One of the main requirements of threaded & coupled connections used in oil-producing wells is the ability to resist high tensile loads. In order to ensure integrity under ever-increasing loads, the geometric parameters of the connection can be modified. In this paper, an FEA study of a 4.5 inch casing connection is reported to examine the effects of a modified load angle in combination with high tensile forces. The focus is on two failure mechanisms: jump-out and plastically deformed zones. Furthermore, a relative motion of pin and box at the contact regions is observed. It is concluded that using a negative load flank might be beneficial in order to prevent jump-out. At the same time, the deformations at the roots of the last engaged threads of the pin appear to be larger and relative sliding increases. Despite an optimization against one failure mechanism, the connection might fail as a result of an inevitable reduction of resistance against another.Keywords: threaded connection; casing; modified load angle; failure mechanisms INTRODUCTIONThreaded pipe connections are widely used in the oil and gas industry for well completion, drill strings and risers in offshore applications [1]. When comparing the nature of threaded connections with welded connections, major advantages can be identified. On one hand, the limited time which is required to connect two pipes in the field reduces the time to complete wells drastically. On the other hand, it is possible to break up the threaded joints without causing excessive plastic deformations. The ability to reuse the pipes in other wells is of vital importance for drill pipes.Due to the introduction of high performance connections which are characterized by a unique geometry consisting of a metal-to-metal seal, torque shoulder and thread profile[2], companies are able to build deeper wells in more extreme conditions. When taking into account the increased depths and hostile environmental effects, different failure mechanisms have to be examined in order to optimise the threaded joint.In this study, two frequently occurring types of failure are being examined. Drilling deeper wells results in the use of longer casing and drill strings, which implies an increase of weight leading to higher axial loads. These axial forces can cause the threaded joints to separate due to a phenomenon known as jump-out [3]. In order to reuse the connections when applied in drill strings, one of the prerequisites dictates that plastic deformation is non-existent or very limited. For this reason, the axial plastic strains within the threads can be used as the basis of a criterion to quantify the plasticity occurring in the connection.A numerical study on a 4.5 inch threaded-and-coupled connection (T&C) with standard API buttress threads and one with buttress threads with modified load angle subjected to an axial tensile load is carried out and a comparison is made. As a result, an indication of which failure mechanism is more likely to occur becomes visible.Sustainable Construction and De...

To ensure a reliable connection between two pipe sections, an initial make-up is applied to the threaded connections to induce a favorable stress state. Using finite element analysis techniques, it is possible to predict the internal strains and stresses of the connection when torque is applied. This article presents the outline of an experimental setup, which allows to directly validate the occurring strains together with the torque versus turn diagram and indirectly the contact pressures. The strains are measured by means of digital image correlation and strain gages. Both methods provide similar results and comply with the predicted finite element analysis strains when taper mismatch is taken into account. In an effort to qualitatively validate the simulated contact pressures, the temperature of the box is measured during make-up by means of infrared monitoring. The maximum temperature increase occurs near the vanishing threads where contact pressures are larger. Despite promising results, no decisive validation for the contact pressures could be obtained

Optimization of total cost of ownership (TCO) is an important, and challenging design target for present day manufacturing machines. This paper is concerned specifically with production machines with fast reciprocating loads (> 1 Hz), e.g. weaving looms and plate punching machines. Subsequent acceleration and deceleration give rise to a reciprocating energy flow that can be handled either mechanically or electrically. The chosen solution will affect the total cost of ownership. In addition to the cost of the energy storage device itself, there are the energy bill, the size and cost of the electric drive and power supply to consider. Moreover, there are certain constraints to be met: lifetime, DC-bus voltage limits and total power factor. This paper presents a methodology that takes all these aspects into account. It applies it to a bar linkage mechanism, which is representative for the targeted applications. In the mechanical domain, springs are considered for energy storage. The structural design of the spring is included in the analysis in order to account for lifetime and inertia added by the spring. In the electric domain, three different topologies are compared: a purely passive front end, where energy is stored directly on the DC-bus, a passive front end combined with a DC/DC converter and a separate storage capacitor, and an active front end.

When establishing oil wells, pipe sections are connected by means of threaded couplings. In an effort to minimize the possibility of failure by jumpout, standard buttress connections were introduced. Part of their strength is directly acquired as a result of radial interference during make-up. This paper discusses the results of a numerical study evaluating the effect of make-up on the performance of a standard 4.5 inch API buttress connection when axial tensile force is applied. In order to characterize the structural performance, the load distribution along the coupling length is evaluated, combined with a parameter defining thread separation. The latter is indicative for jumpout and the tendency of creating a leak path throughout the thread helix. From the results it is clear that relative axial displacement within the coupling occurs, even when made up, because of an initial clearance among the load and stab flanks. This clearance may cause a connection to leak through the thread helix when available thread compound cannot heal this leak path. Despite undesirable effects on the sealability and rigidness of this joint, such a clearance is required to decrease frictional forces during make-up while maintaining the desired radial interference.

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