Further Developments in Drill Pipe Fatigue Management: A Case Study

This paper describes the fundamental behaviour about cumulative damages of nonstructural members such as glass window sashes under destructive cyclic wind disturbances.The analysis consists of wind modelling for fatigue damages and the formulation to obtain the cumulative damage analysis.First, in modelling the observed strong wind information, three steps of wind action in the long period are selected to discuss the fatigue damage properties.The fist wind model is to present the simple strong wind continuing normally during 20 to 30 hours from annual average about 4 5 m/s to the extreme maximum wind velocity.Next step is to represent the whole annual wind actions using the meteorologically obseved wind velocity per hour.Finally, the return period concept is utilized to the overall fatigue damage of a life time of the structure or members.Accordingly, the damage responses of nonstructural members are presented in three parts.The basic concept to give a quantitative expression of a cumulative fatigue damage is proposed when the simple strong wind is subjected to nonstructural member. The annual cumulative damages and fatigue behaviour in the return period are also discussed on the basis of computed results.One of the most important results is to evaluate the cyclic repeated wind action to structural safety rather than the most large extreme value in the previously observed data.

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.

Both Saudi Aramco and Total Indonesia found benefits in selecting 4 in. drill pipe with streamlined double shoulder connections for the drilling of wells, for which the 3 1/2 in. drill pipe was unsuitable. Although dealing with different environments and applications, these benefits can be summarized in "successfully drilling longer slim holes with a drill string having enhanced torsional, tensile and hydraulic characteristics at a lower overall cost". For the Saudi Aramco QTF field, Extended Reach Drilling (ERD) was required with the objective to deliver pay zones located at measured depths of 18,000 ft (for the 1,500 HP rigs) and 25,000 ft (for the 2,000 HP rigs). These depths correspond to step outs ranging from 13,000 ft to 20,000 ft respectively from the drill site. For its Kalimantan field, Total was in a need of higher torsional capacity and also an improvement of the hydraulic characteristics of the drill string. Selecting a larger size of pipe was the retained option against an upgrade of the rig pump installation. The casing and drilling program remained unchanged with the drilling of a 6 in. hole after setting the 7 in. casing, adding a constraint for fishability of the string. In both cases, fishability and torque objectives made the selection of the appropriate connection essential. The selected double shouldered connection maintained a tool joint outside diameter similar to standard 3 1/2 in. drill pipe tool joints, that maintains fishing ability of the 4 in. pipe, in casing and open hole, despite the pipe size increase. The streamline connection design provides 22,000 ft-lb working torque, an outside diameter of 4–7/8 in. and an oversized internal bore that promotes hydraulic efficiency. Other important improvements include considerable gain in pipe resistance under buckling loads, increased available pressure at the bit, better telemetry for the MWD and LWD tools and improved hole cleaning and rate of penetration. Introduction Drilling deeper, slim hole wells has revealed limitations of 3 1/2 in. drill pipe traditionally used to drill the 6 to 6–1/4 in. hole sections. The level of torque that API rotary shoulder, as well as first generation double shoulder connections, can deliver does not match the new requirements for these deeper drilling programs. This increase in drill string length also puts an additional constraint on hydraulic performance. This encouraged drilling engineers to re-evaluate the drill string design requirements and select a new configuration of pipe that would respond to these new requirements. This paper addresses these pipe and connection design considerations and provides two case histories showing the benefits that were realized from using this new drill pipe design configuration. Over 1,400,000 ft of this pipe has been built to date and is in service all over the world. It is also important to mention that this new drill pipe arrangement can also be used for drilling upper hole sections eliminating the need for a string 5 in. drill pipe in many applications. Streamlined Double Shoulder Connections for 4 in. Drill Pipe There has been increasing requirements for drill pipe with improved hydraulic performance and mechanical properties to replace 3–1/2 in. drill pipe traditionally used in slim-hole drilling.

The Bohai Sea is the sea area with the worst ice condition in China, and the ice loads significantly threaten the safety of structures in the sea. The intense vibrations of the pile‐supported bridge under stochastic ice loads will increase the fatigue damage of a bridge structure and reduce the fatigue life of a bridge structure. In the present study, a comprehensive analysis model is presented to study fatigue damage for pile‐supported bridges under ice loads in Bohai Sea. On the basis of measured statistical data of ice parameters and stochastic ice loads spectrum of Bohai Sea, the time histories of the stochastic ice loads of Bohai Sea are simulated. Fatigue damage analysis is carried out in time domain utilizing the finite element method considering soil and bridge structure interaction. The effect of soil conditions and water depth on the cumulative fatigue damage of the pile‐supported bridges is studied. Numerical results indicate that in comparison with stiff soil conditions, pile‐supported bridges in soft oil conditions can increase the cumulative fatigue damage substantially; pile‐supported bridges in deep water also can increase the cumulative fatigue damage obviously. The study presented the first danger position of cumulative damage of the pile cross section under stochastic ice loads. The findings of this study can be used to fatigue damage evaluation and bridge construction in the ice‐covered sea area.

