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Results
Experimental Study of Time-Dependent Behavior of Clays Subjected to Loading And Unloading With Constant Rate of Strain
Lee, M.S. (Graduate School of Engineering, Osaka University) | Oda, K. (Graduate School of Engineering, Osaka University) | Tokida, K. (Graduate School of Engineering, Osaka University)
ABSTRACT Improving soft ground by the preloading method is economical because additional operations are not needed. In this method, the ground characteristics during loading, unloading, and post-loading are studied. In general, settlement during post-loading should be small because the post-loading pressure is less than the loading pressure. However, there have been several examples of settlement occurring during post-loading. In this study, the loading history was simulated by a constant rate of strain (CRS) test to determine the secondary consolidation behavior during the post-loading process. The results of this study were as follows:the loading history is simulated by the CRS test, secondary compression index depends on the over-consolidation ratio, the coefficient of the secondary consolidation changes with time, and when post-loading is induced, the coefficient of secondary consolidation is smaller than when there is no previous loading history. INTRODUCTION In general, standard consolidation tests are used to predict the consolidation behavior of structures and embankment fill constructed on soft clay ground. These tests are used widely because the test methods are simple and various methodologies have been developed for interpreting the test results. However, carrying out the tests can be time-consuming because running one cycle of the run takes one day and several repetitions are required. The constant rate of strain (CRS) test proposed by Crawford(1964) significantly reduces the test duration by measuring the load through successive constant displacements. Its theoretical interpretations have been established by Wissa et al.(1971). The CRS test has been standardized and is now widely used in practice. Various construction methods are employed to enhance soft clay ground. Preloading methods are applied to reduce residual settlement in land development projects such as highway construction. This method utilizes consolidation for a sufficient duration by loading more than the structural load in advance.
- Energy > Oil & Gas > Upstream (0.46)
- Construction & Engineering (0.34)
A Study On Residual Stress Distribution And Relaxation In Welded Components
Polezhayeva, Helena (Lloyd's Register EMEA) | Kang, Joong-Kyoo (DAEWOO Shipbuilding and Marine Engineering CO., LTD) | Lee, Jang-Hyun (Inha University Incheon) | Yang, Yong-Sik (Inha University Incheon) | Kudryavtsev, Yuri (Integrity Testing Laboratory Inc.)
ABSTRACT Systematic studies had shown that welding residual stresses might lead to a significant reduction in fatigue strength of welded components. However the effects of residual stress are not sufficiently reflected in corresponding codes and regulations for fatigue assessments. The objective of the study described in this paper is to identify the residual stress distribution and relaxation in specimens with welded longitudinal attachment and welded panel which represents large scale model of ship structural detail, and compare results of experimental and numerical analyses. The ultrasonic measurements of residual stress were performed using the UltraMARS system developed at ITL Inc. (Markham, Canada) within Lloyds Register/DSME (DAEWOO Shipbuilding and Marine Engineering CO., LTD) Joint Project. A numerical simulation of residual stress relaxation under fatigue load was carried out at INHA University, South Korea. This study is considered as a first stage of a program focused on the analysis of residual stresses and their redistribution in welded elements under the effect of cyclic loading. The obtained data will be used for fatigue analysis of welded joints at different conditions of cyclic loading. INTRODUCTION Residual stresses can significantly affect engineering properties of materials and structural components, notably fatigue life, distortion, dimensional stability, corrosion resistance, brittle fracture (Handbook, 2005). Such effects usually lead to considerable expenditures in repairs and restoration of parts, equipment and structures. For that reason, the residual stress analysis is an important stage in the design of parts and structural elements and in the estimation of their reliability under real service conditions. Systematic studies had shown that, for instance, welding residual stresses might lead to a drastic reduction in fatigue strength of welded elements. In multi-cycle fatigue (N>10 cycles of loading), the effect of residual stresses can be compared with the effect of stress concentration (Trufyakov, V, et al, 1995).
