Core technical solutions and application practices

Core technical solutions and application practices for enhancing the wear resistance of carbon steel elbows 

In industrial piping systems, carbon steel elbows are key components for changing the direction of pipelines. Their wear resistance directly affects the service life and operational efficiency of the entire system. Due to the change in fluid direction at the elbow, the impact and wear on the inner wall of the elbow are particularly severe, especially in gas-solid and liquid-solid two-phase flow conditions, where the wear problem is even more prominent. 

The main causes and impacts of wear on carbon steel elbows 

Carbon steel elbows are subject to severe wear during use, especially when transporting media containing solid particles in fields such as chemical engineering, petroleum, mining, and metallurgy. 

These solid substances will exert a strong abrasive effect on the pipelines during transportation, and the elbows at the flow direction change points will suffer even more severe wear. The service life of some local positions may only be three months, which seriously affects the normal operation of the equipment, and the shutdown for maintenance will cause huge economic losses. 

2 Key Technologies for Improving the Wear Resistance of Carbon Steel Elbows 

2.1 Ceramic Coating Technology 

Ceramic coating technology is one of the efficient solutions to enhance the wear resistance of carbon steel elbows. This technology uses combustion synthesis coating technology to form a continuous and complete Al₂O₃ ceramic coating on the inner wall of the steel elbow. This makes the composite elbow possess both the strength and toughness of ordinary carbon steel, as well as the properties of corrosion resistance, wear resistance and high-temperature resistance. 

An application example of a heavy oil catalytic unit in a petrochemical plant shows that after one year of operation, the composite elbows and pipes with ceramic coating lining remain intact. This solution has addressed the previous issue where the service life of certain local parts was only three months. 

2.2 Surface Treatment and Ion Implantation Technology 

The application of non-metallic ion impregnation treatment technology can significantly enhance the wear resistance and corrosion resistance of medium carbon structural steel. The treatment process involves steps such as clamping and cleaning, preheating, ion impregnation, ion oxidation, polishing, secondary ion oxidation, ion passivation and cleaning. 

Through this technology, diffusion layers of [N], [C], and [O] can be formed on the surface of steel, as well as compound layers of Fe3N, Fe4N, Fe3C, and an Fe3O4 oxide film layer. The thickness of the diffusion layer can reach 90-150 μm, with a hardness greater than 1100 HV0.2, significantly enhancing the wear resistance and corrosion resistance of medium carbon structural steel. 

2.3 Compound Structure Design 

The composite wear-resistant carbon steel elbow adopts a multi-layer composite structure design, usually including: 

· Elbow body 

The first corrosion-resistant layer: Usually made of materials such as polytetrafluoroethylene, it enhances the corrosion resistance of the outer side of the elbow mechanism. 

· Buffer layer: Materials such as ACF artificial cartilage foam are used to provide buffering and protective effects when liquid flows inside the elbow pipe. 

· Second corrosion-resistant layer: Enhance the corrosion resistance of the inner wall of the elbow mechanism. 

Wear-resistant layer: Enhance the wear resistance of the elbow mechanism. 

This design not only enhances wear resistance but also, through a detachable connection design, allows for the replacement of only the severely worn parts, thus avoiding the waste of resources caused by replacing the entire elbow. 

2.4 Applications of Silicon Carbide Materials 

The use of silicon carbide material for reinforcing plates is also an effective way to enhance the wear resistance of elbows. The hardness of silicon carbide products can reach above HRC-55-60, and the wear resistance is increased by more than ten times. 

Meanwhile, an epoxy anti-corrosion coating made of epoxy resin is applied to the inner wall of the reinforcing plate, which can further enhance the overall corrosion resistance. 

3. Special structural design enhances wear resistance. 

3.1 Replaceable Impact-resistant Cover Design 

For the most vulnerable part of the elbow to wear, a replaceable anti-impact cover design can be adopted. A through hole is provided on the back of the elbow body, and a flange is formed around the through hole, on which a mother anti-impact cover is sealed and installed. 

The inner surface of the anti-impact cover is a concave arc shape and is equipped with ceramic plates. The wear resistance and corrosion resistance of ceramics are utilized to enhance the wear resistance of the elbow and extend its service life. This detachable connection design makes it convenient to replace the anti-impact cover worn by the slurry impact without having to replace the entire elbow. 

3.2 Wear-resistant Rib Plate Design 

Welding wear-resistant rib plates on the tail end of the flow surface of the straight pipe for feeding at the elbow and on the impact surface of the box can effectively improve the wear resistance. 

The wear-resistant rib plates at the tail end of the flow surface of the feed straight pipe can be designed as crescent-shaped protrusions, and the wear-resistant rib plates on the impact surface of the box body can be designed as a "#" shaped grid structure. This structure is reasonable, the manufacturing process is simple, it is wear-resistant and impact-resistant, and local damage is easy to replace, which can effectively extend the service life of the elbow. 

4 Material Selection and Heat Treatment Process 

4.1 Material Selection 

The selection of appropriate medium carbon structural steel is crucial for enhancing the wear resistance of elbows. Research indicates that steel with a carbon content of approximately 0.480% has the best comprehensive mechanical properties. As the carbon content increases, the hardness of the steel gradually rises, but the impact toughness decreases accordingly. 

4.2 Heat Treatment Process 

The isothermal quenching heat treatment process has a significant impact on the wear resistance of steel. As the isothermal quenching temperature and time increase, the amount of lower bainite in steel rises, the microstructure becomes coarser, the hardness decreases, while the impact toughness increases, but the wear resistance decreases. 

After the steel with a carbon content of 0.480% was subjected to a heat treatment process of 920℃×1.5h + 290℃×3h, its Rockwell hardness could reach 49.2HRC, its impact toughness could reach 167J/cm², and after 2 hours of wear