The force acting on the cylinder during operation is very complicated. In addition to bearing static loads such as the pressure difference between the gas inside and outside the cylinder and the weight of various components installed in it, it also bears the reaction force to the static part when steam flows out of the stator and the force to the cylinder under the cold and hot conditions of various connecting pipes. Under the interaction of these forces, the cylinder is prone to plastic deformation and leakage.
The cylinder load increases or decreases too fast, especially when the engine starts, stops and the working conditions change rapidly, the temperature of the cylinder changes greatly, the heating mode of the cylinder is incorrect, and the insulation layer is opened too early when the engine stops and overhauls, resulting in large thermal stress and deformation of the cylinder and flange.
The cylinder produces stress during machining or after repair welding, but it is not tempered to eliminate it, which leads to large residual stress in the cylinder and operation deformation.
In the process of installation or maintenance, due to the maintenance process and technical reasons, the expansion gap of the inner cylinder, cylinder diaphragm, diaphragm sleeve and steam sleeve is not suitable, or the expansion gap of the lug pressure plate is not suitable, which causes the huge expansion force to deform the cylinder after operation.
The used cylinder sealant has poor quality, too many impurities or the wrong model; If there are hard impurity particles in the cylinder sealant, it will make it difficult to closely combine the sealing surfaces.
Insufficient tightness of cylinder bolts or unqualified bolt materials. The tightness of cylinder joint surface is mainly realized by the tightness of bolts. Thermal stress and high temperature generated when the unit starts or stops or increases or decreases the load will cause stress relaxation of bolts. If the stress is insufficient, the pre-tightening force of the bolt will gradually decrease. If the bolt material of the cylinder is not good, under the action of thermal stress and cylinder expansion force for a long time, the bolt will be stretched, plastically deformed or broken, resulting in insufficient sealing and cylinder leakage.
The tightening sequence of cylinder bolts is incorrect. Generally, cylinder bolts are tightened from the middle to both sides at the same time, that is, from the place with large vertical curvature or large stress and deformation, the gap in the place with large deformation will be transferred to the free ends before and after the cylinder, and the rear gap will gradually disappear. If it is tightened from both sides to the middle, the gap will be concentrated in the middle, and the joint surface of the cylinder will form an arch gap, resulting in steam leakage.
cause
Leakage inside and outside the cylinder is generally caused by eccentric installation of the piston rod, insufficient supply of lubricating oil, wear or damage of the sealing ring and sealing ring, impurities in the cylinder, scars on the piston rod and other reasons. Therefore, when there is leakage inside and outside the cylinder, the center of the piston rod should be readjusted to ensure the coaxiality of the piston rod and the cylinder. Always check whether the oil mist injector works reliably to ensure good lubrication of the actuator; When the sealing ring and sealing ring are worn or damaged, they must be replaced in time; If there are impurities in the cylinder, they should be removed in time; When the piston rod has scars, replace it with a new one.
The output force of the cylinder is insufficient and the action is unstable, which is generally caused by the piston or piston rod being stuck, poor lubrication, insufficient gas supply, or condensed water and impurities in the cylinder. In this regard, the center of the piston rod should be adjusted; Check whether the oil mist device works reliably; Whether the gas supply pipeline is blocked. When there are condensed water and impurities in the cylinder, they should be removed in time.
The poor cushioning effect of cylinder is generally caused by the wear of cushioning sealing ring or the damage of adjusting screw. At this time, the sealing ring and adjusting screw should be replaced.
The damage of cylinder piston rod and cylinder head is usually caused by eccentric installation of piston rod or failure of buffer mechanism. In this regard, the central position of the piston rod should be adjusted; Replace the buffer sealing ring or adjusting screw.
solution
1. The joint surface of the cylinder with large deformation or serious steam leakage should be polished and leveled.
If the deformation of the upper cylinder joint surface is less than 0.05mm, the upper cylinder joint surface shall be painted with red lead or covered with blue paper, and the lower cylinder shall be scraped according to the trace. If the joint surface of the upper cylinder is deformed greatly, apply red lead on the upper cylinder, grind out traces with a large flat ruler, and smooth the upper cylinder. Or adopt the method of mechanical processing to level the joint surface of the upper cylinder, and then grind and scrape the joint surface of the lower cylinder based on the upper cylinder. There are usually two methods to grind and scrape the cylinder joint surface:
(1) is a bolt with loose joint surface. Gently push the upper cylinder back and forth with a jack, and grind and scrape it according to the red lead on the joint surface of the lower cylinder. This method is suitable for high-pressure cylinders with strong structural rigidity.
