In the oil drilling industry, the mud pump serves as the core power equipment of the drilling system, and the liner in its fluid end directly withstands the continuous impact of high-pressure and highly abrasive drilling fluid. Therefore, selecting a suitable liner is crucial. Mud pump liners are available in various materials, among which the mud pump bi-metal liner is the most common type. Its service life can usually reach 800 hours, and it is also one of the most widely used wearing parts of mud pumps. Structurally, it mainly consists of two layers: an outer sleeve and an inner sleeve.

Ⅰ. Outer Sleeve

1. Structural Support

As the core supporting component ensuring the overall performance, adaptability and durability of the liner, the outer sleeve is manufactured using centrifugal casting technology, with 45# forged steel as the material. It has a tensile strength of >610MPa and a hardness of HB180-200. This type of material exhibits excellent tensile, compressive and impact resistance. During drilling operations, the mud pump delivers drilling fluid at a pressure of 10-35MPa or even higher. The outer sleeve bears the impact of high-pressure fluid in the pump chamber and the lateral force generated by the reciprocating movement of the piston, preventing the liner from deformation or cracking due to excessive pressure. Meanwhile, acting as the "framework" of the liner, the outer sleeve supports the inner sleeve to prevent the inner sleeve from falling off or being damaged due to independent stress, thus ensuring the integrity of the bi-metal structure.

2. Installation Adaptability

The dimensions of the outer sleeve directly determine whether the liner can perfectly match the liner bore of the fluid end. The outer diameter of the outer sleeve is precision-machined according to the pump body specifications to ensure transition fit with the liner bore of the pump body, avoiding radial looseness after installation.

3. Protection for the Inner Wear-Resistant Layer

The inner sleeve of the bi-metal liner is the core wear-resistant layer, which directly comes into contact with sand and drill cuttings in the drilling fluid. However, the inner sleeve material (e.g., high-chromium cast iron) usually has high brittleness. The outer sleeve can buffer external mechanical impacts, preventing the inner sleeve from cracking due to direct stress. At the same time, the outer sleeve isolates the direct contact between the inner sleeve and the pump body metal, protecting the wear-resistant performance of the inner sleeve from additional damage.

Ⅱ. Inner Sleeve

1. Resisting Wear and Erosion to Extend Overall Liner Life

Drilling fluid often contains a large number of hard solid particles and flows at high pressure and high speed inside the pump, causing severe erosive wear to the inner wall of the liner. The inner sleeve is made of high-chromium material with high hardness and excellent wear resistance. Its hardness is much higher than that of the outer sleeve, enabling it to directly withstand the wear caused by drilling fluid and extend the overall service life of the liner.

2. Corrosion Resistance

To meet different drilling requirements, drilling fluid may be acidic or alkaline. Long-term contact with such fluid can cause corrosion to metals. The inner sleeve material has excellent corrosion resistance, which can isolate the direct contact between the drilling fluid and the outer sleeve, and at the same time prevent corrosion products from mixing into the drilling fluid and affecting drilling quality.

3. Ensuring Sealing Performance

The core function of the mud pump is to deliver drilling fluid to the bottom of the well at high pressure, and the sealing between the liner and the piston is the key to maintaining high pressure. If the inner wall of the liner has pits or deformations caused by wear and corrosion, it will lead to drilling fluid leakage, directly reducing the pump displacement and pressure and increasing energy consumption. The inner sleeve can fit tightly with the piston seal, reducing leakage and ensuring the mud pump operates stably at the rated pressure, thus avoiding drilling shutdowns caused by seal failure.

4. Reducing Comprehensive Costs

Compared with mud pump ceramic liners, the inner sleeve of the bi-metal liner has lower cost, which can significantly reduce the overall material cost of the liner and improve the overall cost-effectiveness.

In summary, the manufacturing process of bi-metal liners is relatively simple. Compared with ceramic or zirconia liners, bi-metal liners have a lower purchase price and are widely used in drilling operations. The adoption of bi-metal liners represents an important leap in the field of drilling mud pumps. They combine the strength of steel with excellent wear resistance, making them a highly attractive choice for various application scenarios. With the continuous advancement of technology, bi-metal liners are expected to play an increasingly important role in improving the efficiency of the mud pump industry and extending the service life of equipment.