bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rate of Loading Parameters for Vertically Loaded Piles in Clay
Authors: Briaud J.L. , Garland E. , Felio G.Y. 
Published: October 2008

ABSTRACT
The analysis of 152 laboratory tests and 32 pile load tests confirms that for clays, the faster the rate of loading, the higher the undrained shear strength and the higher the pile capacity. The data shows that the gain in undrained shear strength due to increasing rate of loading increases with increasing water content, plasticity index, liquidity index, over consolidation ratio but with decreasing undrained shear strength
A simple model is proposed to quantify the rate of loading effects on undrained shear strength. The viscous exponent n which is the main parameter of the model can be measured by conventional laboratory tests or possibly by cone penetrometer testing, or as a last resort by the proposed empirical correlations to index properties.
This model is used to develop rate dependent t-z curves and a computer program to predict the response of a pile subjected to a certain rate of vertical loading. The model and the program are checked by comparing the predicted and measured behavior of two piles

INTRODUCTION
The present practice for the design of vertically loaded offshore piles is to calculate the pile length which will allow to resist two times the dead load and one and a half times the sum of the dead load and the extreme storm load. The design is based on static ultimate pile capacity calculations and no explicit consideration of dynamic loads is made.
The data presented in this article is the partial result of an ongoing research project at Texas A&M University sponsored by the American Petroleum Institute. The purpose of the project is to study the explicit influence of rate of loading and cyclic loading effects due to waves on the capacity of long offshore piles in clays. This article is dealing with the rate of loading effect only.

RATE OF LOADING MODEL
An undrained shear strength Su is measured at an average rate of shearing Su/t where t is the time to failure. It has been shown as early as 1951 (Casagrande and Wilson) that the value of Su is dependent upon the rate at which the soil is sheared. Others including Whitman (1970), Bea-Audibert (1979) and Lacasse (1979) addressed this problem. A value SUI is obtained for a time to failure t1 while a value SU2 is obtained for a time to failure to Two models can be used to describe the dependency of upon. The first model is:(Mathematical equation available in full paper)
This model leads to a straight line on a log-log plot and is the one proposed by Riggins (1981). Laboratory data collected from six different studies published in the literature show that Su versus t increases faster than a straight line on a semi log plot and is closer to being a straight line on a log-log plot (Briaud and Garland, 1984). As a result, the second model (Equation 2) was selected.
Erosion, Cavitation, and Abrasion Resistance of Choke Trim Materials
Authors: Seger F.G. , Maroofian I. 
Published: October 2008

ABSTRACT
An experimental investigation was performed to determine the relative erosion, abrasion and cavitation resistance characteristics of selected materials. Testing was conducted under controlled laboratory conditions to simulate service conditions encountered in production and injection chokes. The testing effort is ongoing.
The data accumulated allow informed material selection of conventional and novel trim for all chokes, valves, flow metering orifices, fixed beans and other devices used during drilling, completion and production of offshore and onshore oil and gas wells.
Sintered silicon carbide and tungsten carbide with minimum binder content were the most erosion and abrasion resistant of the materials tested. Cobalt base alloys bar and nickel chrome alloy 625 bar proved to be most cavitation resistant.

INTRODUCTION
Wear of wellhead chokes and other pressure reducing devices is a serious and common problem. Erosion, abrasion, and' cavitation are three types of wear, which is defined 1 as the volume of material removed. As the choke is adjusted to throttle fluid flow, a series of localized, time dependent and very complex flow fields are established in the region of the throttling point, such as the plug/seat gap in a globe valve.
Each flow field is a function of the valve position, fluid phase and properties, pressure drop across the choke and ratio of pressure drop to upstream pressures. Choke trim design parameters, such as trim contours and clearances also greatly affect the flow field.
The nature of the flow field in the gas choke is of particular concern when erosion of the trim material is considered. When the ratio of the pressure drop to the upstream pressure becomes critical, the velocity at the choke gap is sonic.
Small fluid borne particles move with a velocity approaching the mean velocity of the stream, and are influenced, depending on size, shape and density, by the large scale turbulence of the stream. The high velocity conditions at the choke throat and' along the downstream trim are therefore particularly conducive to high rates of erosion. Tests were performed on several materials to determine the wear (volume loss) rates in accordance with special erosion procedure.
Abrasion wear is associated with surfaces sliding along one another, and is greatly accelerated by fluid borne particulates. Those particulates with sharp corners, such as sand particles so often found in natural gas and crude oil are especially effective in promoting material removal when the choke is being adjusted frequently.
Other factors influencing abrasion wear include fluid lubricity, clearances between sliding parts, particle hardness, forces on component parts, and hardness and surface finish of the component parts. Low viscosity fluids, such as gas, provide poor lubricating qualities and negligible protection against abrasive wear.
New API Equation for Grouted Pile-to-Structure Connections
Authors: Karsan D.I. , Krahl N.W. 
Published: October 2008

