Tube fittings, important components in fluid systems, are widely used across diverse fields. including oil and gas, chemical processing, hydrogen energy, and semiconductors. If tube fittings are not inspected and installed correctly during the assembly process, issues such as leaks, pressure drops, or system failures may occur. These seemingly minor mistakes can lead to very serious accidents, resulting in significant economic losses and even casualties. Therefore, it is crucial to install tube fittings correctly. Below, we will introduce some common problems in fitting installation and how to avoid them.

Intermix Fittings of Different Materials and Dimensions

 

When installing fittings and tubes made of different materials, two key factors typically require attention. First is the effect of galvanic corrosion, which occurs when two materials with different electrode potentials come into contact in the presence of an electrolyte. Second is the hardness relationship between the ferrule and tubing materials. The ferrule must be harder than the outer surface of the tube to ensure proper functioning of both front and rear ferrules, thereby creating an effective seal.

In practical applications, we've observed that some customers choose to combine fittings and tubing of different materials to meet specific operating conditions, such as using 316SS fittings and 6MO tubing together. FITOK offers suitable material combinations of fittings and tubes based on customer project requirements. If you have similar needs, please consult FITOK or your local authorized distributor.

Similarly, mixing components of different dimensions can also affect the sealing performance of the tube fitting. Due to size differences, the sealing performance can be significantly compromised after installation. Some metric and fractional sizes are quite similar, such as the 1/4” and 6mm ferrules, making them difficult to distinguish when mixed together. Therefore, fittings of different sizes should be stored separately. Additionally, during installation, it is essential to carefully check that the dimensions are correct to avoid the issues mentioned above.

FITOK has designed steps on the body and nuts of metric straight tube fittings to visually distinguish them from fractional dimension. The forged components, such as elbows, tees, and crosses, do not have a step on the body but are marked with metric sizes on the ports.

Installation of Defective Tubing and Fittings

 

Improper protection during transport or operation can lead to scratches or dents on the tube surface. Scratches and dents can prevent the ferrule from fitting tightly against the tube surface, leading to leaks. Before installing the tube fitting, it is essential to inspect the tube for any dents, scratches, deformations, or other damages. If necessary, operators should cut the tube if it is too long or has unsatisfactory ends to prepare the tube again. To avoid damaging the tube, protective caps should be used during transport, and tubes should not be placed on the ground or dragged. Additionally, the tubes should be kept separately by size and should not be mixed on a shelf when stored.

Scratches or damages to the sealing surface of the fitting may also prevent the ferrule from fitting tightly against the fitting body, resulting in leaks. During installation, ensure the tube is aligned straight and parallel to the fitting when inserted into the fitting. Misalignment can cause the tube to enter at an angle, potentially scratching the sealing surface of the fitting and subjecting the installed fitting to side loads.

Inadequate Tubing Preparation

 

Incorrect cutting and burr removal can affect the sealing capability of the fitting and contaminate the system. Additionally, unremoved burrs will scratch the surfaces of fittings and other tubes, compromising sealing performance. After cutting the tube, it is necessary to clean the inner and outer sides of the cut ends, ensuring that the edges of the burr-free tube ends are smooth and that the inner and outer chamfers do not exceed half the wall thickness of the tube. Finally, a visual inspection should be conducted.

Lacking suitable processing tools is also an important factor. Equipping with the right tools and conducting proper operations can accelerate the installation process while minimizing the risk of failures and reducing losses.

Insufficient Tube Installation Depth

 

If the tube is not fully inserted into the fitting body during installation, it may cause the ferrule to be too close to the tube end, preventing normal sealing and engagement. When exposed to vibrations or impulse pressures, insufficient insertion depth poses risks of loosening or even falling off, which can lead to serious accidents. Furthermore, if the tube is not fully inserted into the bottom of the fitting body, the rear ferrule can push the tube forward, causing deformation of the front ferrule. Thus, before tightening the nut, it is essential to verify that the tube is snugly against the shoulder of the fitting body to avoid shallow installation.

Additionally, improper handling in certain operations might prevent the tube from being fully inserted into the bottom. For instance, if burrs on the tube end are not properly removed, it may hinder the tube from fitting between the front and rear ferrules. Furthermore, directly turning the nut without inserting the tube can cause the inner diameter of the ferrule to compress, preventing the tube from fully inserting.

To prevent such occurrences, FITOK has designed depth marking tools that allow users to mark the corresponding installation depth on the tube, making it easy to check whether the tube is installed at the correct depth.

Under-Tightening or Over-Tightening in Fitting Installation

 

Both under-tightening and over-tightening tube fittings can compromise their performance. Generally speaking, if a fitting is not tightened properly during installation, it may lead to leaks. Accordingly, many people tend to pull the fitting nuts tightly, believing that a tighter screw can ensure better sealing between the fitting and the tube. However, excessive tightening can negatively affect the maintainability and reinstallability of the fittings.

Under-tightening installation of tube fittings can prevent proper sealing between the ferrule and the tube, potentially causing medium leaks during system operation. When initially installing the tube fitting, a gap gauge can be used to determine whether the fitting is tightened sufficiently, helping to avoid leaks caused by loose installation.

Over-tightening the nut can cause severe deformation of the ferrule and tube, making fitting disassembly difficult during maintenance. Moreover, excessive tightening reduces the number of times the fitting can be reinstalled. Furthermore, the need for repairs or replacements of deformed fittings and tubes will also lead to increased costs.

FITOK offers a variety of tube installation tools specifically designed for tube fittings, including tube benders, presetting tools, tube cutters, and deburring tools, to help customers streamline the installation process. The tube presetting tool simplifies the installation of tube fittings in tight spaces while speeding up the installation process for large numbers of fittings. Other tools can better assist operators in preparing tubes and preventing leaks from occurring.

Please refer to the Tools and Accessories catalog for more information. If you have any questions, please consult FITOK or your local authorized distributors, and we will get back to you as soon as possible!