- Asia > South Korea (0.34)
- Europe > United Kingdom (0.28)
- North America > Canada (0.25)
- Shipbuilding (0.68)
- Transportation (0.46)
- Energy > Oil & Gas > Upstream (0.35)
Effects of Temperature And Crack Tip Constraint On Cleavage Fracture Toughness In the Weld Thermal Simulated X80 Pipeline Steel
Xu, J. (School of materials science and engineering, University of Science and Technology Beijing (USTB)) | Sun, D.B. (School of materials science and engineering, University of Science and Technology Beijing (USTB)) | Zhang, Z.L. (Department of Structural Engineering, Norwegian University of Science and Technology (NTNU)) | Østby, E. (SINTEF, Materials and Chemistry) | Nyhus, B. (SINTEF, Materials and Chemistry)
ABSTRACT This paper studies the effects of temperature and crack tip constraint on cleavage fracture toughness of weld thermal simulated X80 pipeline steel at low temperatures. A large number of fracture toughness (as denoted by CTOD) tests together with 3D finite element analyses are performed using single edge notched bending (SENB) and tension (SENT) specimens with different crack depths at −90°C and −30°C. Coarse-grained heat-affected zone (CGHAZ) is considered as the material microstructure in preparation of weld thermal simulated fracture mechanics specimens. The applicability of RKR model as the local fracture criterion in prediction of cleavage fracture toughness is examined. INTRODUCTION Fracture toughness testing of ferritic structural steels reveals a significant effect of crack depth and loading mode (bending vs. tension) on fracture toughness values (Wallin, 1985; Sorem, et al, 1991; Joyce and Link, 1997). These studies show significant elevations in fracture toughness (characterized as KIC or JC) for specimens containing shallow cracks and/or subjected to tensile loading. With increasing loads in a finite body, such as a cracked specimen or a structural component, the crack-tip plastic zone is increasingly influenced by the nearby traction free boundary which relaxes the near-tip stress levels well below the values corresponding to small scale yielding (SSY) conditions. This phenomenon, often termed loss of constraint (Dodds, Shih and Anderson, 1993; Nevalainen and Dodds, 1995; Dodds, Ruggieri and Koppenhoefer, 1997), contributes to the apparent increased toughness of shallow cracked and tension loaded geometries observed in fracture mechanics testing. Once high triaxiality conditions no longer apply, larger crack driving forces in the finite body are necessary to generate a highly stressed region ahead of the crack-tip sufficient to trigger cleavage. Since the crack tip constraint affects the stress distribution around a crack and invalidates the use of single parameter characterization of the crack-tip stress field.
Influence of Cathodic Protection Potential On Corrosion of Carbon Steel In Seamud Containing Sulfatereducing Bacteria
Zhao, Xiaodong (School of Electromechanical Engineering, Zhejiang Ocean University, Institute of Oceanology, Chinese Academy of Sciences) | Yang, Jie (School of Electromechanical Engineering, Zhejiang Ocean University) | Fan, Xiqiu (School of Electromechanical Engineering, Zhejiang Ocean University) | Duan, Jizhou (Institute of Oceanology, Chinese Academy of Sciences)
ABSTRACT The reliability of cathodic protection(CP) on carbon steel buried in seamud containing Sulfate-reducing bacteria(SRB) was evaluated with emphasis on electrochemical impedance spectra(EIS) at different CP potentials. The relationship among CP potential, corrosion rate and bacteria activity was summarized by EIS results, weight-loss test and bacterial counts by most probability number(MPN) method, which showed that the steel at potential of −950 mV (CSE) was relatively well protected, with a stable and low corrosion rate. Bacterial counts showed that the growth activity and stability of SRB were lower at more negative CP potentials. −950 mV or even more negative potential was needed to ensure of efficient protection. INTRODUCTION As the most efficient method of corrosion protection, cathodic protection(CP) technique has been recognized worldwide(NACE Standard, 1969). It is widely used as an anticorrosion technique for the protection of steel structures in marine environment. To achieve the basic protection, the protection potential of −850mV (CSE) is essential. Extensive research has been carried out on microbiologically influenced corrosion (MIC). Microorganisms such as iron bacteria (IB), sulfate-reducing bacteria (SRB), iron-oxidizing bacteria (IOB), sulfuroxidizing bacteria (SOB) are mainly responsible for the corrosion underground. Kajiyama et al(1999) studied the CP reliability of buried pipeline in the sandy soil and sticky sludge containing IOB and SRB. Jung-Gu Kim et al(2001) discussed the CP standards for the buried pipeline with a coating layer of insulation, involving the influence of temperature on the cathodic protection potential. Baorong HOU et al(1993) studied the optimal anti-corrosion potential by AC impedance. Guezennec J et al(1991, 1994a, 1994b) investigated the relationship between CP potential and SRB-induced corrosion in marine sediments by AC impedance technique. Massimo S et al(1998) discussed the corrosion behavior of buried pipeline under CP through EIS study. Research with regard to the polarization effect on MIC is relatively little.
