Spiral wound gaskets, from their inception in the early 20th century, have become a main stay in the fluid sealing industry. Off the shelf spiral wound gaskets are built to fit standard ASME B 16.5 flanges and applications. And are used extensively in standard pressure class rated flanges.
In what I think is an important spiral wound gasket study (PVP2013-97036) documented and presented for the ASME 2013 Pressure Vessel and Piping Division Conference, a number of factors were discussed pertaining to the influences that enhance a spiral wound gaskets sealing potential. While I do not go into all of the details from this study for this blog post, I do cover 2 of the essential findings. Clicking on the link will take you to the full report.
Your typical spiral wound gasket consists of the following main components:
- An outer guide ring that helps center the gasket properly between the flange bolts.
- Windings that make up the sealing element which by design, combine the best of two technologies.
- First, metallic windings designed in a “V” shape and act like a chevron ring, providing resiliency and mechanical strength.
- Second, a filler material. Most often a flexible graphite filler is wound in between the metallic V shaped windings, adding excellent sealing capabilities as the graphite (or other filler material), flows and seals into the grooves of the flange faces.
- And lastly an inner ring which helps prevent the windings from inner buckling, thereby increasing the seal of the gasket and keeps the windings from extruding into the flange bore and possibly unwinding and causing equipment damage downstream of the gasket.
Typical Cross Section Diaphragm of a Standard Spiral Wound Gasket
2 Main Factors That Influence The Sealing Potential of Spiral Wound Gaskets
The metal strips are wound around a mandrel the size of the internal dimensions of the particular gasket being made. Once the metal strips form the ID, the filler material is placed in between the metal windings and wrapped together under pressure. The more windings per inch of sealing surface,the higher density of the sealing area the better the seal. This factor has a greater influence on the sealing ability of the gasket then anything else. This should be taken into account when choosing a spiral wound gasket to use.
Filler material that protrudes above the metal windings (0.008 in) of a spiral wound gasket enhances the seal of the gasket. The filler material comes in contact with the flange face, flowing into the grooves machined into the sealing surface. Filler material that is flush with the metal windings exhibit higher leakage rates. By simply taking a close look at the windings of a spiral wound gasket, one can see if the filler material is flush with the metal windings or completely covers the metal windings.
Beyond winding density and filler protrusion, additional influences that enhance a spiral wound gasket to seal better are:
- An inner ring which prevents radial flow of the windings thereby creating a “tighter” seal. And prevents the winding from inner buckling and coming unwound and causing equipment damage.
- The integrity of the flange finish. Flange faces that are free of nicks and scratches and are parallel to each other and have a recommended 125-250 rms finish, provide the best sealing surfaces.
- No radial grooves, nicks or scratches.
- Proper compressive load applied on the gasket by using the proper torque values per flange classification. And by using a proper torque wrench when tightening the bolts.
- And by following the proper use of gasket installation best practices as outline by ASME PCC-1.
Spiral wound gaskets are dependable across a variety of applications. According to the need, different metals and fillers can be used in various combinations to meet just about any sealing application. For more information about a particular application you have, please don’t hesitate to contact one of our sealing professionals at Four States gasket and Rubber, Inc.