In oil and gas refineries, tube fittings are crucial in connecting sections of tubing and components such as valves or pumps to form a reliable fluid transport system. Depending on the application and their operating conditions, there are various tube fittings to choose from—instrumentation fittings, compression fittings, and flare fittings, to name a few. Despite the difference in application, these tube fittings share some common goals, which are:
A ferrule is a small, ring-shaped piece of metal used to grip and create a leak-tight seal around the tube. Ferrule tube fittings usually comprise a fitting body, a ferrule—single or double, and a nut. When the nut is tightened, it creates compression between the tube and the ferrule, ensuring a secure connection and leak-tight seal.
The choice between single or double ferrule fittings mostly depends on the application and the operating condition of the fluid system. The table below makes a general comparison of single ferrule vs. double ferrule tube fittings.
Single Ferrule vs. Double Ferrule Tube Fittings |
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Single Ferrule Tube Fitting |
Double Ferrule Tube Fitting |
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Design |
This tube fitting uses a single ferrule to establish the tube's seal and grip. |
The fitting contains two ferrules—one creates the seal while the other supports grip.. |
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Installation |
The ferrule compresses onto the tube while the tightening of the nut creates the seal. |
The back ferrule grips the tube, while the front ferrule creates a tight seal. |
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Operating condition |
High-pressure flow tends to cause more vibrations than low-pressure flow does. Due to vibration, single ferrule tube fittings are more likely to lose their grip and sealing capabilities, causing the system to fail. So, these are not suitable for high-pressure conditions. |
Double ferrule fittings are suitable for high temperature and pressure conditions because two ferrules design ensures additional grip and a secure connection against system vibration and pressurization. |
Leaking connections is a major reason for failure in refinery tubing systems. While welds may be used in many cases, tube fittings can also provide a reliable connection, especially when dealing with factors such as vibration fatigue—welds crack, ferrules don’t. Ferrule tube fittings are versatile enough to provide an effective seal and grip with simple installation.
In particular, Swagelok’s dual ferrule tube fittings are designed to solve these fluid system challenges in refineries. These fittings feature:
The safety and reliability of fluid system operation depends on the components in use. In the choice of single ferrule vs. double ferrule tube fittings, although the latter provides a more secure connection, the fitting selection should depend on the process condition and cost-effectiveness desired for the specific application.
If you want to learn more about the tube fitting solutions from Swagelok, you can explore these links on tube fitting training and tube fitting assembly. Also, check out our Swagelok® FK series fittings, the robust ferrule tube fitting that provides excellent grip and seal with easy and cost-effective installation options for medium pressure systems.
To find out more about how Swagelok Northern California can help you make a selection between single ferrule vs. double ferrule tube fittings for your fluid system installation, contact our team today by calling 510-933-6200.
Morgan holds a Bachelor of Science in Mechanical Engineering from University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration and Mechanical Efficiency Program Specification (API 682), and he is well versed in B31.3 Process Piping Code. Before joining Swagelok Northern, he was a manufacturing engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).