ASME B16.20 Standard: Metallic Gasket Types and Requirements

3. Ring-Type Joint Gaskets

Ring-Type Joint gaskets, commonly known as RTJ gaskets, are solid metallic sealing rings designed for use with specially machined RTJ flange grooves. They are commonly installed in high-pressure and high-temperature piping systems where reliable sealing is essential.

Unlike soft gaskets that seal by filling surface irregularities, an RTJ gasket creates a seal through concentrated metal-to-metal contact. As the flange bolts are tightened, the gasket is pressed into the flange grooves. The high contact stress causes controlled deformation of the gasket surface and produces a pressure-tight joint.

The gasket material must generally be softer than the flange material. This allows the gasket to deform without damaging the flange grooves. Common RTJ materials include:

• Soft iron
• Low-carbon steel
• Type 304 stainless steel
• Type 316 stainless steel
• Type 321 stainless steel
• Type 347 stainless steel
• Nickel-based alloys for corrosive or high-temperature service

Material selection depends on process-fluid compatibility, operating temperature, corrosion resistance, flange material, and project specifications.

Type R ring gaskets

Type R is the traditional RTJ gasket configuration. It is available in two cross-sectional profiles:

• Oval Type R
• Octagonal Type R

An oval ring contacts the curved surfaces of the flange groove at specific sealing areas. An octagonal ring has flat sealing faces that match the angled surfaces of the groove.

Both profiles can fit compatible standard Type R grooves of the correct ring number, but they should not be changed without confirming the flange condition and project requirements. Octagonal rings generally provide more direct surface contact and are widely used in modern installations.

Type R gaskets are typically used with ASME B16.5 and ASME B16.47 Series A RTJ flanges. Depending on the applicable flange standard and size, they may be used in pressure classes from Class 150 through Class 2500.

Type RX ring gaskets

Type RX is a pressure-energized RTJ gasket developed mainly for higher-pressure oil and gas equipment. Its asymmetric cross-section allows internal pressure to increase contact between the gasket and groove surfaces.

RX gaskets use designated ring numbers and can fit certain flange grooves originally designed for Type R gaskets. However, RX gaskets are generally taller and may require greater flange separation during assembly. Interchangeability must therefore be confirmed using the applicable dimensional standard.

Type BX ring gaskets

Type BX gaskets are designed for very high-pressure applications, particularly equipment manufactured according to API 6A. Their geometry creates a pressure-energized seal in a specially designed BX groove.

A BX gasket must be used only with the corresponding BX flange groove. It is not interchangeable with Type R or RX rings. BX connections are designed so that the flange faces may come into contact when the joint is properly assembled.

Ring numbers and identification

ASME B16.20 assigns ring numbers to standardized RTJ gasket dimensions. Each ring number represents a particular combination of gasket geometry and flange groove dimensions.

A complete RTJ gasket specification should identify:

• Gasket type
• Ring number
• Material
• Applicable standard
• Any required coating or surface treatment
• Required certification or traceability

For example:

ASME B16.20 Type R octagonal gasket, ring number R45, soft iron.

The ring number should always be checked against the flange size, pressure class, and applicable flange standard. Selecting a gasket only by nominal pipe size can result in an incorrect ring because different pressure classes may require different groove and gasket dimensions.

RTJ gaskets undergo permanent deformation during tightening and should normally be treated as single-use components. Reusing a compressed ring can produce inadequate contact stress or fail to match the groove surfaces correctly. Before installation, both the gasket and flange grooves must be inspected for corrosion, scratches, dents, foreign material, and dimensional damage.

4. Spiral-Wound Gaskets

A spiral-wound gasket is a semi-metallic gasket manufactured by winding alternating layers of formed metal strip and soft filler material into a circular sealing element. This construction combines the strength and recovery of metal with the conformability of a softer sealing material.

Spiral-wound gaskets are commonly used with raised-face flanges in refineries, petrochemical plants, power stations, chemical facilities, and other industrial piping systems. They are suitable for services involving elevated pressure, temperature changes, vibration, and thermal cycling.

