Full-scale burst tests were carried out five times on line pipes of 48 in. o.d. × 0.720 in. w.t., Grad. X-70 manufactured by the controlled rolling and the quenching and tempering processes. It was found that the critical notch ductility for arresting a shear crack depends on the pipe length within which the crack is to be arrested. This result is well explained by solving the equation which governs change of crack velocity. The behavior of shear crack propagation and arrest can be well analyzed regardless of the existence or nonexistence of separation by Charpy energy.
Prevention of shear fracture in the natural gas pipelines is one of the most important problems for the safety of the natural gas transportation. The present paper gives a prediction method for the crack propagation and arrest in the ultra-high pressure pipelines which is the recent trend of the pipeline design and the toughness requirements for the high-grade line pipes to avoid the fracture.
This paper gives the analysis in the natural gas decompression behavior in pipelines as one of the important items for predicting the fracture safety of latest high-pressure natural gas transmission. By combining "British Gas Theoretical Model of Rich Gas Decompression" and "BWRS Equation of State", authors successfully developed the computational program, which can calculate dual-phase decompression curves of the natural gases. In the calculated results, the phenomenon of the "plateau" in the dual-phase decompression curve has been confirmed. Authors also numerically simulated the natural gas decompression behavior in pipelines and analyzed the fracture initiation process. It was shown that the initiation period is too short to influence the gas decompression curves.KEY WORDS: natural gas decompression behavior; high-pressure natural gas transmission; dual-phase decompression curve; fracture initiation process.
When many additional alloying elements are used for high strength of steels, the weldabilrty is usually pcor. The developmentof high-strength steels of 800MPa class vvith goodweldabilky is preferred to prcceed on the basis of a new concept for innovative materials design which may remarkably reduce the carbon equivalent et steels. The higher-strength steels ot 700 to 800MPa class with the same carbon equivalent as mild steels could be achieved by creating uitra fine ferrite grains ot less than 1um.Efficient and high speedjoining processes with low heat input and narrow wioth of heat afrected zone (HAZ) were developed to obtain high-performance welded structures while preserving ultra fme microstructure. The softened region in the HAZ et ultra fin,~grained steels ean be controlled vvith the newly developed welding process
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