Sealing face is critical contact surface of ASME B16.5 flange that mates with gaskets to create a leak-tight seal. The surface’s design, dimensions, and finish directly determine the sealing reliability of piping connections. ASME B16.5 strictly regulates sealing face geometry, surface finish, and tolerances. It ensures universal compatibility across flanges, gaskets, and fasteners from different manufacturers.

Among the various sealing face designs, Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ) are the most widely used in industrial applications. All are engineered to meet specific pressure, temperature, and media requirements while adhering to strict ASME B16.5 compliance criteria.

ASME B16.5 Sealing Face Types: RF, FF & RTJ

ASME B16.5 categorizes RF, FF, and RTJ as primary designs for industrial flanged connections, each with distinct structural characteristics tailored to different operating conditions. All three types must comply with the standard’s dimensional and material specifications. But their unique geometries make them suitable for varying pressure ranges and application scenarios.

The Raised Face (RF) features a surface raised above the flange’s bolt circle plane. The Flat Face (FF) is flush with the bolt circle plane for low-pressure use. And the Ring Type Joint (RTJ) incorporates a circular groove to mate with a metal ring gasket for high-pressure/high-temperature service. Together, these three designs cover the majority of industrial piping needs, from low-pressure water and gas lines to high-pressure refinery and power plant systems, with ASME B16.5 ensuring consistent manufacturing and interchangeability for each type.

Specification for RF (Raised Face)

ASME B16.5 outlines precise technical specifications for Raised Face (RF) sealing faces. And RF sealing face is the most versatile and commonly used design across Class 150 to 2500 flanges. The standard mandates two primary raised face heights: 1.6 mm (1/16″) for Class 150 and 300 flanges, and 6.4 mm (1/4″) for Class 400, 600, 900, 1500, and 2500 flanges. The raised face’s diameter (sealing surface) is strictly defined relative to the flange’s nominal pipe size (NPS) and pressure class, with tight dimensional tolerances to ensure proper gasket fit.

For surface finish, ASME B16.5 requires a 125–250 microinch Ra (3–6 μm Ra) serrated finish. It is typically created by concentric or spiral machining with 45–55 grooves per inch. The serrations enhance gasket contact and create a mechanical seal by trapping fluid within the grooves, preventing leakage.

Additionally, the standard specifies that RF faces must be free of scratches, pits, and deformities. And the raised surface must be concentric with the flange bore to ensure uniform gasket compression during bolt tightening.

All RF flanges must be marked with ASME B16.5 compliance, including pressure class, NPS, and material grade, to verify adherence to these specs.

Specification for FF (Flat Face)

Flat Face (FF) sealing faces are governed by ASME B16.5 specifications tailored exclusively for Class 150 and lower pressure ratings. It’s designed for low-stress, non-critical industrial piping applications. ASME B16.5 mandates that FF surfaces be perfectly flush with the flange’s bolt circle plane, with no raised or recessed areas. This is to ensure full contact with non-metallic full-face gaskets. And it is also the only gasket type approved for FF flanges by the standard.

The surface finish requirement for FF faces is a 250–500 microinch Ra (6–12 μm Ra) smooth finish. This is less aggressive than RF serrations to prevent damage to soft non-metallic gaskets (e.g., rubber, PTFE, non-asbestos) during installation.

ASME B16.5 strictly prohibits pairing FF flanges with RF flanges. Mainly because the mismatched surfaces create uneven gasket compression and almost always result in leakage. The standard also specifies tight flatness tolerances for FF faces (no more than 0.001″ per inch of diameter) to ensure uniform pressure distribution across the gasket, and requires that bolt holes be positioned to avoid interference with the sealing surface.

Like all ASME B16.5 flanges, FF units must include compliance markings and dimensional verification to meet the standard’s quality criteria.

Specification for RTJ (Ring Type Joint)

Ring Type Joint (RTJ) sealing faces are designed for Class 600 to 2500 high-pressure/high-temperature (HP/HT) piping systems. And engineered for extreme operating conditions in oil and gas exploration, refineries, and power generation.

ASME B16.5 defines RTJ faces as a circular groove machined into the flange face, with precise groove dimensions (width, depth, and radius) that vary by pressure class and NPS. The groove is designed to perfectly cradle a metal ring gasket that deforms plastically under bolt pressure to create a metal-to-metal seal.

The standard mandates a ≤ 1.6 μm Ra (63 microinch Ra) mirror-smooth finish on the groove’s sidewalls. Mainly aims to ensure maximum contact with the metal ring and prevent leakage in HP/HT service. ASME B16.5 also specifies that RTJ flanges must be manufactured from high-strength alloy steels to withstand extreme pressure and temperature. And the groove must be concentric with the flange bore to ensure even ring compression.

