Storage tanks are critical equipment used for storing liquids, gases, and other substances. Over time, the roof and bottom of the storage tank are susceptible to corrosion, wear, and operational issues. To ensure the storage tank's safety and stability, it is essential to promptly identify and repair these defects. This article provides an in-depth overview of common corrosion problems in storage tank roofs and bottoms and outlines repair and replacement methods to ensure the storage tank continues to operate effectively.
Storage Tank Roof Corrosion Repair and Replacement
Corrosion of the storage tank roof typically manifests as minor perforations or extensive corrosion, which can affect the roof's sealing and structural integrity. The repair method depends on the severity of the corrosion.
1. Repair for Mild Corrosion and Perforations
For minor corrosion or small perforations, repair can be done without the need for hot work, using the following methods:
Adhesive Repair: Apply an elastic polyurethane adhesive or other bonding agents to seal and repair the corroded or perforated area. This method is simple and effective, ideal for environments where no open flames are allowed, and it quickly restores the roof's sealing integrity.
2. Repair for Severe Corrosion
For more severe corrosion with multiple perforations, more thorough repairs are necessary:
Welding Repair: Perform welding on the perforated areas or replace sections of the roof's steel plate. Welding can effectively restore the structural integrity of the roof and prevent further corrosion.
3. Roof Deformation Repair
In cases where the roof has deformed due to design defects, improper use, or operational mistakes, the inflation pressurization method is an effective repair technique. This method can restore the original shape of the roof but requires strict adherence to safety procedures:
Safety Protection: All workers must wear appropriate protective gear and remain a safe distance from the storage tank during operation.
Crack Treatment: If there are cracks with significant leakage at deformed areas, work must be stopped immediately, and welding repairs should be done before reinflating.
Inspection and Monitoring: During the inflation process, special attention should be given to weak weld joints and the lower corner welds of the tank wall. Any abnormalities should halt operations.
Weather Considerations: Choose favorable weather for restoration and avoid operations during sudden temperature drops. After inflation, ensure ventilation holes are opened promptly to prevent the roof from deflating again.
4. Replacement When Unrepairable
When corrosion or deformation is so severe that repairs cannot restore the roof to its original functionality, a complete replacement is required. This involves removing the original roof and installing a new one based on specific requirements.
5. Changing Truss Roof to Dome Roof
In some storage tank structures where the original design is a truss roof, severe distortion or deformation may prevent continued use. In this case, converting the truss roof to a dome roof can be considered. The modification process typically involves:
Removing the original truss roof and cleaning the existing structure.
Repairing the tank wall by cutting out unrepairable sections and performing welding to install new wall panels.
Installing edge angle steel and welding to meet the standards of a newly constructed storage tank.
Restoring original accessories and adding protective handrails and platforms, followed by applying anti-corrosion coatings.
Storage Tank Bottom Corrosion Repair and Replacement
The bottom of the storage tank is one of the most vulnerable areas for corrosion, typically showing signs such as pitting, corrosion holes, porosity, and cracks. Bottom corrosion affects the storage tank's sealing and can lead to leaks or other safety hazards. The repair method depends on the corrosion extent.
1. Repair for Mild Corrosion
For minor mechanical perforations and small areas of corrosion, the typical repair method is:
Welding Repair: Perform welding directly on the defect to restore the bottom's sealing and strength.
2. Repair for Larger Defects
For extensive corrosion or larger holes, more comprehensive repairs are required:
Cut and Replace Bottom Plate: For widespread corrosion and larger holes, the damaged area should be cut out, and a new bottom plate should be installed.
Crack Repair: For cracks in welds, stop-crack holes should be drilled at both ends, the defect removed, and re-welded. Welding typically requires two passes to ensure quality. If the crack length exceeds 100mm, a cover plate should be used, with a minimum cover length of 2 inches.
3. Repair for Dents Caused by Foundation Settling
If the storage tank bottom has sunk due to local foundation settling, the following methods can be used:
Filling Repair: Cut out the defect area's welds, fill with asphalt sand, compact it, and then re-weld. For small dents, a round hole may be cut in the defective area, the foundation filled, and welding restored.
Large Dents: For large dents that cannot be repaired, the bottom plate may need partial replacement.
4. Replacement When Corrosion is Severe
When corrosion has caused the remaining thickness to fall below acceptable limits, or if large pits, perforations, or other severe defects are present, the bottom plate must be replaced. The replacement range depends on the specific situation:
Replace only the central plate.
Replace both the central and edge plates.
For large storage tanks, edge plates are replaced individually, cutting out the original edge plate and installing new ones. The size of the new edge plate should match the original as closely as possible. For smaller storage tanks, the entire bottom plate is shifted, the old bottom plate cut away, and the new one installed, followed by restoring the tank to its original position.
5. Floating Roof Storage Tank Bottom Replacement
For large floating roof storage tanks (or internal floating roof tanks), special attention is required when replacing the bottom plate:
Before cutting the bottom plate, suspend the floating roof (or internal floating roof) inside the tank to prevent it from sinking or interfering with the operation.
Conclusion
The roof and bottom of a storage tank are critical components in its structural integrity. Corrosion, deformation, and other issues can significantly affect the storage tank's safety and long-term operation. Selecting the appropriate repair or replacement method based on the type and extent of corrosion is vital. Whether it's minor corrosion repairs, welding for larger defects, or replacing the roof or bottom, strict safety protocols must be followed to ensure worker safety and maintain long-term repair effectiveness. Through regular inspections, timely repairs, and necessary replacements, the service life of storage tanks can be extended, ensuring their safe and stable operation.
