General Gasket FAQs
Flange surface finish is a critical aspect of gasket performance. Metallic, semi-metallic and nonmetallic gasket materials interact with flange surfaces differently. Each of these gasket types require specific ranges of surface finish for optimum gasket performance with lowest leakage. Metallic gaskets require a smoother flange finish than either semi-metallic or nonmetallic. Please consult with our technical department to determine the best combination of flange surface finish, gasket design and gasket material(s) for all your projects.
Ring type gaskets have no bolt holes. These gaskets are positioned inside the flange bolts and around the pipe bore and are typically used on raised face flanges. When used on a raised face flange, the ring gasket is positioned on top of the raised surface of the flange. An advantage of ring gaskets is that they can be installed without having to fully disassemble the joint.
A full-face gasket covers the entire face of the flange. Full-face gaskets are typically used on flat face flanges and are cut with bolt holes which allow the insertion of the flange bolts through the gasket. When installing full-face gaskets, the joint must be completely disassembled. View our full product line here.
No. This is highly NOT recommended because it will most often create a leak path. See FAQ: What thickness is best when choosing a gasket?
For a gasket to seal under installed conditions, a minimum stress value is necessary. This value should include the relaxation that will occur during the gasket’s installed life. To prevent damage, it also has a maximum stress value that should not be exceeded, its crush strength. When a gasket’s crush strength is exceeded, the properties that provide the seal break down. An optimized solution targets a stress level that is as high as possible above its minimum value but a comfortably safe margin below its maximum value and a value that may cause a problem to the bolts or flanges.
Sounds like a simple question, but in fact, requires more than a simple answer.
It is not always realistic to repair or adjust the misalignment of flanges. So, if flanges are corroded, uneven or not parallel, a thicker gasket may be recommended because of their compression capabilities.
So why do most gasket manufacturers recommend using thinner gaskets wherever possible?
Thinner gaskets offer many advantages:
- Greater blow-out resistance and lower leakage rates due to the smaller cross-sectional area exposed to the internal medium pressure.
- Environmental concerns
- Better compressive strength and therefore higher gasket surface loads (pressure) can be safely applied to a thinner gasket.
- Better fastener torque retention due to the lower creep relaxation characteristics of thinner gaskets.
- Lower cost of the gasket itself.
Click here to view our line of gasket products.
An O-ring is a precisely molded shape with a specific profile to fit into a specific channel or groove and are known for their ability to seal extremely high pressures.
Gaskets are by far the most versatile seal, with different shapes, materials, coatings, methods, etc. Depending on the type of material chosen, they can seal at a wide range of temperatures and pressures. Click here to view our line of gasket products.
The pH of a solution indicates its level of acidity or alkalinity, based on the concentration of hydrogen ions (H⁺) present. The pH scale ranges from 0 to 14:
Understanding pH is essential in chemical processing, water treatment, and material compatibility, as it helps determine how corrosive or reactive a solution might be with certain materials—such as gasket components.
The modulus of elasticity measures a material’s stiffness or its ability to resist elastic deformation under load. In gasket materials, it plays a key role in determining how well a seal is maintained under varying pressure and temperature conditions.
The “y” value is the minimum stress needed to seat the gasket and create an initial seal. The “m” value is the multiplier that ensures the joint stays sealed under pressure. Together, they help determine the bolt load and flange strength required for reliable sealing. In short, your flange must compress the gasket enough to fill surface imperfections and resist internal pressure.
Hot bolting refers to tightening flange bolts while equipment is in operation. Although occasionally used for minor leak repair, it presents serious safety and reliability risks. It’s best avoided or carried out only with strict engineering controls. For more information see our blog on Hot Bolting Safety Precautions.
Gasket compression depends on the material’s compressibility and how much load is applied. If there’s not enough compression, sealing issues can occur. Proper torque values are key to achieving the right compression for reliable performance. See Gasket Installation Training for more information.
A gasket is a sealing material placed between two mating surfaces (like flanges) to prevent fluid or gas leakage. It compensates for surface irregularities and maintains seal integrity under temperature and pressure fluctuations.
No. Reusing gaskets compromises sealing performance and safety. Always replace gaskets after disassembly to prevent leaks or system failure.
Consider:
- Temperature and pressure limits
- Chemical compatibility
- Flange type and surface finish
- Industry standards (FDA, NSF, API, etc.)
Use Durlon’s Material Selection Guide or contact technical support for personalized recommendations.