The standard prohibits modifying RTJ groove dimensions, as any deviation from ASME B16.5 specs will compromise the metal-to-metal seal and lead to catastrophic failure in critical systems. All RTJ flanges must undergo rigorous dimensional inspection and pressure testing to confirm ASME B16.5 compliance.

ASME B16.5 Flange Types & Sealing Faces

Critical ASME B16.5 Compliance Requirements for All Sealing Faces

Beyond type-specific specifications, ASME B16.5 enforces universal compliance requirements for RF, FF, and RTJ sealing faces.

First, dimensional accuracy is non-negotiable. All sealing face geometries (height, diameter, groove size, flatness) must fall within the standard’s tight tolerance ranges with no deviations that could affect gasket fit or seal integrity.

Second, surface quality is mandated for all types. Sealing faces must be free of scratches, dents, pits, rust, and machining burrs, as any surface imperfection can create a leak path for process media.

Third, material compatibility is required. The flange material (and thus the sealing face material) must be approved by ASME B16.5 for the intended pressure, temperature, and media. Together with corrosion-resistant coatings (e.g., galvanizing, passivation) specified for harsh environments in line with the standard.

Fourth, marking and traceability are mandatory. Every ASME B16.5 flange must be permanently marked with the standard designation (ASME B16.5), pressure class, NPS, material grade, manufacturer’s name, and heat number, enabling full traceability and compliance verification.

Finally, performance testing is required for critical applications. ASME B16.5 specifies hydrostatic and pneumatic testing protocols for flanges with sealing faces to confirm leak-tightness at pressures above the rated operating pressure.

Violation of any of these universal requirements results in a loss of ASME B16.5 compliance and renders the flange unfit for industrial use.

How to Ensure ASME B16.5 Sealing Face Compliance in Production

Manufacturing RF, FF, and RTJ sealing faces that meet ASME B16.5 compliance requires a rigorous, standardized production process with strict quality control at every stage.

The process begins with raw material verification. Only ASME B16.5-approved steel grades (e.g., A105, A350 LF2, A182 F304) are used, with material certificates and heat number traceability to confirm compliance.

Next, precision machining is critical. CNC machines with calibrated tooling are used to produce sealing face geometries (RF height, FF flatness, RTJ groove dimensions) to ASME B16.5’s exact tolerances, with real-time dimensional monitoring to avoid deviations. For surface finish, specialized machining tools are used to create the ASME-specified serrations (RF) or smooth finish (FF/RTJ). With surface roughness testers verifying Ra values meet the standard’s requirements.

After machining, 100% dimensional inspection is performed using calibrated gauges, micrometers, and coordinate measuring machines (CMM) to confirm all sealing face specs align with ASME B16.5.

Surface quality inspection follows, with visual and tactile checks to ensure no imperfections, and non-destructive testing (NDT) (e.g., PT, MT) for critical HP/HT RTJ flanges.

Finally, permanent marking is applied in accordance with ASME B16.5. And a compliance certificate is issued for each flange, documenting material, dimensions, finish, and testing results.

Implementing a certified quality management system (e.g., ISO 9001) further ensures consistent ASME B16.5 compliance, with regular audits and tool calibration to maintain production standards.

Application Scenarios

ASME B16.5-compliant RF, FF, and RTJ sealing faces are engineered for specific industrial application scenarios. Their design and compliance specs match the unique demands of different operating conditions.

Flat Face (FF) flanges are ideal for low-pressure, low-temperature non-critical systems (Class 150 and below). Such as municipal water lines, low-pressure air compressors, and general manufacturing process piping with non-corrosive media (water, air, mild chemicals). They are the preferred choice for applications where easy installation and compatibility with soft non-metallic gaskets are prioritized.

Raised Face (RF) flanges are the all-purpose workhorse of industrial piping, suitable for Class 150 to 2500 systems across oil and gas, petrochemical, and power generation. They are used for a wide range of media and operating temperatures. Also they offer a balance of sealing reliability, cost-effectiveness, and ease of installation. All these characteristics make them the most commonly specified ASME B16.5 sealing face type.

Ring Type Joint (RTJ) flanges are exclusively used for high-pressure/high-temperature critical systems (Class 600 to 2500). For example, oil and gas wellheads, refinery fractionation columns, power plant boiler systems, and chemical reactors handling extreme process conditions. That is, high-pressure steam, corrosive hydrocarbons, high-temperature fluids. Their metal-to-metal seal ensures leak-tight performance in scenarios where RF and FF flanges would fail. Strict ASME B16.5 compliance is critical to prevent catastrophic system failure in these high-risk applications.

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Hastelloy C276 is an alloy that stands out due to its unique combination of elements: its main components are nickel, molybdenum, and chromium, with trace amounts of iron, tungsten, cobalt, and other elements. This combination of elements gives Hastelloy C276 exceptional properties, which are extended to the flanges made from it. The two most commonly used thread standards globally are BSP and NPT threads. Although their purposes are similar, they have different characteristics and applications.