Drill string models are of two major types- Conventional and Periodic. Conventional drill string models are widely used due to their simplicity in manufacturing and dynamics analysis. Drill strings are affected mainly by torsional, lateral and axial vibrations. The dispersive or propagative nature of these vibrations can only be analyzed by using periodic drill string models. Drill pipe makes up the majority of the drill string. In reality, at each end of the drill pipe, tubular, larger-diameter portions called the tool joints are located. Since the dimensions of the tool joint are negligible when compared to the drill pipe, conventional drill string models assume drill strings to be uniform structures. The tool joints in drill strings introduce a geometrical periodicity in the structure.A periodic structural component is comprised of a repeating array of cells, which are themselves an assembly of elements. The elements may have differing material properties as well as geometric variations. The periodic structures act as mechanical filters for the wave propagation. A material or geometrical change in the structure causes a disruption to the continuous propagation of vibration waves.There are three types of waves propagating in rotating structures: torsional, flexural (bending) and longitudinal. Of these waves, torsional and longitudinal waves are dispersive while flexural waves are non- dispersive. The proportions of the waves which are dispersed vary according to the Wavenumber. The wavenumber is a property of the wave and depends on the structural, material and geometrical properties of the wave guide. Waveguide is the medium through which a wave travels. The wave number, and hence the dispersion and propagation characteristics of waves can be tuned by varying the material and geometrical periodicity in the drill strings.This paper presents the vibration propagation and attenuation characteristics in conventional and periodic drill string models. The periodic drill string model is developed such that it can be easily scaled to a real drilling rig model. The research also features a laboratory setting which comprises a mini drilling rig and actual drilling samples. These features ensure robustness of the dynamics analyzed for the periodic drill string model.The research findings are analyzed under zero and non- zero borehole drill string interactions. Vibration information is collected from upper and lower parts of the drill string models to compare the propagation and attenuation characteristics. Proximity sensors are used for the data acquisition which is then analyzed using frequency and power spectrum graphs. The time and frequency domain vibration propagation characteristics are investigated for both the conventional and periodic drill string models. Laboratory testing analyzes (1) introduction of stop and pass band regions in frequency spectra by periodic drill string models, and (2) vibration attenuation in torsional and lateral vibration modes. The tests confirm the introduction of stop bands in frequency spectra for the periodic drill strings, while they were absent and had an all pass-band for conventional drill string models.The research opens up a new method of passive control of drilling vibrations- by introducing tool joint designs which could be tuned to efficiently dampen out the harmful vibrations affecting the drilling rigs.

Fatigue damage of damper increases with applied load cycles in a cumulative manner. Cumulative fatigue damage analysis plays a key role in life prediction of components and structure of dumpers subjected to field load histories. In order to investigate the fracture reasons of some components of coal dumper installed at Qinhuangdao Port, some field measurements of strain and stress were carried out. The field measurement data shows that the first principal stress of structure is less than limited strength of applied material and stress concentration problem has distinct affection to stress distribution for some components. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element model is meshed for assessing and calculating stress distribution and strength characteristics of dumpers. The stress distribution and stress concentration factors of main components of dumper at different loading cases are numerically simulated. A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The Ramberg-Osgood equation is used for constructing cyclic stress-strain relation. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule and finite element model. The investigation shows that fatigue notch factor and stress concentration factor have a significant influence on the calculation of fatigue damage of dumpers. The numerical simulation for fatigue calculation of dumper shows that prediction results of fatigue life agreed good with practical life.

In view of non-conservative prediction of cumulative fatigue life calculated by Miner's and Haibach's methods, the authors proposed in a previous paper a new model providing better and conservative prediction, although it was limited in application to only the bi-linear fatigue diagram in high cycle fatigue regime. If a fatigue diagram will be required to be expressed for a wide range of fatigue life from very low cycle to high cycle regimes, it is a convenient way to express the diagram by Stromeyer's expression.The previously proposed model is developed in the present paper so as to be applicable to Stromeyer's as well as hi-linear expressions of a basic fatigue diagram in undamaged condition. The newly proposed model in this paper is based on a concept consisting of two assumptions ; (i) Fatigue damage will be accumulated as a power function of cycle ratio, and (ii) Fatigue strength at infinite fatigue life or at 107 cycles will decrease functionally according as accumulation of fatigue damage.

