Exposure of metallic parts to cathodic protection (CP) in sea water leads to production and diffusion of atomic Hydrogen into the metal matrix. Absorption of atomic Hydrogen into the metal could lead to hydrogen embrittlement (HE). In order to study the influence of stresses related to HE, FEA and Fracture Mechanics (FM) assessments were performed on a stud bolt threaded geometry. Effects of manufacturing tolerances, interface between nut and stud bolt and a defect in the form of a semi-circular crack placed in highest stress location of a thread root were also considered. Investigations of stress profiles when tension or bending are applied in test samples for measurement of HE threshold were also done, aiming at showing gaps on ASTM F1624-12 [1]. Tolerance assessment shows a relative maximum increase of 260% of nominal linearized membrane plus bending (NLMB) stresses regarding the nut runout [2] and for the proprietary nut geometry, such relative increase drops to 126% of NLMB stresses. Highest Hydrogen concentrations could be observed in the neighborhood of the first loaded thread root. FEA of cracked geometry shows that Hydrogen concentration could increase by around 283% around the crack tip, when compared to stud bolt in unloaded condition. Integrity assessment according to API 579-1 [3] or BS 7910 [4] and tests conducted according to ASTM F1624-12 [1] show less conservative results.

Gas storage well (GSW) is a type of underground pressure vessel. A series of fatigue and burst tests have been carried out on the simplified gas storage wells with/without thread defects. It can be concluded from the test results that: 1) the quality of the threads and the connecting torque of the threads are the key factor influencing the sealing performance and fatigue property of gas storage wells, the technical requirement of which should be described in the design documents. 2) Under the limited pressure, the threads failure first. The failure mode is pulling-out or leakage. 3) The positions such as connection of well pipe to coupling, connection of well pipe to well head equipment, connection of coupling to well bottom equipment, are the weak parts of the gas storage well. More attention should be paid on these parts in time of designing and in service inspection. 4) for the GSW with only axial thread defect (defect depth < thread height, defect length < thread axial length), the fatigue cycles can be higher than 30,000 and the ultimate strength can be basically equal to the one of the GSW without defects.

As there have been many researches for bolt self-loosening and a lot of knowledge have been accumulated, the phenomena has been understood more and more clearly. On the other hand, it is quite difficult to achieve both non-self-loosening and easy bolting tasks. In practical situations, easy and stable bolting is more focused and torque control is employed for tension control in the fields. For the stable bolting, friction of the threads is reduced by lubrication. However, the effect of this friction reduction is not yet investigated in the aspect of self-loosening. In this paper, the effect of frictions between male and female threads and between nut and bearing surface is investigated by FEA simulations. This provides information how self-loosening can be controlled. In this paper, the motion of the fastened plate transverse to the bolt axis is considered. This motion is known as the easiest motion to make self-loosening in experience and also as shown so in the author’s previous researches. The friction seems to increase self-loosening and also decrease self-loosening at the same time. It seems that the friction on the bearing surface drives self-loosening and friction on the thread surfaces prevents it. In this paper, both the frictions are examined in the relative manner with the Finite Element Analyses.

This contribution deals with the efficient numerical modeling of tapped thread joints. Commercial FE packages provide different strategies to tackle the problem of modeling threaded joints, which is a recurrent one for the design engineer. Different modeling techniques are characterised by how the screw is modeled: either three-dimensional elements (thetra, hexa or wedge) or mono-dimensional elements (beam) can be used. In the case of three-dimensional approaches, the thread helix is seldom modeled: the actual geometry is often replaced by a plain cylinder and a suitable choice of contact settings between the screw and the “threaded” hole. In the case of road vehicles, due to the high number of threaded connections to be modeled, it is paramount to reach a trade-off between modeling accuracy and computational effort. This paper aims at comparing two modeling approaches, namely a three dimensional approach (baseline) and a mono-dimensional one (simplified model). Based on several criteria, such as equivalent stress on the screw shank, pressure distribution at the interface of the plates and in the underhead region, optimal contact settings for the simplified model are suggested. These settings allow replicating the results provided by the three-dimensional approach for given load case. The comparison is carried out on single lap, single screw joints, by the ANSYS R17 software. The methodology can be easily extended to other softwares or joint configurations.