- Geology > Mineral > Sulfate (0.56)
- Geology > Sedimentary Geology > Depositional Environment > Marine Environment (0.54)
- Materials (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Constituents > Bacteria (0.70)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Model Experiments On Stressed Grouted Clamps By an Expansive Agent For Offshore Construction
Shia, Xiang (Engineering College, Ocean University of China) | Liu, Ke Fei (Engineering College, Ocean University of China) | Li, Hua Jun (Engineering College, Ocean University of China) | Yang, Bin (Design Department, China Offshore Oil Engineering Co. Ltd.)
ABSTRACT This paper introduces an experimental research on stressed grouted clamp by a new expansive agent with different percentage of content. The test results of expansive pressure and the corresponding slip stress are revealed. It is indicated that the new expansive agent in cement slurry can produce large radial self-stress without reducing the bond strength at the grout/steel interface. Thus it improves the slip capacity of clamp and is suitable for underwater repair of offshore constructions. Meanwhile based on two existing formulas and employing a factor of expansive pressure augmentation, an empirical formula for relationship between expansive pressure and slip stress is proposed for guiding the design of grouted clamp with the new expansive agent. INTRODUCTION The stressed grouted clamp, which has been widely used, possesses the advantage of a high tolerance of imperfection and good fatigue property for repairing steel tube in offshore constructions (Grundy and Kiu, 1991; MSL Engineering Ltd, 2004). So it is a common selection for repairing and strengthening damaged component of offshore structures. But when installing the traditional type of stressed grouted clamp underwater, a workboat is needed again 36 hours after slurry injecting, to tension all stud bolts of the clamp simultaneously by hydraulic tensioning jacks which are themselves expensive equipments, so as to obtain the self-stress after the grout has reached enough compressive strength. So employing the traditional clamp method has to confront the disadvantage of complicated underwater operations and high related cost. With the development of expansive agent for concrete, its quality is from high alkalinity to low alkalinity, from high content to low content (You, 2003). Now the shrinkage-compensating concrete, expansive concrete and self-stressing concrete, which are compounded expansive agent, have been widely used in every field of civil engineering (Shang and Huang, 2007).
ABSTRACT Main target for expanding the possibilities of SCR application is the development of optimized setup and welding parameters which lead to a significant fatigue life enhancement. PURE is a ready for service solution for on- and offshore applications developed by V&M Tubes and qualified in cooperation with TWI. It provides among others an assured pipe end match, minimum stress concentration factors as well as an unaffected media flow. This paper will highlight the key activities of design development and qualification. The design benefit and the welding technology on property profile were determined by comparing the results of PURE design with plain ends. FEM calculations were used to investigate the influence of design parameters on SCF. A specific GMAW technology was applied as joining technology. Complex heat treatment and an optimized chemical composition resulted in an assured X-65 over the entire upset end line pipe. The testing program comprised besides mechanical testing and all weld test on girth weld and HAZ, resonance full scale fatigue tests of single weld pipes to determine fatigue life and location of failure (post mortem investigation). INTRODUCTION Discoveries in the offshore areas for oil & gas are more and more going into deeper waters and therefore require products which can withstand the increased workloads. Main criteria for the selection of products for SCR application is high resistance against fatigue in combination with optimized tolerances at pipe ends. The aim of the study is to evaluate the mechanical properties and fatigue performance of girth welds made using upset and machined pipe ends, and to compare these with standard pipe end (plain design) welds. RISER REQUIREMENTS-OFFSHORE Welding conditions and in operation The application of SCR design for production and export operations from floating production and storage units has significantly increased during past years.
