Technical Information

Flange Bolt Torque Specs for UNAFLEX® PTFE-lined Piping Products

General techniques utilized to install flanged carbon steel piping systems may also be applied to UNAFLEX® PTFE-lined piping systems.

When assembling flange connections, it is recommended that a full complement of clean, new and high-strength A193-B7 bolting is consistently utilized. When stainless steel bolting is used, consist of A 320/A320M Class 2 B8 (304 SS) or Class 2 B8M (316 SS) with A 194/A194M Grade 8 or 8A Nuts (for 304 SS) or Grade 8M or 8MA (for 316 SS). When other bolting materials are employed, user should ensure new bolting material strength properties exceed the calculated bolt stress values generated in establishing the piping connection. The following practices are strongly recommended:

  • Always utilized flat washers on both sides of the connection
  • Ensure that the flange bolts are tightened with a calibrated torque wrench expressly for the specified bolt torques. Note: For anti-seize compounds, the torque values may vary. Please contact UNAFLEX® for more information
  • Firmly secure the flange bolts with a torque wrench utilizing a “crisscross” pattern that alternately tightens the bolts located 180 degrees apart
  • Employing the above mentioned pattern, tighten the bolts in 20% increments of the final bolt torque until 80% of the final bolt torque has been accomplished
  • To tighten the final torque values, firmly tighten bolts sequentially clockwise one time around the flange. This procedure ensures the bolts have been evenly stressed
  • Extreme caution should be taken to avoid over-torquing which can result in damage to plastic sealing surfaces

NOTE: When bolting dissimilar materials, always tighten to the lowest recommended torque of the components in the joint. Employing higher torques may cause excessive deformation of the “softer” material contained in the joint. Position a ½” thick spacer between UNAFLEX® PTFE-lined pipe or fittings and other plastic-lined components, particularly valves, should differences in the diameters of the raised plastic faces occur. *Belleville washers are not recommended for use with PTFE-lined products.

Retorquing
A retorque should be applied a minimum of 24 hours after the initial torque or after the first thermal cycle. Retorquing enables seating of the plastic and allows for the relaxation of the bolts. In the event that the system is intended to perform at elevated temperatures, hot water should be circulated at the maximum operating temperature of the process (if possible) for at least 24 hours. This process will allow the pipe system to experience one full thermal cycle.

After cool-down, retorquing of the system should be completed. Torquing need only be completed on the system in the ambient, cooled state and never while the process is at an elevated temperature. This could cause excessive force to be exerted to the plastic faces. Never attempt to disassemble a flange joint in a hot system. Wait until the system has cooled to ambient temperature.

Hydrotesting
Typically after initial torque and retorque, a hydrotest should be carried out utilizing ANSI requirements. Experience has demonstrated that if the aforementioned procedure is adhered to, very few, if any flange joints will fail the hydrotest. If a flange joint leaks, first re-check the torque values and tighten in 10% increments over the specified bolt torques until completely sealed. If, however, 150% of the specified torque value has been reached and the flange joint continues to leak, stop the process and disassemble the flange joint. It is likely that something else is wrong, i.e, a scratched plastic face. The hydrotest must be successfully completed, and any existing leaks corrected before the pipeline can be approved and commissioned.

Annual Retorquing
Retorquing should be completed a minimum of annually thereafter. This is particularly crucial if the process line experiences elevated temperatures or extreme ambient temperature exposure. Torquing should only be completed on the system in the ambient, cooled state. Never attempt this process at an elevated temperature as damaging excessive force may be applied to the plastic faces.