While standard flange types like Weld Neck and Slip-On dominate general industrial applications, specialized environments—demanding exceptional ease of maintenance, superior corrosion resistance, or ultra-high pressure sealing—require unique design solutions. The Lap Joint flange and the Ring Type Joint (RTJ) flange are two such specialized flange types that offer tailored performance.
This guide explores the design features and specific applications of these two critical industrial flanges.
1. Lap Joint Flanges: The Advantage of Rotational Freedom
The Lap Joint flange is unique because it is designed as a two-piece assembly, offering a distinct advantage during installation:
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Structure: It consists of two parts:
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A standard, rotating Lap Joint flange ring (which holds the bolts).
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A stub end (a short piece of pipe with a flared end) that is butt-welded to the pipe.
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Sealing: The flange ring is free to rotate around the stub end. When bolted, the flange ring presses the back of the stub end against the stub end of the mating flange, and the flared faces form the seal with a gasket.
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Ease of Maintenance: The ability to freely rotate the flange ring makes it extremely easy to align bolt holes when connecting large or heavy pipe sections. This significantly reduces installation time and labor cost, especially in complex, confined piping manifolds.
Ideal Applications for Lap Joint Flanges:
The Lap Joint flange is typically used in applications where:
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Frequent Disassembly is Required: It is favored in systems that need routine cleaning or internal inspection, as the connection is quick to break and re-align.
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Corrosion is a Factor (Material Cost Saving): If the transported medium is corrosive, the flange itself does not need to be made from expensive alloy (like stainless steel flange). Only the stub end, which contacts the fluid, needs to be the costly, corrosion-resistant material; the rotating flange ring can often be a cheaper material like carbon steel flange, reducing material cost.
2. RTJ Flanges: Sealing Under Extreme Pressure
The Ring Type Joint (RTJ) flange is specifically engineered for severe service environments involving ultra-high pressure and high-temperature conditions, where standard flat gaskets might fail.
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Structure: An RTJ flange uses a machined groove (ring groove) on its face, which accommodates a metallic RTJ gasket (a solid ring).
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Sealing Mechanism: When the bolts are tightened, the metal RTJ gasket is compressed between the two flange grooves. The material of the soft metallic ring is forced to plastically deform and "flow" into the grooves, creating an extremely tight, metal-to-metal seal.
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Superior Integrity: This self-energizing seal is less dependent on the initial bolt torque and is highly resistant to pressure fluctuations, vibration, and thermal expansion.
Ideal Applications for RTJ Flanges:
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Ultra-High Pressure: Essential for systems exceeding ASME Class 600, common in deep-sea oil and gas extraction or high-pressure steam lines.
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High Temperature: The metallic gasket maintains its integrity in environments that would degrade non-metallic gaskets.
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Flange Type: RTJ faces are most commonly seen on Weld Neck flange designs due to the high strength required to withstand the tremendous bolting loads necessary to compress the metal ring.
Deepen Your Flange Knowledge
These specialized pipe fittings solve unique engineering challenges. Explore these related technical guides:
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High-Pressure Connections: Understand the base strength required for RTJ joints:
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Gasket Selection: Delve into the specific requirements for metallic vs. non-metallic sealing:
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Core Flange Resource: Return to our complete overview of all flange types and industrial flanges:
Do you need custom flange solutions for extremely corrosive or high-pressure systems? Contact us for specialized RTJ and exotic alloy recommendations.
