What Is a Loose Flange?
A loose flange, also known as a lapped or lap joint flange, is a flange type utilized in piping systems for creating detachable joints. It is especially useful in applications where direct welding of the flange to the pipe is impractical, facilitating easy assembly and disassembly for inspection or modification.
Uses of Loose Flanges
Loose flanges find application across various industries where fluid dynamics involve low pressure and temperature, and the risk of leakage is minimal. These industries include paper mills, chemical plants, shipbuilding (particularly for LNG and chemical carriers), and building infrastructure (e.g., water supply and fire protection systems).
Principle of Loose Flanges
The distinctive feature of a loose flange is its assembly with a stub end, which is welded to the pipe. This configuration allows for rotational adjustment of the flange, facilitating alignment of bolt holes and easing the installation process. Additionally, in systems conveying corrosive fluids, the non-contact nature of the loose flange with the fluid allows for the use of less expensive materials for the flange while maintaining system integrity.
Types of Loose Flanges
Selection criteria for loose flanges include nominal diameter, nominal pressure, and material composition, all of which depend on the specific requirements of the piping system. Common materials for loose flanges include carbon steel among others, selected based on factors like fluid compatibility, environmental conditions, and cost.
Standards and Assembly of Loose Flanges
Loose flanges are manufactured and used per various standards, including JIS B2220 and ASME/ANSI B16.5. Assembly involves inserting the loose flange onto the pipe before welding the stub end, ensuring a secure joint. Proper assembly and tightening practices, including diagonal tightening of bolts, are crucial for leak-free performance.