Critical Hydraulic Gradient of Piping In Sand
Zhang, Jianhong (State Key Laboratory of Hydroscience and Engineering,Tsinghua University) | Jiang, Shubin (State Key Laboratory of Hydroscience and Engineering,Tsinghua University) | Wang, Qiusheng (China Institute of Water Resources and Hydropower Research) | Hou, Yujing (China Institute of Water Resources and Hydropower Research) | Chen, Zuyu (China Institute of Water Resources and Hydropower Research)
ABSTRACT The occurrence and development of piping in dikes is a very complex process due to complicated interactions between water and soil. This paper is based on a study of the physical modeling of piping in sand at 1 g and ng in a centrifuge. The main purpose of the study is to investigate the scaling law governing the centrifuge modeling of piping and also the critical hydraulic gradient when piping begins. A coarse sand with particle size of 3 – 5 mm and a fine sand with particle size of 0.25 - 0.50 mm were mixed at mass ratios of 4:1, 5:1 and 6:1 respectively to prepare the three gap-graded sands used in tests. A series of permeability tests were performed to measure the critical hydraulic gradient which was in the range of from 0.227 to 0.276. The critical hydraulic gradient slightly increased with the fine-grain content. There was no sign of piping when the mass ratio was 4:1. Permeability tests were also carried out on a centrifuge using sand with mass ratios of 5:1 and 6:1. The centrifugal accelerations were set at 5 g and 10 g in order to ensure the Reynold's number (Re) less than 10 in the models. Based on the experiments carried out at 5g, 10g, the critical hydraulic gradients were measured to be 0.20 to 0.23 in the centrifuge, basically consistent with the experiments at 1g. INTRODUCTION Darcy (1865) proposed the famous Darcy law governing seepage through soil, based on a series of experiments carried out at Dijon in France. Ever since then, great progress has been made associated with the movement of groundwater, the spread of heat and pollutant plumes (e.g. Bear1972, Freeze and Cherry 1979, Zhang et al. 2001).
- Asia (0.48)
- North America > Canada (0.28)
- Europe > France (0.24)
Determination of Critical Factors Affecting On Hydrogen Induced Cracking And Type I Sulfide Stress Cracking of High Strength Linepipe Steel
Kim, Wan Keun (Graduate Institute of Ferrous Technology, Pohang University of Science and Technology) | Park, Gyutae (Graduate Institute of Ferrous Technology, Pohang University of Science and Technology) | Kim, Kyoo Young (Graduate Institute of Ferrous Technology, Pohang University of Science and Technology) | Koh, Seong Ung (POSCO Technical Research Center) | Jung, Hwan Gyo (POSCO Technical Research Center)
ABSTRACT The metallurgical factors affecting HIC and SOHIC of high strength linepipe steel are investigated and the cracking resistance is correlated with diffusible hydrogen. Internal cracks were initiated at elongated MnS and TiNb(C, N) cluster regardless of the cracking mode. Increase in diffusible hydrogen content by cathodic charging or applying the external load makes the steel more susceptible to the cracking and it can imply that both of critical factors, inclusion clusters as well as diffusible hydrogen in the steel, should be carefully controlled to improve the cracking resistance. INTRODUCTION For the safe operation of pipeline in the wet H2S (hydrogen sulfide) condition, it should satisfy high corrosion cracking resistance. (NACE MR0175, 2002) Cracking phenomena has been classified into HIC (hydrogen induced cracking) and SSC (sulfide stress cracking) according to the presence of external loading. Also, SSC has two different cracking modes, SOHIC (stress-oriented HIC or type I SSC) and type II SSC and particularly, SOHIC has been of primary concern in the application of HSLA (high strength low alloy) steel which is preferred material in the oil and gas industry because of its cost effectiveness. Metallurgical key factors affecting HIC and SOHIC have been well introduced and many cracking mechanisms have been proposed. (Takahashi and Ogawa, 1995) Nevertheless, the relationship between HIC and SOHIC is still not clearly understood and it makes the application of HIC resistant steel to SSC condition difficult. (Pargeter, 2007) Even if HIC resistant steel has been believed to have high resistance to SOHIC because of its similar cracking characteristics, the uncertainty of relationship has been also reported. Cayard et al. indicated (2002) that HIC resistant steel may be more susceptible to SOHIC compared with the conventional HSLA steels and Pargeter reported (2007) about the uncertainty of relationship between HIC and SOHIC in his review paper.
