At present, a significant number of well pumps in domestic oilfields use rod pumps, with most being plunger pumps. Conventional plunger pumps have become one of the primary methods for oil recovery. However, due to the high water cut phase that many domestic oilfields are currently experiencing, along with factors such as high sand content, high-temperature steam-based heavy oil extraction, polymer injection, and exposure to highly corrosive environments, the wear and corrosion of pump barrels and plungers have become increasingly severe. As a result, the average inspection cycle for these pumps has been steadily decreasing, with some requiring maintenance in less than 30 days. This not only affects operational efficiency but also significantly impacts the overall economic performance of oilfield development.
Many research institutions around the world have invested considerable effort into understanding the causes of pump failure and developing protective measures. One of the most effective strategies is optimizing the materials and surface treatments used for the pump barrel and plunger. The friction pair between the cylinder and plunger, along with their working environment, forms a tribological system. The total wear and corrosion in this system depend on the properties of the materials involved, the motion dynamics between them, and the operating conditions. Ultimately, the choice of material and finishing process for the pump components plays a critical role in determining the extent of wear and tear.
The goal of selecting and optimizing materials and surface treatments for the pump barrel and plunger is to minimize corrosion and wear within the tribological system. However, due to the numerous influencing factors, there is still no comprehensive theoretical framework guiding material selection and matching. Currently, R&D teams focus on testing various combinations of materials and surface treatments under controlled laboratory conditions. By conducting indoor friction and wear tests, they evaluate which material pairs perform best under specific conditions.
For instance, in one test, different combinations of pump cylinder and plunger materials were evaluated, including electroless nickel-phosphorus coatings on 45 steel, chrome plating on 303 steel, and nitriding on 4%-6% chromium steel for cylinders, while plungers were tested with chrome-plated carbon steel, laser-treated carbon steel, electroless nickel-phosphorus coated navy brass, and Monel alloy chrome plating. These combinations were tested using ring-and-block configurations under water at 60°C and low viscosity. Results indicated that carbon steel with electroless nickel-phosphorus coating paired with chrome-plated carbon steel showed the best wear resistance.
Another test involved nine different material combinations, including chrome-plated carbon steel, electroless nickel-phosphorus coated carbon steel, nickel-based alloy spray-welded carbon steel, and nitrided 38CrMoAl. The test medium was oily wastewater containing 5% oil, with specific mineral content and temperature. The results suggested that carbon steel spray-plungers paired with chrome-plated cylinders performed best, as did nitrided 38CrMoAl plungers with chrome-plated cylinders.
Despite these findings, the laboratory results are limited by the specific conditions under which they were conducted. Changing test parameters would require extensive work, and the results may not directly translate to real field conditions. Moreover, differences in test setups and friction pair geometries make it difficult to compare results across different studies.
Through these experiments, it becomes clear that material selection for pump components is a complex and time-consuming process. Without theoretical guidance, a large amount of trial and error is required. Additionally, the materials tested are often those already known, limiting the potential for discovering new, more effective options.
With advances in material engineering and the development of new surface treatment technologies, there is great potential for applying innovative materials and coatings to pump barrels and plungers. However, the current approach of purely experimental material matching is insufficient to meet the growing demand for longer-lasting pump systems. Therefore, integrating principles from material science and other disciplines to design optimal material combinations for pump components is an urgent challenge that needs to be addressed.
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