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Why didn’t my thread sealant cure?

Anaerobic thread sealant (pipe sealant) fills all of the voids or airspace between metal threads creating a permanent plastic seal.  They do not shrink or relax over time.

Anaerobic adhesives and sealants require only two conditions to cure. They are 1. The presence of metal ions and 2. The absence of oxygen.  Seems easy enough right?  Yes and no.  Following are some common issues that can adversely affect curing thread sealants.

thread sealant

Contact with metal

  1. The presence of metal ions must be in contact with the thread sealant. Paint and coatings can prevent that.  Similarly, well-meaning users will apply PTFE tape (Teflon® tape) to “help” seal.  The tape blocks contact with the metal and the exact opposite occurs.   Instead of helping the seal, the tape prevents cure making a leak path possible.
  2. Mind the Gap! Note the maximum gap on the datasheet of the product you are using.  Generally, if the gap exceeds 0.5mm (0.020 in.) the sealant at the center of that gap may have difficulty curing as it isn’t close enough to the metal needed to cure.
  3. Pipe sealant also covers the metal ions. Pipe joints sealed with low-strength thread sealants can be dismantled using normal tools. Heating parts with a hot air gun or blow torch will make parts easier to disassemble. Before reapplying sealant, clean pipe joints with a wire brush to expose the metal.

Lack of contact with oxygen

When the thread sealant is contained in the threads, oxygen is excluded.  Following, are the directions for using anaerobic pipe sealants on both parallel and tapered pipe joints.

  • Parallel to parallel pipe joints: Apply sealant to the leading edge of the male component.
  • Tapered to parallel pipe joints: Apply sealant several threads back from the leading edge of the male component to ensure maximum contact.

* IN EACH CASE EXCESS SEALANT SHOULD BE VISIBLE AFTER TIGHTENING –The purpose of the excess is to visualize complete 360° coverage to ensure no leaks.  The exposed sealant will not cure as it is in contact with air.  This excess can be wiped away. 

Often users will expect that exposed area to cure and not realize that within the joint the anaerobic thread sealant has cured as expected.

These basics apply not only to pipe sealants but to all anaerobic adhesives and sealants which are used for threadlocking, retaining, and FIP gasketing.

For more information contact Permabond.