Hollow Bar in PTFE 150/130x1830 mm natural

Tubes in PTFE are used where the media transport is so chemically or thermally demanding that steel, rubber and ordinary engineering plastics drop out. The material is inert against practically all industrial chemicals, handles 260 degrees of continuous service and keeps its shape down to minus 200 degrees. The low friction of the inner surface gives low flow resistance and makes deposits hard to form, which is valuable both for clean media and for processes where fouling would cause a stoppage or contamination between batches.

In the process industry, PTFE tubes are used for transporting acids, bases, solvents and oxidizing media. The tube wall is not affected by the medium, which means the same type of tube can be used for sulfuric acid, caustic, chlorine gas and alcohol without the material choice having to be adjusted per medium. For pharmaceuticals and food, the purity and the low adsorption of the material are put to use; the PTFE surface does not take up flavors, aromas or trace substances from the process, so the same line can be used for different product batches with shorter cleaning cycles than metal or rubber allows.

Thermally, PTFE tubes handle steam cleaning, CIP cycles and processes with rapid temperature changes. The material is rated V0 per UL 94, so a tube that fails thermally does not spread the fire further into the installation. On the cold side the same tube takes direct contact with liquid nitrogen cooled systems and cryogenic transport, which is unusual for a thermoplastic. The thermal expansion is relatively high for the material, though, which means long straight runs need expansion joints or bends that take up the change in length at start-up.

Mechanically, PTFE is not a pressure vessel material. The tube wall creeps under internal pressure, above all at elevated temperature, and the pressure rating drops considerably over time. For systems with a high pressure load, a reinforced version or a liner design where the PTFE tube sits inside a load bearing metal pipe is chosen. For tension and tensile stress, joints and bends should be relieved with supports, since PTFE does not take a bending load without changing shape. When sizing, pressure, temperature and expected service life have to be taken in at the same time, since the creep figure is temperature dependent.

Joining is done with flange connections using PTFE coated gaskets, mechanical couplings with clamping rings or TIG welding where that version exists. Adhesive and ordinary bonded joints do not work, since the PTFE surface does not take adhesive without etching pretreatment. At assembly it is important not to overtighten bolted joints; the PTFE flange creeps and the torque has to be adjusted per the manufacturer's curve to avoid pressing the gasket out of shape. Retightening after a first heat-up in service is common and recommended for installations that will run with pressure or at higher temperature.

The inner and outer diameter are chosen according to flow, pressure rating and coupling standard. Thin wall thicknesses are used where flexibility matters and the pressure is low, for example in sampling loops and dosing systems. Thicker walls are chosen when the tube has to take mechanical handling or longer free spans between supports. The natural color is semi opaque and white; any translucency comes from the wall thickness rather than the quality. A special version with an antistatic modification is available for installations where static charging of non-conductive media is a risk.

In practice, PTFE tubes are cut with a sharp knife at thin walls and with a band saw at heavier dimensions. The cut has to be square to the axis of the tube for the coupling to seal evenly. For bends, preformed fittings are in most cases a better solution than hot bending, since PTFE does not bend easily without the wall thickness changing locally. Supports and pipe saddles are placed closer together than for steel because the material creeps, and fixed anchor points should be complemented with sliding saddles between them.

For installations with food or pharmaceutical contact, PTFE is specified in an FDA or EU 10/2011 approved quality. That is nothing you can see on the tube; it has to be confirmed at order. The same goes for an electrostatically conductive version or for specially approved media classes; the specification comes from the order, not from the appearance of the material.

For bending on site, special tools and controlled heating are used, but in an industrial setting prefabricated bends or flexible sections are easier to trust. Checking that the cut is square before assembly reduces the number of failed seals and is worth the extra minute per joint.

Need to discuss dimension, wall thickness or joining method for your application? Get in touch and we will go through it before a quote.

The heavy bar at 150/130x1830 mm in natural has a large diameter and a thin wall, good for large liners and lining rings.