and used, failed drill pipe. These show it is possible to obtain drill pipe that will washout before parting but a criterion of 54 J will not guarantee it.