- Asia (0.70)
- North America > United States (0.16)
Safety Analysis On Welded Joint of Submarine Oil And Gas Pipeline
Li, Chunrun (Research Institute of Engineering Technology, CNPC) | Niu, Huli (Research Institute of Engineering Technology, CNPC) | Fang, Zongtao (Research Institute of Engineering Technology, CNPC) | Wang, Zhijian (Offshore Engineering Division of CNPC offshore Engineering company Ltd.) | Zhang, Xiao (Offshore Engineering Division of CNPC offshore Engineering company Ltd.) | Guan, Yougeng (Offshore Engineering Division of CNPC offshore Engineering company Ltd.)
ABSTRACT According to API Std 1104–2005 "welding of pipelines and related facilities", under the premise of the known lay stress and fracture toughness value of welded joints, the safety analysis was applied to the welded joints of mixed submarine oil and gas pipelines from NP1–29P to NP1–2D in Nanpu oilfield in east Hebei province in the laying stage. And the allowed sizes of the planar defects as well as the relationship between CTOD values and the defects height are determined. The allowable values of the surface defects and buried defects at the three types of CTOD values are specifically analyzed under the same operating condition. The assessment results show that under the same condition, with the CTOD values increasing, the sizes of the surface defects firstly increase, and then remain unchanged after reaching a certain value, while the sizes of the buried defects have remained unchanged. The safety analysis results provide a basis for security in pipeline laying stage, with practical engineering and economic significance. INTRODUCTION Submarine oil and gas pipelines, as transportation pipelines of offshore oil, are growing with the rate of tens of thousands of kilometers every year. Although the pipeline is a very safe oil and gas transportation, there have been numerous pipeline failure incidents in the past few decades. This not only affects the conduct of the normal production order and threaten the safety of workers, but also be bound to bring huge losses to the country's economy and national life. The reason is that distortion, scratches and other defects will be produced during the laying process of submarine pipelines [Xia and Huo, 2005; Tan and Xiao, 2005; Song and Xiao, 2004]. Therefore the qualified limits of welding defects have been clearly provided in submarine pipeline system specification of each country.
ABSTRACT The correlation between the micro-structural changes and mechanical characteristics for the newly developed pulsed GMAW (gas metal arc welding) of A5083 aluminum alloy has been investigated. In this study, the mechanical properties of seam were performed. Tensile and yield strengths did not show a great variation with test temperature at +25°C to −85°C, but increased greatly at −196°C. Charpy absorbed energy was lowest in the weld metal, and increased in the fusion line, base metal, and HAZ in that order. It was thought that as an aluminum alloy has a face centred cubic (fcc) crystal lattice, there was no low temperature toughness effect. It was probably due to the crack/defect free microstructure with a notable grain refinement produced by pulsed GMAW process. INTRODUCTION There have been growing concerns about the environment in recent years, with increasing importance being placed on global environmental problems such as global warming or the effects of greenhouse gases on humans. Under such circumstances, clean and renewable natural energies are expected to replace current fossil fuels as next-generation energies. The effective use of large-scale structures for hydrogen is currently being studied, such as storage tanks or supertankers for liquid hydrogen. However, there are concerns that the structural materials used in such large scale structures for handling liquid hydrogen may be subjected to highly rigorous service conditions that differ from the conventional conditions, such as long-term use in cryogenic temperatures, hydrogen environment, the application of various welding processes, and complicated loading conditions. Among aluminum alloys, Al-Mg alloy A5083 has been widely used for liquefied natural gas (LNG) tanks to date because of its excellent strength and weldability. However, there are few reports on the mechanical properties of A5083 welds at cryogenic temperatures (Zinkham, R, E, Ashton, R, F,1975).
- Energy > Oil & Gas > Midstream (0.91)
- Materials > Chemicals > Industrial Gases (0.88)
- Materials > Metals & Mining > Aluminum (0.77)