Specifications of Hastelloy C276 Flanges

Hastelloy C276 Flange Standards

Material Standards: ASTM B564 (forged flanges), UNS N10276, Werkstoff Nr. 2.4819, etc.

Dimension Standards:

ASME B16.5 (for pipe flanges and flange fittings from NPS 1/2“ to NPS 24”)

ASME B16.47 (for large-diameter steel flanges from NPS 26“ to NPS 60”)

EN 1092 (European flange standard)

DIN (German standard)

JIS (Japanese standard)

Common Types of Hastelloy C276 Flanges

Chemical Composition of ASME SB 564 N10276 Flanges

· High nickel (Ni) content: Ensures the stability of the alloy in reducing media, forming the foundation for corrosion resistance;

· Chromium (Cr): Provides oxidation resistance and corrosion resistance in oxidizing media (such as nitric acid);

· Molybdenum (Mo) + Tungsten (W): Significantly enhances resistance to localized corrosion (pitting corrosion, crevice corrosion), especially in chloride-containing environments;

· Low carbon (C): Prevents the formation of carbides between carbon and chromium, thereby preventing intergranular corrosion.

ASTM B564 Hastelloy C276 Mechanical Properties

Equivalent Grades of Hastelloy C276 Flanges

Key Features

✅ Exceptional corrosion resistance: exhibits outstanding resistance to strong oxidizing and reducing media such as hydrochloric acid, sulfuric acid, chlorides, and chlorine gas.

✅ Superior mechanical properties: maintains stable strength and toughness even under high-temperature, high-pressure conditions or in strongly acidic environments.

✅ Strong resistance to localized corrosion: Effectively resists pitting corrosion, crevice corrosion, and intergranular corrosion.

✅ Good weldability: Easy to process and weld, with no reduction in corrosion resistance in the welded area.

✅ High-temperature performance: Hastelloy C276 exhibits excellent stability, particularly maintaining strength and structural integrity at high temperatures around 700°C.

Hastelloy C276 Flanges Dimension

Application Scenarios

Hastelloy C276 flanges, renowned for their exceptional corrosion resistance, are primarily used in extreme environments where conventional materials cannot withstand the conditions. Typical applications include:

Chemical and Petrochemical Industries

Environmental Protection Industry

Pharmaceutical and Food Industries

Marine Engineering

Nuclear Industry

Installation and Maintenance Guidelines

Avoid contact between dissimilar metals: When in contact with metals of lower potential, such as carbon steel, galvanic corrosion may occur. Insulating gaskets (e.g., PTFE) or coatings should be used to isolate the metals;

Gaskets selection: Prioritize gaskets with matching corrosion resistance, such as PTFE or metal-backed gaskets, to prevent gasket material corrosion by the medium and subsequent leakage;

Cleaning and Pre-Treatment: Before installation, remove oil stains and oxide scale from the flange surface using a stainless steel wire brush or specialized cleaner to prevent impurities from affecting sealing performance;

Torque Control: Apply tightening torque according to flange specifications and pressure ratings in accordance with standards to avoid over-tightening, which can cause flange deformation or bolt breakage.

You can get an offer for products in below material forms:

-Pipe and Tube (EN 10216-5, ASTM A213, ASTM A249, A312, A790,)

-Forged Fitting and Flange (ASTM A182 , ASTM A105,ASTM B564 )

-Butt Weld Fittings (ASTM A234, ASTM A403,ASTM A815)

-Round bar , Billet (ASTM A276, ASTM A479)

– Plate, Sheet, Strip(ASTM A240, EN 10028-7, A480)

-Bolting, Nuts（ASTM A193, A194, A320）

Hastelloy C276 Flanges Exported Countries

We Export  Hastelloy C276 Flanges to Saudi Arabia, United Arab Emirates, Qatar, Bahrain, Oman, Kuwait, Turkey, Egypt, Yemen , Syria, Jordan, Cyprus, Singapore, Malaysia, Indonesia, Thailand, Vietnam, South Korea, Japan, Sri Lanka, Maldives, Bangladesh, Cambodia, Argentina, Bolivia, Brazil, Venezuela, Colombia, Ecuador, Guyana, Paraguay, Uruguay, United States Of America, Canada, Mexico, Panama, Jamaica, Bahamas, Denmark, Norway, Germany, France,Italy, United Kingdom, Spain, Belgium, Greece, Czech Republic, Portugal, Hungary, Albania, Austria, Finland, Ireland, Croatia, Malta, Nigeria, Algeria, Angola, South Africa, Libya, Egypt, Sudan, Europe, Africa, Asia, North America, South America, Middle East.etc

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This customer has always been very demanding on product quality and material performance, and this time chose 904L flanges because of its excellent performance and extraordinary durability in extremely corrosive environments. We are well aware that these flanges will become an indispensable “connection point” in their key projects, carrying the safe transportation of fluids and the stable operation of equipment.

