Research on Correlation between Insulation Performances and Damage Degree of Burned Cable

In this paper, the insulation near the fault point of a breakdown 220 kV cable joint for burned cable, which kept burning for about one hour, was investigated. The relationship between insulation performance and damage degree of burned cable was analyzed by comprehensive test of material performance. Differential scanning calorimetry (DSC) test results showed that the shoulder peak temperature could reflect the heat history of the materials. There was a correlation between damage degree and the characteristic absorption peak of spectrum (IR) graph. The result of mechanical performance was different obviously. The results of broadband dielectric spectrum showed that the relative permittivity and dielectric loss factor for samples close to the fault point were smaller. By the microstructure observation of sample crystal distribution form, the above conclusions were proved. As a conclusion, DSC, IR, SEM and dielectric performance analysis results matched the real situation, showed that these methods was feasible and effective to judge the damage degree of burned cable.

The Study on the Orderliness of Change of Microstructure and Mechanical Properties in Simulating the Heating Process of Bending of X80 Pipeline Steels

As the development of oil gas transportation project for long distance over the world, the pipeline steel are developed to high grade to reduce the construction cost and increase the efficiency of the gas transportation. But the statistics of the built pipeline engineering in the world showed that most of the steels are below the grade of X70, and the used X80 grade steels are less than 5000km. In 2008, the second west-east pipeline project will startup in China, and the whole line will use X80 grade pipeline steels. So the matched bend pipes should be studied. In this paper, the X80 pipeline steels were reheated under selected condition to simulate the heat history of bending process of it. And the deduced microstructure was observed, also the relationship between microstructure and mechanical properties were discussed. The optimum heat treatment technics were gained. This research will be helpful to the field hot bending in the second west-east gas project.

EVALUATION OF IMPACT PROPERTIES TO FORGED 3CR STEEL BY BARKHAUSEN NOISE

This paper reports that the Barkhausen noise method can be used to accurately characterize forged reactor vessels. The Charpy V-notch impact tests were conducted on the respective specimens with three different types of heat history. Various test results including fracture appearance transition temperature (FATT) were obtained. The Barkhausen noise voltage changed with heat treatment temperature (870~1000°C) and conditions (Tempered, PWHT). The fracture appearance transition temperature can be predicted using the Barkhausen noise voltage.

Configuration and Adjustment of Substrate Preheating Device

Laser Metal Deposition Shaping (LMDS) is a state-of-the-art technology that combines rapid prototyping and laser processing. There are many factors affecting the quality, precision, microstructure and performance of LMDS-deposited parts. Among them, substrate preheating is a significant one since it can change the heat history of the LMDS process. Preheating is often used to reduce the residual stresses and the risk of thermal distortion and cracking. In this work a set of substrate preheating device for LMDS system employed with dual-channel control, namely intelligent PID temperature control and realtime serial-port temperature acquisition and feedback control, is designed and developed. In addition, the heating up rule gained through the relative experiment is introduced to reduce the overshoot amplitude of substrate preheating device by cascade control method. The results show that not only can this substrate preheating device realize the dual-channel control and continuous adjustment of substrate preheating temperature, but also can realtime collect and record the substrate temperature.

Physical Phenomena of Thermoplastic Articles in the Vicinity of Their Glass Transition Temperatures

It is well known that environmental conditions impact the performance of thermoplastic articles, therefore requiring selection of appropriate raw materials. Nevertheless, frequently due to business reasons, when selecting a material, the rigor of understanding the fundamental physical events responsible for the desired performance is shortchanged. In this study, we investigate the effects of cyclic heat history on the dimensional stability of articles made with commercial grade rigid thermoplastic resins, particularly, in the temperature range close to the material’s glass transition temperature, as more materials are used in hot & arid environments. The two physical events identified as most relevant to desired article performance are the relaxation of the processinduced residual stresses within the material and the dynamic phenomena brought about by the material’s coefficient of thermal expansion, CTE. We find that the periodic development of convexconcave surfaces on an article matches the periodic development of a non-uniform temperature gradient within the article. We demonstrate that this periodic heat exposure leads to an irreversible concave deformation of the article’s exposed surface. Moreover, articles exhibit this deformation phenomenon regardless of the level of the initial process-induced stresses. We offer explanations of these behaviors and discuss their practical implications.