How To Choose the Material for the Compressed Air Piping?
Several materials can be used to make compressed air piping.
The choice of material depends not only on its cost but as well as other parameters in the compressed air system, on several factors.
The main ones are:
• quality of compressed air
• pipe sizes
• environmental conditions
• scope of installation work
• material cost
• pressure drop
• wear resistance.
ADVANTAGES AND DISADVANTAGES OF THE MOST FREQUENTLY USED MATERIALS FOR MANUFACTURING COMPRESSED AIR PIPELINES:
• threaded pipes: inexpensive, there are various types of shapes
• seamless: there are various nominal diameters; but: have low corrosion resistance and high resistance to flow movement
• galvanized: resistant to corrosion; but: have high resistance to flow movement
• made of stainless steel: resistant to corrosion, have low resistance to flow, sealed; but: have a limited number of types of forms, expensive.
• resistant to corrosion, low resistance to flow movement; but they require a high technical level of pipeline laying and brazing.
• polypropylene (PPR)
• polyamide (PA)
• polyethylene (PE)
• acrylonitrile-butadiene-styrene polymer (ABS)
the following applies to all plastics: various types of molds, non-corrosive, generally easy to install; but: have a high expansion in length, low elasticity under pressure at high temperatures.
Typically, the maximum design pressure of a pipe is indicated in its specification (designation PN followed by the pressure value in bar, for example PN16).
Today the most popular material for laying pneumatic lines is polypropylene. PPR pipes are easy to install, have a relatively low cost and can withstand compressed air pressure up to 20 bar. The main diameters (external) of polypropylene pipes: 20 mm, 25 mm, 32 mm, 40 mm, 50 mm, 63 mm. The inner diameters depend on the maximum pressure for which they are designed and, accordingly, depend on the thickness of the pipe walls, therefore, when choosing the materials for the pneumatic line, you need to carefully read the characteristics of the PPR pipe selected for installation.
The main "secrets" when laying PPR pipes:
- for rigid polypropylene pipes, L- or U-shaped ones are made or purchased loop-shaped expansion joints are used. The dimensions of the L- and U-shaped expansion joints are calculated. The length of the bending arm depends on the stiffness of the pipe, which is set by a special factor that takes into account the safe bending of the pipe. The coefficient is indicated in the technical characteristics of the pipe material, most often for polypropylene (PP) - 25.
- Most often, U- and L-shaped expansion joints are obtained automatically, when the pipe goes around various building structures. If the line is straight and long, then the expansion joints in it must be designed in advance both on the risers and on the branches.
- The issue of thermal expansion of polymer pipelines is largely solved by the correct use of supports and the choice of the configuration of the piping. It is necessary to create as flexible an elastic system as possible with a minimum of rigid short knots with little deformation capacity.
- When placing pipes on walls and ceilings, it is not recommended to use fixed supports. For ceiling mounts, strap supports are a good solution. The number of supporting supports should be small, preference should be given to special plastic supports that do not damage the pipe surface. However, it is recommended to use movable plastic supports with an interval of 20-30 pipe diameters.
- Fixed supports, as a rule, fix heavy pipe assemblies or heavy pipeline elements that do not have their own fasteners (for example, filters or taps). In all cases, it is necessary to consider the joint placement of fittings and movable supports: with linear extension of the pipe, the fittings will not have to rest against the shoulders of the supports.