Corrugated pipe
A corrugated pipe is a pipe made of rigid material with a wave-shaped changing diameter that has become flexible due to the corrugation. Corrugated metal pipes ( metal bellows or metal bellows ) are used in machine and equipment construction, corrugated plastic tubing is primarily used for electrical installations .
use
- In the automotive industry , mechanical and plant engineering , shipbuilding and medical technology , corrugated pipes are used to protect and bundle electrical or other lines and also to make flexible connections to peripheral devices. There are also installation pipes that can be opened lengthways for this purpose.
- In electrical installations, corrugated conduits are mainly used as or instead of so-called empty conduits both outdoors and inside building walls and ceilings.
- Corrugated pipes are used for lines and heat exchangers / heat exchangers (e.g. made of stainless steel in buffer storage tanks or made of various plastics (e.g. polyethylene pipe ) in geothermal energy ). The corrugated structure increases the surface area and thus ensures good heat exchange on the pipe wall. The flow behavior is changed compared to the smooth tube because the flow velocity is reduced by the turbulence that occurs. In addition, the wall thickness of 0.2 to 0.4 mm is significantly less than that of the smooth tube. The construction becomes easier and more efficient.
- Corrugated pipes for lines in solar systems are often used, although it should be noted that the pressure loss is significantly higher than with a pipe with a smooth inner wall. Example for conveying medium: water 20 ° C, volume flow: 0.216 l / s (10 m² collector surface), pipe length: 40 m: pipe element: circular pipe inside smooth, inside diameter: 20 mm, flow velocity: 0.69 m / s, pipe roughness: 0, 0015 mm, pipe friction coefficient: 0.03, pressure loss: 134.89 mbar, pipe element: corrugated pipe DN20, inner diameter: 20.4 mm, flow velocity: 0.66 m / s, pressure loss: 666.33 mbar, pipe element: corrugated pipe DN25, inner diameter : 25.4 mm, flow velocity: 0.43 m / s, pressure loss: 195.23 mbar. In order to have an approximately comparable pressure loss, the corrugated pipe must be dimensioned much larger.
- Corrugated plastic pipe ensures mechanical protection of the pipe carrying the medium in underfloor heating or water pipe installations.
- Corrugated pipe pieces ( metal bellows ) are used to compensate for axial misalignments (lateral-compensatory) or to compensate for changes in length and angle (angular-compensatory):
- Flexibility, compensation of thermal expansion or decoupling of vibrations: pipe compensator for connecting pipes;
- For connecting shafts that are slightly offset in position : Corrugated pipe couplings, metal bellows couplings or metal bellows .
- Metal bellows as working or pumping cylinders or for valve sealing.
material
- Polyamide (PA)
- Polyethylene (PE)
- Polypropylene (PP)
- Polytetrafluoroethylene (PTFA)
- Polyvinyl chloride (PVC)
- stainless steel
- Stainless steel
- copper
Shape and characteristics of the corrugation
The most common are parallel annular formations. If such corrugated pipes are used for lines, this shape leads to a greatly increased pressure loss. Depending on the application, spiral-shaped waves with different shapes are preferably used in heat exchangers, as these result in less pressure loss and better swirling of the medium.
Manufacturing
The manufacture of thermoplastic corrugated pipe takes place using extruders and then in the corrugator that gives the corrugation . First, extruders press the heated and plasticized plastic material into the mold jaws of the corrugators via the injection head. A fixed nozzle is also installed in the spray head to hollow out the plastic strand from the inside with compressed air. In the corrugator, several divided, consecutive, circumferential corrugated half-segments as a negative form move at a steady pace. The half-segments are pressed together and the plastic material is pressed into the molds by the compressed air. This hardens when it cools, creating an endless tube. The outside diameters that can be produced with corrugators are between 3 mm and 2,400 mm outside diameter.
Metallic corrugated pipes are made of materials with the material numbers 1.4404, 1.4541, 1.4571 or 1.4301. They can be used up to 650 ° C. Parallel corrugated pipes are divided into different groups according to the molding techniques used:
- mechanically (continuously) formed and longitudinally TIG- welded. This method is generally used for internal diameters from 6 mm to 50 mm. Instead, larger dimensions are usually formed hydraulically. The ISO standard 10380 applies. The wall thickness of standard designs is 0.15 mm to 0.25 mm, depending on the nominal size. The bursting pressure can be over 100 bar; when the pressure builds up, the test specimen stretches into an almost smooth pipe. The operating pressure is specified in such a way that one can expect a plastic linear expansion of less than 1% at 1.5 times the test pressure. The operating pressure is lower in the case of tightly corrugated versions and thin walls. So that a corrugated pipe can withstand higher loads, it is reinforced with one or two stainless steel braids. This is mainly used to limit the length (to prevent expansion). 1.4301 is used as the braiding material. This means that an operating pressure of over 100 bar can be achieved.
- hydraulically formed (mostly 6 m, sometimes up to 12 m in length) and made of metallic tape. This solution is more flexible and safer, as the wall thickness is more homogeneous and is produced with less friction. However, it is significantly more expensive.
- mechanically shaped
roll seam welded and corrugated hydrodynamically or by means of rollers.