Plunger pump and pump cylinder material should be how to choose

At present, the number of well pumps with rod pumps in domestic oilfields occupies a large proportion, most of which are plunger pumps. Conventional plunger pumps have become one of the major oil recovery methods.

Due to the fact that most domestic oilfields have entered the period of high water cut, coupled with the factors such as high sand content, high temperature steam heavy oil exploitation, polymer injection and strong corrosive medium conditions and poor well conditions, the plunger pump barrel And plunger wear, corrosion, scratches more and more serious, average well pump inspection cycle is getting shorter and shorter, and some even less than 30 days you need to pump, seriously affecting the overall economic benefits of oil field development. Many institutions at home and abroad have invested a lot of effort to study the cause of pump failure and protective measures. One of the most effective methods is to optimize the material and finish of the pump barrel and plunger.

Cylinder and plunger friction pair and the surrounding working environment and conditions constitute a tribological system, the system of corrosion wear and tear by the pump barrel and the corrosion of the plunger wear and tear of the total amount of the decision. The respective wear and tear on the barrel and plunger are determined by the physical-mechanical-chemical properties of the constituent materials, the relationship of their mutual motions, working conditions and conditions. Ultimately, from the pump standpoint, the choice of materials for the barrel and plunger and the choice of finishing process are decisive factors in determining the amount of wear and tear on the tribological system.

The purpose of selecting and optimizing the pump barrel and plunger material and surface treatment process is to minimize the amount of corrosion wear on this tribological system. Due to a large number of factors, so there is still no theoretical guidance on the material selection and matching of the pump cylinder and the plunger. The most important work done by R & D personnel at present is to select the material and surface treatment technology of various pump cylinders and plungers, Wear indoor friction and wear test conditions, from the test results to determine in this test conditions, what kind of pump plunger plunger material should be selected. Here are two test results:

The first result: pump cylinder material and surface treatment process for the 45 steel surface electroless nickel-phosphorus alloy, 303 steel chrome, 4% -6% chromium steel pressurized nitriding and other 3; plunger material and the surface treatment process For carbon steel chrome, carbon steel laser processing, navy brass electroless nickel-phosphorus alloy, Monel alloy chrome and other 4 kinds. The above materials were paired abrasion resistance test, the friction pair for the test by the ring and block composition. The medium is water, the temperature is 60 ℃ and the viscosity is 0.000653Pa / s. Testing machine for MG-200 high-speed high-temperature friction and wear testing machine. The applied load 1kN, specimen total friction stroke of 20km. Through the pair of different cylinder and plunger material and surface treatment process of paired abrasion resistance test research, and according to the principle of plunger failure principle for the selection of pump cylinder and plunger friction pair are the best matching material carbon steel chemistry Nickel-phosphorus alloy and carbon steel chrome plating.

The second result: pump cylinder material and surface treatment process for the carbon steel surface chrome, carbon steel surface electroless nickel-phosphorus alloy and 38CrMoAl nitriding; plunger material and surface treatment of carbon steel surface chrome, carbon steel surface electroless nickel Phosphorus alloy, carbon steel surface spray welding nickel-based alloy and 38CrMoAl nitriding, were paired into nine pairs of friction pair. Test friction pair by the ring and column. The test medium is oily wastewater containing 5% oil; the mineral content in the water is chloride ion 11000mg / 1, carbon dioxide 25mg / 1, calcium ion 25mg / 1, bicarbonate ion 30mg / 1, magnesium ion 13mg / 1, 8mg / 1; sand 0.4%; temperature 60 ℃. The same use of domestic MG-200 high-speed high temperature friction and wear testing machine. Test load 100N, the total friction of about 6km. Based on the comprehensive analysis of the test results, it is concluded that the carbon steel spray plunger is paired with the carbon steel chrome-plated cylinder, and the 38CrMoAI nitriding plunger is paired with the carbon steel chrome-plated cylinder.

As can be seen above, the laboratory test results are obtained under the set conditions. If different test conditions are changed, the workload will be huge. Even if the conditions are different, it is not necessarily consistent with the downhole conditions in the field. Therefore, the experimental results are limited. Due to the different test conditions and the shape of the friction pair, there is no comparability among the test results.

It can be seen through the experiment to determine the pump cylinder and plunger material match its deficiencies, the test without theoretical guidance and therefore a large amount of test work. The material chosen for the test is only the well-known material already available and it is difficult to come up with other materials that may not have been used on the pump but may perform better.

With the development of material engineering and the emergence of new material surface treatment processes, many materials and surface treatment processes are likely to be applied to the surface of the barrel and plunger. The trade-off between the friction and wear tests of purely matched laboratory materials is far behind Far can not meet the current requirements to improve pump barrel and plunger life expectancy, how to use material science and other disciplines of principles and techniques to design cylinder and plunger matching material is the urgent problem to be solved.

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