How to Replace Gaskets and Seals on a PTFE Heat Exchanger

One opened a PTFE heat exchanger for cleaning, reused the old gaskets and tightened. It came out a week later. The gaskets had suffered a permanent compression set. The lesson learned: always replace the gaskets when you open a PTFE exchanger. Here's the appropriate way to do it:
PTFE gaskets and seals are peculiar in that the material slips under sustained compression and does not entirely spring back. The gasket loses its elastic rebound once compressed, forming microscopic pores through which corrosive fluids can escape with pressure or heat cycling. Even a seemingly complete gasket reused is virtually a sure bet to leak in days or weeks. A replacement gasket is cheap, a leak is expensive. Proper replacement consequently includes new gaskets every time the exchanger is opened and good surface preparation, proper torque technique and post-installation verification .
Start with the right gasket for the service conditions. For low pressure applications, a PTFE envelope gasket (a thin PTFE sheath around a compressible core) provides excellent chemical resistance and conformability. In applications with greater pressure demands, a full face PTFE gasket provides uniform loading across the entire flange face and reduces the possibility of extrusion. The spiral wrapped gasket with PTFE filling and outer centering ring is resilient for services with frequent temperature cycling, while yet providing the needed fluoropolymer compatibility. Always double check the selection against the manufacturer's data sheet, as mismatched gaskets can extrude or crush under stress.

With the exchanger isolated, emptied and cooled to ambient temperature, remove the old gaskets and prepare the flange faces. Clean all surfaces thoroughly with a non-abrasive solvent such as isopropyl alcohol. Clean out any remnant gasket material or carbonized deposits with a plastic scraper or a soft nylon pad – never use metal instruments, since they can gouge the PTFE lining or scratch the steel flange. Wipe the faces clean of grease, scale, or imbedded debris. Check each flange carefully with a bright light for scratches, pitting or warping. A thicker full-face gasket will accommodate small surface flaws, but deep scratches or grooves deeper than 0.1 mm will likely require professional resurfacing or replacement of the flange. If the PTFE lined nozzle face is damaged in any way it must be assessed by a qualified lining specialist before proceeding. A small nick can create a leak path when the new gasket is compressed.
Place the new gasket so that it is exactly centered on the flange. The bolt holes should be flush and the gasket should reach completely to the inner diameter of the raised face or full face arrangement without overhanging or folding. Don't use gasket cement unless the equipment maker recommends it. Most PTFE gaskets are designed to seal by compression alone. If the flange design includes a centering ring or locating pins, ensure the gasket is seated against these.
The most important stage is bolting and should never be rushed. Insert the bolts and finger-tighten to hold the unit in position. Torque in a star or crisscross pattern never sequentially around the circle using a calibrated torque wrench Perform a three-step sequence: first to 30 % of the goal torque, then to 60 % and lastly to 100 %. PTFE gaskets require very low torque values, sometimes 30–50 % of the torque required for similar metal spirals, unlike metal or rubber gaskets, because too much compression causes the PTFE to cold-flow outward and shatter at the edges. See the exact torque table supplied with the exchanger. Over-compression is equally destructive as under-compression. After final pass, wait 1 hour for first creep, then go back to each bolt and re-torque to full value. In this second run the relaxation, which is an inherent property of PTFE, is compensated.
After tightening, the exchanger must be pressure tested before being returned to service. Isolate the unit, then pressurise with clean water or inert gas to 1.5 times the usual working pressure (or to the manufacturers specified test pressure) and hold for a minimum of 30 minutes examining every flange with a soap solution for bubbles. Any leak necessitates urgent depressurization, disassembly and re-inspection of the gasket seating and flange faces.
Establish a regular rotation schedule. Always replace gaskets and seals whenever the exchanger is opened for maintenance, cleaning or inspection never reuse old ones. For essential or high temperature services, schedule proactive replacement at a minimum of every two years, even if the unit stays unopened. PTFE ages, hardens and loses its sealing integrity over time when subjected to continuous compression and thermal exposure. Keep a record of each replacement in the equipment maintenance log, including gasket type, torque levels, and test results for future reference.
PTFE tape is much too thin to replace a gasket, extrudes too quickly under pressure, and provides none of the structural support necessary for a proper flange seal. Nor should you mix gasket styles in the same exchanger unless the manufacturer approves the mix.
Leak-free operation requires proper gasket selection, surface prep and torque technique. Always replace PTFE gaskets when opening the exchanger – overuse invites failure. Maintenance crews guarantee the PTFE heat exchanger is reliable, safe and leak-free throughout its service life by installing fresh, properly torqued gaskets on thoroughly prepared surfaces each time a flange is opened. The extra few minutes to replace carefully paid rewards in uptime and averted environmental or safety concerns.