As one of the most critical and basic components of downhole drilling equipment, the seals can ensure the performance and service life of the equipment, which is an important index for evaluating the efficiency of downhole equipment. However, the complex and harsh working environment in the underground causes seals to be susceptible to abrasive wear leading to failure, which reduces the reliability of downhole equipment and drilling efficiency. As a sealing material with excellent abrasion resistance, it is necessary to study the abrasion failure mechanism of ultra-high molecular weight polyethylene (UHMWPE) in abrasive environments, which is helpful for improving sealing performance and prolonging sealing life. In order to simulate the damage and failure behavior of UHMWPE materials in fluid dynamic sealing conditions, the pin/disk friction pair composed of UHMWPE pin specimens and 304 stainless steel metal disks was studied. Orthogonal analysis was used to analyze the damage characteristics in environments with different particle concentrations and different particle sizes, and the influence of the particle environment on the tribological behavior of UHMWPE was discussed.
The analytical results of orthogonal tests showed that the effect of particle size on the tribological properties of the material was stronger than that of particle concentration. Analysis of the behavior of friction coefficient and material wear in different particle concentration environments revealed that the material friction coefficient and mass loss changed less with the increase in particle concentration. The main reason for this was that the change in particle concentration did not change the wear mechanism of the material and consequently had a weak effect on its tribological properties. And the wear state of friction pairs in different sizes particle environments demonstrated a significant deterioration trend with increasing particle size. Scanning electron microscopy (SEM) analysis of the wear surface of UHMWPE showed that the surface of the material exhibited different forms of damage in the environment of different particle sizes, that was, the results of the research under different particle sizes followed the "particle size effect". Performance was as follows: small sized particles on the material wear was very slight, the material in this particle environment was mainly manifested in the pleated deformation; medium sized particles on the material in the form of damage to the ploughing, and produced plough grooves along the sliding direction on the wear surface; and the sealing material in the large sized particles environment was mainly subjected to the three-body abrasive wear, the wear surface was mainly manifested in the fibrous abrasion debris generated by the particles rolling micro-cutting.
This study established the abrasive media environment for the drilling tool seals, clarified the damage behavior characteristics of UHMWPE in different concentrations and sizes of abrasive particles, revealed the failure mechanism of UHMWPE in abrasive wear, provided theoretical and technical references for the design and optimization the sealing structure in abrasive environment, and was helpful for the promotion of the application of UHMWPE materials in complex engineering environments.
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