Bolted flange connections are heavily used within the chemical production/processing, transportation, marine, and power generation industries to contain processes while minimizing leaks. These leaks could cause unsafe working conditions, environmental hazards, and/or loss of product which, in turn, can cause fines or higher operating cost for plants. A way to deter this from happening is to correctly load the fasteners of the bolted flange connections to ensure the fasteners are properly stretched to apply an adequate contact stress to the gasket. Good understanding of how bolted flanged connections are optimally loaded limits leakage. When applying load via controlled torque to a fastener, the torsional energy applied is translated into a perpendicular force acting on the nut’s face and threads that is mirrored on the other side of the fastener thus inducing the clamping force on the connection. To determine the clamping force generated from the applied torque, a typical torque equation is applied using an empirically derived composite friction term called the nut factor. The nut factor is a dimensionless constant that includes all of the friction effects in the torque-clamping force relationship. The friction occurs between the surfaces of bolt and nut threads and the faces of the nut and flange or washer. The higher the friction, the higher the nut factor resulting in a higher fastener torque to achieve the same clamping force load. This study looked at several variables that can cause changes in assembly nut factor magnitude including bolt grade, bolt load, lubrication, washer presence, and bolt diameter.

The thread ring block heat exchangers, served at the high temperature and pressure, are the key equipment in the petrochemical industry. Due to the severe operational conditions and unsuitable assemble, internal leakage problem commonly occurs, especially for the seal gasket between the tube sheet and shell. Many failed gaskets are collected. Through a series of experiments including chemical composition, metallographic analysis, SEM and fracture analysis, the gasket damage and leakage causes are analyzed. For further interpretation, the gasket stress analysis is completed by the finite element method. It shows that the gasket stress is a main factor that affects the sealing performance for the thread ring block heat exchanger. Under long term operation at high temperature and pressure, the gasket stress between the tube sheet and shell becomes loose and creep. The gasket material also deteriorates with increasing time. Therefore, in order to prevent the internal leakage, the stress should be controlled in an appropriate range. And periodical inspection must be performed.

Pedicle screws (PS) are frequently used in medical spinal column fixation. Despite 7 out of 100 pedicle screws fracture inside of the patients’ body and under the claim that lateral bending is the main failure mode, little research has addressed the stress characteristics and the fracture location of the PS under lateral bending. This study focuses on the effect of thread design on the magnitude and location of maximum stress concentration. Four types of thread shapes are considered including V-shape, square-shape, buttress, and reverse buttress. Three-dimensional (3D) finite element (FE) methods are used in this investigation. A load of 150 Newton is applied at the screw head to simulate lateral bending. The models are created in SolidWorks. The 3D FE analysis is performed using the standard coding of ANSYS Workbench 19.1. Based on this study, it is found that the high stress concentration is located at the cortical bone region rather than at the cancellous bone region. Although the general stress patterns are similar, the PS thread shape design and the thread fillet radius may significantly affect on the magnitude and location of maximum stress concentration.

During tightening, the amount of torque given by the difference between the tightening torque, which is directly applied by the torque wrench, and the underhead torque, flows through the screw shank towards the threaded portion. This torque combines with the axial preload to bring about the overall stress state of the screw at tightening. Upon release of the torque wrench, a certain amount of the shank torque is released due to the elastic springback of the screw-plates system. In the literature [1], this phenomenon is just briefly treated by a few authors: they generally agree that approximately a half of the initial shank torque is released just a few seconds after torque wrench removal. This indication is given regardless of the frictional [2] and stiffness [3] parameters, which govern the joint. The present contribution aims at assessing, if there is any effect of the following parameters on the amount of shank torque being released after wrench removal: (i) the ratio between the torsional stiffness of the screw and of the plates, (ii) the friction coefficients in the underhead and in the thread. The experimentation has been run on a M20 8.8 class socket head screw, which has been instrumented by a double array of strain gauges, to simultaneously measure both the axial preload and the torque acting on its shank. Two different types of joined members have been examined: a cylindrical sleeve whose diameter is twice the screw diameter (compliant joint) and a rectangular plate whose transverse dimensions are more than ten times larger than the screw diameter (stiff joint). The underhead and thread friction coefficients have been controlled by properly selecting lubrication conditions. The main outcome of the work is that the torsional stiffness of the joined members does have an impact on the residual shank torque. A simple mathematical model has also been implemented, in order to predict the residual shank torque during the design phase.

