**1. Scraping the Cylinder Joint Surface for Large Deformations or Leaks**
If the cylinder joint surface is deformed by more than 0.05 mm, it should be used as a reference. The upper cylinder is combined with the next one, and red lead or blue paper is applied to identify the contact points. Then, the lower cylinder is scraped according to the markings. If the deformation is significant, red lead can be applied to the upper cylinder, and a straightedge can be used to remove high spots and flatten the surface. Alternatively, mechanical processing can be used to level the upper cylinder, and then the lower cylinder can be scraped using the upper one as a guide.
There are two common methods for scraping the joint surface:
(1) When bolts are not tightly fastened, a jack can be used to slightly move the upper and lower cylinders forward and backward, and the surface is scraped based on the red lead marks from the lower cylinder. This method is ideal for high-pressure cylinders with high rigidity.
(2) For tight joints, the feeler gauge is used to check the tightness. The gap size and pressure marks are measured, and the joint surface is repaired accordingly. This approach helps eliminate the influence of cylinder curvature on clearance.
**2. Use of Appropriate Cylinder Seal Materials**
Since there is no unified national or industry standard for turbine sealants, the materials and formulations vary widely, leading to inconsistent quality. When selecting sealants, it's essential to choose reputable manufacturers known for reliable product quality. This ensures proper sealing after maintenance.
**3. Local Welding Method**
When the cylinder joint surface is severely damaged due to steam erosion or grooves, an appropriate electrode should be selected. The weld bead must be leveled and aligned with the surrounding surface. If the deformation or leakage is severe, small gaps (about 10–20 mm wide) can be welded onto the lower cylinder. After welding, a straightedge or measuring tool is used to check the flatness. Red lead is applied, and the process is repeated until the gap is eliminated. The procedure is straightforward: preheat the cylinder to 150°C before welding, use sub-arc or back welding at room temperature, select austenitic electrodes like A407 or A412, cover with asbestos cloth for slow cooling, and finally polish and scrape the surface.
**4. Coating or Spraying the Cylinder Joint Surface**
When there is a large leakage area or a gap of about 0.5 mm, coating or spraying can reduce the need for extensive scraping. In electroplating, the cylinder acts as the anode, and the coating material serves as the cathode. Electrolyte is applied repeatedly to the joint surface, and the coating thickness is adjusted based on the gap size. The type of coating depends on the cylinder material and the scraping process.
Spraying involves using a high-temperature flame gun to melt metal powder and spray it onto the treated surface. This method is simple, efficient, and produces strong coatings without causing thermal deformation. The cylinder temperature remains around 70–80°C, making it safe for the structure. It can create heat-resistant, wear-resistant, and corrosion-resistant layers. Before applying any coating, the surface must be cleaned, degreased, and roughened. After coating, the surface should be scraped to ensure a tight fit.
**5. Bonding Method**
For small leaks, copper mesh (80–100 mesh) can be heated and softened, then cut to fit the leak area and coated with sealant. For larger gaps, grooves (50 mm deep, 5 mm wide) can be cut into both upper and lower surfaces. A toothed mat made of IGr18Ni9Ti is placed in the middle, with a thickness 0.05–0.08 mm greater than the groove depth. A stainless steel gasket can also be used for adjustment.
**6. Controlling Bolt Stress**
If the deformation caused by bolt stress is minimal and uniform, new bolts can be installed, or the preload can be increased. Bolts should be tightened gradually from the center outward, starting from the highest point of the vertical arc or the area with the most deformation. While the theoretical formula d/L ≤ A exists for calculating pre-tightening force, it is still under study and not widely used. Most professionals rely on experience based on the maximum allowable stress of the bolts.
**7. Polymer Materials in Modern Applications**
With technological advancements, polymer composite materials are increasingly used in cylinder maintenance. Compared to traditional methods, they offer excellent heat resistance, pressure resistance, and superior sealing properties. They remain flexible even when heated and do not cure, ensuring long-term sealing performance. Additionally, they are easy to remove—just wipe with anhydrous ethanol or acetone, leaving no residue. Due to their outstanding performance, more companies are adopting them for cylinder repairs.
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