Sreekanta Das

Mechanical Properties of Fiber-Reinforced Concrete Made with Basalt Filament Fibers

AbstractFiber-reinforced concrete (FRC) has become a viable new material used in various constructions such as building pavements, large industrial floors, and runways. In this research, basalt chopped fibers in filament form were used to develop an FRC material called basalt fiber-reinforced concrete (BFRC) to study the possible improvement in the 28-day compressive strength and modulus of rupture, though the latter one is more important for the construction of pavements, industrial floors, and runways. The basalt fiber specimens were cast using basalt filament fibers of three different lengths and three different amounts. Clumping of fibers at high fiber amounts caused mixing and casting problems. These problems become even more severe when long fibers are used at the high fiber dosage amount. The results indicated that 36-mm-long chopped basalt filament fiber and a fiber amount of 8  kg/m3 are optimum for achieving high performance in both the compressive strength and modulus of rupture. This paper dis...

Fatigue Life Assessment for NPS30 Steel Pipe

Pipeline is the common mode for transporting oil, gas, and various petroleum products. Aging and corrosive environment may lead to formation of various defects such as crack, dent, gouge, and corrosion. The performance evaluation of field pipelines with crack defect is important. Accurate assessment of crack depth and remaining fatigue life of pipelines with crack defect is vital for pipeline’s structural integrity, inspection interval, management, and maintenance. An experimental based research work was completed at the University of Windsor for developing a semi-empirical model for estimating the remaining fatigue life of oil and gas pipes when a longitudinal crack defect has formed. A statistical approach in conjunction with fracture mechanics was used to develop this model. Statistical analysis was undertaken on CT specimen data to develop this fatigue life assessment model. Finite element method was used for determining the stress intensity factor. The fatigue life assessment model was then validated using fullscale fatigue test data obtained from 762 mm (30 inch) diameter X65 pipe. This paper discusses the test specimens and test data obtained from this study. Development and validation of the fatigue life assessment model is also presented in this paper.

Behavior of a Large Steel Field Silo Structure Subject to Grain Loading

AbstractSilos are structures made of steel commonly used as storage facilities for grains and other bulk foods. This study presents monitoring of the structural behavior of a recently constructed l...

Distributions of residual stresses in stiffened plates with one and two stiffeners

This study was undertaken for a better understanding of the residual stress distributions associated with welds typically found in ship hulls. Specimens that represent small sections of an actual ship hull were built and tested using the neutron diffraction method at the Canadian Neutron Beam Centre in the Chalk River Laboratories. The specimens comprised 9.5 mm thick steel plates stiffened by L127 × 76 × 9.5 steel angles. This paper presents one- and three-dimensional distributions of all three components of residual stress created from the production of the steel plate and from the welding of one and two stiffeners onto the parent steel plate. Subsequently, the longitudinal stress in the transverse direction of the stiffened plate specimens was compared with the Faulkner model. It was found that the Faulkner model is able to predict the general distributions of this stress; however, it was unable to predict the stress values correctly.

Out-of-Roundness in NPS30 X70 Pipes Subjected to Concentrated Lateral Load

Pipeline is the common mode for transporting oil, gas, and various petroleum products. Structural integrity of oil and gas transmission pipelines is often threatened by external interferences such as concentrated load, impact load, and external pressure. These external interferences can cause ‘mechanical damage’ leading to structural failure in onshore and offshore linepipes. Lateral load is applied as a concentrated load on a small area of pipe segment and can cause local buckling, bend, dent, or out-of-roundness in the pipe. As an example, a concentrated load in buried onshore linepipe can occur if a segment of the linepipe rests on a narrow rock tip or even a narrow hard surface. Such concentrated lateral load may or may not cause immediate rupture or leak in the linepipe; however, it may produce out-of-roundness with or without a dent in the pipe cross section, which can be detrimental to the structural and/or operational integrity of the pipeline. Hence, the pipeline operator becomes concerned about the performance and safety of the linepipe if a pipe section is subject to a sustained concentrated load. A research work using full-scale tests and finite element method (FEM) was undertaken at the Centre for Engineering Research in Pipelines (CERP), University of Windsor to study the influence of various internal pressures and diameter-to-thickness ratios on the out-of-roundness of 30 in diameter (NPS 30) and X70 grade pipes with D/t of 90 when subjected to a stroke-controlled concentrated load. This paper discusses the test specimens, test setup, test procedure, test results, and FEM results obtained from this study.Copyright

Effect of Dent Depth on the Burst Pressure of NPS30 X70 Pipes With Dent-Crack Defect

