Different industrial plants use stainless steel compression tube fittings for a range of applications. The reason behind their wide usage is the high working pressure rating which is typically above 6000 psi. This introduces a high safety factor for the operation.
The pressure rating depends on wall thickness and construction, both of which are related to the size of tubing. A variety of different tube fitting sizes are used, depending on the application requirement. Hence, the pressure rating of a tube in a particular operation varies based on these factors.
Similarly, the type of tubing is significant too. There are mainly two different types—single ferrule and double ferrule tubings. Let’s learn a bit more about them.
What’s the major difference?
Out of the two types, single ferrule tubings have comparatively less pressure rating.
Mostly manufactured from 316 stainless steel or brass, single ferrule tube fittings are available in sizes ranging between 1/16 to 2 inches. These fittings are designed in a manner that makes it almost impossible to install them incorrectly. These have fewer pieces than most other types of fittings.
The design is more suitable for applications performed in high pulsation and vibration conditions.
In contrast, double ferrule or two-ferrule fittings are available in various materials, but the size ranges are same as that of single ferrule ones. These fittings prominently enable consistent leak-tight connections, due to strong mechanical grip.
These can be used for both thick- and thin-walled tubings and for hard and soft tubings.
Design of double ferrule tube fittings
The basic design consists of four main pieces: nut, front ferrule, back ferrule and the body. Upon installation, the addition of tubing makes it a five-component connection. This ensures a leak-free joint.
The two-ferrule system allows for a tight grasp around the tube, without any risk of damage to the wall. The inside ferrule is called the locking ferrule, while the one on the outer side is called the sealing ferrule.
These are thus resistant to abnormal temperature, pressure and vibration variations. This makes them an excellent choice for mechanical equipment in industrial plants.
Why are single ferrule still used in industry?
There is no doubt that high pressure rating and leak-free connections of double ferrule fittings make them a choice option.
However, there are some applications where single ferrule fittings are more suitable. This is because of the following characteristics of these fittings:
- No backward movement- Single ferrule means only a single direction, hence ensures correct installation.
- Single ferrules are easy to install as not installing a ferrule would be hard to miss. Hence, there is a lesser chance of assembly errors compared to double ferrule fittings.
- Some instruments or facilities have been made using single ferrule fittings. So, you can use our single ferrule designs for replacements, without needing to modify the system.
- Under certain conditions, single ferrule fittings prove to resist vibration and pulsation better. Users may thus prefer use of these fittings for such applications.