Thicker gaskets fill uneven flanges but may increase creep and reduce blowout resistance. Thinner gaskets provide better seal stability and torque retention. Always use the thinnest functional thickness.
Common causes:
- Under- or over-torquing bolts
- Using the wrong material for pressure/chemical conditions
- Reusing old gaskets
- Misaligned or damaged flanges
Proper installation and material selection are key.
Material-Specific Questions
The inner retaining ring increases the axial rigidity and resilience of the gasket. Its purpose is to help avoid excessive compression due to high seating stress in high-pressure service and to reduce turbulence in the flange area. The advantages to using an inner ring include the following: Provides additional compression stop and blowout resistance, prevents build up of process fluid, minimizes erosion and turbulence, shields the gasket, prevents buckling and promotes tightness. To view our line of Spiral Wound Gaskets, click here.
Metallic gaskets are engineered for high-pressure environments, often rated up to 20,000 psi. Material choice matters—316L stainless steel handles moderate corrosion, while Inconel, Monel, or Hastelloy are ideal for aggressive media.
Top picks:
Electrically insulated gaskets prevent current flow between metal flanges, helping to avoid galvanic corrosion and maintain electrical isolation in cathodic protection systems.
Explore our iGuard™ Isolation & Sealing Kits for complete solutions.
Use Durlon® 9000 Series (filled PTFE) or Durlon® 9200W for high chemical resistance in acids, caustics, solvents, and chlorine. Always confirm compatibility with the specific media.
Yes. Durlon® 8500 is widely used for saturated steam, while Durlon® 8400 (high-temp mica-based) and HT1000® (ceramic fiber) handle higher temps in superheated systems. Match with temperature and pressure specs.
Durlon® 9000, 9002, 9600, 9645, and Joint Sealant meet FDA 21 CFR 177.1550 and USP Class VI for food, beverage, and pharmaceutical use. Certifications are available upon request.
Durlon® 7910 is certified to NSF/ANSI 61 for use in drinking water systems up to 82°C (180°F). Ideal for municipal and residential water applications.
PTFE: Excellent chemical resistance, non-stick, FDA-compliant. Best for aggressive media.
Graphite: High temperature tolerance and sealability. Ideal for steam and hydrocarbons.
Choose based on media, temperature, and pressure.
Installation and Maintenance FAQs
The compressed height of the gasket must be considered when installing gaskets in grooves or tongue and groove flanges. The fully compressed thickness, not the original thickness, must be greater than the groove depth or the space between the tongue and groove when flanges contact each other. Ideally, the tongue should be at least as tall as the groove depth.
Achieving the proper gasket compression via the torque placed on the bolts is a well-engineered, tested and verified process based on the specific type of gasket material.
Sometimes the torque values aren’t followed, or a material gets replaced, and flange surfaces change throughout the repetitive heat cycles. When this happens, you must trust the performance of your gasket material. In some cases, over-compression can happen, and that can lead to problems. View our gasket installation video to learn more.
Here at Durlon®, our prime design objectives are to maximize the sealability of our gasket materials to meet fugitive emissions requirements. We offer two specific product categories that have been tested and proven to offer exceptional sealability in challenging conditions. Our filled-PTFE products – notably the most versatile product, Durlon® 9000 glass-filled PTFE, offers exceptionally tight sealing characteristics. Secondly, our specially engineered machined metal core gasket, Durlon® Durtec®, is ideally suited to fluctuating pressure and temperature conditions while being fire-safe and offering unparalleled sealability. When it comes to the hazardous and challenging conditions present in the oil & gas, chemical and mining industries, to name a few, these product specifications ensure safety, reliability and the assurance of a significant reduction in overall fugitive emissions.
The use of premium gasket materials with good seal ability numbers are the easiest ways to reduce emissions. Read more
Never scrape off old gaskets with a razor blade or anything that can scratch the metal surfaces and create a leak path. Doing so may compromise the seal and the operation of the assembly. But failure to clean off old gasket or gasket materials may result in the mating surfaces coming together in an uneven alignment. Instead, use a plastic scraper or nylon brush. Click here to view our CNA enhanced anti-stick gaskets.
Torque wrench’s come in many shapes, sizes and styles ranging from the basic beam, clicker wrench or even electronic wrench. In 65-70% of gasket failures, the main cause of the failure is linked to under loaded gaskets. Applying the correct torque helps ensure that you are properly stretching the bolts, which in turn act like a spring pulling the flanges together, creating load on the gasket and achieving an effective seal. Torque wrenches can range in price and accuracy, however, despite the tool’s price tag, a torque wrench is only as good as its last calibration. So be sure to do this before putting it to use. Read more about Gasket Installation Training.