There are two types of combination between external and internal threads used in threaded pipe connections for pressure piping specified in industrial standards like JIS as well as ISO. One is the combination that taper external thread of pipe is engaged with taper internal thread of a fitting. The other is that taper external thread of pipe is engaged with parallel internal thread of a fitting. Taper thread is always used for external thread outside the pipe wall. Both taper thread and parallel one are applicable to internal thread inside the fittings. This paper evaluates the mechanical behaviors of threaded pipe-socket joints (or pipe-coupling joints) and the difference due to the thread type combinations by means of axisymmetric finite element analysis for 3/4” and 3” joints. The analysis shows that the taper-taper threads combination establishes the full-length contact over the engaged threads but the taper-parallel has only a pair of threads in contact at the 1st engaged thread from the end of socket, and the difference results in the different behaviors of the joints. Stress and strain pattern also completely differ due to the difference in the engaged thread length. No significant effect of the size has been found in the present analysis for 3/4”and 3” joints. Experimental tightening tests and pressure leak tests have also been carried out for 3/4” and 3” joints with taper-taper threads combination. The measured experimental stress for 3/4” joints has shown an agreement with the simulated one fairly well. The pressure leak tests have demonstrated that the taper-taper threaded pipe-socket joints can hold internal pressure without leakage without using thread seal tape or jointing compound under low-pressure service condition. The 3/4” joints have started leaking at 1–4MPaG of internal pressure. The 3” joints haven’t shown leakage even at 6MPaG of internal pressure applied.

Our objective is to evaluate precisely a life-cycle of bolted joints under an eccentric load against a bolt axis. Many approaches to achieve the objective based on a lot of theories and practices have been proposed so far [1–12]. As we can refer from their approaches, the opening of the structural interface between clamped plates of bolted joints occurs by the eccentric load, which is over a bolt preload, and then the opening gradually propagates as the eccentric load increases. In the case, nonlinearity appears remarkably on the tensional and bending stress of bolts in the axial direction. In addition to the above, the axial bolt stress larger than expected occurs due to the principle of leverage depending on the load position and the bolted joints layout in the early phase of the pull-out action. Accordingly, the stress evaluation of bolted joints under the eccentric load is very important in order to ensure the safety of industrial machines. If dimensionless quantities of the bolt stress are found out considering the influence of the structural opening and the load eccentricity, we can have a few advantages as follows. First, bolt stress evaluations can be conducted by easily converting the dimensionless quantities of the bolt stress to the physical dimension quantities in a lot of cases where the bolt preload and the load eccentricity are different. Second, the number of times of verification tests can be reduced. We are developing a lot of industrial machines which have bolted joints used under eccentric load. In such development [13], bolt stress analyses are usually conducted under the combinations of the following conditions: (i) tapped thread joints, (ii) thin clamped plates than the bolt diameter, (iii) large eccentric loads, (iv) permitting the opening of the structural interface. Therefore, we propose a concept of a normalized bolt stress considering the effect of the structural opening and the load eccentricity. We validated this concept through theoretical studies, finite element analyses, and experiments under the direct load and the centrifugal load. As a result, the dimensionless quantities of the bolt stress caused by the bolt preload and a lever ratio of bolted joints under combined conditions was determined in this study. We can easily evaluate the bolt stress by simple conversions in a lot of cases in which the bolt preload and the load eccentricity differ.

In its 2016 Edition, ASME B31.3 [1] removed its long held provision for thread engagement that deemed the lack of complete engagement acceptable if the lack of engagement is not more than one thread. This change can have implications on existing piping assemblies which prompted some clarifications in ASME PCC-1 [2]. This paper reviews some of the reasons for the change, the issues around determining a specific measurable criterion of an acceptable amount of thread engagement, and proposes alternate criteria for the new construction codes to consider that are easily measurable and enforceable.

