- Chemical Resistance
- 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 Pipe
- Detecting Buried Pipes
- FLUFF – Friction Loss in Uniform Fluid Flow
- Technical Notes
Expansion and Contraction
Expansion and contraction of PE pipes occurs with changes in the pipe material service temperature.
This is in common with all pipe materials and in order to determine the actual amount of expansion or contraction, the actual temperature change, and the degree of restraint of the installed pipeline need to be known.
For design purposes, an average value of 2.0 x 10-4 /°C for Vinidex PE pipes may be used.
The relationship between temperature change and length change for different PE grades is as shown in the Figure below.
A 100 metre long PE80 pipeline operates during the day at a steady temperature of 48°C and when closed down at night cools to an ambient temperature of 18°C. What allowance for expansion/contraction must be made?
- The temperature change experienced = 48 – 18 = 30°C.
- The thermal movement rate(Figure 4.5) in mm/m for 30°C= 6.0 mm/m.
- The total thermal movement is then 6.0 x 100 = 600 mm.
Where pipes are buried, the changes in temperature are small and slow acting, and the amount of expansion/contraction.of the PE pipe is relatively small. In addition, the frictional support of the backfill against the outside of the pipe restrains the movement and any thermal effects are translated into stress in the wall of the pipe.
Accordingly, in buried pipelines the main consideration of thermal movement is during installation in high ambient temperatures. Under these conditions the PE pipe will be at it’s maximum surface temperature when placed into a shaded trench, and when backfilled will undergo the maximum temperature change, and hence thermal movement. In these cases the effects of temperature change can be minimised by snaking the pipe in the trench for small sizes (up to DN110) and allowing the temperature to stabilise prior to backfilling.
For large sizes, the final connection should be left until the pipe temperature has stabilised.
Above ground pipes require no expansion/contraction considerations for free ended pipe or where lateral movement is of no concern on site.
Alternatively, pipes may be anchored at intervals to allow lateral movement to be spread evenly along the length of the pipeline. Where above ground pipes are installed in confined conditions such as industrial or chemical process plants the expansion/contraction movement can be taken up with sliding expansion joints. Where these cannot be used due to the fluid type being carried such as slurries containing solid particles the advice of Vinidex design engineers should be sought for each particular installation.