A typical spiral-wound gasket may contain four main components:

• Metal winding
• Soft filler
• Inner ring
• Outer centering ring

The metal strip is normally formed into a V-shaped profile before winding. When the flange bolts are tightened, the winding compresses and develops the sealing force required to resist internal pressure. The formed metal layers also provide a degree of recovery when the joint experiences temperature or pressure changes.

The filler is wound between the metal layers and creates the primary sealing interface. Common filler materials include flexible graphite and PTFE.

Flexible graphite is widely used for steam, hydrocarbons, and many high-temperature services. PTFE provides excellent chemical resistance but has lower temperature capability and different mechanical behavior. The filler must be selected based on the actual fluid, operating temperature, pressure, and fire-safety requirements.

Outer centering ring

The outer ring positions the gasket between the flange bolts and helps prevent excessive compression of the sealing element. It does not normally form part of the primary seal.

Centering rings are commonly manufactured from carbon steel and protected against corrosion. Their markings and color identification help installers verify the gasket size, pressure class, winding material, and filler material before installation.

Inner ring

The inner ring is installed on the bore side of the spiral-wound element. It performs several important functions:

• Supports the inner edge of the winding
• Reduces the risk of inward buckling
• Protects the sealing element from process flow
• Reduces turbulence and erosion
• Helps limit the accumulation of process fluid in the flange bore
• Provides additional control over gasket compression

The inner-ring material should be compatible with the process fluid and operating conditions. In many cases, it matches the winding material, although the complete material specification must be confirmed for the application.

ASME B16.20 defines dimensional and construction requirements for spiral-wound gaskets used with compatible raised-face and flat-face flanges. The appropriate gasket dimensions depend on nominal pipe size, flange pressure class, and flange standard.

A typical gasket designation may be written as:

ASME B16.20 spiral-wound gasket, NPS 6, Class 300, 316L stainless-steel winding, flexible graphite filler, 316L inner ring, and carbon-steel outer ring.

Spiral-wound gaskets should be compressed within their intended operating range. Insufficient compression may leave leakage paths through the filler. Excessive compression can crush the winding, damage the filler, or cause the sealing element to buckle inward.

Correct bolt tightening is therefore essential. Bolts should normally be tightened in a controlled cross pattern using several incremental passes. Flange alignment, bolt condition, lubrication, and tightening method all affect the final gasket stress.

5. Metal-Jacketed and Grooved Metal Gaskets

Metal-jacketed and grooved metal gaskets provide alternative sealing solutions for equipment and piping connections where standard spiral-wound or RTJ gaskets may not be the preferred choice. They are frequently used in heat exchangers, pressure vessels, reactors, boilers, and large-diameter flange connections.

Metal-jacketed gaskets

A metal-jacketed gasket consists of a soft compressible filler enclosed partly or completely by a metallic jacket. The filler allows the gasket to conform to the flange surface, while the jacket provides mechanical strength and protects the filler from operating pressure, temperature, and process exposure.

Common jacket materials include stainless steel, carbon steel, copper, aluminum, and nickel alloys. The filler may be made from flexible graphite or another material suitable for the service conditions.

Metal-jacketed gaskets can be manufactured in several configurations, including single-jacketed and double-jacketed designs. Double-jacketed gaskets provide greater coverage of the filler and are commonly used in heat exchanger applications.

They can also be produced with internal bars for heat exchangers containing multiple flow passes. The bars must align correctly with the pass partitions to separate the fluid paths and minimize internal leakage.

Metal-jacketed gaskets generally have limited recovery compared with spiral-wound gaskets. They require adequate and relatively uniform compressive load to create an effective seal. Flange-face condition and surface finish are especially important because the metallic jacket may not conform easily to deep scratches, corrosion, or flange distortion.

Grooved metal gaskets with covering layers

A grooved metal gasket consists of a solid metallic core with concentric grooves machined into its sealing surfaces. Thin layers of a softer material, normally flexible graphite or PTFE, are applied over the grooved faces. These products are commonly called kammprofile gaskets.