The flying of missile will severely jeopardize the structural integrity in control rod ejection accident. In order to analyze the strength of a new type of shielding plate under control rod drive mechanism (CRDM) missile impact, this article develops the simulation model and conducts the response analysis of the missile under 4 cases. In addition, the strain analysis and evaluation of protection shielding plate at the most dangerous case are performed. The motion analysis of CRDM missile indicates that the fracture at trapezoid thread place as well as the shielding plate rim under impact is most dangerous because the maximum kinetic energy of the impact can be obtained. So only this case should be examined when performing the evaluation of the shielding plate. Stress analysis shows the maximum stress intensity of the shielding plate will exceed the yielding stress and thereby local plasticity will occur. Strain analysis shows that compared with the extension ratio at structural failure, the computed strain still has margin to ensure the shielding plate will not be penetrated. Meanwhile the strain analysis of bolts which fix shielding plate are calculated. The strain level of two bolts are exceed limit and others is relatively low. The shield plate can be firmly fixed. Hence, this new type of the protection shielding plate is capable to prevent the damage of other components by the flying of CRDM missile.

This research analyzes the interaction between fibers and the air jets that are used to accelerate them in fiber processing industries. Typically, supersonic flow is used to achieve sufficiently high thread speeds. However, this flow contains shocks and expansions, resulting in large longitudinal variations in force on the thin and flexible thread. Consequently, a complex fluid-structure interaction (FSI) occurs between the supersonic air flow and the thread. In this research, the fluid-structure interaction between a supersonic air flow and a thread is studied numerically using three-dimensional simulations. The thread is represented by a smooth and flexible cylindrical body. The displacement of the thread is calculated for a given traction on its surface using a finite element structural dynamics code. The compressible flow around the thread is calculated using a finite volume computational fluid dynamics (CFD) code, using the arbitrary Lagrangian-Eulerian (ALE) framework to account for the thread deformation. In these partitioned simulations, the kinematic and dynamic equilibrium conditions on the fluid-structure interface are satisfied using a coupling algorithm. Two coupling algorithms are compared and the influence of numerical parameters is investigated. The fluid-structure interaction simulations reveal transversal running waves in the thread. By comparing the speed of these waves with the propagation speed of the shock waves in the tube, it can be concluded that these phenomena are not related.

There are two types of pipe threads, i.e., parallel and tapered ones. The former is used for mechanically connecting hollow cylinder-shaped structures, and the latter is usually employed for connecting thin pipes and tubes. The primary function required for taper pipe threads is to prevent the leakage of contained fluids. In order to ensure the sealing performance, target taper pipe threads need to be tightened with proper conditions. However, it seems that a standard tightening guideline with sufficient mechanical background has not been established. In this paper, using helical thread models, the relationship between assembly torque and rotation angle of threaded pipe is studied by FEA. The relationship between rotation angle and radial contact force between male and female threads, which is regarded as an index of the sealing performance, is also evaluated in like manner. In the numerical calculations, finite element analyses are performed as elastic and elastic-plastic problems, in which nominal dimeter of threads, pipe wall thickness and coefficient of friction on the thread contact surface are changed systematically, aiming at the establishment of a practical tightening guideline. Additionally, a simple method is proposed to evaluate the contact force between male and female threads, using elementary theory of solid mechanics. It is shown that the simple method can predict the contact force with sufficient accuracy, comparing to the calculation results by FEA.

A series of tests on NAS1352-06-6P threaded fasteners were coupled with analysis to fit constitutive models, evaluate multiple modeling approaches, and ultimately predict failure. Experiments loading the fasteners in tension at both quasistatic and dynamic loading rates were performed to obtain calibration and validation data for the analysis. The fastener was modeled with two low-fidelity approaches — a “plug” of hex elements retaining the nominal fastener geometry (without threads) and a “spot weld”, which incorporates similar geometry but the fastener is sliced near its mid-plane to define a tensile load-displacement relationship between the two exposed surfaces — to accommodate the use of these modeling methods in a larger, more detailed finite element analysis. Both modeling approaches were calibrated using quasistatic test data and then extended to the dynamic analyses to compare with the analogous test results. The analysis accurately reproduces most acceleration time-histories observed in the dynamic testing but under predicts failure, indicating the possible presence of strain rate effects that have been neglected in the constitutive models.

