Experimental Stress Analysis of Tool Joints

This paper proposes a method to calculate the maximum allowable bending moment on pipe flange connections for leak tightness design of piping systems in process plants. The method evaluates the gasket stress reduction due to the bending moment as well as internal pressure based on the load factor of the bolted-gasketed pipe flange connection and the equivalent axial force. It determines the critical load combination of pressure and bending moment causing leakage. The calculated maximum allowable bending moment has shown fairly good agreement with experimental results with reasonable conservativeness. The paper also shows the advantage of the proposed method against the conventional methods such as the equivalent pressure method, NC-3658.3 method, B31.8 method, and so on.

This paper describes the further improvement of the simplified method of progressive collapse analysis of a ship's hull under longitudinal bending proposed by the authors. Here, the method of analysis of flexural behaviour of stiffener elements was extended to deal with coupled flexural-torsional behaviour of angle bar stiffeners welded to continuous plating.A series of elastoplastic large deflection analysis was performed and the rationality of the proposed method was examined.With the improved computer code 'HULLST', two alternative analyses were performed on existing bulk carrier including and neglecting tripping of stiffener elements. It was found that the ultimate strength of stiffener elements decreases when stiffener tripping takes place, which results in reduction of ultimate bending moment of the cross-section. The load carrying capacity of stiffener elements in the post-ultimate strength range was more decreased and so that of the cross-section. The allowable bending moment according to the Lloyd's Register of Shipping was calculated and the reserve strength above it until the initial local collapse was 22.4% of the allowable bending moment. Interaction diagram for longitudinal hull strength under bi-axial bending is also presented.Progressive collapse analysis was performed also on a large scale frigate model tested by Dow, and the applicability of the present method was demonstrated.

There are many types of flange and clamp connectors in use and described by different standards. Most of them are based on the linear elastic methodology and allowable stress concept (ASME, API flanges). More modern designs (ISO 27509 and NORSOK L-005 Compact Flanges, NORSOK U-001 subsea flanges) are based on elastic plastic principles and plastic collapse capacities. For all of them defining the tensile structural and functional limits is relatively transparent and seamless process. Often the external allowable Bending Moment load at rated Pressure is one of the most critical characteristics for subsea use and High-Pressure connections. To predict capacity and allowable Bending Moment is more complicated especially for modern flange types. In this paper author will focus and explaining already existing design methods with relation to the FEA assessment and modern connections structural and functional capability. The topic will be discussed based on the Compact Flange (ISO 27509 and NORSOK L-005) connection example and in related structural FEA long term functionality check based on DNVGL-RP-F112 recommendations (Hydrogen Induced Stress Cracking for subsea Duplex and Super Duplex material). In the presented example the focus will be on the flange itself, but the attached pipe also be included in the evaluation. The topic discussed in the paper and the conclusions are included in the FEA recommendation in the newest national NORSOK L-005 flange design code release.

Although nuclear power plant piping system is designed conforming to design specifications, the piping systems are deteriorated with increase in service life. In this study, monotonic and cyclic loading tests were carried out on TP316 stainless steel pipe specimens, and the effect of local wall thinning and cracking on failure behavior was investigated. In the tests, 0%, 35% and 75% wall thinning and cracking of initial thickness were artificially introduced to inside elbow and straight pipe specimens, and internal pressures of 20MPa were applied to simulate real operation condition. From the test results, the effect of local wall thinning and cracking on failure mode, ultimate load, number of cycle and strain energy was presented, and maximum bending moment was compared with allowable bending moment calculated by ASME code.

The construction industry is increasingly developing and growing rapidly with more advanced technologies. The world timber demand is increasing at a rapid rate but the timber supply is however depleting. It has been found through research that bamboo can suitably replace timber and other materials in constructions. This study was conducted to investigate the structural strength of bamboo connections involving only spliced joint and compared with control samples strength of bamboo which were not connected. Bending test was conducted on four types of bamboo connection structures which werehalf-lapped splice joint using 3 bolts, half-lapped splice joint using 2 bolts, side plate splice joint, sleeves and insert joint and control sample bamboo. Every connection had six samples to determine the structural strength of the bamboo connection. From the tests conducted, the maximum load that can be borne by the bamboo structure and the bending ofthe bamboo structure will be obtained. Data were compared with the theoretical calculation based on the study of Janssen's. The connection structure that can bear maximum load was sleeves and inserts which was 5.997 kN. The control samples bamboo maximum load was 4.504 kN. Meanwhile, half-lapped splice joint using 3 bolts and 2 bolts were 4.789 kN and 4.04 kN. Structural connections that carriedthe lowest load was side plate splice joint which was only 2.659 kN.Compared with the bending moment of Janssen’s theory, all the connections did not exceed the maximum allowable bending moment. This showed that the study was in accordance with the standards approved by Janssen's theory. The study found that the structure of connections that can be used in the construction work was sleeves and inserts.