During flange tightening, the soft covering material conforms to small flange imperfections. The peaks of the metal grooves create concentrated sealing stresses, while the solid core controls compression and provides resistance to internal pressure.

Grooved metal gaskets offer several potential advantages:

• High mechanical strength
• Good blowout resistance
• Controlled compression
• Good recovery under thermal cycling
• Suitability for high-pressure and high-temperature service
• Ability to accommodate relatively low available bolt loads
• Potential reuse of the undamaged metal core after inspection and refacing, when permitted

The core material must be compatible with the process fluid and flange material. Stainless steels are commonly used, while special alloys may be required for corrosive applications. Flexible graphite coverings are suitable for many elevated-temperature services, whereas PTFE coverings may be selected for chemically aggressive fluids within their temperature limits.

Grooved metal gaskets may be manufactured with or without an outer centering ring. The centering ring assists installation and positions the sealing element correctly on the flange face.

Although these gaskets provide strong sealing performance, correct selection remains essential. Dimensions, core material, facing material, flange type, available bolt load, operating temperature, and fluid compatibility must all be evaluated. A gasket complying dimensionally with ASME B16.20 is not automatically suitable for every service condition.

6. ASME B16.20 Gasket Dimensions and Designations

ASME B16.20 provides standardized gasket dimensions to ensure compatibility with the corresponding flange size, pressure class, and facing configuration. Correct dimensional matching is essential because even a small difference in gasket diameter or ring geometry can affect gasket positioning, compression, and sealing performance.

The dimensions specified by the standard vary according to several factors:

• Gasket type
• Nominal Pipe Size
• Flange pressure class
• Applicable flange standard
• Flange facing or groove configuration
• Gasket construction
• Series A or Series B flange design, where applicable

Nominal Pipe Size and DN

Gasket sizes are generally identified using Nominal Pipe Size, abbreviated as NPS. Metric-based project documents may also show the corresponding nominal diameter, or DN.

NPS and DN are nominal designations rather than direct measurements of the gasket inside diameter. For example, an NPS 4 gasket does not necessarily have an inside diameter of exactly 4 inches. The actual dimensions depend on the gasket type, flange standard, and pressure class.

Pressure-class designation

ASME flange and gasket systems commonly use pressure-class designations such as:

• Class 150
• Class 300
• Class 400
• Class 600
• Class 900
• Class 1500
• Class 2500

The class number is a designation and should not be interpreted as the maximum allowable pressure in psi under every operating condition. Actual pressure-temperature capability depends on the flange material, temperature, applicable flange standard, and governing piping code.

A gasket selected for one pressure class may have different dimensions from a gasket of the same nominal size intended for another class. For this reason, both NPS and pressure class must appear in the gasket specification.

Spiral-wound gasket dimensions

Important dimensions for a spiral-wound gasket include:

• Inside diameter of the inner ring
• Inside diameter of the winding
• Outside diameter of the winding
• Outside diameter of the centering ring
• Gasket thickness

The outer centering-ring diameter must allow the gasket to fit within the flange bolts while remaining centered on the raised face. The sealing element must remain within the appropriate flange sealing area.

The inner-ring diameter is also important. If it is too small, the ring may project excessively into the pipe bore and disturb fluid flow. If it is too large, it may not properly support the inner edge of the winding.

Spiral-wound gaskets must therefore be selected from the dimensional table corresponding to the applicable flange standard and configuration. A gasket intended for an ASME B16.47 Series A flange may not have the same dimensions as one for a Series B flange of the same nominal size and pressure class.

RTJ gasket dimensions

Ring-Type Joint gaskets are normally designated by a ring number rather than only by pipe size and pressure class. Critical dimensions include:

• Ring width
• Ring height
• Pitch diameter
• Oval or octagonal cross-sectional geometry
• Dimensional tolerances

The ring number must match the flange groove. Incorrect matching may prevent proper flange assembly or create insufficient contact between the gasket and groove surfaces.

