Overview
Threaded flanges, also known as screwed flanges, are pipe flanges with internal threads that mate with externally threaded pipes or fittings. They are commonly used in low-pressure systems (e.g., water, air, or fuel lines) where welding is impractical or disassembly is required for maintenance. Unlike weld-neck or slip-on flanges, threaded flanges eliminate welding, reducing installation time and costs. They are standardized under ASME B16.5 (for dimensions) and ASME B1.20.1 (for thread specifications), ensuring compatibility across industrial applications.
Structure and Working Principle
A threaded flange consists of a flat face with bolt holes (for connecting to other flanges) and a central bore with internal threads. The threads typically conform to standards like NPT (National Pipe Thread) or BSP (British Standard Pipe). During installation, the flange is screwed onto the threaded pipe end, and a sealant (e.g., PTFE tape or thread compound) is applied to prevent leaks. The flange is then bolted to a mating flange, creating a sealed joint. This design allows for easy disassembly but lacks the strength of welded connections.
Key Features
Threaded flanges are lightweight and cost-effective for small-bore piping systems (typically under 4 inches). Their primary advantage is simplified installation—no welding or specialized labor is required. However, they are unsuitable for high-pressure or high-temperature applications due to the risk of thread deformation or leakage. Common materials include ASTM A105 (carbon steel), ASTM A182 (stainless steel), and ASTM A350 (low-temperature alloys), selected based on corrosion resistance and mechanical requirements.
Application Areas
Threaded flanges are widely used in industries where quick assembly and disassembly are prioritized over structural integrity. Examples include fire protection systems, irrigation, compressed air lines, and low-pressure chemical processing. They are also common in retrofit projects or confined spaces where welding is hazardous. However, alternatives like weld-neck flanges are preferred for critical services (e.g., oil and gas pipelines) due to their superior leak resistance.
Maintenance and Precautions
Regular inspection for thread wear or corrosion is essential to prevent leaks. Avoid overtightening, which can strip threads or crack the flange. For gas or hazardous fluid systems, consider using a backup seal (e.g., gasket) alongside thread sealant. Threaded flanges should never be used in cyclic loading conditions (frequent pressure changes) or temperatures exceeding material ratings, as threads may loosen over time. Always follow torque specifications during installation.
B2B Procurement Guide
When sourcing threaded flanges, specify material grade, thread type (e.g., NPT, BSPT), size, and pressure class (e.g., 150# or 300#). Bulk orders often reduce unit costs, but verify supplier certifications (e.g., ISO 9001) for quality assurance. Leading manufacturers include Texas Flange, Pro-Flange, and Metal Udyog. Prices vary by material—stainless steel flanges cost approximately 2–3 times more than carbon steel. For reference, a 1-inch ASTM A105 threaded flange may range from $10–$20 per unit.
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