Deposition of hydrogenated amorphous silicon films from SiH4/He gas mixtures was performed by using a square wave amplitude modulated rf discharge. The modulation was used for controlling radical densities in plasmas which led to a high rate deposition of good quality films. The fairly high deposition rate of 6 Å/s was obtained for a low concentration of 5% SiH4 and a high rf peak power 200 W (0.8 W/cm3) without any appreciable amount of powder particles in the reaction chamber. The optical gap of the films was 1.8–1.95 eV. Emission intensities of HeI 388.9 nm and SiH 413.5 nm linearly increased with rf peak power and were well correlated with the deposition rate.

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.

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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.

The fracture arrest of high pressure gas pipelines is one of the keen subjects for application of high strength line pipes. To examine the arrestability of high strength line pipes against crack propagation, several full scale fracture propagation tests have been conducted. The fracture propagation tests of X100 or X120 under high pressure revealed that the existing models of arrest energy prediction failed to predict the arrest energies. By careful investigations of the test results, it is found that the failure in prediction is mainly due to the uncertainty of crack velocity curve prediction. On the other hand, accuracy of predicted gas decompression curve is relatively high even in the case of high pressure condition. Experimentally, the arrest energies have been determined by full-scale fracture propagation tests with increasing toughness arrangement. Different from actual pipeline, extremely low toughness pipe has been employed in crack initiation pipe with intention of getting steady state propagation. However, arrestability of pipe might be underestimated in the increasing toughness arrangement test as the initial crack velocity increases. Together with recalibrated crack velocity curve, Sumitomo model (HLP method with Sumitomo’s crack velocity curve) predicts that even toughness arrangement, which is the case of real pipelines, could arrest the propagating shear fracture in high pressure gas pipelines by X100.