Issue 27

H. Liu et alii, Frattura ed Integrità Strutturale, 27 (2014) 53-65; DOI: 10.3221/IGF-ESIS.27.07 53 Fracture failure analysis of baseplates in a fluidic amplifier made of WC-11Co cemented carbide H. Liu, K. Yin, J.M. Peng, Q.L. Yin College of Construction Engineering, Jilin University, Changchun (China) 523772622@qq.com A BSTRACT . A fluidic amplifier is a crucial automatic control component in a liquid jet hammer used to drill hard formations in the oil industry. This study aims to determine the true causes of the fracture failure of baseplates in a fluidic amplifier made of WC-11Co cemented carbide in a very short period of time. Computational fluid dynamics (CFD), theoretical estimation, and finite element analysis (FEA) were employed to analyze the effect of static and dynamic loads on the strength of the baseplates. Fractographic, metallographic, and processing defect analyses were also carried out. The FEA results showed that the static and dynamic loads caused stress concentrations at the actual fracture locations, and the effect of working loads on material strength was allowable and safe. Fracture surfaces exhibited typical characteristics of a brittle fracture. The metallographic analysis revealed that a specific amount of brittle eta-phase (η-phase) was present in the material. The microstructure of the processing cutting zone was inspected and the results revealed that some voids, pores, and microcracks were formed on the processing surface. The manufacturing and processing defects resulted in low stress fracture failure of the baseplates. K EYWORDS . Fracture analysis; Fluidic amplifier; WC-Co cemented carbide; Numerical simulation; Microstructure. I NTRODUCTION n an oil drilling field, drilling hard formations is an arduous problem that demands prompt solution all the time, especially in deep wells. As deep-oil resource exploration continues to increase, the depths of oil wells have become increasingly deeper and the rocks at such great depths have become harder to drill. The hydraulic hammer was considered as one of the best tools to drill hard formations for many years [1-3]. The application of conventional rotary drilling to drill hard formations have several weaknesses such as high cost, low rate of penetration (ROP), and short service life of drilling tools [4-9]. The liquid jet hammer technique is a highly efficient method that overcomes the disadvantages of conventional drilling methods for hard formations. The liquid jet hammer is a down-the-hole tool that is used to exert an impacting force on the drill bit [4]. It has been widely applied in exploration core drilling since its invention in the 1970s and was crucial in drilling the No. 1 hole of the Project of China Continental Science Drilling [5-7]. Exploration core drilling efficiency can be improved by more than 30%, higher core recovery rates can be obtained, and straighter holes can be drilled when a liquid jet hammer is used [4, 5]. In oil and gas drilling, a number of field tests have proven that liquid jet hammer could increase drilling efficiency by more than 120% in hard formations [8-10]. As shown in Fig. 1, the YSC178 liquid jet hammer [5, 11] is placed at an oil drilling platform of the Zhongyuan oil field and is connected at the bottom of the drill pipes. I