Facing Types
Threaded flanges are available in two facing types: ring joint flanges and raised face flanges.
Raised Face Threaded Flange
Raised face flanges can be easily identified when the gasket surface area extends above the bolted line of the flange. They are compatible with a wide range of gaskets, including flat, semi-metallic, and metallic types, available in both ring and full configurations.
The primary purpose of the raised face flange design is to concentrate the pressure of the two mating flanges on a small surface area, thereby enhancing the strength of the seal.
The height of the raised face surface varies depending on the flange pressure rating. For instance, for pressure classes 150 and 300, the height typically measures 1.6 mm or 1/16 inch, whereas for pressure classes ranging from 400 to 2500, the raised face height is approximately 6.4 mm or 1/4 inch.
RTJ Threaded Flange
The Ring Joint Flange features a circular groove designed to accommodate the ring joint gasket. This configuration is preferred for applications necessitating metal-to-metal seals, particularly under conditions of high pressure and high temperature.
Referred Standard and Grades
ASTM A105: Standard forged carbon steel pipes components for environmental and high temperature / high-pressure systems.
ASTM A182: The standard for alloy and stainless threaded flanges. Common Stainless steel grades: F304, 304/, F316, F316L, alloy grades: F5, F9, F11, F22, F91.
Convenient Installation and Maintenance
The threaded flange is attached to the threaded pipe via threading, which is machined into the inner hole of the flange. This eliminates the need for welding, making installation and maintenance considerably more convenient compared to other flange types like slip-on flanges or socket weld flanges.
Application in Special Circumstance
Threaded flanges find application in situations where welding is challenging or not feasible, such as when preserving the galvanized layer of a pipe. However, they should not be employed on pipes experiencing frequent temperature fluctuations or operating in extreme temperature conditions, specifically above 260°C or below -45°C.
According to the ASME B31.3 standard, when steel pipe is threaded and utilized for steam service above 250 psi or for water service above 100 psi with water temperatures exceeding 220°F, the pipe must be seamless and possess a thickness equivalent to at least schedule 80 of ASME B36.10.
Measurement
If threaded pipe flange can be measured accurately, the following data shall be required:
O: Outside Diameter of flange
C: Thickness of flange
R: Diameter of raised face
X: Hub Diameter at base
Y: Length through the hub
T: Minimum thread length
Q: Minimum diameter of the bolt circle