Kolsterising ® is a low temperature carbon diffusion treatment, referred to as carburization, in which carbon is forced into the surface of metal. This results in a significant increase of surface hardness without the formation of crystalline solids or chemical elements. 1 Carburization is not a coating process therefore the possibility of delamination is eliminated with the process. 2 Low temperature carbon diffusion treatment is being considered by a chemical company to possibly aid in the disassembly of higher alloy fasteners in attempts to reduce maintenance and equipment overhaul time during plant outages. This paper will explore the effects surface carburization, or carbon diffused surface hardening, has on the resistance of thread galling for B8M Class 1, B8M Class 2, and Hastelloy ® C-276 fasteners. 3 With the data provided from this initial study, a better understanding of the benefits low temperature carbon diffusion treated fasteners provides will be obtained. This paper has a limited scope that will utilize hand torqueing at various percentages of bolt yield to analyze the resultant clamping force of carburized fasteners in comparison to that of standard fasteners. This study is a milestone to further clarify the thread galling resistance that carburized fasteners provides.

Many people know that bolted fasteners are loosened and they sometimes suffer from the loosening. It is also the case for any plants who have hundreds of thousands of bolts. Any of these bolts may cause serious problems when they are loosened. Many countermeasures are proposed to prevent bolt loosening, but few of them are really effective. So far, only three bolting systems passed NAS 3350 tests. They are Eccentric nuts, based on nut eccentricity, Lock’n bolt, based on outer expansion of bolt threads, and L/R nut, whose principle is not open. As L/R nut is unknown how it works, this paper addresses the effectiveness of the Eccentric nuts and Lock’n bolts and compare them in simulation. The author have been working in bolt system loosening for a long time and succeeded the simulation of the phenomenon. This paper is the continuous work of this research.

Japan began constructing and upgrading HRS (Hydrogen Refueling Stations) for its FCV (Fuel Cell Vehicle) demonstration program in 2002, as shown in Fig. 1. In 2013, Japanese energy providers started constructing commercial HRS for refueling FCV with 70 MPa hydrogen, and almost 100 HRS are now in service. Maintaining the reliability of refueling equipment is essential for safe, stable operation of commercial HRS. However, as a result of experience with commercial HRS operation during the past few years, Japanese energy providers have recognized that maintenance for small leaks from cone and thread mechanical joints involves a significant loss of resources.

Torque control method is commonly used when tightening bolted joints because of its easy operation. However, the method involves an essential problem of fairly large scatter in bolt preloads. It has been reported that even if the same torque is applied, bolt preloads show a considerable scatter, e.g., ranging from 25% to 35%. A scatter in coefficients of friction on nut bearing surface and thread pressure flank is a primary source of bolt preload scatter. Meanwhile, the effect of Equivalent Friction Diameter at the bearing surfaces of nut and bolt head cannot be ignored. The scatter in Equivalent Friction Diameter is caused by imperfect geometry, i.e., the flatness deviation at the bearing surfaces. In this paper, the magnitudes of Equivalent Friction Diameter are quantitatively evaluated by FEA, using the experimental data of flatness deviation measured for a number of commercial nuts and bolts. It is shown that the bolt preload is likely to be scattered by as much as plus minus 10% of the target value, owing to the flatness deviation. Based on the comprehensive calculations by considering the imperfect geometry, a strategy to effectively suppress the bolt preload scatter is proposed.

Coated bolting has been widely used on flanged joints of pressure vessels and piping whenever there is a potential for atmospheric corrosion. The applied bolt coating has to be dimensionally accommodated, typically by over tapping the nut or less frequently, under sizing the bolt threads. A recently published technical paper by MacMoy, Ian [7], alleged that this practice is not in compliance with relevant industry standards and potentially compromises the sealing integrity of the flange joint. MacMoy’s paper recommended that any coating that requires over tapping in order to apply a coating’s optimal thickness should be avoided. In this paper, the authors investigated relevant industry practices, and performed proof testing of some sample bolt sizes. The outcome of this investigation and the details and results of the proof-testing are shared in this paper.