Type R, RX, and BX gaskets use different dimensional systems. They must not be considered interchangeable unless the applicable standard specifically permits the intended combination.

Dimensional tolerances

Gasket tolerances control how closely the manufactured product must match the specified dimensions. These tolerances are necessary because the gasket must fit correctly within a limited flange sealing area or machined groove.

A gasket outside the permitted tolerance may:

• Interfere with flange bolts
• Extend into the pipe bore
• Sit off-center on the flange face
• Contact the wrong part of an RTJ groove
• Receive uneven compression
• Reduce the reliability of the joint

A complete purchase description should clearly identify the standard, gasket type, size, class, and materials. For example:

Spiral-wound gasket, ASME B16.20, NPS 8, Class 600, 316L stainless-steel winding, flexible graphite filler, 316L inner ring, and carbon-steel outer ring.

The applicable edition of ASME B16.20 should also be stated in the purchase order or project specification.

7. Gasket Materials and Selection Criteria

Selecting the correct gasket material is as important as selecting the correct gasket dimensions. A gasket may fit the flange perfectly but still fail if its materials are incompatible with the process fluid, temperature, pressure, or flange material.

ASME B16.20 establishes material requirements and identification practices for covered gasket types. However, the standard does not select the best material for a specific application. That responsibility remains with the piping designer, equipment engineer, or project material specialist.

Metallic materials

Common metallic materials used in ASME B16.20 gaskets include:

• Soft iron
• Low-carbon steel
• Type 304 stainless steel
• Type 304L stainless steel
• Type 316 stainless steel
• Type 316L stainless steel
• Type 321 stainless steel
• Type 347 stainless steel
• Nickel
• Nickel-copper alloys
• Nickel-chromium alloys

The selected metal should provide adequate corrosion resistance and mechanical performance at the design temperature.

For an RTJ gasket, hardness is especially important. The ring material should generally be softer than the flange groove material so that the gasket deforms preferentially during tightening. A gasket that is too hard may fail to conform properly or may damage the groove.

For spiral-wound gaskets, the winding metal must withstand the process environment and operating temperature. Type 316L stainless steel is widely used because of its general corrosion resistance, but it is not suitable for every chemical service.

Filler and covering materials

Flexible graphite is one of the most common filler materials for spiral-wound gaskets. It offers good temperature resistance, conformability, and sealing performance in many steam, hydrocarbon, and process applications.

PTFE provides excellent resistance to many corrosive chemicals. However, its temperature capability is lower than that of flexible graphite, and its tendency to creep under sustained load must be considered.

Similar soft materials may be used as covering layers on grooved metal gaskets. The covering layer fills minor flange-face imperfections, while the grooved metal core provides strength and compression control.

Temperature

Temperature affects the gasket material, flange, bolts, and process fluid. When selecting a gasket, engineers should consider:

• Normal operating temperature
• Design temperature
• Startup and shutdown conditions
• Temperature cycling
• Fire exposure requirements
• Oxidation limits of the filler
• Low-temperature toughness for cryogenic service

A material suitable at room temperature may lose strength, oxidize, harden, creep, or become brittle at the actual service temperature.

Pressure and gasket stress

System pressure creates a force that attempts to separate the flanges and push the gasket out of the joint. The gasket must withstand this pressure while maintaining sufficient contact stress.

Available bolt load must also be evaluated. Some gasket constructions require greater compression than others. A gasket requiring high seating stress may not seal properly when used with weak bolts, thin flanges, or equipment nozzles with limited allowable loads.

Fluid compatibility

Every part of the gasket exposed to the process should be chemically compatible with the fluid. This includes:

• Metal winding
• Inner ring
• Metal core
• Jacket material
• Filler
• Covering layer

The selection must consider both the main process fluid and possible contaminants, cleaning chemicals, steam-out conditions, or startup fluids.