The lifetime of a gasket is dependent upon its quality and what it is exposed to and how it is installed. Additionally, inertia of the fluid may create a large spike in pressure resulting in pushing or forcing the gasket from the flange sealing surface and can cause leakage or even blow out. Learn more in our blog about gasket temperature and pressure limits.
Durlon® 9000 is designed for use in process piping and equipment exposed to strong oxidizers and highly aggressive chemicals. It is ideal for a wide range of industrial applications requiring superior chemical resistance.
This PTFE-based gasket material contains non-wicking inorganic fillers that help prevent flange face corrosion, a common issue in aggressive chemical environments. Durlon® 9000 also meets demanding fire safety standards. A 6-inch Class 300 Durlon® 9000 gasket successfully passed the API 6FA Fire Test, withstanding a flame of 875°C (1607°F) for 30 minutes and recording a leakage rate of only 1.8 ml/min, well below the allowable limit of 1200 ml/sec.
Compressive stress is the pressure applied to a gasket to help it seal. It’s crucial because too little stress can cause leaks, while too much can damage the gasket. Softer gaskets seal with lower stress, while harder ones—like metal gaskets—need more. For a deeper look at how stress levels affect sealing, check out our blog on ideal gasket stress.
Torque depends on flange size, bolt material, gasket type, and application. Use the Durlon Bolt Torque Calculator or consult the Pressure-Temperature chart. Improper torque is the #1 cause of gasket failure.
Creep is the gradual loss of gasket thickness under load and heat, leading to loss of sealing force. Durlon materials are engineered for low creep under high-temperature cycling.
Generally not recommended. Durlon gaskets are designed to seal without extra compounds. Sealants may interfere with material properties or proper compression. Use only if specified by the manufacturer.
Store flat in a cool, dry, UV-free area. Avoid rolling or folding sheets. Do not hang gaskets on pegs—this can deform them. Use FIFO (first-in, first-out) inventory management.
A surface roughness of 125–250 µin RMS is ideal. Too smooth reduces grip; too rough cuts into the gasket. Match finish to gasket type for reliable sealing.
Application and Industry-Specific FAQs
For refrigerant service, Durlon® offers gasket materials engineered for performance, reliability, and chemical compatibility:
Both materials are trusted for long-term performance in HVAC and refrigeration systems where chemical resistance, pressure, and temperature stability are critical.
Yes, Durlon® manufactures several high-performance gasket materials that meet Military Specification standards. Specifically, the following Durlon® gaskets have passed the MIL-G-24696B Navy Adhesion Test (366°F for 48 hours):
Durlon® iGuard™ gaskets are designed for use in flange isolation kits to seal and electrically isolate flanges while providing cathodic protection. They perform in a wide range of applications—from water and natural gas to aggressive chemicals—up to 232°C (450°F). Available in Type E (full face), Type F (raised face), and Type D (RTJ) styles, they meet all major piping standards.
Choose gaskets with low emissions certifications:
- Durlon 9000/9200
- Durlon Kammprofile with graphite or ePTFE facing
These meet TA-Luft, API 622, or ISO 15848 emission standards.
Yes. Many styles (e.g. Durlon 9000, Kammprofile, Spiral Wound) are tested to API 6FA/607 and ISO 10497 for fire safety in critical applications. Our Durlon SWG DRI ETG has passed the API 6FB, Fourth Edition 2019, Type 2 (Offshore Test) with zero leakage. Read more about our high temperature sealing products.
For gas applications, use:
- Durlon 8700 (LPG/propane-rated)
- Durlon 9000 Series (PTFE)
- Metallic gaskets (e.g., Spiral Wound, Kammprofile)
Ensure materials meet CSA, API, or local utility specifications.
Rubber-bound (CNA) Durlon® gaskets have a typical shelf life of approximately five years. PTFE, graphite, and metal gaskets have an unlimited shelf life when stored properly; however, always refer to the specific product datasheet for exact shelf life and handling guidelines.
For gasket cutting, precision tools such as rotary cutters, hydraulic gasket cutters, or steel rule dies for high-volume production are recommended. Avoid hand-trimming or making jagged cuts, as they can compromise the gasket’s seal integrity.