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Oscillography impact properties were studied in four different temperatures. The research indicated that impact energy of sampled 4145H DC met the standard of“SYT5144-2007 Drilling collar” and “API SPEC7” in four different temperatures. With temperatures getting down, impact energy, crack propagation energy, and crack propagation energy/impact energy ratio decreased, cracking energy/impact energy ratio increased, crack propagation rate increased and dynamic fracture toughness decreased. In drilling, crack growth rate in DC was slow; the DC was not liable to fracture in normal temperature. On the contrary, crack growth rate was fast, as a result, the DC was easy to fracture in low temperature. The results provide reliable experiment resources for research on 4145H DC fracture. The research results provide reliable guidance for DC production and use in drilling and offer basic experimental evidence to the analysis of 4145H DC fracture mechanism.

The design or assessment method to identify the safety of all the materials or components in accordance with the specific service environment is called design or assessment method for applicability. The assessment method for material applicability is set forth in Standard API 579.The most important step in applicability design is to simulate the practical conditions on the site as close as possible. However, limited by material, manufacturing level and cost, etc., it is hard to simulate the real environment in the laboratory test. Therefore, the testing condition and method should be designed scientifically to allow the testing result to close to the practical condition as much as possible. At present, as for the design of the gas component, the content of each component during the test is designed based on the principle of partial pressure equalization of corrosive component according to the actual pressure and the gas components on the site. But the author assumes that the principle of dissolved amount equalization for the corrosive components in the solution shall be adhered to in the process of applicability assessment. The paper mainly introduces the method to calculate the partial pressure of each component, the model to calculate the solubility of the corrosive components in the solution, and finally gives the example of calculation and points out the problem existing in the partial pressure equalization principle.