Corrosion and galvanic compatibility

Using dissimilar metals in the same joint can create galvanic corrosion when an electrically conductive fluid is present. Corrosion products can also damage the flange face and reduce long-term joint reliability.

Gasket material selection should therefore consider the flange material, process fluid, moisture exposure, and expected service life. Special alloys may be necessary for seawater, sour gas, strong acids, chlorides, or other severe environments.

The final gasket selection should be based on the most severe credible operating condition, not only the normal operating point. Manufacturer limitations, piping specifications, material compatibility data, and project requirements should all be reviewed.

8. Marking, Identification, and Quality Requirements

Correct gasket identification helps prevent the installation of an incorrect size, pressure class, or material. Because many metallic gaskets have similar external appearances, reliable marking and traceability are important parts of quality control.

Depending on the gasket type, ASME B16.20 marking may identify:

• Manufacturer’s name or trademark
• Nominal pipe size
• Flange pressure class
• Gasket type or ring number
• Winding material
• Filler material
• Inner-ring material
• Applicable standard designation

The markings must remain legible and should not damage the primary sealing surface.

Spiral-wound gasket identification

For spiral-wound gaskets, information is commonly marked on the outer centering ring. This provides a visible location where the gasket size, pressure class, manufacturer, and materials can be checked before installation.

Industry color-coding systems may also be used to identify winding and filler materials. The outer edge of the centering ring commonly indicates the winding material, while an additional stripe may identify the filler.

Color coding is useful for quick visual checks, but it should not replace reading the permanent markings, purchase documents, or material certificates. Paint may fade, become contaminated, or be incorrectly interpreted in the field.

RTJ gasket identification

Ring-Type Joint gaskets are normally marked with information such as:

• Manufacturer identification
• Ring number
• Material designation

The marking is placed where it does not interfere with the sealing contact surfaces. Installers should confirm that the ring number matches the flange groove and that the ring material meets the piping specification.

Dimensional and visual inspection

Before installation, the gasket should be inspected for:

• Correct dimensions
• Correct markings
• Surface damage
• Corrosion or contamination
• Distorted winding
• Loose filler material
• Damaged inner or outer rings
• Dents, scratches, or cracks
• Improperly attached components

RTJ sealing surfaces should be smooth and free from defects that could form leakage paths. Spiral-wound elements should not show buckling, separation, or excessive deformation.

Material certification and traceability

Critical-service projects may require additional quality documentation, including:

• Material Test Reports
• Certificates of Conformance
• Positive Material Identification records
• Dimensional inspection reports
• Hardness test results
• Heat-number traceability
• Manufacturing and inspection records

These documents are not automatically required for every gasket simply because it complies with ASME B16.20. The purchaser must clearly state any additional certification, testing, inspection, or traceability requirements in the purchase order.

Receiving inspection should compare the gasket markings and documentation against the material requisition. Any mismatch in type, size, pressure class, material, or ring number should be resolved before the gasket is released for installation.

9. Installation Guidelines for ASME B16.20 Gaskets

Even a correctly specified ASME B16.20 gasket can leak if it is improperly installed. Reliable flange sealing depends on the combined condition of the gasket, flange faces, bolts, nuts, washers, lubrication, alignment, and tightening procedure.

Before installation, confirm that the gasket matches the following joint information:

• Nominal Pipe Size
• Flange pressure class
• Flange standard
• Flange facing or RTJ groove
• Gasket type
• Gasket and filler materials
• Project piping specification

The flange faces must be cleaned without damaging the sealing surface. Old gasket material, rust, paint, grease, dirt, and foreign particles should be removed. Metallic tools that may scratch the flange should be used carefully.

Raised-face flanges should be inspected for radial scratches, dents, corrosion, warping, and other surface damage. A radial scratch extending across the sealing area can create a direct leakage path.