ABSTRACT
A new equation for the design of axial load transfer in grouted pile-to-structure connections, with or without shear keys, has been written into the latest edition of API RP 2A. The general form of the equation was obtained from an ultimate strength formulation for a predicted failure mode, then safety factors were applied. The reliability of the equation was studied by comparison with the results of 147 tests, and results are presented. The paper al sodiscusses 1 imitations on the equation, compares it to the equation in the U. K. Department ofEnergy Code and presents some numerical examples.

ORIGIN OF NEW EQUATION
In 1982 the American Petroleum Institute (API) Task Group on Fixed Platform Criteria asked member Demir 1. Karsan to form a mini committee on grouted pile-to-structure connections in order to review the current state-of-the-art and identify possible changes in recommended design practice. The first meetings of this new committee generated considerable discussion of grouted pile-to-structure connections, both with and without shear keys, and of tests which had been performed on this type of connection. Committee Chairman Karsan and member Nat W. Krahl reviewed the available test data and, in late 1982, presented to the committee two equations, one for estimating the ultimate strength of such a connection, and the second a modified form which could be used for design.
The ultimate strength equation was based upon test observations that two separate mechanisms occur during the failure of a grouted tubular connection containing shear keys: first, a slippage between the steel and grout, and second, a crushing of the grout against the shearkeys (see Fig. 1). Such a connection normally fail s in a ductile manner, so that the ultimate strength of the connection is the sum of the two separate sources of strength. Before final failure occurs, diagonal cracks tend to open across the grout, frequently between diagonally opposite shear keys, or from one shear key to the opposite pipe. The ultimate strength equation presented to the committee stated that;(Mathematical equation available in fullpaper)

EVALUATION OF NEW EQUATION BY API COMMITTEE
Eqs. 1 and 2 were of sufficient interest that committee members issued a call for all available test data of grouted pile-to-structure connections so that a comprehensive reliability analysis could be performed on the equations. Additional data were indeed made available to the committee, so that data from a total of 201 separate tests were accumulated. The committee was of the opinion that a minimum unconfined grout strength should be specified for actual field connections, and a minimum unconfined strength of 2,500 psi (17.25 MPa) on 28-day old specimens was chosen. Hence, in comparing Eq. 2 to the test data, all tests were excluded in which the measured grout strength was less than 2,500 psi (17.25 MPa). 147 tests remained, including 62 tests of plain pipe (without shear keys), and 85 tests of pipe with shear keys.
Field Results of Curved Conductors in the Main Pass Area, Offshore Louisiana
Authors: Broussard G.C. 
Published: October 2008

ABSTRACT
Over the past fifteen years, the oil industry has developed the use of curved conductors in the Gulf of Mexico as an effective means of increasing horizontal displacement when drilling from offshore platforms. This paper reviews the results of utilizing curved conductors on several platforms. A discussion of the concept is presented as a preview, followed by drift angle performance of actual field results compared to design expectations. Case histories from four Main Pass area platforms are described where curved conductors were successfully used. Bearing performance is illustrated on a per platform basis before and after driving by rig operations. Conclusions are based on a comparison of directional programs for both curved and vertical conductors to the same target.

