Instrumentation and control engineers working in fuel piping, water and gas, condensate and recirculation systems … among all the metallic sealing solutions, SS304/SS316 flexible graphite spiral wound gaskets continue to be the most heavily specified options for use in changing temperature, vibration, and high pressure flange joints. Gasket construction, material differences, standard limits and common pitfalls form the basis of proper gasket selection for engineering for most systems and critical service lines.
A standard spiral wound gasket follows ASME B16.20 specification. The strip is formed by spirally winding alternating V-shaped or W-shaped stainless steel metal strips and flexible graphite filler. Start and end of the winding strip are secured by spot welding to prevent extent. An industrial version typically has inner ring and an outer centering ring. It is designed to “center” the gasket force on the flange and limit over-compression during bolt tightening, with the inner ring that restrains the winding from collapsing inward under high line pressure and protecting the winding layer from erosion by the process media. Two common thickness options are 3.2 mm and 4.5 mm, and the sizes are available from 1/2 to 60 inches, covering pressure classes from 150# to 2500#.
Engineers really have a hard decision – SS304 or SS316 (or 316L) winding strips? Typically SS304 is the low cost material. It is commonly used for Fresh water, steam/ non-chloride mild chemical media, as well as low corrosion piping systems, offers good corrosion resistance up to approximately 650º C. Better corrosion resistance against chloride ion corrosion, pitting and crevice corrosion is provided by the molybdenum in SS316 and SS316L. The best choices for seawater, brine, acidic process fluid, and offshore oil & gas environments are often achieved with the latter. Being low alloy, low carbon, SS316L also has the benefit of lowering the risk of intergranular corrosion after welding. The flexible graphite filler has great thermal stability, compressibility and recovery. It compresses like rubber gaskets, but retains the sealing performance through repeated heat cycles which is most needed in the case of heat exchangers, valves and pressure vessels.
The most common cause of gasket failure, even with the best materials, is poor selection/install. The gasket pressure class must be compatible with the flange rating. A 150# gasket should not be used on a 900# flange joint. Also the surface finish and flatness of the flange face have to be taken into consideration – if you have scratched or warped flanges, they will form leakage paths, even if the graphite spiral wound gaskets are high quality. Proper bolt torque (cross sequence) to allow uniform compression is also required. Excessively tightening can crush the graphite filler and eventually ZIP the elastic recovery of the metal winding, not allowing the gasket to seal with pressure surges. It is also critical to check for chemical compatibility: This graphite is well suited for use in steam and hydrocarbon services, but it will degrade quickly when exposed to strong oxidizing media such as concentrated nitric acid.
Gaskets are common in these applications. They are used in joints with cyclic thermal load, where a solid flat gasket or a rubber seal cannot maintain their lubrication quickly. Custom drawings are accepted to produce non-standard flange dimensions, but standard stock gaskets are ASME B16.20 approved for quick delivery.
To sum up, SS304 & SS316 graphite spiral wound gaskets provide the desired combination of compliance, high temperature tolerance and corrosion resistance. SS304 is the clean service grade to manage the budget, while SS316 is kept for corrosive chloride-containing working environment. An engineer can choose the material grade, pressure rating, bolt load and the soundness of flange maintenance to ensure the long term life, zero leak critical industrial flange connection of this type of gasket.
Post time: Nov-02-2026