For RTJ connections, inspect both grooves for:

• Scratches and dents
• Corrosion or pitting
• Incorrect groove dimensions
• Residual material from the previous gasket
• Mechanical damage caused during gasket removal

The gasket must also be clean, dry, correctly marked, and free from damage. Spiral-wound gaskets should not have loose windings, distorted rings, exposed filler, or inward buckling. RTJ gaskets should not contain dents, deep scratches, corrosion, or damaged sealing surfaces.

The flanges should be aligned before the gasket is inserted. Bolts should not be used to force severely misaligned piping into position because the resulting external loads can rotate the flanges and produce uneven gasket compression.

The gasket should be centered carefully. The outer ring of a spiral-wound gasket normally assists with positioning between the flange bolts. The gasket must not extend unintentionally into the pipe bore or sit partially outside the raised-face sealing area.

RTJ rings must be placed evenly in the appropriate flange groove. The ring number, type, and material should be verified before the flanges are brought together.

Bolts and nuts must be inspected for corrosion, damaged threads, incorrect size, or incompatible materials. Any required washers should also be checked. The specified lubricant should be applied consistently to the relevant thread and nut-bearing surfaces unless the approved assembly procedure states otherwise.

Lubrication has a major influence on the relationship between applied torque and achieved bolt load. Applying a torque value intended for lubricated bolts to dry fasteners may produce insufficient bolt tension. Conversely, using a low-friction lubricant with an inappropriate torque value may overstress the bolts or gasket.

Bolts should normally be tightened in a controlled cross pattern using multiple incremental passes. A typical procedure may include:

• Initial hand tightening
• Alignment or snugging pass
• Intermediate torque passes
• Final target-torque pass
• Circular verification pass

The actual sequence, number of passes, and target torque should follow the approved project procedure. Torque values should not be taken from a generic table without considering bolt material, lubricant, flange design, gasket type, and required gasket stress.

Gasket compounds, sealing paste, grease, or adhesive should not be applied unless specifically approved. These substances may affect friction, gasket compression, chemical compatibility, and long-term sealing performance.

Used spiral-wound, metal-jacketed, and RTJ gaskets should generally not be reused because they experience permanent deformation during assembly. A new gasket should normally be installed whenever a flange joint is opened.

10. ASME B16.20 Compared With Related Standards

ASME B16.20 works together with several flange, gasket, piping, and bolted-joint standards. Understanding their different scopes helps engineers avoid using one document for requirements actually controlled by another.

ASME B16.20 versus ASME B16.21

ASME B16.20 covers metallic and semi-metallic gaskets, including:

• Ring-Type Joint gaskets
• Spiral-wound gaskets
• Metal-jacketed gaskets
• Grooved metal gaskets with covering layers

ASME B16.21 covers nonmetallic flat gaskets for pipe flanges. Typical materials include rubber, compressed fiber, graphite sheet, PTFE, and other nonmetallic gasket materials.

The principal difference is therefore the gasket construction. ASME B16.20 is used for metallic and semi-metallic designs, while ASME B16.21 addresses nonmetallic flat gaskets.

The two standards should not be considered interchangeable. A soft gasket and a spiral-wound gasket may require different flange surface conditions, bolt loads, pressure-temperature limitations, and installation practices.

ASME B16.20 and ASME B16.5

ASME B16.5 establishes requirements for pipe flanges and flanged fittings within its applicable size and pressure-class ranges. It covers subjects such as:

• Flange dimensions
• Bolt-hole patterns
• Flange facings
• Materials
• Pressure-temperature ratings
• Tolerances
• Marking

ASME B16.20 supplies the corresponding requirements for metallic gaskets. In simple terms, ASME B16.5 defines the flange, while ASME B16.20 defines compatible metallic gasket dimensions and construction requirements.

Compliance with ASME B16.20 does not establish the pressure-temperature rating of a flange. That rating must be determined from the applicable flange standard and material group.

ASME B16.20 and ASME B16.47

ASME B16.47 covers large-diameter steel flanges. It includes two flange families:

• Series A
• Series B

Series A and Series B flanges of the same nominal size and pressure class may have different dimensions, bolt patterns, and gasket dimensions. The gasket must therefore be specified for the correct series.

