Valve leakage commonly occurs at three critical positions: packing glands, flange connections, and valve bodies. Prolonged untreated leakage causes severe erosion on valve stems and flange sealing surfaces, ultimately leading to permanent valve scrapping. Additionally, the loss of process media increases plant energy consumption, operational costs, and reduces overall economic efficiency.
Leakage becomes extremely hazardous when the conveyed media is toxic, flammable, explosive, or corrosive. Uncontrolled external leakage may trigger poisoning, fire, and explosion accidents, accelerate equipment corrosion, shorten service life, and cause environmental pollution. Moreover, valve leakage raises the frequency of unplanned shutdowns and poses severe threats to industrial operational safety.
This article systematically analyzes the common causes of valve external leakage, elaborates on the principles, advantages, and practical implementation methods of in-service leak sealing (live leak sealing), and provides professional maintenance guidelines for power plant valves for industrial reference.
2. Forms and Root Causes of Valve External Leakage
2.1 Packing Gland Leakage
Relative movements including rotational and axial displacement continuously occur between the valve stem and packing during daily operation. With frequent valve switching, coupled with fluctuations in temperature, pressure, and varying medium properties, the packing area ranks as the most leakage-prone part of a valve.
The primary causes include gradual decline of packing contact pressure, material aging, and elasticity degradation. Pressurized media seeps outward through the gaps between the packing and stem. Long-term scouring blows away partial packing and creates grooved scratches on the valve stem, further aggravating leakage severity.
2.2 Flange Connection Leakage
Flange sealing relies on the pre-tightening force of connecting bolts to compress gaskets and form sufficient specific sealing pressure to prevent medium outflow. Multiple factors contribute to flange leakage:
• Insufficient compression force on sealing gaskets and unqualified flange surface roughness;
• Gasket deformation, mechanical vibration, aging, elasticity loss, and surface cracking;
• Bolt deformation and elongation under long-term operating pressure;
• Human operational errors: misaligned gasket placement, uneven bolt tightening force, and offset flange centerlines resulting in false compression.
Valve body leakage is mainly attributed to inherent manufacturing defects such as sand holes, air holes, and casting cracks generated during casting or forging processes. Besides, long-term medium scouring and cavitation erosion gradually damage the metal body, forming permanent leakage passages.
3. Working Principles and Core Advantages of In-Service Leak Sealing
In-service leak sealing is a non-stop maintenance technology based on the solid sealing mechanism under dynamic liquid medium conditions. Specialized fixtures are installed at leakage points to form an enclosed sealed cavity. High-pressure injection tools inject customized sealant into the cavity until the internal extrusion pressure balances the medium pressure. A new stable sealing structure is established to block leakage gaps and medium outflow channels permanently.
3.2 Core Technical Advantages
Compared with traditional offline maintenance, in-service leak sealing boasts irreplaceable industrial advantages, especially suitable for continuous production systems such as power plants:
1. No Shutdown Required: There is no need to halt unit operation or isolate production pipelines;
2. No Pressure Relief: Maintain the original operating pressure of the entire system without pressure reduction;
3. Cost Saving: Greatly cuts energy consumption and manual maintenance labor costs;
4. Reduce Power Loss: Avoid massive power loss caused by equipment isolation and shutdown;
5. Minimize Economic Losses: Eliminate economic losses triggered by unplanned production downtime.
4. Practical In-Service Sealing Methods for Common Valve Leak Points
For conventional leakage under accessible maintenance conditions, common solutions include valve replacement, packing renewal, gasket replacement, and weld repair. Nevertheless, for valves in continuous operation with non-isolable media pipelines, professional in-service sealing technologies are essential to guarantee stable unit operation. This chapter summarizes mature on-site construction methods combined with power plant application cases.
4.1 Packing Gland Leakage Solutions
Injectant-based in-service sealing is the safest and most reliable technology for packing chamber leakage. With specialized fixtures and hydraulic injection equipment, sealant is injected into the sealed cavity to fill defects rapidly. When the injection pressure exceeds the medium pressure, leakage is forcibly blocked. The sealant transforms from a plastic state to an elastic solid in a short time, forming a durable elastic sealing structure without affecting the original valve switching function.
Industrial sealants are classified into two categories: heat-curing sealants (solid at room temperature, cured under specific high temperatures) andnon-heat-curing sealants (applicable for low, normal, and high-temperature dynamic sealing scenarios).
4.1.1 Direct Drilling Injection Method (Wall Thickness ≥ 8mm)
For packing glands with a wall thickness above 8mm, drill reserved injection holes directly on the gland outer wall. The detailed operation steps are as follows: retain 1-3mm wall thickness after preliminary drilling with an 8.7mm or 10.5mm drill bit; tap M10 or M12 threads and install a dedicated plug valve; penetrate the remaining wall with a 3mm long drill bit, and install a baffle to prevent high-temperature, high-pressure, toxic medium from splashing and causing personal injury. After drilling, close the plug valve and connect a high-pressure injection gun for sealant filling.
Application Case: In June 2003, this technology successfully solved the self-sealing gland leakage of the electric main steam valve of Unit 3 in Panzhihua Iron and Steel Power Plant, avoiding an unnecessary shutdown.
4.1.2 Auxiliary Fixture Sealing Method (Thin-Wall Glands)
For thin-wall packing glands incapable of direct drilling, customized auxiliary fixtures are adopted as external connectors for high-pressure injection guns. Polish the outer wall to ensure tight fitting; pad asbestos rubber sheets at gaps for complex-shaped casings to eliminate clearance. After installation, inject sealant following the standard process. Do not switch the valve arbitrarily until the sealant is fully cured.
