Hossein Ghaednia

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...

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,

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

Structural Performance of Oil and Gas Pipe with Dent Defect

AbstractEnergy-transmission buried pipelines are often susceptible to externally applied concentrated loads that may cause dent defects. A dent or dent defect can be best described as a local defec...

Dependence of Burst Strength on Crack Length of a Pipe with a Dent-Crack Defect

AbstractA defect in a field-buried pipeline that has both a crack and a dent, commonly described as a dent-crack defect, may result in a devastating failure resulting from a rupture or leak in the ...

Measuring Critical Strains in Dent Defect of Oil and Gas Pipes

Steel pipelines are exposed to harsh environmental, geotechnical and other conditions and hence, they can be damaged. The damage can threaten the structural integrity of the pipeline and can cause economic loss and environmental damage if a failure occurs. A common way for pipelines to be damaged is through physical contact, creating a structural imperfection, dent, wrinkle, crack, and/or other damages or defects. A dent disrupts the pipeline’s circularity causing increased strains in concentrated areas. A research program was established and carried out to study the strain concentration of dented pipes. The study was completed using full-scale laboratory testing and numerical analysis at the Centre for Engineering Research in Pipelines (CERP). This study included four lab tests on two different pipe materials (X70 and X56) and finite element analysis (FEA) based parametric study.Copyright

Strain Localization in the Dent of a Linepipe

Steel pipelines used for transporting oil and gas can develop various damages such as mechanical damages, corrosion, wrinkle, and crack. One of the mechanical damages is a dent with or without other defects such as corrosion, gouge, and crack. The dent without other defect is often referred to as plain dent. Depending on the severity, a dent can lead to a failure of a field linepipe. The strain concentration in a dented pipeline wall can be used to determine the level of severity of a dent. Hence, a research program was undertaken at the Centre for Engineering Research in Pipelines (CERP) using full-scale tests and finite element analyses. The prime objective of this research was to determine comparative strain distributions in and around the dent and locations of high strains developed from the denting process. This information will help the pipeline operators to determine the severity of dents in their field linepipes. Hence, the outcome of this research will allow the pipeline operators to take an informed decision on whether or not an imminent remedial action for the dented segment of the line pipe is required. This paper presents test data and finite element simulation to discuss the locations and values of crucial strains in dents.Copyright