Pipeline is the common mode for transporting oil, gas, and various petroleum products. Buried linepipe can be exposed to various external interferences and corrosive environment and as a result, damage in the form of dent or corrosion or crack or gouge or combination of any of these damages can form in the pipe wall. Such damage or combined damages can reduce the pressure capacity of the pipeline. A defect combining dent and crack, often known as dent-crack defect, can develop in the wall of a buried oil and gas linepipe. This combined defect may lead to a leak or a rupture in the pipe wall and hence, the pipeline operator becomes concerned about the performance and safety of the pipeline when a dent-crack defect is detected in the field pipeline. A long-term research program is currently underway at the Centre for Engineering Research in Pipelines, University of Windsor to study the influence of various parameters such as dent depth and operating line pressure on the pressure capacity or burst strength of 30 inch diameter and X70 grade pipes with D/t of about 90. From the study completed so far, it has been found that the dent depth of 8% with crack depth of 4 mm or more can reduce the pressure capacity by 32%. This paper discusses the test specimens, test setup, test procedure, test results, and data obtained from finite element analyses. INTRODUCTION Steel pipelines are the primary mode of transporting natural gas, crude oil, and various petroleum products in North America. In Canada alone, more than 110,000 km of buried energy transmission pipelines are in operation [1]. Damages or defects resulting from third party interference, more commonly known as mechanical damages are serious threat to the structural integrity of buried pipeline. Corrosion, crack, puncture, dent, gouge, and combination of such damages are some common examples of mechanical damage in pipelines. Mechanical damage of oil and gas pipelines is believed to be the major cause of failure of pipelines in service, and this damage may result in loss of product, explosions, fire, human and/or animal casualties, and pollution. It has been reported that the failure of oil and gas transmission pipelines resulting from mechanical damages ranges from 55% in the USA to around 70% in Europe [2-5]. Incidents of accidental impacts are not uncommon in onshore and offshore pipelines. Construction and excavation equipment can accidently impact the field pipeline causing mechanical damages such as dent and/or gouge with or without cracks. A dent is an inward permanent deformation in the pipe wall which causes a gross distortion of the pipe cross section [6]. A dent also causes stress and strain concentrations, ovalization, and a local reduction in the pipe diameter. A gouge is a metal loss defect that occurs in the pipe wall due to the scraping action of the excavating equipment or due to the rubbing action of the pipeline with a foreign object such as rock. Crack can also develop in a dent or gouge as a result of impact action or because of exposure to the corrosive environment or due to fatigue loading arising from pressure fluctuation and/or geotechnical movements [7]. Dent defects in energy pipeline have been a concern for pipeline operators. As a result, several research works were completed to understand the behavior of plain-smooth dents [8,

Failure of Pressurized Corroded Pipeline Subject to Axial Compression: A Parametric Study

Onshore buried steel pipelines are used for transporting oil and gas to various cities and locations. These pipelines can be subjected to various loading, such as axial, bending, shear, and other complex loading from the geotechnical movements and temperature variations. For example, a buried pipeline situated on an unstable slope can be subjected to axial load and axial deformation. In addition, this pipe experiences pressure loading from the fluids that it transports. The buried pipelines also need to endure corrosive environmental and as a result, corrosion occurs in these pipelines. Corrosion is the primary cause for structural failure of buried oil and gas pipelines and corrosion may lead to a catastrophic rupture failure causing environmental damage, injuries to human and animals, and loss of production and revenue. Hence, understanding the structural behavior and failure conditions of corroded pipelines is important for the pipeline operators. Therefore, this project was undertaken to determine the conditions required for failures of corroded steel pipes when subjected to axial deformation and internal pressures. Then the effect of internal pressure, dimensions of the corrosion, and depth of corrosion on the failure condition and failure mode was studied. It was found that the increasing value of these parameters is beneficial for achieving a favorable failure mode, however it can reduce the axial load carrying capacity significantly.

Changes in residual stresses caused by an interruption in the weld process of ships and offshore structures

Residual stresses are present in welded stiffened steel plates that are used to construct ships and other offshore structures. These locked-in stresses can exceed the yield stress of the parent plate material. Interruptions due to stop and restart in the welding process in these structures cannot be eliminated completely. It is suspected that weld interruptions are detrimental, though the effect of an interruption on the residual stress distribution is not well understood. Hence, this study was undertaken to determine the change in the residual stresses due to various stop durations in the weld process. The stop time varied from 10 to 60 seconds and the resulting stresses were compared with those observed when the weld is not interrupted. Neutron diffraction was used to determine the residual stresses. The study revealed that, compared to the residual stresses observed for a continuous weld, immediately before the stop location there is a decrease in the resulting residual stresses which is balanced by a concomitant increase immediately following the restart of the weld. The difference between the low and the high stress points in the distribution increased as the stoppage time (duration) increased. This paper presents the specimen design, specimen preparation and construction, test method, and test data obtained for four steel plate specimens.

Effect of Combined Cold Temperature and Fatigue Load on Performance of G40.21 Steel

Many structures such as bridge decks and ship hulls are required to withstand fatigue load cycles throughout their service life. These structures are also required to withstand zero and subzero temperatures if located in northern and Arctic regions, where winter temperatures can drop down to −40°C. The combined effects of cold temperature and cyclic loads can lead to potential damage to the material performance and subsequent failure. In this study, CSA G40.21 350WT steel, which is typically used in ship building, was tested in strain-controlled fatigue load cycles to determine the effect of zero and subzero temperatures on the mechanical properties and fatigue life. The experimental results show a significant effect of temperature on the fatigue life of this steel. The tensile strength was not affected by low temperatures. The yield strength and fracture strength increased and the ductility decreased at low temperatures. This paper discusses the test procedure, test parameters, and test data obtained from this study.

BEHAVIOR OF NPS30 PIPE SUBJECT TO DENTING LOAD

Pipeline is the common mode for transporting oil, gas, and various petroleum products. Structural integrity of oil and gas transmission pipelines is often threatened by external interferences such as concentrated lateral loads and as a result, a failure of the pipeline may occur due to “mechanical damages”. Sometime, this load may not cause immediate rupture of pipes; rather form a dent which can reduce the pressure capacity of the pipeline. A dent is a localized defect in the pipe wall in the form of a permanent inward plastic deformation. This kind of defect is a matter of serious concern for the pipeline operator since a rupture or a leak may occur. Accordingly, an extensive experimental study is currently underway at the Centre for Engineering Research in Pipelines (CERP), University of Windsor on 30 inch (762 mm) diameter and X70 grade pipes with D/t of 90. The aim of this research is to examine the influence of various parameters such as dent shape and service pressure on strain distributions of dented pipe. Also, three-dimensional finite element models were developed and validated for determining strains underneath the indenter. The load-deformation behavior of pipes subject to this type of lateral denting load obtained from experimental study and finite element analysis is discussed in this paper. In addition, distributions of important strains in and around the dent obtained from the study are also discussed.Copyright