INTRODUCTION
As oil companies have expanded their search for oil and gas farther offshore in the Gulf of Mexico, they have encountered increasing difficulty in economically removing hydrocarbons for use. One common problem which first surfaced nearly two decades ago was the drilling for shallow sands in the range of 3000 ft. to 6000 ft. from a platform in water depths to 450 ft. With conventional methods, the horizontal displacement of drilling operations imposed certain limits on the area covered by a single platform, prompting the creation of curved conductors in order to increase horizontal displacement of wells and reduce the number of platforms required to develop these shallow prospects.
A curved conductor initiates the well angle deviation in the jacket typically above sea level instead of 200 ft. below the end of a driven conductor as is normally encountered with vertical conductors. A curved conductor allows a directional well to achieve a greater horizontal displacement when the well angle of deviation is built to its maximum. Angles greater than 55° have been found to cause mechanical problems for completion and workover operations because friction resistance exceeds the weight factor of tools, thereby making well work difficult. A curved conductor also allows a directional well to reach a target at a smaller average angle than would be encountered by a vertical conductor. Figure 1 illustrates a comparison of wells drilled through both type conductors and built to 55° average angle. As shown by Figure 1, horizontal displacement is significantly greater with a curved conductor. Also illustrated is a comparison of a straight versus curved conductor to the same target requiring a smaller average angle by using the curved conductor.

DESIGN EXPECTATIONS
Two variables are important to the successful use of curved conductors in a directional program. They are the bearing and rate of build angle. The ideal design expectations assume that the conductor's bearing and rate of build angle remain the same before and after driving. However, there is limited control over the drift angle and bearing during driving.
Seawater Corrosion Fatigue of 2¼ Cr-1 Mo and 4130 Steels for Marine Riser Application
Authors: Cozens K.O. , Burnside P.J. 
Published: October 2008

ABSTRACT
This paper reports on a corrosion fatigue study of 4130 and 2 1/4 CR-1 Mo steels immersed in seawater which addressed the reduction of fatigue life for these steels in a seawater atmosphere, and developed fatigue life design curves. The study has evaluated the effect of shot peened and nitrided surface treatments on sea water corrosion fatigue, and demonstrated that a significant loss of fatigue life is caused when unprotected 4130 and 2 1/4 Cr-1 Mo steels are fatigued in seawater. Shot peening of the material surface improves the seawater fatigue life for these steels, but does not restore it to the full atmospheric fatigue life of these steels in air. The test results for the effect of nitriding material surfaces prior to seawater fatiguing were not conclusive, but nitriding may be beneficial. Manufactures of subsea hardware need to take appropriate precautions to minimize or negate the life shortening effect of seawater corrosion fatigue to 4130 and 2 1/4 Cr-1 Mo steels.

INTRODUCTION
The study of the effect of seawater Immersion on 4130 and 2 1/4 Cr-1 Mo fatigue life was divided into two parts, a literature view, and speech tests which were used to develop specific design limits. These two steels were selected for evaluation because of their frequent use in the manufacture of oil tool, and because their use has ken considered for marine drilling risers. The study was expanded to include an examination of the effect of shot peen and nitride surface treatments on the seawater fatigue life of the materials. These surface treatments are recognized as proving fatigue properties of steels in air atmosphere, but their effectiveness in proving fatigue life of steel immersed in seawater is unknown and hence, was the reason for inclusion in this study.
In reviewing the literature on the effect of corrosion on steel fatigue life, the authors found no literature pertaining directly to corrosion fatigue of 2 1/4 Cr-1 Mo steel, but did find literature pertaining to corrosion fatigue on other low alloy steels. Because 2 1/4 Cr-1 Mo steel is a number of the low alloy steel grouping, it is expected to follow the same general set of rules by which other family numbers abide. Hence, the following discussion of steel corrosion fatigue is considered applicable to both steel seven though the literature survey possessed no information specifically on 2 1/4 Cr-1 Mo steel.
Fatigue of unprotected steel immerse in Seawater will always possess a shorter fatigue life than fatigued steel in an air atmosphere. Hence, all air fatigue data should be down graded to account for the loss of properties when subjected to seawater fatigue. However, it is important to note that there are certain variables, when appropriately altered, may maintain fatigue properties of steel immersion in seawater equivalent to those exhibited within air. Table 1 (1) summarizes the basic variables of fatigue in seawater and how they effect fatigue life of steel.
The Arctic Cone Exploration Structure: A Mobile Offshore Drilling Unit for Heavy Ice Cover
Authors: Byrd R.C. , Coleman R.K. , Weiss R.T. , Boaz L.B. , Sauve E.R. , White R.M. 
Published: October 2008

