How to Handle Leakage in High-Pressure Butterfly Valves

Dealing with leakage in high-pressure butterfly valves in high school is a common issue, particularly in critical systems where such leaks can disrupt industrial production and, in severe cases, jeopardize public safety and property. High-pressure butterfly valves in power plants connect primary and auxiliary machinery and systems, highlighting their significance. Below are several methods for handling external leakage in high-pressure butterfly valves in power plants:

1. Leakage of valve packing:

There is a dynamic movement between the valve stem and packing during operation, which intensifies with increased switching frequency of the valve. Factors like temperature and pressure further increase the likelihood of packing leakage. Over time, the pressure on the packing gradually decreases, leading to aging and loss of elasticity. This results in the leakage of pressure medium from the contact gap between the packing and the valve stem. If not addressed properly, this issue can escalate, leading to blown-out packing and detachment of the valve stem from the groove, causing an increase in leakage area.

2. Flange leakage:

Flange leakage can stem from various factors such as insufficient compression force on the sealing gasket, roughness mismatch between mating surfaces, or gasket deformation, resulting in gaps between the sealing gasket and the flange and subsequently causing leakage. Other reasons for inadequate flange sealing include bolt deformation or elongation, gasket aging, reduced rebound force, and cracking. Human factors also play a significant role in flange leakage. Additionally, valve body leakage is another potential problem, which won't be elaborated on here due to space constraints.

3. Methods for addressing external leakage in power plant high-pressure butterfly valves:

Pressure-sealed plugging for packing chamber leaks:

Among the various methods for addressing external leakage in power plant high-pressure butterfly valves, one with high safety is the injection-based pressure-sealed plugging technique, which has been extensively studied. This method employs special fixtures and hydraulic injection tools to inject sealant into the sealing cavity formed between the fixture and the leaking area of the valve. This remedial approach effectively addresses leakage defects and has a relatively short application time. When the injection pressure exceeds the pressure of the leaking medium, leakage is forcibly stopped, causing the sealant to transform from a plastic state to an elastic state. At this point, the sealing structure gains a certain elasticity, creating a secondary seal, thus enhancing sealing effectiveness. Currently, two main types of sealant are widely used in China:

Thermosetting sealant: This sealant requires specific temperature conditions for use. When the temperature reaches a certain degree, the sealant becomes elastic, usually solid under normal conditions.

Non-thermosetting sealant: This type is more versatile, usable across various temperature conditions. It exhibits good injectability and fillability, preserving the operational sealing function of high-pressure butterfly valves. When the wall thickness of the packing chamber of the high-pressure butterfly valve is over 8 millimeters, the injection-based plugging method can be directly applied to the valve's packing chamber wall by setting injection holes, and the sealing cavity formed by the injection sealant exhibits the same sealing effect as the packing.

Pressure-sealed plugging for flange leaks using copper wire containment:

This method is suitable for sealing leaks between two flanges with small gaps, uniform clearances, and low-pressure medium leakage. The bolt-specific sealant joint is placed on removed bolts, ensuring that at least two bolts are loose before installing the sealant joint. After installing the sealant joint, immediately tighten the bolts. It's essential not to loosen all the required joint nuts simultaneously, as it may reduce the sealing pressure on the gasket, leading to increased leakage. In severe cases, the leaking substance may blow away the gasket, rendering salvage efforts difficult and incurring immeasurable losses.

Pressure-sealed plugging for valve body leaks:

Adhesive method: For small pressure medium leaks with minimal leakage, the area around the leakage point can be polished to a metallic luster. Then, a taper pin can be driven into the leakage point with appropriate force to reduce leakage or temporarily seal it. As adhesive curing is relatively rapid, adhesive can be applied around the taper pin to form a new solid sealing structure, which can effectively mitigate leakage to some extent. For high-pressure medium leaks with significant leakage, sealing operations can be carried out by using a pressure application tool. During the operation, the pressure application mechanism is fixed on one side of the high-pressure butterfly valve, and the pressure screw is turned to align with the leakage point. Rotating the pressure screw presses the rivet at the end of the pressure screw firmly against the leakage point, effectively stopping the leakage. If the rivet tip is smaller than the leakage point area, a soft metal sheet can be placed under the rivet. After the leakage stops, timely cleaning of the metal surface around the leakage point is necessary.

Welding method: For valve body leaks with low-pressure medium and small leakage, a bolt with an inner diameter twice the leakage point's diameter can be used to allow the medium to flow out of the bolt. The bolt can then be welded to the valve body, and a bolt of the same specification as the bolt can be fitted. A rubber or asbestos pad can be placed at the bottom of the bolt, and the bolt can be twisted into the welded bolt. Wrapping the bolt top with adhesive tape ensures effective leakage reduction. For valve body leaks with high-pressure medium and large leakage, drainage welding is the preferred method. First, a piece of iron plate with a hole in the center is welded, and an isolation valve of the same diameter as the hole is welded to the iron plate's hole. By opening the isolation valve, the iron plate's central hole is aligned with the leakage point, allowing the leakage medium to flow out through the hole and the isolation valve. If the fit surface is poor, rubber or asbestos pads can be placed on the fit surface. After welding the iron plate around the valve body and closing the isolation valve, a good sealing effect can be achieved.

These methods provide effective solutions for addressing external leakage in power plant high-pressure butterfly valves, ensuring continued safe and efficient operation of industrial systems.