Nobuhisa Suzuki

Effects of Geometric Imperfection on Bending Capacity of X80 Linepipe

Validation of finite element modeling to predict bending capacity of linepipes and effects of geometric imperfection on the bending capacity are presented. A bending test of an X80 linepipe was conducted to discuss the validation and investigate the effects. The geometric imperfection of the linepipe about the outside diameter, the wall thickness and the longitudinal blister of the linepipe was measured in the round. Consequently, the results obtained by FEA taking into account the geometric imperfection present good agreement with the experimental data. And the moment capacity is virtually independent of the geometric imperfection however the strain capacity of the linepipe is quite susceptible to the geometric imperfection.Copyright

Design, Application and Installation of an X100 Pipeline

Traditional pipeline technology will be severely challenged as design-operating pressures continue to rise and gas field developments occur in more remote locations including the arctic. Cost-effective solutions to these issues can be found through innovative designs using new technology and its implementation. Some of these designs have considered the use of high-pressure natural gas pipelines resulting in the development of high strength steel. In order to meet these increases in pressure TransCanada and JFE/NKK have been working extensively on the application of X100 (Grade 690) linepipe and this has culminated in the construction and installation of a X100 project in the fall of 2002. This paper will discuss the development of the related research projects that allowed the successful completion of the field project. The topics will include the material properties and fracture control plans for X100. In addition the approach to strain based design for X100 will include the analysis for both the tensile strain limits (weld mismatch consideration) and compressive strain limits (i.e. buckling capacity). The development of the field welding process will also be covered. The paper will discuss the implications of using X100 from the perspective of the successful field project and the application of a strain-based design.Copyright

Critical Compressive Strain of Linepipes Related to Workhardening Parameters

An approximate solution to predict a critical compressive strain at the peak load (the peak load strain hereinafter) of linepipes subjected to axial compression is proposed in this paper. The approximate solution is derived from the deformation theory applying the stress-strain relationship with non–linear hardening properties, which have not been taken into account in a number of current equations applied for pipeline design. The approximate solution proposed in this paper is a closed form equation, which is useful and effective for the practical application. The parameters in the Ramberg-Osgood representation expressing workhardenability of the linepipes are successfully introduced for the approximate solution. The effectiveness and accuracy of the approximate solution are verified comparing the critical compressive strains of several API 5L grade linepipes obtained by finite element analyses.Copyright

Tensile Strain Capacity of X80 Pipeline Under Tensile Loading With Internal Pressure

This paper presents the results of experimental and finite element analysis (FEA) studies focused on the tensile strain capacity of X80 pipelines under large axial loading with high internal pressure. Full-pipe tensile test of girth welded joint was performed using high-strain X80 linepipes. Curved wide plate (CWP) tests were also conducted to verify the strain capacity under a condition of no internal pressure. The influence of internal pressure was clearly observed in the strain capacity. Critical tensile strain is reduced drastically due to the increased crack driving force under high internal pressure. In addition, SENT tests with shallow notch specimens were conducted in order to obtain a tearing resistance curve for the simulated HAZ of X80 material. Crack driving force curves were obtained by a series of FEA, and the critical global strain of pressurized pipes was predicted to verify the strain capacity of X80 welded linepipes with surface defects. Predicted strain showed good agreement with the experimental results.Copyright

Material Development and Strain Capacity of Grade X100 High Strain Linepipe Produced by Heat Treatment Online Process

Linepipes installed in permafrost ground or seismic region, where larger strains can be expected by ground movement, are required to have sufficient strain capacity in order to prevent local buckling or girth weld fracture. On the other hand, strain capacity of linepipes usually degreases with increasing strength, and this is one of the reasons for preventing wider use of high-grade linepipe for high strain application. Furthermore, external coating is necessary for corrosion resistance of pipe, but coating heat can cause strain-aged hardening, which results in increased yield strength and Y/T. Therefore, there is a strong demand for developing high strength linepipe for a high strain application with resistance to strain-aged hardening. Extensive studies to develop Grade X100 high strain linepipe have been conducted. One of the key technologies for improving strain capacity is dual-phase microstructural control. Steel plate with the microstructure including bainite and dispersed martensite-austenite constituent (MA) can be obtained by applying accelerated cooling followed by heat treatment online process (HOP). HOP is the induction heating process that enables rapid heating of the steel plates. Variety of microstructural control, such as fine carbide precipitation and MA formation, can be utilized by this newly developed heating process. One of the significant features of the HOP process is to improve resistance to strain-aged hardening. Increase in yield strength by coating can be minimized even for the Grade X100 linepipe. Trial production of X100 high strain linepipe with the size of 36″ OD and 15mm WT was conducted by applying the HOP process. Microstructural characteristics and mechanical properties of developed X100 linepipe are introduced in this paper. In order to evaluate compressive strain capacity of the developed pipe, full-scale pipe bending test was carried out by using the trial X100 high strain linepipe after external coating. Full scale bending test of developed X100 linepipe demonstrated sufficient compressive strain capacity even after external coating.Copyright

