PTFE Tube – Properties and Characteristics

The Steel Industry along with the Chemical Processing Industry has been using the fluoropolymer tubing pipes and products made from materials like PTFE and hoses for transferring some of the most highly caustic or corrosive chemicals. The popularity of PTFE tubes is now sky-high and it is gradually replacing carbon and other metal piping that has a low shelf life.

The Chief Properties of PTFE Tube

 PTFE Tubing has some distinctive properties that set it apart from other tubings. There are three factors which determine the properties of PTFE tubes, that is their different sizes, how it is processed and its’ end-applications.

Dimensional stability

The outer and inner diameters of the PTFE tubes are significant. In most cases, the tube is used in an assembly, where fittings have been so designed so that it accommodates the tube.

However, small variations in dimension are usually allowed, but it must be kept in mind that the tube needs to cater to the fitments used with it. 

Burst Pressure

In applications, which involves high pressures, it is imperative that the tube does not capitulate at the time of the service.

There are two critical parameters here that define the burst pressure.

The first one is the tensile strength.  A tensile strength of 28-31Mpa on PTFE tubes, meaning that the value of 25Mpa can pass muster. An under-processed tube can often have a tensile strength of less than 20Mpa.

The other factor that determines the burst pressure is the difference in the wall thickness. The non-concentric tube shows a higher wall thickness on one side as compared to the other side.

 The burst pressure of such tubes is inferior to the good quality tubes, even though the ID and OD may be the same. This issue results in problems galore, especially when you try to braid the PTFE Tube using stainless steel. The problem that you may face in such a situation is, the unevenness in the wall thickness causes one side of the tube to collapse at the time of the braiding due to the immense pressure applied by the stainless steel.

The lesson from this? Try to make the concentricity exceed 95%.

Calculating the concentricity of PTFE is quite simple. If you calculate the ratio of the minimum wall thickness to the maximum wall thickness of the PTFE Tube, you will get the concentricity. So, take for example a 6mm x 4mm tube, which has a wall thickness of 1mm, will require a tolerance of +/-0.025 to achieve such a degree of concentricity.

Visual

Good quality PTFE tube will have properties such as smooth even surface without any signs of pitting or discoloration. Visually, the concentricity is also an important feature. As concentricity influences the extrusion process. Similarly, there are other factors such as quantity of extrusion aid, extrusion speed, and pressure, sintering temperatures and finish on the die, together determine as to how the tube appears. The outward visual factors such as pitting, waviness, and discolouration give clues about the fundamental properties, for example, the tensile strength, elongation, and dielectric strength. 

The above-mentioned characteristics are some of the basic aspects of PTFE tubing that a PTFE tube manufacturer should maintain while making quality tubes.