Application of Pressure Seal Technique in Leakage Treatment of Power Plant Valve

Abstract: In this paper, the types and causes of valve leakage in power plants are summarized and analyzed. According to the different leakage locations, pressure and the structural characteristics of valve universal parts, the application of pressure plugging technology to the on-line plugging of valve universal parts method. Keywords: power plant valve; pressure plugging; operation method 0 Introduction Power plant valves are used to change the pipeline access section in order to achieve closure, open, or regulate the flow of the pipeline system and other media medium parameters in order to achieve the normal operation of the pipeline system s installation. The leakage of the valve not only causes the loss of working fluid, but also poses a potential hazard to the surrounding equipment and personnel, affecting the safety and economic operation of the generator set. The use of pressure plugging technology to control the leakage of the valve, is aimed at different parts of the leaks, pressure and the general characteristics of the valve parts to take appropriate technical measures to implement online plugging the valve, changing only the shutdown or cut off Medium to repair the valve to eliminate leakage repair methods to ensure the safe and stable operation of the unit. 1 valve common parts of the type of external leakage and analysis of reasons 1.1 packing leakage valve stem and valve cover seal between the packing structure. Valve in use, the stem has by its axis of rotation and in the axial direction of the two movements up and down the form of movement. With the increase in the number of valve switch, the relative movement of the number also increases, so that filler wear increased, with the filler due to the use of time is too long, the loss of elasticity of aging, high temperature coke shrinkage failure, the filler contact pressure Tight gradually weakened, then the pressure medium along the gap between the filler and the valve stem leakage to the outside, a long time the leak will blow some of the filler or the stem flushing out of the trench, so that leakage further expanded. 1.2 bonnet or flange leakage valve cover or flange seal is achieved by tightening the bolt compression gasket to achieve sealing. Pre-tightening bolts, the flange elastic or plastic deformation, through the gasket filled with small irregularities on the flange surface, to achieve adequate pressure than the seal, to prevent the sealed fluid medium interface leakage. Leakage caused by the following reasons: 1, the bolt heated elongation, resulting in the bolt pre-tightening is not enough; and fastening bolts, the tightening uneven, inconsistent gap surface, the formation of mouth and leakage. 2, Gasket hardness higher than the flange, aging failure, mechanical vibration and so will cause gasket seal with the surface of the joint lax strict leak. 2.2.3 contact surface groove, cut lines and other defects, as well as medium corrosion, leakage and leakage. 2.2.4 Center did not find a good assembly, resulting in partial installation of gaskets, so that the local over-force, over the gasket design limits, resulting in partial pressure than the lack of sealing, and the occurrence of leakage. 1.3 leakage outside the valve body is mainly due to the valve manufacturing process caused by casting or forging defects, such as trachoma, porosity, cracks, etc., and erosion of the fluid body fluid erosion of the body, such as power plants are often used for ash system, Drainage slag system of the valve. 2 pressure sealing principle and the choice of sealant Seal with pressure is the use of high-pressure injection gun pressure is greater than the media leak pressure, the sealant is injected into the special fixture and the leakage surface of the seal formed by the outer cavity , And in a short period of time by the plastic body into an elastomer to form a flexible new sealing structure, instead of the sealing filler has failed, to plug the leakage of the pores of each channel, blocking the media leakage, and to maintain a certain working seal Specific pressure, to re-seal. Sealant selection is mainly based on the chemical properties of the leakage medium and temperature requirements of the sealant does not contaminate the sealed fluid medium is not dissolved by the medium or chemical reaction with itself does not corrode the stem and filler wall surface at the use temperature Contact with the medium should maintain its flexibility and sealing performance unchanged, and has good anti-aging properties, and should have good self-lubricating properties, plugging to ensure that the valve opening and closing functions. 