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Threaded connections are widely used in connecting drill pipes into a drill string. During drilling operations, the threaded connections are subjected to various external loads, including the load from the unevenness of rock formation at the bottom, impact from the well bore and axial hook load etc. These loads are primarily random, and will cause...
Contexts in source publication
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... connections serve as connections between adjacent drill-pipes or drill-collars to form a whole drill string. There are several different types of connections used in the industry; the most commonly used type shown in Figure 1 is called threaded and coupled connection. This type of connections mainly contains three parts: two pins and one box. ...
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... calculation results at the position of x = 1,500 m are given in Figures 9 and 10. Figure 9 represents the results of step 1 and Figure 10 gives results of step 2. ...
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... calculation results at the position of x = 1,500 m are given in Figures 9 and 10. Figure 9 represents the results of step 1 and Figure 10 gives results of step 2. ...
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... assumes that the equivalent stress (E.S) follows the Gaussian distribution; thus, the resulting E.S within 1σ is assumed at the level of 68.3%, E.S within the 2σ is at the level of 27.1%, and the E.S within the 3σ is at the level of 4.33%. The computation results for the connection at different locations under the random intensity of 0.08 G 2 /Hz are presented in Figure 11. Then, the number of cycles causing failure (N i ) is calculated with the DEL method by substituting the 1σ, 2σ, and 3σ corrected equivalent stress ranges into equation (21). ...
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... this section the effect of the intensity of the random excitation, the location of the connections and the static load to which the connection is subjected are analysed. Keeping the other factors the same and simulating with three white noise intensity as 0.04, 0.06 and 0.08 G 2 /Hz, the damage levels for different locations are shown in Figure 12. From the figure, we can make the following observations. ...
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... random input is set as 0.08 G 2 /Hz, and five different tensile loads (56.3, 84.15, 112.6, 140.75, 168.9 MPa) are simulated. The corresponding results of fatigue damage are illustrated in Figure 13. It can be seen that with the increase of tensile load the fatigue damage increases monotonously. ...
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... equations (4) to (7), the stiffness of the upper spring and the lower spring can be calculated and the results are as shown in Table 6. The calculation results of the fatigue are given in Figure 14. Obviously the fatigue damage decreases monotonously with the location changes from the bottom to the top. ...
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Citations
... The cap acts as an external thread, while the rocket tube acts as an internal thread. In some studies, the cap acts as a pinned thread, while the rocket tube acts as a box thread [7][8][9][10][11][12][13][14] . ...
The thread joints are often used to connect a rocket tube to a cap and a rocket tube to a nozzle. The connection of two components using a thread joint needs to be considered carefully. The joint is the part that most often fails because it is the location of the stress concentration. The study aims to examine the effect of load variations and thread types on the joint strength between the cap and rocket tube using the finite element method. The analysis was carried out with the help of the Ansys Workbench software. Loads of thread joint was varied 70, 80, 90, 100, and 110 kN. The rocket cap and tube material are Al 6061-T6. Static stress simulation results show that the thread joints both square thread and trapezoidal threads can withstand static loads of up to 100 kN because it has a safety factor of more than 1.25. The trapezoidal thread has a better safety factor than the square thread.
Failure of three drill pipe connections occurred relatively early in the service life and without the more gradual reduction in operating pressure or other factors that are typically associated with a pending fatigue failure. Of the three drill pipe connections, two had fractured and the third had cracked but remained intact. The drill pipe connections were investigated to determine the mode and likely cause of the failure. Failure of the drill pipe connections was the result of fatigue that had initiated on the outside surface within the first thread root adjacent to the change in section to the barrel or at the change in the section itself. Crack propagation was radially inwards towards the connection bore. Chlorine was present in the drilling mud at low concentrations and fine pitting was identified, but overall, the rods were free of corrosion. However, positive identification of corrosion pits, albeit few in number and significant cracks emanating from said pits, suggest failure of the drill pipes could be attributed to a corrosion fatigue mechanism. This would more so be the case for two of the drill pipe connections, as the stress concentration associated with a corrosion pit would be exacerbated in the threaded region. Fatigue had subsequently propagated under bending loads, likely reverse bending loads, applied to the drill string. Such loads would likely be the result of directional drilling within strata of higher than usual hardness.
Kajian ini bertujuan untuk meneliti pengaruh jumlah ulir dan variasi beban terhadap kekuatan sambungan cap dan tabung roket Dextrose menggunakan metode elemen hingga. Cap dan tabung roket menggunakan Al 6063-T5. Ulir yang digunakan yaitu jenis ulir persegi dengan variasi jumlah ulir 5 dan 6 buah. Pembebanan divariasikan 4, 5, 6, dan 7 kN. Analisis elemen hingga dilakukan dengan bantuan software Ansys Workbench. Hasil simulasi tegangan statis menunjukkan semakin besar pembebanan, maka semakin tinggi tegangan von Mises maksimum. Tegangan von Mises maksimum menurun seiiring peningkatan jumlah ulir. Sambungan ulir persegi dengan variasi jumlah ulir 5 dan 6 dapat menahan beban statis hingga 6 kN karena memiliki faktor keamanan lebih dari 1,25.
Drilling is one of the costliest and risky activities in oil and gas industry due to complexity of interactions with downhole formation. Cyclic loads while drilling cause the initiation and growth of cracks in oil tubulars. This phenomenon, known as fatigue, results in permanent reduction of the failure-free service envelope of a certain tubular. Further, most of the drill string failures are triggered by fatigue, which results from repetitive cyclic bending loads and stresses in tensile or buckled drill strings. Fatigue is a cumulative and non-reversible condition induced by repetitive cyclic bending loads and tensile or buckled drill pipe stresses. Fatigue exists even though cyclic tension of the drill pipe material is much lower than static strength limit. Present work investigates fatigue capacity of the 4” WT38 drill pipe connection where cracks have been observed. In accordance with the geometry of connection, a hot spot stress from bending moment is calculated in the crack location in the first thread (upper) of the pin. The DNVGL-RP-C203 SN-curve B1 “in air” is used as relevant fatigue SN curve for the drill pipe thread location. Finite element method (FEM) is employed in modeling and analyzing of drill pipe on pin-box connections. With this method, various connections can be investigated relatively faster and cheaper compared with experimental tests. It is found that the fatigue failure may have been caused as a result of the cyclic load level and number of load cycles. A detailed discussion of the fatigue damage assessment concludes the paper.
