How do I achieve desired threadlocker and pipesealant strength?

Laurie Gibbons
Adhesive Selection and Use, Troubleshooting
October 15, 2009

There are two main things to consider when troubleshooting threaded adhesive sealant failure.

  1. Correct Adhesive Selection
  2. Proper Adhesive Application

First, check the manufacturer’s technical data sheet and compare the relevant properties to the specifications of your engineering or design group. Threadlocker formulations come in a wide range of strengths and viscosities for specific compatibility with straight, tapered, fine, or coarse thread patterns in pipe, pipe fittings, and fasteners like bolts and screws.

Choose the appropriate sealant strength.

Threadlockers come in a variety of strengths to serve applications that require a permanent lock or to lock fasteners in place but still allow for disassembly.   If the listed strength does not match your experience with the product, the following may help uncover the cause.

  1. Not strong enough: Insufficient sealant coverage will provide lower strength. Anaerobic threadlockers prevent loosening due to vibration by filling all the voids between the threads. For optimum results, make sure that the threads are covered.
  2. Not strong enough: High temperatures that go beyond the adhesive rating can interfere with the cured properties. Some manufacturers report values as Fahrenheit, others as Celsius. Check for conversion errors and confirm design specs with adhesive selection. Specialty, high temperature anaerobic threadlockers resist 230 °C, but conventional threadlockers resist up to 150 °C.
  3. Too strong: If the strength is higher than expected, consider the diameter and engagement length of the components.  Doubling the diameter will increase the strength six-fold!  For example, if the torque required to break away an M4 fastener is 2Nm (17.5, it will be 12Nm (106 on M8 and 72Nm (630 on M16.  Use this calculation to select a more appropriate strength threadlocker for your application.

Choose Adhesive for compatibility with substrates.

Slow or passive substrates: Anaerobic adhesives & sealants cure in the presence of metal and absence of oxygen.  Some metals cause anaerobic adhesives to cure faster than others.

Very Fast Fast Slow Passive (Activator Required)
Anodized aluminum
Cadmium finishes
Chrome finishes
Passivated metals
Stainless steel
Painted finishes
Lacquered finishes

Using anaerobic sealants on plastics or other non-metal surfaces is generally not recommended. However, an anaerobic activator will cause the product to cure.  Activators also speed the cure on slower substrates but may reduce the strength of the cured threadlocker.

When satisfied with the adhesive choice, review the application process to see if any of the following conditions that may cause sealant failure exist and can be corrected.

Sealant failure from insufficient sealant in the bond area.

Threadlockers fill the natural voids between threads. The adhesive cures to lock the fastener and component into a single unit and prevent loosening due to vibration.  Any air pockets trapped in the bond area will interfere with the ability to achieve desired results. Some common applications and general guidelines follow:

  1. Parallel to Parallel pipe joints
    1. Apply a bead of sealant to the leading edge of the male part sufficient so that when the pipe is seated, a small bead of ‘squeeze out’ is visible around the circumference of the assembled joint.
    2. Do not apply the sealant to the internal threads of the female pipe fitting to ensure full coverage and to avoid pushing adhesive into the pipe as the joint is tightened to specs.
  2. Taper to Parallel pipe joints and Taper to Taper pipe joints
    1. Count back several threads from the leading edge, then apply the sealant to the male pipe at the point where you expect the threads to engage.  The bead of ‘squeeze out’ around the circumference of the assembled fitting is your evidence of correct adhesive application.
  3. Fasteners
    1. Open hole: Apply the sealant to the fastener’s threads where it will engage with component.  Check for visible squeeze out around the circumference of the fastener assembly.
    2. Blind hole: Apply the sealant inside and at the bottom of the hole, taking care to fill the void before inserting the fastener. Air pockets at the bottom will be forced upwards as the fastener is tightened, and can create air pockets along the length of engagement and prevent a cure to full strength.

This covers some common scenarios concerning sealant failure. Contact the manufacturer if you continue to experience difficulty achieving desired results.

anaerobic sealant failure

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