Here’s a breakdown of the process for fitting a hydraulically tensioned bolt suitable for main propulsion shaft flanges:
Preparation:
- Lockout/Tagout: Implement proper lockout/tagout procedures to isolate the shaft and ensure safety before starting the fitting process.
- Cleaning: Thoroughly clean the flange surfaces and the threads of the bolt to remove any dirt, oil, or debris that could affect the tightening process or compromise the joint integrity.
- Lubrication: Apply a thin coat of a lubricant specified by the manufacturer to the threads of the bolt. This reduces friction during tightening and ensures proper bolt load is achieved.
Bolt Installation:
- Screw the Bolt In: Manually screw the hydraulically tensioned bolt into the threaded hole in the flange until finger tight. Ensure the bolt engages with the threads properly and isn’t cross-threaded.
Hydraulic Tensioning Process:
- Hydraulic Nut and Pump: The hydraulically tensioned bolt will have a special nut designed to work with a hydraulic tensioning pump. Attach the hydraulic nut to the bolt on the flange.
- Pressure Gauge and Calibration: Connect the hydraulic pump to the hydraulic nut via a high-pressure hose. The pump will have a pressure gauge to monitor the applied tension. Ensure the pressure gauge is calibrated to ensure accurate readings.
- Tensioning Procedure: Follow the manufacturer’s instructions for the specific hydraulic tensioning system. This will typically involve slowly increasing the hydraulic pressure applied to the nut.
- Target Load: As the pressure increases, the bolt stretches, applying a specific tension (load) to the flange joint. The target load will be specified by the manufacturer based on the bolt size, material, and the flange design. This target load is typically achieved at a specific pressure value on the gauge.
- Holding the Load: Once the target pressure/load is reached, the hydraulic pump will typically have a mechanism to hold the pressure, maintaining the tension on the bolt.
Verification and Completion:
- Verification of Load: After holding the load for a specified time (as per manufacturer’s instructions), some systems might require a verification step to ensure the load hasn’t bled off. This might involve checking the pressure gauge again or using a separate load verification tool.
- Locking the Nut (Optional): Depending on the specific design, some hydraulic tensioning systems might incorporate a mechanical locking mechanism on the nut to prevent relaxation of the tension over time.
- Repeat for All Bolts: Following the same procedure, tighten all the remaining hydraulically tensioned bolts around the flange to achieve the specified target load.
Additional Considerations:
- Tightening Sequence: The manufacturer’s instructions might specify a specific tightening sequence for the bolts around the flange to ensure even load distribution.
- Torque Verification (Optional): While hydraulic tensioning achieves the desired load on the bolt, in some cases, a final torque verification check using a calibrated torque wrench might be performed for additional assurance.
- Safety Precautions: Hydraulic tensioning systems operate at high pressures. Always wear appropriate personal protective equipment (PPE) and follow the manufacturer’s safety instructions for the specific equipment being used.
By following these steps and adhering to the manufacturer’s recommendations, you can ensure the proper fitting and tensioning of hydraulically tensioned bolts for critical applications like main propulsion shaft flanges. This ensures a secure and reliable connection for optimal performance and safety.