904L is a high alloy austenitic stainless steel, known for its excellent corrosion resistance, especially in dealing with strong acidic environments (such as sulfuric acid, phosphoric acid) and chloride corrosion (pitting, crevice corrosion and stress corrosion cracking). Therefore, 904L flanges are important components for connecting critical piping systems to ensure long-term stable operation under harsh conditions.

Contact us

Purchase List

Dimensional Inspection of 904L Flange

1. Outer Diameter
   Ensure overall compatibility: Verify that the flange can be properly installed within the reserved space in the piping system without interference from surrounding equipment or structures.
2. Thickness
   Ensure pressure resistance: Flange thickness is a critical factor in determining its pressure-bearing capacity. Sufficient thickness ensures the flange will not deform or crack under rated pressure, maintaining system sealing performance.
3. Sealing Face Diameter
   Ensure sealing integrity: This is one of the most critical inspection points. The sealing face diameter must precisely match the selected gasket size to ensure uniform compression under pressure and form an effective seal to prevent fluid leakage.
4. Bolt Circle Diameter (BCD)
   Ensure bolt hole alignment: This is a decisive factor for proper flange connection. An accurate bolt circle diameter ensures full alignment with the mating flange’s bolt holes, allowing bolts to pass through smoothly and be evenly stressed, avoiding damage from forced installation.
5. Number and Diameter of Bolt Holes
   Ensure connection strength: The number and diameter of bolt holes must meet the standard to ensure enough bolts are available to bear the stress at the flange connection and to apply uniform preload on the gasket.
6. Pipe End Outside Diameter
   Ensure match with pipe OD: This is the core objective. The outside diameter of the weld neck portion of the flange must closely match the pipe’s outside diameter to ensure proper alignment during welding, reduce misalignment, and achieve a high-quality weld joint.

Specification of Forged Steel Flange

ASTM A182 F904L Flange Chemical Composition

ASTM A182 F904L Flange Mechanical Property

PN16 Forged Flange Dimensions

Applications of 904L Weld Neck & Blind Flanges

Sulfuric acid treatment and production

Seawater and brine treatment

Marine engineering and offshore platforms

Desalination plants

Coastal power plants

Pollution control equipment

Flue gas desulfurization (FGD) systems

Chemical and petrochemical industries:

Pharmaceutical industry

Food and beverage industry

Pulp and paper industry

The post 904L Weld Neck & Blind Flange Order appeared first on Quality Manufacturer of Industrial Pipe Fittings.

Product Descriptions

Weld Neck Flange Chemical Composition

Weld Neck Flange Mechanical Properties

316L Weld Overlay Chemical Composition

316L Weld Overlay Mechanical Properties

Weld Neck Flange with 316L Weld Overlay Inspection

According to ASME B16.5, the flange dimensions have been inspected, and all critical measurements including outside diameter, inside diameter, bolt circle, flange face height, and sealing surface dimensions are within the specified tolerance range. And these product passed inspection and are qualified.

Weld Neck Flange with 316L Weld Overlay Package

We package our export flanges in sturdy wooden boxes to prevent shipping damage and ensure easier handling and stacking. They also provide reliable protection against shock and moisture, helping to ensure your products arrive safely and intact.

Class 150 lb Weld Neck Flange Dimensions & Weight 

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What is Hot Dip Galvanized Threaded Flange

Hot-Dip galvanized is a process in which the flanges are immersed in a bath of molten zinc to prevent the steel from corroding. This is done after a pervasive chemical cleaning to remove rust, oil, and mill scale for the flange. A rule of thumb says that it generally corrodes at a 1/30 rate of bare carbon steel.

Hot dip galvanized Threaded flange is connected to pipes or other equipment through threads. It is a detachable connection method. In the pipeline system, threaded flanges play the role of connecting, sealing and supporting pipelines. Carbon steel threaded flanges are widely used in industrial fields such as petroleum, chemical, electric power, metallurgy, and pharmaceuticals to connect various pipelines, valves, pumps and other equipment.

Hot dip galvanized threaded flanges are renowned for their ability to withstand the harshest environments. We offer HDG Flanges in Norms: EN 1092-1,ASME B16.5 etc.

Materials & Grades of Threaded Flange

ASEM B16.5 Class 150 Threaded Flange Dimensions & Weight

Uses and Applications

ZIZI is pleased to introduce to you that we are a professional company engaged in the production and processing of pipes and fittings, hot dip galvanized threaded flange able to meet the various requirements of customers in the following fields:

● Construction

● Bridges

● Petrochemical industry

● Shipbuilding industry

● Engineering

● Offshore and onshore services

● Power generation industry

● Food processing industry

● Oil and gas industry

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