Temporary Severe Reduction in Drill Pipe Load Capacity Due to Frictional Heating

Abstract Numerous cases of drill pipe overload failures have occurred while rotating and reciprocating the drill string under packed off conditions where circulation is either low or lost completely. These failures are typically known as "down-hole heating" failures. The failure mechanism and forensic evidence needed for identification of the failure mode has been presented in a technical paper (SPE/IADC 92429). This failure mechanism occurs when frictional heating, along with poor or no circulation of drilling fluid results in extremely high localized temperatures in the tube. Material temperatures above the steel's austenitic transformation temperature can be reached causing a microstructural transformation and alteration of the material properties. However, when the material temperatures do not exceed the austenitic transformation temperature, the microstructure does not change but the mechanical properties can be drastically altered temporarily, leading to an overload failure. The understanding of failures occurring under this scenario and the supporting forensic evidence is still in the developing stages due to a lack of empirical data. This paper provides multiple case studies where packed hole conditions with lost circulation were present and drill pipe tubes failed from overload deep in the well with low tensile loads relative to the rated tensile capacity which is consistent with "down-hole heating" overload. In these cases, the failure samples did not provide the physical evidence and microstructural transformation signatures described in the previous work paper SPE/IADC 92429. It was postulated that the failure occurred due to frictional heating but the material temperature did not reach austenitic transformation temperatures required to change the material microstructure. The paper presents experimental data that demonstrates the effect of elevated temperature on material strength for S-135 drill pipe tube materials at temperatures ranging from room temperature to austenitic transformation temperatures. Two separate tensile tests were conducted for each temperature throughout the range: one set of tests were pulled while the samples were at the elevated target temperature, the other set of tests were pulled after the samples had air cooled to room temperature from the target temperature. The experimental data obtained in this study documents that the yield strength of S-135 drill pipe tubes can be temporarily reduced up to approximately 90% when heated to elevated temperatures below the austenitic transformation temperature with no change of material microstructure. The data provided in this paper provides the industry with valuable information when evaluating down-hole heating failures.