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EngRx Bolted Flange and Bonnet Leaks Solutions

One of the most common leakage paths is through a failed gasket.

EngRx has designed hundreds of leak repair fittings to solve flange and valve bonnet leaks. Process leakage from flanges and valve bonnet are among the most common type. The common cause of these leaks is:

  • Damaged gaskets or gasket faces (warped, scored, corroded, etc.)
  • Improper flange joint assembly
  • Thermal cycling
  • Vibration and dynamic forces
  • Inadequate stud preload


Most flange leaks are sealed using a mechanical Leak Sealing enclosure that encapsulates the flange “gap” void using a Tongue Clamp, or alternatively using a Peripheral Clamp that lands on both flange OD’s. A Tongue Clamp is a more localized solution as it seats only into the flange gap. The leak sealing compound (“sealant”) is injected into the encapsulated void volume, including the stud cavities,  through the Tongue Clamp OD. Peening the flange OD to the tongue clamp is commonly practiced to achieve a mechanical seal between the Tongue Clamp and the flanges. In cases where a narrow flange gap exists (less the 1/4″, 6.4mm), the installer may need to consider alternative injection routes such as: drilling ports through the flange, Injection Rings and Cap Nuts. These alternatives are often costly or deleterious, and the Peripheral Clamp is chosen to seal the leak. A Peripheral Clamp (often referred to as a “Channel Clamp” or “Flange OD Clamp”) lands on the flange OD’s and provides an effective means of injecting the flange gap and stud cavities. Injection compound ports are most commonly designed through the clamp outside shell. Flange mismatch is an important consideration in the proper fit of the Peripheral Clamp. Peening is normally not practiced with Peripheral Clamps as mechanical seals such as packing or crush tubing are designed to seal on the flange OD’s.

EngRx will assist with the proper selection and engineering of your flange Leak Sealing Enclosure. Difficult field measurement involving: obstructions, flange mismatch and even pre-existing direct mounted injectors can be tackled using our 3D Laser Scanning services. The 3D Laser Scan will provide a precise solution to inaccurate field measurements resulting in improper Leak Sealing Enclosure seal fits.

Common sealing techniques and designs

In many cases, the flange studs will be re-torqued to the the design pre-load in an attempt to stop the leak. If this does not work, or the studs are in poor condition, then an enclosure is designed and installed. If information is required on torquing procedures or recommended torque/tensioning values, please contact EngRx.

Tongue Clamps

Tongue clamps are designed with precision to insert into the flange gap, and then filled with sealant to stop the flange leakage. The sealant fills the flange cavity, and the stud holes in the flange to prevent future leakage. These are used when there is a sufficiently large flange/bonnet gap to “tongue” into, and also when the flanges are misaligned.

Peripheral Clamps / Channel Clamps

Peripheral clamps (also called channel clamps) are designed to seal on the outside face of the existing flange or bonnet. These designs are ideal for small gaps or leaking welds where the flanges are in close alignment.


In cases where the flange bolting is compromised, or the additional pressure area from the addition of a clamp overcomes the stud preload, strongbacking is applied to hold the flanges together. Below is an example of custom C-clamps designed to hold the flanges together and prevent catastrophic failure.

Contact Us Today to Speak with an Engineer

Reach out to us with your questions or needs and discover why we are one of Western Canada's fastest growing mechanical engineering firms. Call us at 780-784-9710 to speak with a staff member.

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