Application Case: In November 2002, auxiliary fixtures were used to repair the balance valve flange leakage of the high-pressure heater inlet valve in Panzhihua Iron and Steel Power Plant, achieving one-time sealing success.
4.2 Flange Leakage In-Service Sealing Technology
4.2.1 Copper Wire Encirclement Method
Applicable Conditions: Small uniform flange gaps and low medium pressure. Install at least two injection joints on disassembled bolts without loosening all nuts simultaneously (to prevent gasket blow-off). Embed copper wire matching the gap size into the flange clearance to form a closed sealed cavity. Inject sealant from the position opposite to the leakage point and gradually move toward the leakage source.
Application Case: In June 2003, this method repaired the vertical flange leakage of the low-pressure communicating pipe of Unit 1 in Panzhihua Iron and Steel Power Plant, preventing unplanned shutdown.
4.2.2 Steel Band Encirclement Method
Applicable Conditions: Flange gap ≤ 8mm and medium pressure ≤ 2.5MPa. Adopt 1.5-3.0mm thick and 20-30mm wide steel bands fixed by welding or riveting. Add transition gaskets at joints to form an integral sealed cavity. This method requires high flange coaxiality and has low requirements for gap uniformity.
4.2.3 Convex Flange Fixture Method
Applicable Conditions: Flange gap 8mm or medium pressure 2.5MPa. Customize high-precision integral pressure-resistant flange fixtures with pre-installed plug valves. Operators must stand at the upwind position; keep the fixture gap below 0.5mm after bolt tightening. Inject sealant from the farthest point toward the leakage point until leakage stops. This versatile method is also applicable for pipeline leakage repair and widely used in power plant routine maintenance.
Typical Application Scenarios: Flange leakage of feedwater pump warming drain valves and auxiliary steam deaerator isolation valves in Units 1, 2, and 3 of Panzhihua Iron and Steel Power Plant.
4.3 Valve Body Leakage Repair Methods
Valve body leakage treatment technology is universally applicable to industrial pipelines. Two mainstream mature processes are adopted for different working conditions:
4.3.1 Adhesive Bonding Sealing Method
For low-pressure small-scale sand hole leakage: polish the leakage area to metallic luster, drive taper pins into the leakage points to reduce outflow, and apply high-strength adhesive around the pins to form a solid sealing layer.
For high-pressure large-flow leakage: fix an external jacking tool to compress the leakage points with rivets. Fill gaps with soft metal gaskets, then coat the surface with adhesive and reinforce with glass fiber cloth after rust and oil removal to enhance pressure resistance.
4.3.2 Welding Repair Method
• Low-pressure micro-leakage: Weld a nut larger than the leakage hole on the valve body, and seal it with bolts and rubber gaskets;
• High-pressure heavy leakage: Adopt drainage welding. Weld an isolation valve on a perforated steel plate, fit the steel plate to the leakage point for drainage, and seal the plate by welding before closing the isolation valve;
• High-temperature high-pressure micro-leakage: Weld peripheral gaps first, then connect a customized bypass pipe with a matched valve to cover the leakage point, and cut off the medium flow by closing the bypass valve.
4.4 Universal Wrapping Sealing Method
As an all-purpose solution for complex leakage points, the wrapping method manufactures customized metal boxes to wrap the leakage area and weld them firmly to the valve body. For difficult welding operations, reserve exhaust holes and complete sealing via the drainage welding process. This method features high stability and excellent on-site adaptability.
Application Cases: Successfully applied to the main steam pipeline drain system and high-pressure heater drain pipelines of Panzhihua Iron and Steel Power Plant Units 1, 2, and 3. It ranks as the most widely used and effective maintenance process for daily pipe and valve overhaul.
5. Conclusion & Industry Recommendations
In-service leak sealing delivers remarkable economic benefits for thermal power plants. A single startup-shutdown cycle of a 100MW unit causes direct economic losses of over 300,000 RMB. Reasonable application of live sealing technology effectively reduces unplanned downtime and operational costs. Based on on-site construction experience, four key conclusions are summarized for industrial users:
1. Emergency Temporary Maintenance: In-service sealing serves as an emergency disposal measure with time-limited effectiveness. Complete shutdown overhaul is still required to eliminate hidden dangers fundamentally when production conditions permit.
2. Strict Safety Control: Sealing operations feature harsh working conditions, high labor intensity, and uncertain risks. Comprehensive pre-operation risk assessment and complete safety protection measures are mandatory.
3. High Professional Requirements: This technology demands proficient mechanical knowledge, on-site adaptability, and skilled operation of professional sealing tools. At present, most on-site construction is undertaken by specialized engineering teams.
4. Continuous Technological Improvement: Restricted by material and structural limitations, in-service sealing cannot solve all leakage problems. The technology is still in iterative optimization to expand its applicable working condition range.
6. About Us - Shanghai Xiazhao Valve
Shanghai Xiazhao Valve Co., Ltd. is a professional manufacturer and service provider of industrial valves, focusing on high-performance valves for power, chemical, petroleum, and pipeline industries. We provide one-stop solutions including valve customization, on-site leakage detection, and in-service leak sealing maintenance.
Adhering to strict international manufacturing standards, our products feature high pressure resistance, corrosion resistance, and stable sealing performance. We support customized valves for extreme working conditions and provide global after-sales technical services. For valve selection, technical consultation, and on-site maintenance cooperation, please feel free tocontact Shanghai Xiazhao Valve.
industrial valve, valve leakage solution, in-service leak sealing, live leak repair, power plant valve, flange sealing, packing gland maintenance, valve body repair, high pressure valve sealing
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