The key methods for extending the service life of control valves

Control valves play a vital role in the automatic control systems of modern chemical plants. The success of production processes depends heavily on the accurate distribution and control of flowing media. Whether it is energy exchange, pressure reduction, or simple material feeding into vessels, final control elements such as control valves are essential. Here are several effective methods to significantly extend the service life of control valves:

Control Valves

1.Operating at Large Openings

Starting the valve operation at as large an opening as possible, ideally around 90%, helps extend its life. In this way, cavitation and erosion initially occur only at the tip of the valve plug. As the plug erodes and flow increases, the valve can be gradually closed to maintain control. This method ensures full use of the valve plug until its root and sealing surface are damaged. Moreover, a larger opening creates a bigger throttling gap, which reduces erosion intensity. Studies show that operating at larger openings can extend valve life by 1 to 5 times. For example, a chemical plant reported doubling valve service life using this method.

2.Reducing S to Increase Working Opening

Reducing “S” means increasing the system losses outside the control valve, thereby decreasing the pressure drop allocated to the valve. This forces the valve to operate at a larger opening, which weakens cavitation and erosion. Practical ways to achieve this include installing a throttle plate downstream to consume pressure drop or partially closing manual valves installed in series with the control valve. This method is especially simple and effective when the valve is oversized and operating at a small opening initially.

3.Reducing Valve Size to Increase Opening

Another effective strategy is reducing the valve size to force a larger working opening. There are two main approaches:

Replace the valve with a smaller size model (e.g., change from DN32 to DN25).

Keep the valve body but replace the trim (valve seat and plug) with a smaller diameter set.

For instance, a chemical plant replaced a dgl0 trim with a dg8 during a major overhaul and successfully doubled the valve’s service life.

4.Shifting the Damage Location

This technique involves transferring the most heavily damaged areas to less critical locations to protect the valve plug and seat sealing surfaces. By doing so, the valve’s most important functional parts can remain intact longer, thus extending service life.

5.Lengthening the Throttling Passage

Increasing the length of the throttling passage can effectively extend the valve’s service life. A simple way to achieve this is by thickening the valve seat, creating a longer throttling passage. This design moves the sudden flow expansion downstream, away from the sealing surface, and reduces pressure recovery, thus mitigating cavitation. Some valve designs use stepped or wavy seat holes to achieve higher resistance and minimize cavitation. This method is commonly applied in high-pressure valves in imported equipment and when upgrading old valves.

6.Changing the Flow Direction

Changing the valve flow direction can greatly affect longevity. In “flow-to-open” designs, cavitation and erosion attack the sealing surface and valve plug root, leading to rapid deterioration. In contrast, “flow-to-close” designs move the cavitation and erosion effects downstream of the throttling point, protecting critical surfaces. Therefore, simply changing the flow direction from open to close can extend valve life by 1 to 2 times.

7.Using Special Materials

To resist cavitation (characterized by honeycomb-like pits) and erosion (seen as streamline grooves), it is recommended to use special, more durable materials for throttling parts. Materials like 6YC-1, A4 steel, Stellite alloys, and hard alloys are known for their resistance to such damage. For corrosion resistance, both non-metallic materials (such as rubber, PTFE, ceramics) and metallic materials (such as Monel and Hastelloy) can be used, depending on the application requirements.

8.Changing Valve Structure

Finally, modifying the valve structure or choosing valves specifically designed for harsh conditions can also significantly increase service life. Options include multi-stage valves, anti-cavitation valves, and corrosion-resistant valves. These specialized valves are engineered to withstand extreme conditions better than standard designs.

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