Super duplex is a shorthand term for a family of high-performance stainless steels designed with around 25% chromium content in the alloy’s makeup. As the duplex name suggests, this family of alloys have a microstructure made up of both austenitic and ferritic grains of steel. This duplex nature provides Super Duplex’s unique combination of physical and mechanical properties.
History of Super Duplex Materials The original duplex stainless steel was developed in Sweden for use in the sulfite paper industry. These early alloys were developed to combat corrosion problems common in that industry as a result of chloride-bearing cooling waters. However, while these duplex stainless steels proved to be an excellent development in the field, they did not meet all needs. As a result, further innovation was needed.
A Spiral Wound Gasket is the most widely used common metallic gasket used in industrial applications involving a range of pressure and temperatures. They are popular in the oil and gas, chemical, petrochemical, power, and food industries and prevents leak through flange joints. The concept of spiral wound gasket was first developed by Flexitallic in the year 1912 to serve US refinery operations involving severe temperature and pressure fluctuations.
Spiral wound gaskets are used for High-Temperature service applications. High-pressure applications. Corrosive fluids. Flammable Fluids. Hydrogen, etc.
Construction of Spiral Wound Gaskets A spiral wound gasket is a semi-metallic gasket. It consists of a spirally wound v-shaped metallic with a non-metallic filler material. There are three elements that constitute a spiral wound gasket. They are: Outer ring: Also known as a guide ring or centering ring, the outer ring of a spiral wound gasket is usually made of carbon steel material. The main purpose of this element is to center the gasket while inserting it into a bolted flange joint. Inner ring: The inner ring is one of the most important parts of a spiral wound gasket as it prevents windings from buckling inside the pipe. In the situations of buckling of a gasket, parts of it get sucked into the pipe and eventually flow through the piping system to get caught/wrapped on something. Inner rings prevent this phenomenon and help in avoiding the problem. Sealing element: This is the element of the spiral wound gasket that creates a tight seal to prevent leaks. The sealing element encompasses both windings and filler material. In general, spiral wound gaskets use a flexible graphite filler material rated for high temperatures. The graphite as filler material also helps the gasket to avoid flange distortion and joint misalignment. Another common filler material is PTFE (Polytetrafluoroethylene). However, PTFE is not suitable for use in high-temperature applications. The most widely used winding materials are Stainless Steel and Monel.
Refer to Fig. 1, which clearly shows these three elements of a spiral wound gasket.
Markings on Spiral Wound Gasket Spiral wound gaskets are identified using different markings on the gasket. Each marking provides brief information about the spiral wound gasket specification important during the gasket selection process. Some of the necessary information that the markings on the spiral wound gasket provide are: Design Standard or Code: The code based on which the spiral wound gasket is designed and manufactured is clearly marked. In Fig. 1, you can easily find the standard ASME B16.20. Name of the Spiral Wound Gasket Manufacturer: One can easily understand the manufacturer of the gasket by looking at the manufacturer name mentioned on the gasket. Winding and Filler Material: Both the winding and filler materials are clearly specified on the spiral wound gasket. Specific gasket colors also provide a lot of information regarding the materials. Diameter and Pressure class: The size of the gasket and the load the spiral wound gasket can handle, are specified by the Diameter and Pressure Class marking on the gasket. The usual pressure classes for spiral wound gaskets are 150, 300, 400, 600, 900, 1500, and 2500. With an increase in pressure class, the ability of the spiral wound gasket to withstand pressure increases. Inner and Outer ring material
Materials for Spiral Wound Gaskets The usual materials that are used in a spiral wound gasket are provided in table-1 below: