Crude oil mining and handling of the various processes inevitably carry highly abrasive fluid. Without proper protection, the pump suffers severe wear and tear in the short term. In this article, Paul Meuter of Sulzer Pumps explains how Sulzer Pumps works with both Sulzer Metco and Sulzer Innotec subsidiaries to look into how to deal with this condition. Figure 1. In oil exploration, produced water injected into the field to raise pressure is often entrained with a large amount of abrasive solids, such as grit. Jet pumps are used in crude oil production to force water back to the field to maintain the pressure required to lift the oil to the surface. Water often contains many abrasive substances, such as gravel and so on. In the pump, these substances with the fluid flow through all the channels, impeller side walls and all the narrow running clearance. Areas with high flow rates, such as narrow, circuitous tubing, will suffer the most severe wear. Figure 2. Scanning electron microscope image of damaged surface erosion. Through the cellulose acetate surface compounding technique to analyze the destruction of the in-situ composition, the abrasion process can be observed under a scanning electron microscope. Particles that are smaller than the size of the labyrinthine gap can move freely, contacting the sidewalls at an oblique angle, resulting in aggressive wear. In addition, if the size of the particles is comparable to the running clearance, they will get stuck between the two walls, resulting in severe three-body wear (see Figure 3). Due to the low flow rates at the pump impellers, diffuser tubes and nozzles, these parts are usually only moderately abrasive. Figure 3. Three-body wear (A) occurs in the clearance near the pump body and in the balance drum if the size of the particles is almost equivalent to the clearance. Corrosive wear (B) in impeller, diffuser or pump nozzle Sulzer Innotec has studied the causes and effects of abrasive wear and has developed a set of experimental methods for predicting material damage. If the designer knows the type and amount of particles entrained in the fluid, it is possible to know the mechanism by which the pump is worn out, and this can be taken into account during the design phase. Solid particles pass through the pump at the same rate as the fluid itself. The degree of wear usually increases at a rate of 3.4 on the flow rate, and wear will be very efficiently controlled if it is possible to reduce the flow rate in every part of the pump. There are two ways to reduce the risk of wear: one is to run the pump at a lower speed, and secondly, take this into account at design time, allowing the fluid to pass through a narrow operating clearance at low speeds. However, in many cases it is impossible to change these parameters. Figure 4. The vertical particle impact on the surface produces 10-20 times more wear than the parallel flow. Wear protection and surface treatment The wide range of coating materials that can be used makes the earlier use of thin, hard, conventional ceramic coatings Today, the layer has been relegated to second-tier. For certain forms of wear and tear, the elasticity and toughness of the material are important, whereas for other types of wear, the hardness of the surface is the decisive factor. Carbide coatings are deposited on the surface by high-speed flame spraying (HVOF) and have extremely high wear resistance. Usually more suitable material is tungsten carbide and cobalt, nickel, cobalt-chromium alloy composite materials. Thanks to advances in powder coating and thermal spray technology, these materials are both durable and robust and can be used at any angle of erosion. Thermal spray coatings can be used on most substrates, but as a line-of-sight process, it is somewhat difficult to spray some complex-shaped and microporous parts. Figure 5. Tungsten carbide-cobalt-chromium alloy cross-section sprayed by high-speed flame spraying. The coatings are very tight, bond well with the substrate, and are very thick, up to 600 μm Hydrodynamic Applications Experience labs and field tests have demonstrated high-speed flame spray coating performance. Based on these experiences, this technique is also applied to the pump. Cobalt-chromium alloy powders are commonly used because of their highest abrasion resistance and a certain degree of corrosion resistance. As we all know, in some harsh conditions, corrosive fluid corrosive and corrosive effects will significantly increase the wear rate. The ability of thermal sprayed coatings to resist erosion and corrosion is therefore an important factor in assessing material quality. Tough tungsten carbide has been used for a long time in surface wear protection. To date, they still rank among the most erosion-resistant materials for situations where other approaches have not worked. Tungsten carbide is stronger than single-phase ceramics by using a metal bond. However, this material is expensive and can only be used under extremely abrasive conditions. Chemical vapor deposition (CVD) Boron coating technology is used for complex components that are difficult to spray by thermal spraying. This process can form an extremely hard surface layer, but requires operation at temperatures in excess of 850 ° C. High temperature limits the choice of substrate due to possible structural and local deformation during cooling. Wear Mechanism Two-body wear describes a protrusion on the surface of an abrasive in contact with the surface of a part, say an embedded abrasive moving over a soft surface. When the sandpaper rubs on the surface, typical two-body wear is shown. For three body wear (A), the abrasive is between the two sliding part surfaces. In the case of a pump, it refers to the abrasion caused by solid particles falling into the ground between the rotor and the stator. The wear rate (B) due to the effect of solid particles under abrasive conditions is closely related to the penetration angle and velocity. The surface of the pump body through which fluid containing solid particles flows will be affected by this wear. This type of wear is greatly influenced by the fluid direction. Pump life improvement Sulzer Pumps' installed production jet pump installed in Alaska, USA, is delivering sand containing water, which contains a large amount of quartz particles up to 1.5 mm in size. Wear parts were originally Stellite 6 and 12 solder plating. After 700 hours of full load operation, the pump has to be overhaul due to damage to the worn parts. At the first upgrade, a cobalt-based tungsten carbide coating was applied to the wear parts using a high-speed flame spray process, extending the life of the pump from 700 hours to 8700 hours. In the second upgrade, the more wear-resistant material was used in the most wear-resistant parts of the pump, but ultimately did not reach the expected service life. The original goal was to achieve 44,000 hours (5 years) of life through the use of highly abrasive materials. Later, a solid tungsten carbide impeller was installed and the drum wear components were balanced, then the pump was put into operation and the expected service life was achieved. As a result of this incentive, Sulzer Pumps uses the same wear protection measures in other pumps. Figure 6. Wear parts made of solid tungsten carbide to extend the life of a field jet pump. Benefited from improvements in powder coating and thermal spray technology, these materials are both durable and robust and can be used at any angle of attack Profitable experience Sulzer Pumps' experience in Alaska has helped them to complete their operations in the North Atlantic Water jet pump maintenance. The pumps were put into operation in the mid-1990s and the initial wear parts were made from double steel steels coated with stellite 6 and 12. Overhaul after 6,700 hours of operation showed that the narrow running clearance between the impeller and the balancing drum was severely worn due to grit grinding. Customers take this opportunity to propose the performance of the pump to enhance, including the pump core redesign. In laboratory tests, the company used specific grit to determine material properties to determine the best type of wear protection possible. There is an exceptionally good correlation between the predicted abrasive wear and the measured wear. Sulzer chose the final protective material based on the results of laboratory studies predicting material wear and the beneficial experience gained during other pump maintenance. They designed robust tungsten carbide inserts for balancing drums and balancing drum sleeves. Taking into account the fragile material and the steel with different thermal expansion, they also use some appropriate treatment. Impeller closely operates the wear surface by high speed flame spray coating of cobalt-based tungsten carbide coating. Figure 7. Solid tungsten carbide is the solution to extreme operating conditions. There were no signs of abrasive wear after 4,800 hours of pump operation, such as increased vibration or increased balance of water. One of the pumps was suspended for 4800 hours due to operational needs. Inspecting the pump wear parts revealed that there was almost no evidence of wear on the part of the impeller entrance through the spray coating and the tungsten carbide inserts of the balance, demonstrating the effectiveness of this wear protection solution.
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