- Chemical Resistance
- Safety Data Sheets (SDS)
- Material Properties
- PRO Systems
- PE Pressure Pipe
- PE Pipe Selection
- MAOP for PE Pipes
- Temperature Influences
- Selection of Wall Thickness for Special Applications
- Hydraulic Design for PE Pipes
- Surge and Fatigue
- Slurry Flow
- Pneumatic Flow
- Expansion and Contraction
- External Pressure Resistance
- Allowable Bending Radius
- Thrust Block Support
- Conductivity, Vibration and Heat Sources
- Polyethylene Jointing
- Handling and Storage
- Trench Preparation for Buried Pipes
- Relining and Sliplining
- Pipeline Detection
- Above Ground Installation
- Accommodation of Thermal Movement by Deflection Legs
- Service Connections for PE Pipes
- Concrete Encasement
- Fire Rating
- Testing and Commissioning
- PVC Pressure Pipe
- PVC Pressure Pipe Standards
- Pressure Considerations
- PVC Temperature Considerations
- Mine Subsidence
- Water Hammer
- Thrust Support
- Air and Scour Valves
- Soil and Traffic Loads
- Bending Loads
- PVC Pipe Jointing
- Jointing Components with Ductile Iron Flanged Joints
- Service Connections for PVC Pipe
- PVC Pipe Handling and Storage
- Below Ground Installation
- Above Ground Installation for PVC Pipe
- Testing and Commissioning for PVC Pressure Pipe
- Detecting Buried Pipes
- FLUFF – Friction Loss in Uniform Fluid Flow
- Technical Notes
Vinidex PE pipe systems are ideal for the transmission of gases both in the high and low pressure range.
The use of compressible liquids in PE pipes requires a number of specific design considerations as distinct from the techniques adopted in the calculation of discharge rates for fluids such as water.
- Compressed air may be at a higher temperature than the surrounding ambient air temperature, especially close to compressor line inlets, and the pressure rating of the PE pipes require temperature re rating accordingly. For air cooled compressors, the delivered compressed air temperature averages 15°C above the surrounding air temperature. For water cooled compressors, the delivered compressed air temperature averages 10°C above the cooling water temperature.
- For underground applications where the PE pipes are exposed to ambient conditions, the surrounding air temperature may reach 30°C, and the pipe physical properties require adjustment accordingly.
- High pressure lines must be mechanically protected from damage especially in exposed installations.
- Valve closing speed must be reduced to prevent a build up of pressure waves in the compressible gas flow.
- Where gaseous fuels such as propane, natural gas, or mixtures are carried, the gas must be dry and free from liquid contamination which may cause stress cracking of the PE pipe walls.
- Vinidex PE pipes should not be connected directly to compressor outlets or air receivers. A 21 metre length of metal pipe should be inserted between the air receiver and the start of the PE pipe to allow for cooling of the compressed air.
- Dry gases, and gas/solids mixtures may generate static electrical charges and these may need to be dissipated to prevent the possibility of explosion. PE pipes will not conduct electrical charges, and conducting inserts or plugs must be inserted into the pipe to complete an earthing circuit.
- Compressed air must be dry, and filters installed in the pipeline to prevent condensation of lubricants which can lead to stress cracking in the PE pipe material.
Polyethylene pipes have many attributes which make them ideal for compressed air applications. More information about PE for compressed air applications can be found in an Industry Guideline at http://www.pipa.com.au/images/pdf/POP002.pdf
Compressed air systems contain substantial stored energy, which, if released suddenly, could cause injury. For this reason, a greater factor of safety is applied to compressed air systems than to liquid systems under the same pressure. It is also recommended that pipe system design, installation and maintenance be conducted by those with appropriate knowledge and experience. Care is needed to avoid unplanned overheating of the system.
The following tables for PE 100 and PE 80B pipe systems are based on a safety factor of 2 and give maximum operating pressures in kPa. Under these conditions, system life is expected to exceed 50 years. However, for continuous operation at temperatures above 40°C or for variable temperatures contact Vinidex for advice:
|Pipe Class||SDR||Operating Temperature|
|Pipe Class||SDR||Operating Temperature|
It is customary to find the Inside Diameter of the pipe by using formulas such as shown below. The formulas usedare generally for approximation purposes only, surmising that the temperature of the compressed air corresponds roughly to the induction temperature. An acceptable approximation is obtained through the following equation:
d = Pipe Internal Diameter in mm
LE = Pipe Length in m
Q = Volumetric Flowrate in L/s
Δp = Pressure Decrease in bar
p = Working Pressure in bar
The use of a nomogram is a quicker and easier method to source information (see Figure 4.4). In this nomogram the Pressure Decrease (Δp) is indicated in bar, the Working Pressure (p) in bar, the Volumetric Flowrate (Q) in L/s, the Pipe Length (LE) in m, and the Pipe Nominal Diameter DN.
The advantage of using the nomogram is that no further conversion factors are required for pipe sizing. Also, when four of the parameters are known the fifth can be determined by reading directly from the nomogram.
- Working Pressure 7 bar
- Volumetric Flowrate 30 L/s
- Nominal length 200 m
- Pressure Decrease 0.05 bar
- Utilising the above operating figures, proceed to mark those positions around the perimeter of the nomogram.
- Locate the separation line between (Δp) & (p). (See base of nomogram.)
- Commencing at the lower right hand side of the nomogram draw a line up from the Working Pressure (p) to the line indicating the Volumetric Flowrate (Q).
- Using point (3) draw a diagonal line to the separation line.
- Go to top of nomogram and use the point indicating the Length of Pipe and draw a line down to meet horizontal line from point (4).
- Move to the Pressure Decrease in the Pipe (Δp) at the bottom of nomogram and draw a vertical line up to meet the diagonal drawn from point (5).
- The Nominal Diameter of Pipe can now be found by reading from point (6) across to the left hand side of the nomogram. From this example DN63 pipe should be selected. If the completed nomogram falls between two sizes of pipe, always use the larger size.
The Table below indicates the approximate pressure loss for fittings in terms of an equivalent length of straight pipe in metres. For each pipeline fitting, add the equivalent length of pipe to the original length of pipeline. This length is used for the calculation of the equation above or for the nomogram.
|Fitting||equivalent pipe length in m|
|socket welding joint||0.2||0.2||0.3||0.4||0.5||0.6||1.1|