⑵ It is a bolt with tight joint surface. According to the tightness of the joint surface checked by the feeler gauge, measure the value and the marks pressed out, and scrape off the joint surface. This method can eliminate the influence of vertical circular arc of cylinder on clearance.
2. Adopt suitable cylinder sealing material.
Because there is no unified national standard and industry standard for steam turbine cylinder sealant, the raw materials and formulas are also different, and the product quality is uneven; When choosing sealant for steam turbine cylinder, we should choose a regular manufacturer with good reputation in the industry and guaranteed product quality to ensure the rigor of cylinder after overhaul.
3. The method of local repair welding
Because the joint surface of the cylinder is washed or corroded by steam, a suitable covered electrode is selected to polish the joint surface, and the trace is polished with a flat plate or a flat ruler, so that the weld and the joint surface are in the same plane. When the joint surface of the cylinder is deformed greatly or the steam leakage is serious, repair weld one or two sealing strips with a width of 10-20 mm to eliminate the gap of the joint surface of the lower cylinder, then measure or buckle the cylinder with a level, and polish and scrape it with red lead until the gap is eliminated. The process of this operation is also very simple. Before welding, preheat the cylinder to 150℃, and then retreat or skip welding at room temperature. Austenite covered electrode, such as A407 and A4 12, is selected, and after welding, it is covered with asbestos cloth for thermal insulation and slow cooling. After cooling to room temperature, grind and scrape.
4. Coating or spraying of cylinder joint surface
When the cylinder joint surface leaks steam in a large area and the gap is about 0.50mm, coating technology can be adopted to reduce the grinding and scraping workload. With the cylinder as anode and the coating tool as cathode, the electrolyte is repeatedly brushed on the joint surface of the cylinder. The thickness of the coating depends on the gap between the joint surfaces of the roller, and the type of the coating depends on the material of the roller and the scraping process. Spraying is a method that metal powder is heated by a high-temperature flame spray gun to melt or reach a plastic state, and then sprayed on the surface of the treated cylinder to form a coating with required properties. Its characteristics are simple equipment, convenient operation and firm coating. After spraying, the cylinder temperature is only 70℃-80℃, which will not deform the cylinder and can obtain a heat-resistant, wear-resistant and corrosion-resistant coating. Note that before painting and spraying, the cylinder surface should be polished, degreased and roughened, and after painting and spraying, it should be scraped to ensure the tightness of the joint surface.
5. Method of joint surface filling
If there is little leakage in the local gap of the joint surface, the hardness of the joint surface can be reduced by heat treatment with 80- 100 mesh copper mesh, then cut into appropriate shapes, spread on the steam leakage part of the joint surface, and then matched with cylinder sealant. If there is a big gap between the joint surfaces and the leakage is serious, a groove with a width of 50mm and a depth of 5mm can be opened on the upper and lower joint surfaces, and an IGr 18Ni9Ti tooth pad is embedded in the middle. Generally, the thickness of the toothed pad is about 0.05-0.08 mm greater than the depth of the groove, which can be adjusted by stainless steel gaskets with the same shape.
6. Method of controlling bolt stress
If the deformation of cylinder joint surface is small and uniform, new bolts can be replaced at the gap, or the pre-tightening force of bolts can be appropriately increased. Tighten the bolts from the middle to both sides at the same time, that is, from the place with large vertical curvature or large stress and deformation. Theoretically, the formula d/L≤A can be used to calculate the pre-tightening force of control bolts, but the calculation data and measurement methods are still under study and have not been popularized, and most of them are determined according to experience within the allowable large stress range of bolts.
7. Polymer material method adopted in the new period
With the further development of technology, polymer composites have been successfully applied to the maintenance of gas cylinders. Compared with the traditional method, the polymer composite material has excellent temperature resistance, good pressure resistance, better sealing performance, and good plasticity, and will not be solidified when heated, and the sealing film will not be destroyed, thus ensuring the sealing of the sealing surface of machine parts; In addition, it is easy to remove, and the used sealing surface can be easily wiped off with anhydrous ethanol or acetone without adhering to the sealing surface; Because of its excellent performance, it is gradually favored by more and more cylinder enterprises.