INTRODUCTION
The offshore oil and gas industry has been required by circumstances in recent years to place increasing emphasis on the very hostile, relatively remote, oil provinces. The Alaskan Beaufort Sea, ranks near the top of the list of new offshore development areas in terms of both remoteness and the harshness of its environment. Nevertheless, this area and the nearby Chukchi Sea offer among the best prospects for major oil finds of the U.S. Outer Continental Shelf waters remaining to be explored.
Two lease sales have been held to date in the Beaufort Sea offshore Alaska's North Slope, the most recent being OCS Sale No. 71, which was held in October 1982. The first major offshore sale in this area took place in December 1979. The majority of tracts leased in the 1979 sale are in water depths of less than 50 ft and can be explored using gravel islands. However, over 70% of the tracts made available for Lease Sale 71 are in water depths beyond 50 ft. A similarly high percentage of tracts scheduled for future lease sales in the Beaufort and Chukchi Seas are in depths beyond the range of economical development from gravel islands. Even within the 50 ft depth contour, multi well drilling programs do not look attractive from gravel islands. Industry has responded to this situation in the last year and a half by offering designs for a number of different caisson based mobile drilling units. These have generally been designed for water depths between the range of 25 and 70 ft and for operations in relatively sheltered waters where they will not be exposed to the most severe ice conditions.
This paper reports on the results of a rig development program which began in 1981 to design a mobile drilling unit which could operate beyond the 50 ft depth contour in the most exposed ice conditions. The Arctic Cone Exploration Structure (ACES) project has produced the design of what is likely to be the prototype for heavy-duty, bottom-founded mobile rigs for arctic offshore drilling. The current ACES rig design has focused on developing the drilling capability for the water depth range of 50 to 110 ft. Approximately 68% of tracts made available during the recent OCS Sale 71 fell within this depth range.
The latest phase of the ACES rig design was sponsored by Exxon Company, U.S.A.; Shell Oil Company; and Standard oil Company of California/Chevron. An earlier conceptual design phase of the program included three additional U. S. oil and gas companies. Brian Watt Associates, Inc. (BWA) of Houston, Texas, was the prime contractor for the design. Zapata Off-Shore Company of Houston was responsible for the drilling related systems.
The objective of this paper is to show the level of effort which has gone into the development of the ACES mobile rig design. The results of that effort are presented, including the design criteria and performance objectives used.
A Prestressed, High-Strength Grouted Connection for Offshore Construction
Authors: Elnashai A.S. , Carroll B.C. , Dowling P.J. 
Published: October 2008

ABSTRACT
This paper concerns newly developed prestressed grounted connections for steel tubu1ars in offshore applications. A mechanical prestressing method has been devised and shown to give an increase in ultimate bond strength of 6 or more times that of a plain bonded connection.
The method was developed by small scale testing using models with varying degrees of prestress. The test information was appreciably augmented by the results of a parametric study carried out using a new non-linear finite element program.
The information obtained from the small scale tests and numerical study was used to design a series of large scale models. During the testing of these large models an alternative method of prestressing using expansive grout was also shown to produce satisfactory results. This test series confirmed that the results of the small scale tests and computer studies could be safely extrapolated to full scale connections.
Based on these studies a new comprehensive equation is proposed for designers which accounts more accurately for pile length/diameter ratio than existing design rules and which for the first time predicts the increase in bond strength in prestressed connections.

INTRODUCTION
Grouted connections are used in forming the main structural connections between steel jacket structures and their foundation piles, and in repairs to damaged tubu1ars. Both plain and shear keyed connections have been adopted in practice. Plain connections are known to have very unreliable and low bond strengths, since they are very sensitive to shrinkage and imperfections in the tubu1ars. To overcome these problems shear keyed connections, using weld beads, have in recent years become the more common solution.
Billington and his co-workers (1,2) have carried out extensive testing of both types of connection and have presented an empirical design formula.
An alternative to the use of shear keys for strength enhancement, is the use of a radial prestress in the grout annulus, which will increase the frictional bond strength. The radial prestress may be generated either by employing a mechanical system of active stressing, or a passive chemical system, using expansive grout. In both cases, the tubu1ars are being used in the most efficient manner, since both hoop and axial strength are utilised, and the annulus provides an ideal environment for the triaxial confinement of the grout. A new mechanical system of stressing, based on the high pressure grouting, has been developed at Imperial College, the general details of which are shown in Figure 1.
The validity of the prestressing concept was the first established by small scale model testing, the details of which are discussed below. In parallel with the test program, a nonlinear numerical model was developed and calibrated to the available experimental data. It was then used to perform a large number of analyses to quantify the effect of geometric configuration and applied prestress on the ultimate bond strength of grouted connections.