Fracture toughness of HSLA coiled tubing used in oil wells operations

Coiled Tubings are thin walled steel tubes of 25-89 mm diameter and thousands meters long, used in the oil industry for production and maintenance services. They suffer plastic deformation during unwinding of the reel, passing through a goosneck arch guide and an injector unit. Strain levels are of 2-3%, making the tubing fail by low cycle fatigue in around 100 wrap-unwrap cycles. As coiled tubing material generally behaves in a ductile manner at surface and down well temperatures, the R curve has to be known to make instability analyses. J-R curves were determined to characterize the fracture toughness of nonused coiled tubing, using nonstandard specimens due to difficulties with their small thickness and diameters. Different crack lengths and crack locations were tested to analyze the 2C 0W ratio and the influence of the longitudinal weld. The R curves obtained show crack arc length dependence and are influenced by the position of the longitudinal weld.Fil: Wainstein, Jessica Elvira. Universidad Nacional de la Patagonia "san Juan Bosco". Facultad de Ingeniería - Sede Comodoro. Departamento de Mecanica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez Ipiña, Juan Elias. Universidad Nacional del Comahue. Facultad de Ingeniería. Grupo de Mecánica de Fractura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The Spb method used to estimate crack extension for coiled tubings fracture toughness tests

Coiled tubings are widely used in oil and gas industries. Fracture toughness test of coiled tubing is a challenge. Non-standard specimen has to be used due to its geometrical difficulties, ie small thickness and diameter. Taking into account these factors, fracture toughness resistance curves, J-R curves, of coiled tubings were determined using the Spb method for the first time. The separability parameter, Spb is defined as the load ratio between two specimens at constant displacement, a precracked one that exhibits crack growth during its test and a blunt notched specimen with constant crack length when tested. Spb method, which uses Spb parameter, estimates stable crack growth in fracture toughness tests. It has been applied to different standardized specimen geometries. In this work, the method is applied to non-standard coiled tubing specimens. The geometry function was experimentally obtained testing four-point bending specimens. Stable crack growth results are compared to those measured using DC potential drop method used as reference method. Encouraging results were obtained.Fil: Wainstein, Jessica Elvira. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia Golfo San Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia Golfo San Jorge. Universidad Nacional de la Patagonia "San Juan Bosco". Centro de Investigaciones y Transferencia Golfo San Jorge; ArgentinaFil: Perez Ipiña, Juan Elias. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería. Grupo de Mecánica de Fractura; Argentin

Load-separation method, Spb, used to estimate crack extension for J-R curves, modified for geometric variations in blunt-notched remaining ligament

The Spb method estimates stable crack growth in fracture mechanics precracked specimens test. It compares the load ratio between a precracked specimen that exhibits stable crack growth and a blunt-notched specimen with apparent constant crack length when tested at constant displacement. When it was applied to very tough material, it was found that bluntnotched remaining ligaments varied by as much as 11.83 %, affecting visibly the results. Therefore, to apply the Spb method to very tough material for which non-standard specimens could be used as coiled tubing, the methodology limits are investigated. In this work, particularly the effect of geometry changes through an incipient crack growth produced on the blunt-notched specimens for very tough materials is analyzed. Hence, a modified Spb method is presented that takes into account the change in geometry of the blunt-notched specimens. Results provided in this paper are quite encouraging.Fil: Wainstein, Jessica Elvira. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de la Patagonia Austral; ArgentinaFil: Perez Ipiña, Juan Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería. Grupo de Mecánica de Fractura; Argentin

Influence of the calibration points on the Spb parameter behavior

The present work studies the separability parameter Spb behavior to estimate crack lengths when two or three calibration points are used. A set of precracked and blunt notched specimens with three-point bend ASTM-SE(B) geometry were prepared from three materials: AA 6061-T6 aluminum alloy with different side groove ratio, high-strength low-alloy welded steel, and 2.25Cr-1Mo steel. For each precracked specimen, initial and final crack length were measured on the crack surface. Intermediate crack lengths were determined by two methodologies: the standard elastic unloading and the Spb parameter method using two and three calibration points. The Spb crack lengths were very close to those estimated using the standard methodology; differences between them were less than 15 % Δa, suggested as a difference limit value in ASTM E 1820-99 to alternative methods for measuring crack extension. The performance of Spb parameter was evaluated using two and three calibration points. J-R curves were constructed. The JIQ values obtained by the standard methodology and the Spb method were similar.Fil: Wainstein, Jessica Elvira. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional del Comahue; ArgentinaFil: Cocco, Roxana. Universidad Nacional de Mar del Plata; ArgentinaFil: de Vedia, Luis Alberto. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Cassanelli, Aníbal Norberto. Universidad Nacional de San Martín. Instituto Sabato; Argentin