A simple method for calculating the shakedown behavior of the hull girder of a ship or marine vehicle is presented herein. The requirements for shakedown demand allowable bending moments which are generally smaller than those necessary to " break the back of a ship."

This paper discusses bending test results of steel pipe pile jointed footing by simple method, i.e. , a pile 60 cm in diameter and 9 mm in thickness is buried simply in footing with 10 cm depth, and plain concrete is filled inside up to l.5 times as long as pile diameter. Three cases of axial load condition are selected. The first and second tests are 0 t and 180 t in compression corresponding to the pullout load and push-in load, respectively, by rocking vibration of superstructure with load change equal to 90 t of the estimated bearing capacity of the pile. The third test is 30 t in tesion. which is supposed as pullout load condition. Loading system is as follows ; in order to simulate bending moment of pile in the ground by horizontal load, an concentrated load is applied at intermediate point between pile head joint and the other pinned supporting point of pile. Conclusions derived from tests results are summarized in the followings. 1) The degree of restraint for rotation at pile head α_r is small as 0.26 without axial load and 0.81 with axial load at the allowable bending moment of pile. But the apparent α_r becomes extremely large in both cases at the ultimate state as if the pile head is completely fixed condition. 2) The ultimate strength of steel pipe piles with simple joint method under the horizontal force is controlled by the occurrence of local buckling of pile. The local buckling strength is affected by the thickness-radius-ratio t/r as well as the case of uniform compression. It is necessary, therefore, to apply Eq. (3) or (4) which are derived as functions of r/t or t/r. Concrete filled inside of pile is available to prevent the occurrence of local buckling. 3) Even though the case of large degree of restraint for rotation between pile and footing, the apparent α_r is reduced if the overall rotation of frame is produced, and the bending moment becomes larger at the lower part of pile than at the pile head joint. It should be noticed, therefore, that there are some cases the ultimate strength may be controlled by the bending capacity of pile itself than that of pile head joint, even if α_r between pile and footing is large.

The accurate makeup of Rotary Shouldered Connections (RSC) is a critical step in optimizing the connection lifetime under complex downhole conditions. The makeup torque value of RSC depends on the friction coefficient of the assembly and the lubricant, which cannot normally be individually measured or determined, so that the API RP7G gives a recommended makeup torque based upon an assumed, yet constant, friction coefficient while a certain safety margin is considered. Therefore, the field induced stress state of the connection may differ from the connection optimum torque under reference conditions. This will lead to the following consequences: the lifetime of each connection is not maximized based on its drillstring position and the torque and axial force that can be transferred through the connection is different from the technical maximum limit. Due to the technological development, a wide spectrum of power tongs can accommodate the increasing interest in mechanized operations at the rig floor today. The importance of a torque-turn recording was stated in many papers as a good control method of the makeup process, especially for casing running applications. However, we believe that the reliability of a drill string can be improved by using feed back of torque turn recordings. State-of-the-art devices not only allow the precise mechanized makeup of connections, but they also provide sufficient data to analyze the quality of the connection make-up. The motivation behind the research is the desire to make use of the data that is already provided for the benefit of increased lifetime of the connections and the reduction of drill string failures, especially for drilling under extreme downhole conditions like long horizontal, HPHT or deep water. This paper presents a short overview of the state-of-the-art of current technology followed by a discussion of how technological advances can be used to improve the drill string reliability. Also, the readers are challenged to find the answer to the title question: "Do we need an Intelligent Makeup Solution for Rotary Shouldered Connections?"

Numerical and experimental distribution of stress fields for double shoulder tool joint