3 pressure sealing technology common parts in the valve common leakage treatment application According to the actual situation of the power plant production site, you can use to replace the valve packing, flange gasket replacement, welding holes to replace or replace the valve method to eliminate leakage. For the production of online valves in operation, the use of injection-type pressure plugging technology to carry out pressure on the valve plugging, valve leakage is the more direct and effective management of a technical means. It should be specially pointed out that: Each injection of sealant should be carried out evenly and smoothly, and to fully fill the seal cavity in every corner. After each injection of sealant should close the injection valve, and then unload the pressure of the injection gun, the entire pressure plugging operation is completed, do not rush to remove the injection valve to plug, do not immediately valve Switch operation, until the sealant fully cured before it can be put into normal use. 3.1 Pressure Seal Technology in the elimination of valve packing leakage in the application of injection hole from the sealant into the stuffing box, the use of the valve packing box to form a sealed chamber, with the filler to establish the same role of the new seal structure. This dynamic pressure conditions under the use of plugging technology, will be able to eliminate the valve packing leakage. Here are two commonly used methods. 3.1.1 packing box wall thicker or larger diameter valve directly on the outer wall of the valve stuffing box in the appropriate position (generally select the stuffing box in the middle), with Φ8.4mm drill hole, leaving about 1--3mm left the drill . Tapping tap with M10 to form a shot hole. Screw M10's special injection valve in the "on" position. In order to prevent drilling high temperature, high pressure, toxic or corrosive medium spray wounding, before drilling a hole, first make a hole bored Φ5mm baffle through the baffle holes with Φ3mm long rod Drill bit through the injection valve to the remaining valve packing box wall penetration. If the valve stuffing box media pressure is low, you can also use the long drill Φ3mm directly through the stuffing box wall drilling. Drill through the hole and exit the drill bit, the injection valve screwed to the "closed" position. Loosen the packing gland nut to allow the gland to move up and increase the packing box space. Access to high-pressure injection gun injection sealant, sealant filled in the sealed chamber and fully cured, with the injection of sealant, stem and gland gap leakage gradually reduced until the elimination of leakage. Close the injection valve, remove the injection gun, screwed into the plug seal hole, tighten the stuffing box gland nut plugging ends. 3.1.2 stuffing box wall thinner valve with special auxiliary fixture for dynamic sealing. Auxiliary fixture to compensate for the lack of valve packing box wall thickness, increase its wall thickness and strength connected to high-pressure injection gun. Auxiliary fixture is generally difficult to get the ideal local fit surface, under conditions permitting, you can properly trim the outer wall of the valve stuffing box, so that the partial fit with the auxiliary fixture better fit. If the shape of the stuffing box of the leak valve is complicated or the condition of dressing is not allowed, a piece of asbestos rubber or rubber plate can be padded on the bottom of the auxiliary fixture, and the fixture bolt can be tightened so that the rubber plate can well fill the auxiliary fixture and the outer wall of the stuffing box Surface of the gap. The next operation is the same as 3.1.1. 3.2 Pressure Seal Technology in the Elimination of Valve Flange Leakage Treatment 3.2.1 Gap is small, uniform gap, low leakage medium pressure flange bolts on the demolition of the bolt directly to install a dedicated injection connector to ensure leakage There are more than two injection holes near the point. The method is as follows: Loosen a nut when installing the injector connector, install the injector connector, tighten the nut, and then install another injector connector. Can not at the same time the required nut all loose, causing the bolt preload is not enough, so that gasket gasket pressure drop, resulting in increased leakage, or even leakage of media will be blown away gasket phenomenon. G-clamps can be used to maintain a balanced seal pressure ratio if the amount of leakage is large. After installing the bolting agent, with a small hammer to gradually insert the copper wire or packing into the flange gap, both ends of the lap length of 50mm or more; can also be used with smaller cross-section of the copper wire or packing method Lan pay the gap on the lap a few laps, smashed dense. At the same time the outer edge of the flange out of the lip, so that copper wire or packing fixed in the flange gap, thus forming a new sealed chamber. Install the injection valve, connect the high-pressure injection gun, inject sealant from the screw hole farthest from the leakage point, and gradually approach the leakage point until the leakage is eliminated. 3.2.2 large gap, high leakage medium flange When the leakage flange gap larger leakage medium pressure is high, in order to increase the safety and reliability of the operation, should be designed and processed high pressure, the overall performance of the convex seal Shape fixture. Fixture injection hole should be located in the middle of the two flange bolts, and to ensure that there is injection hole near the leak, do not make the injection hole aligned with the bolt, so as not to increase the resistance of the sealant. Install the fill valve and leave the fill valve open. Operators should stand on the vents, if the leakage pressure or flow larger, the compressed air can be used to purge the leakage of media to the operator to avoid or less contact with the media leaks. After the clamp bolt is tightened, the maximum gap between the clamp and the flange surface should not exceed 0.5mm. The direction of the injection should be followed from the opposite point of the leakage point, and the end point should be near the leakage point until the leakage is eliminated. 