Strain Capacity of X80 High-Strain Line Pipes

Two compression tests and two bending tests of X80 high-strain line pipes were conducted to investigate the compression capacity and the bending capacity. The high-strain line pipes had the outside diameter of 762 mm (30”) and the D/t ratio of 49. The compression tests revealed that the pipes had the critical compressive strains of 0.90 and 0.78%. The bending tests of the pipes clarified that the 2D average critical compressive strains were 2.40 and 2.15% and the 1D average were 2.67 and 2.28%. The analytical solutions gave very fine predictions about the critical compressive stress and strain of the pipes subjected to axial compression. Based on the FEA results, while almost no effects of the geometric imperfections on the compression capacity were recognized, the effects of the geometric imperfections on the bending capacity were significant.Copyright

Application of WES2808 to Brittle Fracture Assessment for High Strength Gas Pipelines

This paper presents the results of a preliminary study to establish an assessing method for the tensile strain limit against brittle fracture of pressurized gas pipelines subjected to axial tensile deformation. The basis of the assessment method is the Japan Welding Engineering Society standard WES2808–2003. WES2808 provides a procedure for evaluating the fracture limit using the CTOD design curve relating flaw size, applied strain and fracture mechanical parameter (CTOD). The main characteristics of the method are a consideration of the deterioration of the fracture toughness of material resulting from large cyclic and dynamic straining, a correction of CTOD fracture toughness for constraint loss in structural components in large scale yielding, and an estimation of critical CTOD value from Charpy test results. Modifications of the procedure to enable evaluation of the fracture properties of high strength gas pipelines under biaxial loading conditions are studied.Copyright

Local Buckling Behavior of X100 Linepipes

Local buckling behavior of API 5L X100 grade linepipes subjected to axial compression and/or bending moment is discussed in this paper based on results obtained by finite element analyses. Yield-to-tensile strength (Y/T) ratio and design factor were taken into account in the finite element analyses in order to discuss their effects on the local buckling behavior. The local bucking behavior of such lower strength linepipes as X60 and X80 grade linepipes is also discussed for comparison. Two-dimensional solid elements and four-node shell elements were used for the finite element modeling of the linepipes subjected to axial compression and bending moment, respectively. The study has improved the understanding of local buckling behavior of the X100 grade linepipes and observed the following trends. When a linepipe is subjected to axial compression, the critical axial stress decreases with increasing design factor and Y/T ratio. However, the nominal critical strain increases with increasing design factor and decreasing Y/T ratio. When a linepipe is subjected to bending moment, the critical bending moment decreases with increasing design factor and Y/T ratio. Similarly, the nominal critical strain increases with increasing design factor. However, the nominal critical strain increases with decreasing Y/T ratio when the design factor is less than and equal to 0.6 and decreases with decreasing Y/T ratio when the design factor is equal to 0.8.Copyright

Local Buckling Behavior of 48″, X80 High-Strain Line Pipes

Two bending tests of X80-grade, 48″ high-strain line pipes pressurized to 60% SMYS were conducted to investigate local buckling behavior. The thickness and D/t ratio of the line pipes were 22.0 mm and 55.4, respectively. The mean Y/T ratio of the high-strain pipes was 0.82. A full-scale bending test apparatus was constructed to conduct the bending tests. The bending test results clarified that the pipes have the 2D average critical compressive strain of 1.51 and 1.67%, which satisfy the strain demand of 1.35%. Validation of FEA is conducted taking into account geometric properties of the pipes in terms of outside diameter and thickness and longitudinal flatness. The FEA results coincide with the test results with respect to peak load, critical displacement, critical rotation and critical compressive strain. The FEA results about the load and displacement relationship also show good agreement with the test results during post-buckling deformation. One developed wrinkle and some small wrinkles were observed on the pipe surface during post-buckling deformation, whose cross sections were fairly captured considering the geometric properties.Copyright

Strain Capacity of X100 High-Strain Linepipe for Strain-Based Design Application

In recent years, several natural gas pipeline projects have been planned for permafrost regions. Pipelines laid in such areas are subjected to large plastic deformation as a result of ground movement due to repeated thawing and freezing of the frozen ground. Likewise, in pipeline design methods, research on application of strain-based design as an alternative to the conventional stress-based design method has begun. Much effort has been devoted to the application of strain-based design to high strength linepipe materials. In order to verify the applicability of high-strain X100 linepipe to long distance transmission, a large-scale X100 pipeline was constructed using linepipe with an OD of 42″ and wall thickness of 14.3mm. This paper presents the results of experiments and Finite Element Analysis (FEA) focusing on the strain capacity of high-strain X100 linepipes. The critical compressive strain of X100 high-strain linepipes is discussed based on the results of FEA taking into account geometric imperfections. The critical tensile strain for high-strain X100 pipelines is obtained based on a curved wide plate (CWP) tensile test using specimens taken from girth welded joints. Specifically, the effect of external coating treatment on the strain capacity of X100 high-strain linepipe is investigated. The strain capacity of the 42″ X100 pipeline is considered by comparing the tensile strain limit obtained from girth weld fracture and critical compressive strain which occurs in local buckling under pure bending deformation.Copyright