The Technology | Lokring Technology LLC

ESP^® Technology

Installed fitting forms a perfect 360° circumferential, permanent, metal-to-metal seal.

The leak-free seal of a LOKRING^® fitting is the result of LOKRING Technology LLC^®'s patented elastic strain preload™ (ESP^®). During installation, the axial movement of the LOKRING^® driver over the fitting body swages the body onto the pipe or tube surface, compressing the pipe/tube wall, first elastically and then plastically. The pipe/tube wall resists this swaging action, generating high unit compressive loads at the contact points between narrow sealing lands inside the fitting body and the pipe/tube surface.

These contact stresses are sufficiently high to plastically yield the pipe/tube surface under the sealing lands, forming a perfect 360° circumferential, permanent, metal-to-metal seal between the pipe/tube and the fitting body. The driver, which experiences a small increase in diameter (elastic strain) during installation, exerts an elastic, radial preload on the metallic seals for the life of the connection.

The Right Way to Join Pipe and Tube

Gas-Tight, Permanent Seal:
The unique metal-to-metal seal of the LOKRING^® connection provides extraordinary sealing integrity in both liquid and gas services. Unlike other mechanically attached fittings, there are no elastomeric or rubber seals, O-rings or gaskets which can degrade and leak over time from chemical attack, fire, vibration, temperature cycling, cold flow or loss of elasticity.

As a result, fugitive emissions typical of leak-prone screwed or flanged connectors are eliminated.

Helium Leak Tight:
No other connector (flanged or threaded) is capable of passing helium leak testing anywhere close to the level of a LOKRING^® fitting. In fact, the fitting meets all criteria of a welded connection, except that heat is not required to make the connection. The quality of a LOKRING^® connection has been recognized by the California Air Resources Board (CARB) by granting LOKRING^® pre-certification status through executive order G-096-029-033 which gives LOKRING^® equivalent to welded status.

ANSI B31 Qualifications and Testing

Both stainless and carbon steel LOKRING^® fittings are qualified to the requirements of the ANSI/ASME B31 pressure piping codes for pressure and fatigue design and materials of construction. Extensive mechanical and environmental testing has demonstrated the mechanical and sealing integrity of the LOKRING^® connection in a wide range of applications and environmental conditions.

Pressure-torsion testing

The 1/2" NPS stainless steel test fitting was subjected to torsional loading high enough to twist the pipe in a spiral without leakage of the joint. Afterwards during hydraulic testing, the pipe ruptured at 22,000 psi (1,497 bar).

Flexural testing

The 2" NPS carbon steel coupling above has been deflected to 3x the yield strength of the matching pipe without leaking. The performance of this fitting in severe bending, fatigue and vibration loads are comparable or superior to a socket weld fitting.

Fire testing

The metal-to-metal LOKRING^® seal remains intact when subjected to extreme thermal loads, including fire (above). Both stainless and carbon steel LOKRING^® fittings are qualified to the Exxon API-607 Rev 4, fire test standards. Stainless steel fittings are also qualified to F1387 (U.S. Navy) fire test standards. Both are widely used on volatile and flammable services.