3.2.3 large diameter, low pressure medium leakage flange with local pressure plugging method, that is fixed with the fixture as a whole, and from the local injection of sealant. This method is mainly taken into account because of the large flange diameter, the dynamic leak after the elimination of points if there are other new leaks are also easy to handle. The width of the jig shall be the outer circumference of the cover flange. The length of the jig should cover at least the small space between the two bolts on the two adjacent sides of the leakage point, and each small sector has more than two injection holes. Relying on the bolt on both sides of the leak point baffle, the baffle plugged into the bolt, the upper part of the fixture groove bolted, the lower part has reached the flange bosses and shims, the width equal to the flange to pay the gap To prevent injected sealant from overflowing from the local seal chamber. Install the fixture, all wrapped flange clearance, tighten the fixture bolts, forming a complete sealed cavity. According to the flange size to determine the number of injection fittings installed, adjust the gap, the connection of high pressure injection gun injection agent from the injection hole sealing agent dynamic sealing operations until the elimination of leakage. 3.2.4 medium leakage pressure is low, the leakage of a faint flange to produce a width equal to the flange to pay the gap arc plate, the middle of open injection hole, the soft packing filled leak holes, quickly press plate, tighten The plunger, through the plunger to the leak point injection of sealant, which can eliminate leakage. 3.2.5 Rugged sealing surface flange, tongue and groove sealing surface Flange in the convex sealing surface or tongue and groove sealing surface flange near the leak point to open the injection hole to the groove, and then injected into the sealant to eliminate leakage . The key to this method is that the drilled hole must be aligned with the leak in the groove. 3.3 pressure plugging technology in the elimination of valve body leakage 3.3.1 medium pressure is low, the amount of leakage is small For medium pressure is low, the amount of leakage of small trachoma, pores, confirm the valve body around the leak has not been obvious Of the corrosion thinning, you can first polish the metal luster around the leak, and then use the right size taper pins alignment leaks, the appropriate force slowly and smoothly into the leakage significantly reduced or temporary closure. The use of adhesive curing speed and sealing tape has a certain strength and toughness, when heated by a certain self-Zhan and curing properties. In a timely manner around the pin coated with adhesive, winding a certain width of the sealing tape, and finally wound into a spindle shape to increase its strength, the leakage point is wrapped around the seal in the center, to form a new seal structure to achieve the purpose of leakage. 3.3.2 Medium pressure is high, the amount of leakage Large leaks allow the premise, with a larger than twice the leak point of the nut, the leakage medium from the nut outflow, the nut welded to the valve body, Matched with a nut with a plug, the plug thread and the top are wound on the raw material belt screwed into the nut, to prevent the purpose of preventing leakage. For the leakage of a larger valve body, available drainage welding method. First, open a hole in the middle of a piece of iron, a hole with a diameter of the valve is welded to the round hole in the iron plate, the iron plate center hole aligned with the valve body leak and fit, if Fitting surface is not good, can be placed on the surface of the rubber pad or asbestos pad. Open the isolation valve, the leakage of media in a timely manner to discharge, the seal cavity pressure equal to zero. Then around the iron plate and the body welded, and then close the isolation valve can achieve the purpose of re-sealing. 4 Conclusion Pressure plugging leakage in the valve in the treatment of the use of not only do not need to shut down or isolate the system, the system does not need to relieve pressure, but also to ensure that the valve opening and closing functions can reduce the number of unplanned downtime , Save a lot of energy, reducing the economic losses of enterprises. At the same time pressure and sealing is a nature of emergency repair work, poor working conditions, uncertainties in the operation and more risky, pre-job risk analysis must be full, safety measures must be put in place. The treatment of the leakage point is a kind of temporary measure, which has some limitations and timeliness. Under the condition, it is necessary to overhaul the leakage part. References: 〔1〕 Yang Yuanquan. Valve Design Manual 〔M〕. Beijing: Mechanical Industry Press, 1992. 〔2〕 Hu Yi 沩. Dynamic Sealing Technology - Leakage and plugging 〔M〕. Beijing: National Defense Industry Press, 1998 . 〔3〕 Wang Xun Kui. The use of valves and maintenance technology 〔M〕. Wuhan: Hubei Science and Technology Press, 1985. 〔4〕 Shanxi Electric Power Industry Bureau. Turbine equipment overhaul 〔M〕. Beijing: China Electric Power Press, 1997. About the author: Lin Bo (1974-), male, thermal assistant engineer, engaged in power plant thermal equipment overhaul and technical management.