A non-destructive, visual failure analysis of a failed 4½ inch, 16.6 lb./ft., 0.337 inch nominal wall drill pipe was conducted by J.E.I. Metallurgical, Inc. No destructive testing (tensile and/or core hardness) was conducted.
The drill pipe failure had been cut from the failed joint and only about 15 inches on each side of the fracture was provided for analysis. The two failed drill pipe sections are shown in Photographs 1 and 2
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Photograph 1 Profile of one side of the drill pipe failure.
Photograph 2 Matching fractured drill pipe.
Examination of Photographs 1 and 2 revealed that the drill pipe diameter had been dramatically reduced near the fracture. The technical term, necking, is used to describe this diameter reduction. The two fracture surfaces are shown refitted in Photograph 3.
Photograph 3 Two fracture surfaces refitted.
The necking of the outside diameter of the pipe is clearly evident in Photograph 3. Both fractured sections were examined visually and at various magnifications. Both fracture surfaces exhibited slant fracture, indicative of overstress or overload. Overload is the result of stressing the object, in this case the drill pipe, beyond the yield strength so that permanent deformation and fracture resulted. A close-up view of the two individual fractures is shown in Photographs 4 and 5.
Photograph 4 Slant fracture on failed section of drill pipe.
Photograph 5 Adjacent (mating) drill pipe fracture surface.
Drill pipe diameter measurements were taken along the drill pipe toward the fracture. Results indicated that the drill pipe diameter diminished as the fracture surface was approached. That is, necking was evident and demonstrated by the variation in diameter.
The drill pipe wall thickness was also measured around the entire fracture surface. The thinning of the drill pipe wall thickness was clearly evident, proving necking and an overload fracture. This section of drill pipe was literally “pulled apart” by the application of a pulling load beyond the strength of the drill pipe joint.
