The selection of a flange face type—primarily Raised Face (RF), Flat Face (FF), or Ring Type Joint (RTJ)—is a critical decision in piping system design. This choice directly influences the joint’s sealing integrity, pressure-handling capabilities, and maintenance requirements. While RF flanges are ubiquitous in process industries, RTJ flanges are specified for high-pressure, high-temperature severe service. This guide compares the design, application, and sealing mechanisms of each type to ensure proper selection for safety and reliability.
Flange Face Types: An Overview
What Is a Flange Face?
The flange face is the machined surface of a flange that comes into contact with a gasket to form a seal. The specific geometry of this surface (RF, FF, or RTJ) dictates the type of gasket used and the way sealing stress (bolt load) is concentrated. This, in turn, determines the joint’s suitability for different pressures, temperatures, and media.
Key Differences at a Glance
| Flange Type | Design & Sealing Mechanism | Primary Applications |
|---|---|---|
| Raised Face (RF) | Has a raised gasket surface to concentrate bolt load. Uses soft or semi-metallic gaskets. | Most common type in oil & gas, petrochemical, and power plants. Versatile for low to high pressures. |
| Flat Face (FF) | Entire face is flat. Uses a “full-face” gasket. Spreads bolt load over a wide area. | Low-pressure systems (e.g., waterworks) and for mating with brittle materials like cast iron. |
| 링 타입 조인트(RTJ) | Features a machined groove for a solid metal gasket, creating a high-integrity metal-to-metal seal. | Severe service: high pressure (>Class 600), high temperature, and critical applications. |
Raised Face (RF) Flanges
Design and Features
A Raised Face (RF) flange is the most common type used in process plant applications. It is characterized by a small portion of the flange face that is raised above the bolting circle. This design serves a critical purpose: it concentrates the bolt load onto a smaller gasket area, increasing the contact pressure (gasket stress) and creating a more robust and reliable seal.
The surface of the raised face typically features a specific serrated finish (either spiral or concentric, per ASME B16.5) to “bite” into the gasket material, further enhancing sealing integrity.
응용 프로그램
RF flanges are the workhorse of industrial piping. Their versatility makes them suitable for a vast range of conditions, from low to high pressures and temperatures. They are the standard choice in 판막 manufacturing (e.g., flanged gate valves, flanged globe valves) for industries like:
- Oil & Gas (upstream, midstream, downstream)
- Petrochemical & Refining
- 발전
- 화학 공정
- 수처리
Pros & Cons
| 장점 | 단점 |
|---|---|
| Strong, reliable seal for a wide range of conditions. | Higher bolt load concentration can damage brittle (e.g., cast iron) mating flanges. |
| Versatile gasket compatibility (soft, semi-metallic). | Not suitable for the extreme pressures/temperatures that require RTJ. |
| Common and readily available. |
Flat Face (FF) Flanges
Design and Features
A Flat Face (FF) flange features a sealing surface that is in the same plane as the bolting circle. This design requires a “full-face” gasket that covers the entire flange face, from the bore to the outside diameter, including the bolt holes. The primary function of this design is to spread the bolt load over the maximum possible area, thus reducing the contact pressure and minimizing the risk of flange bending or cracking.
응용 프로그램
FF flanges are predominantly used in low-pressure applications (e.g., ANSI Class 125/150) and where the mating flange is made of a brittle material. It is standard practice to mate an FF flange only with another FF flange, typically using a soft, non-metallic gasket.
- Mating to cast iron valves, pumps, or equipment.
- Waterworks and utility lines.
- Low-pressure HVAC systems.
Pros & Cons
| 장점 | 단점 |
|---|---|
| Prevents point loading, protecting brittle flange materials. | Low contact pressure, making it unsuitable for high-pressure service. |
| Generally lower in cost. | Gasket seating is less precise than RF. |
| Full-face gasket is stable and easy to align. | Limited temperature and pressure range. |
Ring Type Joint (RTJ) Flanges
Design and Features
A Ring Type Joint (RTJ) flange is a high-integrity design for severe service conditions. It features a precision-machined groove cut into the flange face, which accommodates a solid metal ring gasket (e.g., oval or octagonal cross-section). As the flange bolts are tightened, the gasket is compressed, coining (deforming) to create an extremely tight, robust metal-to-metal seal.
This design is self-actuating; as internal pressure increases, it pushes the gasket further into the groove, strengthening the seal. The gasket material is specified to be softer than the flange material to ensure it deforms before the flange.
응용 프로그램
RTJ flanges are the default choice for critical, high-pressure, and/or high-temperature applications where leak integrity is paramount.
- High-pressure systems (ASME Class 600 and above).
- High-temperature (e.g., >800°F / 427°C) services.
- Offshore oil and gas production.
- Refining and petrochemical applications.
- Wellhead and Christmas tree equipment.
Pros & Cons
| 장점 | 단점 |
|---|---|
| Extremely robust, leak-proof metal-to-metal seal. | Significantly higher cost (flanges and metal gaskets). |
| Suitable for the highest pressures and temperatures. | Installation requires high skill and precision. |
| Seal is self-energizing under pressure. | Gaskets are single-use and must be replaced. |
| Resistant to vibration and thermal cycling. | Groove can trap debris and is susceptible to damage. |
How to Choose the Right Flange Face
Selecting the correct flange face type requires a review of several key factors. Mismatching flange types (e.g., bolting an RF to an FF) is a dangerous practice that can lead to gasket failure and flange damage.
- Pressure and Temperature: This is the primary driver.
- Low-Pressure (Class 125/150): FF is common, especially with brittle materials.
- Medium-High Pressure (Class 150-600): RF is the standard choice.
- High/Extreme Pressure (Class 600+): RTJ is generally required.
- Mating Materials: If mating to brittle materials like cast iron or some plastics/FRP, an FF flange with a full-face soft gasket is necessary to prevent cracking the flange.
- Service Fluid & Safety: For hazardous, toxic, or highly flammable fluids, or where “zero-leak” performance is critical, the superior integrity of an RTJ or a high-quality RF joint is essential.
- Cost & Maintenance: FF and RF flanges are generally lower in total cost (installation and components) than RTJ flanges, which require more expensive gaskets and skilled labor.
For demanding industrial applications, JH 밸브 products are typically supplied with Raised Face (RF) flanges as standard, ensuring a reliable and robust seal. We also provide RTJ flange connections for our 고압 and severe service valves.
자주 묻는 질문
What is the main difference between RF, FF, and RTJ flange faces?
The main difference is the sealing geometry. A Flat Face (FF) is completely flat. A Raised Face (RF) has a raised surface to concentrate gasket pressure. A Ring Type Joint (RTJ) has a groove that compresses a metal ring for a metal-to-metal seal.
Can you mix different flange face types, e.g., RF and FF?
No. Mating different flange types is highly dangerous and not permitted by piping codes. For example, bolting an RF flange to an FF flange will create a high-stress point load on the brittle FF flange, likely causing it to crack and fail.
How do you choose the right gasket for each flange type?
FF flanges *must* use a full-face gasket (typically soft non-metallic). RF flanges are versatile and use gaskets that sit inside the bolts (soft, spiral wound, metal-jacketed). RTJ flanges *must* use a specific metal ring gasket (oval or octagonal) that matches the groove.
Do RTJ flanges require special installation?
Yes. RTJ installation requires high precision. The grooves must be perfectly clean and undamaged, and the gasket must be new (they are single-use) and correctly seated. Bolts must be tightened to a high torque using a calibrated wrench in a specific pattern to ensure the metal gasket deforms correctly.
