LENS RING
Lens ring gaskets are characterized by a spherical sealing surface that touches the conical surface of the flange. These gaskets are used in special applications with specific values of pressure, temperature and their changes over time.
Usually you can find these gaskets on flange connections of high-pressure reactors where there are heavy working conditions and a perfect sealing is needed. In this case a loss of material could create high risks both for the workers and the environment.
WELD RING
A weld ring gasket is a sealing system thought up for critical applications where a weathertight joint is needed (heat exchangers, thermal reactors, chemical plants, etc.).
The main reasons to install a weld ring are the containment of dangerous fluids and difficult working conditions (thermal shock, vibrations, axial or lateral movements of the flange, etc.).
Each individual gasket is made of a couple of rings with a mirrored cross-section. Every ring is welded individually to its flange and then welded together on the external diameter. In this way you can achieve a completely welded joint guaranteeing a weathertight sealing.
To avoid welding problems like galvanic corrosion or differential thermal expansion, the material of the gasket must be the same or as similar as possible to the flange material.