Structural safety is of utmost importance for polar icebreakers under both navigation and icebreaking conditions. In this research, the Palmgren–Miner linear cumulative damage theory is employed to evaluate the structural fatigue lifespan of polar icebreakers. A spectral analysis, incorporating the time distribution coefficients for three load conditions, is executed to assess the fatigue damage at typical hot spots during navigation. For icebreaking activities, the ship–ice interaction loads with time history are simulated using the discrete ice element method, taking into account five sub-operating conditions. This simulation is coupled with rainflow counting to evaluate the fatigue damage. The results show that the cumulative fatigue damage during navigation is much less than that during icebreaking. Additionally, shoulder areas suffer more serious fatigue damage during icebreaking as a result of the direct impact of broken ice. Consequently, both navigation and icebreaking conditions should be considered in the design of hull structures and the assessment of fatigue strength for polar icebreakers.

Electrical resistivity of an incrementally fatigued lead alloy: Lawson, L. and Meshii, M. Scr. Metall. Mater. July 1991 25, (7), 1713–1717

On some basic problems of fatigue research in engineering

The life of a component subjected to a constant stress can be determined using the S-N diagram. Prediction of cumulative fatigue damage or fatigue life of a component subjected to a given stress sequence of varying amplitude is difficult, if not impossible. Miner's rule and Kramer's equation can predict cumulative fatigue damage with a reasonable degree of accuracy for limited cases. The development of Kramer's equation was studied and a modification suggested. Cumulative fatigue data generated using aluminium alloys 2011-T3 and 2024-T4, were analysed using Miner's, Kramer's and the modified equations. While Miner's rules and Kramer's equation predict cumulative fatigue damage with tolerable error for a few cases, the modified equation has shown close agreement between the experimental and theoretical values of fatigue life or cumulative fatigue damage for the materials studied in this investigation.

The present study intends to investigate the effect of temperature on cumulative fatigue damage of laminated fibre-reinforced polymer (FRP) composites. The effect of temperature on fatigue damage is formulated based on a previously proposed residual stiffness fatigue damage model. The fatigue strength of FRP composite laminates is also formulated to have temperature dependent parameters. The research work is divided into three main parts; the first part reviews the fatigue damage mechanism is fibre-reinforced composites based on stiffness degradation. The recent residual stiffness of Varvani-Shirazi was used as the backbone structure of damage analysis in this thesis. This model is capable of damage assessment while the effects of maximum stress, stress ratio and fibre orientation of FRP composites were recognized. The Varvani-Shirazi damage model was further developed to assess fatigue damage of FRP composites at various temperatures (T). Inputs of the damage model are temperature dependent parameters including Young's modulus (E), ultimate tensile strength(ðult) and fatigue life (Nf). As the next part of the proposed analysis, the temperature dependency of each parameter is formulated, and the relations of E-T and ðult-T are substituted in the Varvani-Shirazi fatigue model. Finally, all terms and equations are evaluated with the experimental data available in the literature. Six sets fatigue data were used in this thesis to evaluate fatigue of FRP specimens. The predicted results were found to be in good agreement with the experimentally obtained data. The proposed fatigue damage model was found promising to predict the fatigue damage of unidirectional (UD) and women FRP composites at different temperatures. Temperature dependant parameters of Young's modulus, ultimate tensile strength, and S-N diagram were also found to be responsive when used of UD, cross-ply, and quasi-isotropic FRP laminates.

Frequency based fatigue analysis and temperature effect

Rotary tiller blades are usually required to achieve the performances of more efficient and longer lifetime. Shapes and processing techniques play a key role in their fatigue life. A Simulation model and data of field experiments were conducted to use are used synthetically for on the evaluation of fatigue life, which is related with the geometric features of rotary tiller blades and their working conditions. In simulation model, the weakest section of rotary tiller blade was identified by the finite element method with ANSYS software. The weakest section was loaded by statistical random load spectrum using severe conditions in the working environment including sandy soil and clayey soil. The modal analysis method was adopted in studying dynamic effects. Fatigue analysis methods (SN curves, rain flow counting and mean stress theory) were used to determine the fatigue damage imposed on the components. The simulation model analyzed the fatigue sensitivity of input parameters to obtain a discrete fatigue life, and important factors affecting the fatigue life. The comparisons between rain flow matrix and damage matrix reveal corresponding relationship between loading cycle and fatigue damage. Based on these, cumulative fatigue damage was calculated by the software (ANSYS Workbench) according to linear damage theory, and the fatigue damage was evaluated. The predictions were based on linear elastic fracture mechanics theories combined with the finite element method. The results indicated that it can be used to anti-fatigue design of rotary tiller blades in the designing stage of product, and provide technical support for further optimization and evaluation of rotary tiller blades.

System reliability analysis of mooring system for floating offshore wind turbine based on environmental contour approach