Originally posted by efuu00
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The burst pressure for tube is given by tensile strength x internal radius / wall thickness. Your 6 x 4 tube has an internal radius of 2mm and a wall thickness of 1mm so the burst pressure is tensile strength / 2
For extruded PTFE the theoretical tensile strength is around 12 MPa* at 0 oC so the burst pressure for your tube will be around 6 Mpa (approx 60 Bar). At 121 oC it declines to 3.4 MPa* so the burst pressure would be around 1.7 MPa (approx 17 Bar).
No engineer ever specifies a material at its maximal strength, it's normal to apply a safety factor of at least x 3, so the working pressure of that tube at 121 oC should be about 0.5 MPa (5 bar).
BTW 121 oC is used because it's the temperature at which an autoclave operates when the internal pressure is 1 Bar. The internal temperature of a coffee machine boiler is usually a bit higher than this.
* Figures sourced from Dupont PTFE Properties Handbook p12



no way to prove though
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