Study on the integrity detection and evaluation method of damaged pipeline
To detect the integrity of damaged pipeline and accurately evaluate its damaged condition, a CCD image data guided digital automatic ultrasonic testing system was designed to realize the dynamic measurement of a pipeline damaged surface, and extract the characteristic parameter of damaged pipeline. Based on the three-dimensional discrete point set which gathered to describe the integrity of damaged pipeline, we establish a damaged pipeline entity model which is closer to the actual condition, analyze and simulate mechanical properties under the actual load by using the numerical simulation software (ABAQUS), to get the most dangerous region and the trend of stress and displacement. This method provides more reliable reference for integral safety analysis and evaluation of damaged pipeline.
Finite element analysis and experimental research on the buried pipelines in case of uneven settlement of the building foundation
This paper is dedicated to the study of the stress of buried pipelines to find the regularity of the pipeline-soil interaction under the foundation of uneven settlement through finite element analysis In DOIng our research, we have adopted electrical measurement method to monitor the mechanical behavior of the buried pipelines in case of uneven settlement of the building foundation.As is known, buried pipelines are the material basis of urban survival and development.A considerable number of buried pipelines are laid down over the soft soil underground basis of a non-linear and uneven settlement, making the mechanical analysis complicated.Actually, high-stress areas of pipelines were found in the intersection connecting the pipelines on the surface as well as the buried pipelines.Therefore, it would take four months to complete a circle of successful monitoring work of the pipelines.The test results have shown that the stress of the buried pipelines tends to become greater and greater with the uneven settlement of foundation, which indicates that the pipeline-laying stress seems to be greatly influenced by the uneven settlement of the foundation. However, when the mechanical behavior of the buried pipelines in the case of the foundation uneven settlement was analyzed by using numerical simulation and emulation software ABAQUS, it proves possible to gain the uneven settling amount of the foundation needed in the finite element analysis from the test.Furthermore, the initial conditions of the finite element analysis turn out to be in accordance with the experiment.The results of finite element analysis also prove to be in conformity with the experimental results except for the place of pipeline with portiforium and fluid impact.In addition, we have also analyzed the influential factors of the buried pipelines stress.The results show that the main factor of the fluctuation of pipes stress comes from the vibration of the internal pressure.But the vibration of internal pressure was not the main factor of the pipeline-soil interaction. Deformation modulus and position ratio, which serve as the main factors of the pipeline-soil interaction, have actually little influence on the piping stress.Thus, the paper has developed a stress analysis and numerical simulation method of the stress of buried pipelines in case of uneven settlement on the basis of our research work in hoping to provide an excellent technical support for the mechanical analysis and safety evaluation of buried pipeline stress.
Hygroscopic Expansion of some Casting Investments
CREDIT is generally given to Taggart1 for introducing the cast gold inlay to the dental profession. Although he realized that gold shrinks when cooled from molten state to solid state of room temperature, the investment available to him did not supply sufficient compensation. In 1910, Van Horn2 published a paper dealing with a method by which he obtained the compensation by means of wax expansion. The next major research in connection with this problem was the work of Coleman3 at the National Bureau of Standards. He determined the gold shrinkage to be 1.25 per cent and presented a casting technic with compensation values of quantitative nature. The total compensation for the gold shrinkage was obtained by the combination of the setting and thermal expansion of the mold. This procedure is the general practice followed at the present time for compensation. There are some disadvantages to this method. Skinner has indicated the difficulty of obtaining smooth castings and the improper compensation for the casting shrinkage.4 It has been found by Hollenback5 and Scheu6a that castings made at a high temperature are rougher than those made at a low temperature (450° C.), depending upon the great difference in thermal expansion between plaster of Paris and silica, which causes a poor union of the fine particles. This may also result in friability and there may be some warpage due to the differential expansion. A method which provides sufficient compensation at a low mold temperature is the hygroscopic casting technic.b Wilson7 showed that certain plasters expand as much as 0.0044 inch to the inch by taking up moisture from the air. With this information at hand, Scheula, b tested some commercial investment to determine what results the addition of moisture would have. He found6b: (1) All of the casting investments that were tested expanded. (2) The thicker the mix, the greater the expansion. (3) A mix with hot water expanded more than one with cold water. (4) The time at which the mix is placed in the water is of great importance. It was found that if the mix is placed in the water early, it would not expand so much as when placed in a little later. It was also found that if the mix was placed in the water after a certain time, it could not expand to the maximal amount. (5) The temperature of the water in which the mix is placed is important, for two reasons; (a) the temperature of the water controls slightly the expansion of the investment, and (b) water at a temperature of 1000 F. slightly softens the wax pattern so that the fine margins are not marred while expansion is taking place. The mix should remain in the water at least 20 minutes to obtain the full expansion, after which time no further expansion is obtained.