The same general techniques used to install flanged carbon steel piping systems can be applied to plastic lined piping systems.
When assembling flange connections, always use a full compliment of clean, new high strength A197-B7 bolting. If using stainless steel bolting, the bolts should be A193 Gr. B8M, class 2A and nuts should be A1193 Gr. B8M Class 2B. If other bolting materials are used, the end user must ensure that the new bolting material strength properties exceed the calculated bolt stress values to be generated in making the piping connection.
- Always use flat washers on both sides of the connection.
- Tighten the flange bolts with a calibrated torque wrench to the specified bolt torques. NOTE: If using anti-seize compounds, the torque values will be different.
- Tighten the flange bolts with a torque wrench using a crisscross pattern that alternately tightens the bolts located 180° apart.
- Using this pattern, tighten the bolts in 20% increments of the final bolt torque until 80% of the final bolt torque has been achieved.
- For tightening to the final torque values, tighten the bolts sequentially clockwise once around the flange. This will help insure that the bolts are evenly stressed.
- Care should be taken to prevent over-torqueing, which will cause damage to the sealing surfaces.
NOTE: when bolting together dissimilar materials, always tighten to the lowest recommended torque of the components in the joint. Using higher torques may cause excessive deformation of the ‘softer’ material in the joint. Install a 1/2” thick spacer between plastic lined pipe or fittings and other plastic lined components, particularly valves, if the diameters of the raised faces are different. Belleville washers are not recommended for use with PTFE lined products.
Re-torqueing
A re-torque should be applied a minimum of 24 hours after the initial torque or after the first thermal cycle. This allows for seating of the plastic and for relaxation of the bolts. Torqueing should only be done on the system in the ambient, cooled state, never while the process is at elevated temperature or excessive force could be applied to the plastic faces. Never disassemble a flange joint in a hot system. Wait until the system has cooled to ambient temperature.
Hydrotesting
Normally, after initial torque and re-torque, a hydrotest should be performed following ANSI requirements. If a flange leaks, first check the torque values and then tighten in 10% increments over the specified bolt torques until sealed. However, if 150% of the specified torque value is reached and the flange joint still leaks, stop and disassemble the flange joint. Something else is likely wrong such as a scratched plastic face. Only after the hydrotest has been successfully completed and any leaks corrected, can the pipeline be signed off and commissioned.
Annual Re-torqueing
Re-torqueing should be done at least annually thereafter, especially if the process line experiences elevated temperatures or thermal cycling. Torqueing should only be done on the system in the ambient, cooled state and never while the process is at an elevated temperature, excessive force will likely be applied to the plastic faces.
NOTE: the maximum recommended torque values are suggested for lined systems operating at or near the maximum recommended pressures and temperatures. Systems operating under less severe conditions can in general experience leak-free performance using lower torque values. Additionally, any time gaskets or spring type washers are used, we suggest using the minimum recommended torque value and that the torque be increased only to obtain satisfactory sealing. For systems that will require frequent disassembly, we suggest using the minimum recommended torque value initially to avoid distortion of the plastic face.