Gaskets for Newbies

A flange is a physical device to connect pipes, pumps or valves to create a piping system.  The flange also allows easier access for cleaning and inspection, and provides a logical place for system modification.  Most often, flanges are fastened via tightened bolts, but they can also be welded.  In most piping systems, flanges are joined together with a gasket between them to provide a seal.

We know from above that the purpose of a gasket is to fill the space between two joints and create a seal.  This keeps the fluid or gas on the inside of the process line in, and air and contaminants that are outside of the process line, out.  

The key factors for what kind of gasket to use are:  temperature and pressure of the fluid or gas being processed, surrounding temperature and pressure of the flanges and environment, and the nature of the materials (fluid and gases) a gasket will come into contact with (are they acidic, corrosive, etc.).  

If all we were doing was running a line of 70°F non-corrosive wastewater, at room temperature, under minimal pressure, in a standard indoor facility, we would use red rubber or an inexpensive synthetic rubber.  These options would contain the fluid, create a satisfactory seal, and be the most cost effective. 

However, the above use case does not describe 99.99999% of use cases for gaskets.  Therefore, while red rubber is commonly used due to its sealing capabilities and low cost, other materials are also commonly used. 

For instance, what if the process line is moving a solvent at a high temperature and under significant pressure?  Such a fluid could potentially degrade a red rubber gasket.  Hypothetically, the wrong material, at a high temperature and under pressure, could escape the process line and endanger employees, and possibly the facility.  Consequently, it is extremely important to use the right gasket material at all times.  We are here to help and just a phone call away.  

 

Gasket Shapes

Standard gaskets typically come in two shapes: Full Face and Ring.

Full Face Refers to a gasket shape where the gasket material includes the face of the flange. Bolt holes are pre-cut into the gasket material at precise locations to allow installation. For installation, the joints must be disassembled.

A Ring gasket refers to a gasket shape where the gasket material does not include or cover the bolt areas of a flange. While providing an equally satisfactory seal, ring gaskets may be harder to align during installation.

 

Pipe Flanges and Pressure Classes

Pipe flanges that are made to standards called out by ASME B16.5 are typically made from forged materials and have machined surfaces. B16.5 refers to nominal pipe sizes (NPS) from ½" to 24". Each specification further delineates flanges into pressure classes: 150, 300, 400, 600, 900, 1500 and 2500 for B16.5. However these classes do not correspond to maximum pressures in psi. Instead, the maximum pressure depends on the material of the flange and the temperature. (source and more info)

Flange applications of the 150 lb. pressure class are the most common.  In fact, we sell the most gaskets that are rated and sized for the 150# pressure class.  But, we regularly sell products for 300# pressure class systems.  (We can also provide materials in even higher pressure classes.)  When choosing a gasket, it is not only important to make sure your gasket is the right material, but also key to select the right pressure class.  Given different gasket shapes for different pressure classes, your system's safety and performance depend on it.  

 

Gasket Thickness

Most of the standard gaskets we sell are 1/16" or 1/8" thick. Gaskets should be as thin as possible to create an effective seal, but not be so thin that they can't compress enough to fill all flange irregularities. Thinner gaskets face less blow out risk because less surface area is exposed to the internal system pressure. Thinner gaskets also have fewer issues with creep relaxation (material spreading out and losing seal as bolts lose torque from said material spreading). Finally, thinner gaskets have fewer leakage issues as less surface area is exposed to the system. Ultimately, thickness will depend on the application, the gasket material used, its compressibility, and the condition of the flanges. Irregular or worn flanges may require thicker materials.