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Does the seal ring fit? Avoid bad surprises.

Learn in my new post how you can guarantee a leak-free flange connection even at high temperatures and when to use a PTFE or a graphite gasket.

Direct mount manifolds for direct mounting on pressure and differential pressure transmitters are normally protected against overheating by hot process  media by means of correspondingly long impulse pipings. Nevertheless, many users demand that the manifolds and their flange connection to the transmitter can easily withstand even higher temperatures. For this, the manifolds must be equipped with gaskets made of graphite. This means they can easily be used at up to 550 degrees Celsius – much more than required by the current EN 61518 / IEC 61518 standards.

Leak-free flange connections even at high heat

The international standard EN 61518 / IEC 61518 describes the flange connection between the manifolds and the pressure transmitters. Here, among other things, the temperature limits of these compounds are described: For seals made of PTFE, this is 80 degrees Celsius, for graphite seals at 120 degrees Celsius. The temperature limit of 120 degrees Celsius refers to the limits to be applied to the transmitter. The limit for the flange connection itself may be higher according to the pipe standard.

From my experience, however, I can say  that there are many users who demand much higher temperature limits than 120 degrees Celsius for their manifolds. In normal operation, the manifolds are not exposed to such temperatures, but there is a possibility in exceptions, for example, in a system failure. Many customers therefore want to be optimally prepared for such cases.

It depends on the seal

The manifolds are usually equipped with either PTFE gaskets or graphite gaskets. The former are clearly at a disadvantage when used at high temperatures. PTFE becomes very soft at high temperatures, which is why the pressure of the process medium forces the plastic into available cavities. In addition, PTFE has a significantly higher thermal expansion coefficient than steel. This has the consequence that the seal ring expands more than the body and thus flows into the existing gap. If the connection cools down again, the melted PTFE will not return, which leads to a loss of tension in the sealing ring and thus to the risk of leaks.

Graphite or PTFE seal ring assembly on transmitter.

The situation is different with graphite: The graphite seal ring has no appreciable deformation even at extreme temperatures and thus ensures a permanently leak-free flange connection. Extensive laboratory tests allowed my development team to prove the reliability of the material. The graphite gasket is not extruded even at 350 degrees Celsius, the flange connection was as stable after the test as before. The maximum possible operating temperature is even higher. The E Series Manifolds with graphite packing from AS-Schneider can be used at up to 550 degrees Celsius. However, the user is responsible for ensuring the compatibility between the materials of the selected seal ring, including the screws and the process requirements such as pressure, temperature and chemical compatibility. Then, maximum safety and smooth plant operation can be achieved.

Image Source: © Marina/Fotolia & AS-Schneider