Writing only “NPS 30 Class 300 gasket” may not provide enough information for a large-diameter connection. The flange standard and series should also be included.

ASME B16.20 and API 6A

API Specification 6A applies primarily to wellhead and tree equipment used in the oil and gas industry. ASME B16.20 includes dimensional requirements for certain RTJ gaskets used with API 6A equipment, including pressure-energized RX and BX rings.

Selection must be based on the correct ring type and ring number. Type R, RX, and BX gaskets have different geometries and are not universally interchangeable.

ASME B16.20 and ASME PCC-1

ASME B16.20 is a gasket product standard. It does not provide a complete procedure for assembling all bolted flange joints.

ASME PCC-1 provides guidelines for assembling pressure-boundary bolted flange joints. It addresses subjects such as flange inspection, bolt tightening, lubrication, gasket installation, assembly procedures, and personnel qualification.

The two documents serve complementary purposes: ASME B16.20 defines the gasket, while ASME PCC-1 supports proper joint assembly.

11. Common Gasket Selection and Installation Mistakes

Many flange leaks result from selection or installation errors rather than a defect in the gasket itself. The following mistakes should be avoided.

Selecting by pipe size only

A gasket cannot be selected using only NPS or DN. Pressure class, flange standard, flange facing, and gasket type must also be identified.

Confusing the flange standard with the gasket standard

ASME B16.5 and ASME B16.47 specify flanges, while ASME B16.20 specifies metallic gaskets. Listing only ASME B16.20 does not fully describe the flange connection.

Mixing Series A and Series B dimensions

Large-diameter ASME B16.47 Series A and Series B flanges may require different gaskets, even when their nominal size and pressure class are identical.

Using the wrong RTJ ring

An incorrect ring number or gasket type may not fit the groove or produce the required sealing contact. R, RX, and BX rings must be carefully distinguished.

Installing an unsuitable material

The gasket material must be compatible with the process fluid, temperature, flange material, and environmental conditions. General-purpose stainless steel or graphite is not automatically suitable for every service.

Omitting the required inner ring

An incorrect spiral-wound construction can allow inward buckling, filler damage, or exposure of the winding to process flow. The specified inner ring should not be removed to simplify installation.

Using a damaged gasket

A spiral-wound gasket with distorted winding or an RTJ ring with scratched sealing surfaces should not be installed. Damage may prevent uniform sealing contact.

Applying incorrect bolt torque

Both insufficient and excessive bolt load can cause leakage. Tightening should follow an approved procedure based on the complete joint design rather than an arbitrary torque value.

Reusing a compressed gasket

Most ASME B16.20 gaskets undergo permanent deformation during tightening. Reuse may result in insufficient compression and unreliable sealing.

Ignoring flange condition

A new gasket cannot reliably compensate for severe flange misalignment, damaged grooves, excessive corrosion, deep radial scratches, or unacceptable flange rotation. These conditions should be corrected before assembly.

Conclusion

ASME B16.20 is a key standard for metallic and semi-metallic gaskets used in industrial flange connections. It establishes requirements for the materials, dimensions, tolerances, construction, and marking of Ring-Type Joint, spiral-wound, metal-jacketed, and grooved metal gaskets with covering layers.

Compliance with ASME B16.20 helps ensure that a gasket is dimensionally compatible with the corresponding standardized flange. However, dimensional compliance alone does not guarantee a leak-free joint. Engineers must also consider the flange standard and facing, pressure class, operating temperature, process-fluid compatibility, available bolt load, gasket material, and applicable project specifications.

Correct installation is equally important. Flange faces and RTJ grooves should be inspected and cleaned, the gasket must be accurately centered, and bolts should be tightened using a controlled procedure. Damaged, incorrectly specified, or previously compressed gaskets should not be installed.

By correctly combining ASME B16.20 gasket requirements with compatible flange standards and proper assembly practices, engineers can improve flange reliability, reduce leakage risks, and increase the safety of piping and equipment systems.

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