Hongyuan Chen

Influence of Dual-Phase Microstructures on the Properties of High Strength Grade Line Pipes

Abstract The influence of dual-phase microstructures on mechanical properties of X70, X80, and X90 line pipes is investigated. It is found that the line pipes with dual-phase microstructures possess both larger uniform elongation and higher hardening exponent, especially for high grade steel X90. The tensile deformation of dual-phase line pipe does not follow the trend predicted by the Hollomon formula, and a stable strain-hardening exponent is not found. This stress-strain behavior is different from the normal line pipe. In the initial stage of plastic deformation, the strain-hardening capacity of dual-phase line pipe increases rapidly. However, it reaches a stable stage after 2.0% total strain. The dual-phase pipeline steel is composed of soft phase (polygonal ferrite) and hard phase (bainite), and thus the relatively soft ferrite is good for its deformability. Besides, the fraction of large angle grain boundaries in the dual-phase microstructures is greater than that of the normal line pipe, which is proven to be critical for improving the resistance to plastic deformation and crack propagation.

Hydro-Burst Investigations in Large Diameter Tee-Joints

In order to reduce the tee-joints thickness and manufacturing cost, a series of large diameter and high-strength tee-joints are manufactured based on the equivalent strength design principles. The burst pressure of tee-joints is obtained directly by a series of burst tests. In addition, numerical simulations are carried out to evaluate the burst pressure capacity of a tee-joint. The influence of the fillet radius and the thickness of the branch are also discussed. The results of this paper may provide guidance in the design and manufacture of a tee joint.

Microstructure and Deformation Mechanism of High Strain Line Pipe

Strain-hardening mechanism of high strain line pipe was investigated and discussed in terms of microstructure and grain orientation. It is concluded that X70 high strain line pipe does not fit to the Hollimon formula in the entire deforming process, but the normal X70 line pipe does. At the beginning of plastic deformation, the strain-hardening capacity of X70 high strain line pipe is excellent. It decreases rapidly as the stain increases, then becomes stable after 2.0% total strain. The high strain line pipe is composed of soft phase (polygonal ferrite) and hard phase (bainite). When plastic deformation initiates, the strain-hardening capacity of high strain line pipe is better because of the ferrite deformation firstly ahead of the bainite, due to strain-hardening capacity of the ferrite is much better than that of the bainite. With ferrite deformation decreasing and bainite deformation increasing, the strain-hardening capacity declines until the micro-deformation is homogeneous. Besides, it is obvious that the large angle grain boundaries of more than 15° are in the majority of the microstructure of high strain line pipe without deformation, so the strain-hardening capacity is highest at the beginning of plastic deformation. As strain

Investigation on Axial Deformation of High Strain Line Pipe

A systematic investigation of the effect of material inhomogeneity on pipe buckling is presented in this paper. The material properties of the pipe were obtained by a series of tensile tests. Numerical simulations were carried out to evaluate the effect of material inhomogeneity on pipe buckling. Post-buckling behavior was also simulated. This paper also explains the mechanism of cracking.The authors show how pipe buckling can be caused by weakened sections, and how both internal pressure and the ratio of diameter to thickness can significantly affect pipe buckling.

Evaluation Method of Large Inclusions in High-Grade Pipeline Steel

Good internal quality of steel pipes is a basic guarantee for the safe and efficient operation of pipeline system. While presence of large inclusions has adverse effect on the mechanical properties, weldability and corrosion resistance of the steel pipes, and then it would bring huge risk to the safe operation of oil and gas transmission pipeline. In order to reduce the risk to a minimum extent, it is quite necessary to analysis and study the characteristics of large inclusions in high grade pipeline steel, and then it would provide evidence for the formulation of level-determination standard of large inclusions during steel pipe acceptance. Optimized production technology such as electromagnetic stirring is put forward accordingly to prevent the occurrence of large inclusions in pipeline steel.Copyright

Strain-Hardening Capacity and Microstructure Analysis of X70 High Strain Line Pipe

Strain-hardening capacity is the most effective way to improve the deformability of line pipe. In this paper, four kinds of new X70 high strain line pipe have been produced by four manufactures respectively. Microstructure, strain-hardening capacity, and characterization of the X70 high strain line pipe have been analyzed. It is concluded that X70 high strain line pipe steel does not fit to the Hollimon formula in the entire deforming process, and a stable strain-hardening exponent is not available. At the beginning of plastic deformation, the strain-hardening capacity of X70 high strain line pipe steel is excellent. It decreases rapidly as the stain increases then becomes stable after 2.0% total strain. The stress ratios of Rt₁.₅/Rt₀.₅, Rt₂.₀/Rt₁.₀ and Rt₅.₀/Rt₁.₀ are proved to characterize the strain-hardening capacity of X70 high strain line pipe steel. When Rt₁.₅/Rt₀.₅≥1.070, Rt₂.₀/Rt₁.₀≥1.025, and Rt₅.₀/Rt₁.₀≥1.050, the average strain over the gauge length of 2 times the outer diameter, centered at the wrinkle on intrados peak, is above 1.3%.

Key Issues in the Specification of High Strain Line Pipe Used in Strain-Based Designed Districts of the 2nd West to East Pipeline

The 2nd West-East Pipeline Project which are building now is the longest of X80 gas pipeline in China even in the world. The geological conditions along it are very complicate. Both stress-base and Strain-based design are all used in the pipeline design. Strain-based design are considered when the pipeline shall via seismic activities, fault crossing and other geological disaster area where ground moving may happen. The pipe which will be used in this kind of special area shall have some special properties besides the properties requirement of the ordinary line pipe. So Tubular Goods Research Center of China National Petroleum Corporation drafted “the Supplementary Technical Specification of High Strain LSAW Line Pipe for the 2nd West-East Pipeline Project”. In this specification, the strain capacity of current X80 line pipe and the testing methods for the mechanical properties are considered. In the mean time, the risk of aging when the pipes are coated is also be noted, and the coating temperature is specified in the specification. Certainly, besides the deformability of the pipe, strain-based design also needs more measures from pipeline construction, girth welding, etc. to ensure the pipeline can endure certain deformation. This paper introduced the general situation of the 2nd West-East Pipeline Project, and several key issues in the specification of high strain line pipe used in strain-based designed districts. At the end of the paper, the mechanical properties and the deformability of X80 pipe which are possible to be manufactured and used in this gas line are be presented.Copyright