Many problems in a drilling operation can be caused by excessive contact forces between the drill pipe and the casing or hole wall. The contact force pipe and the casing or hole wall. The contact force is mainly controlled by the hole curvature, drill pipe stiffness, and the axial load on the drill pipe. pipe stiffness, and the axial load on the drill pipe. This paper discusses the relationship between the magnitude of the contact forces and the above three variables, as well as several other less significant variables. Introduction The lateral force with which the drill string interacts with the casing or open hole wall should be of vital concern in a drilling operation. Large lateral forces can result in excessive casing wear, excessive drill pipe and tool joint wear, and key seats in the hole wall. An understanding of the factors that control the lateral contact forces may allow preventative action to be taken before a problem develops. The problem of excessive contact force between the drill pipe and the hole wall has been recognized for many years. It was addressed in 1960 by Lubinski, but it has only been during the last few years that detailed computer modeling of the problem has been feasible. This paper presents the results of a finite element computer study of the variables that affect the magnitude of the contact forces under a variety of conditions. The parameters were chosen to represent conditions that may occur in realistic drilling operations. Finite Element Model During 1975 a consulting firm was contracted and directed by Amoco to write a dynamic triaxial finite element computer program for the analysis of bottom hole assemblies. This program can be used to analyze any multi-component drill string in a wellbore. The drill string can be divided into a maximum of 51 elements of uniform cross sectional geometry and uniform material. An iterative process of solving for deflections and forces is then performed until the drill string deflections converge within the boundary conditions of the borehole. The required input data is a description of the drill string, wellbore diameter, wellbore survey, drilling fluid density, and axial load (weight on bit). The computed data includes the forces and deflections for each node point. Further discussion of the program is included in the appendix. Two drill pipe models were investigated before one was chosen for the study. The first model represented a joint of drill pipe with five equal length finite elements and the tool joint as a single element with its length equal to the tool joint length. This model was unstable under certain combinations of axial load and hole curvatures. The second model represented a joint of drill pipe with two finite elements and the tool joint as a zero length element. The zero length element resulted in a single point of contact with the hole wall rather than a point of contact on each end of a short element. Both models gave the same results for the cases in which the first model would converge, thus the second model was used for the study. Figure 1 shows a diagram of the drill pipe configuration that was used for decreasing curvature and Figure 2 shows the increasing curvature configuration. Table 1 gives the drill pipe and tool joint dimensions that were used in the study. Cases were run for 3-1/2", 4-1/2", 5", 5-1/2", and 6-5/8" drill pipe, with 20", 13-3/8", 9-5/8", and 7" casing sizes. pipe, with 20", 13-3/8", 9-5/8", and 7" casing sizes. The 13-3/8", 9-5/8", and 7" casing sizes will give approximately the same results as 12-1/4", 8-3/4", and 6-1/4" open hole sizes. The effects of hole size, drill pipe size, axial load, hole curvature, length and orientation of the curve, and hole inclination were investigated. Unless otherwise noted, the drill pipe was positioned in the hole so that a tool joint would be at the center of the hole curvature. All the results presented in this paper were generated from a static (non-rotating) model. The results accurately represent the forces which develop while going in or out of the hole with the drill pipe. pipe.

Summary The only standard drillstring model in use today is the torque/drag model because of its simplicity and general availability. Field experience indicates that this model generally gives good results but sometimes performs poorly. For example, some friction loads predicted for casing running in horizontal wells have not been consistent with field data. In the standard torque/drag model, the drillstring shape is taken as the wellbore shape. However, given that the most-common method for determining the wellbore shape is the minimum-curvature method, this assumed wellbore shape forces the bending moment to be discontinuous at survey points. This defect is dealt with by neglecting the bending moment. A different approach assumes that the drillstring position corresponds with the minimum-curvature wellbore only at discrete points. The obvious choice for these discrete points is at the positions of the tool joints in the drillstring. Although these tool joints are fixed in position, they are allowed to rotate within the wellbore. These extra degrees of freedom allow solution of the bending-moment problem, because continuity of bending moment can now be ensured at each tool joint. This paper gives a complete description of the drillstring calculation. Typical torque/drag problems are studied to compare the two torque/drag formulations. These studies give comparisons in drag forces and torques for the two models, and for the new formulation, the magnitude of the bending moments.

Dynamic phenomena when a stand of drillpipe is run into the hole may result in pipe failure, either through exceeding the yield or through kicking the pipe off the slips. Two computer programs based on longitudinal wave propagation have been developed. Results are presented and recommendations are made.

Comparison of fatigue failure criterion in flexural fatigue test

The structure of wellbore and coupling is connected by thread, it is the position where fatigue failure accidents are happened in gas storage well, and the make-up torque of thread is the key factor that influences the mechanical properties of this structure. In this pa- per, a finite element method was established to discuss the calculation method of make-up torque and the influence law on the stress of coupling in the gas storage well. Results show that the make-up torque cannot be simply ignored due to its great impact on internal stress distribution of gas storage well. Experimental results showed the correctness of the model. Under the action of the make-up torque, the overall stress level inside the wellbore is higher than the external coupling. However the maximum stress exists in the external coupling. The overall stress grad- ually increases with the increase of interference rotation number (abbr. RN) between coupling and wellbore, but the overall distribution trend is almost the same. The first thread on the left of the connection part is the area where fatigue failure is most likely to occur. The make-up torque between threads increases linearly with the increase of RN between cou- pling and wellbore.

Fatigue failure is a grave technical issue in welded structures; it is caused by the stress concentration at the discontinuity of the weld toe or root. Therefore, many research studies have been performed to establish appropriate S–N curves for welded joints via fatigue tests and Finite element analysis (FEA). In almost all fatigue tests, it has been found that the loading point is far from the points of concern where fatigue life is investigated, and the fatigue life of the welded joint is not affected by the stress singularity at the loading points. However, when the loading point is close to the welded joint, the peak stress at the welded joint is affected by both geometry discontinuity at the welded joint and uneven stress distribution at the loading point. This paper presents the validity of S–N curves for welded structures with a concentrated load close to the welded joint. The stress behaviors of structures with a concentrated load are defined via stress measurements and FEA. Fatigue evaluations are performed via fatigue tests and corresponding FEA.