Expansion-Contraction

All raw materials have a linear thermal expansion coefficient. In construction for example windows and bridges are deliberately built using thermal gaps filled with expandable rubber or foam to compensate for expansion and contraction caused daily and seasonally by ambient temperature differences.
Piping systems are no different, whether metal, composite pipes or thermo-plastic pipes, straight lengths of pipe will contract or expand as ambient temperatures vary. Calculation of the linear movement can be done accurately by following the simple formulas as outlined in GF documentation below or by using the relevant digital tools. GF has been manufacturing and selling plastic pipe systems for >50 years : the practical experience gained over these years how to best compensate for this movement is explained below and in attachments. Please feel free to ask your local GF expert if you have any questions or require specific project support.
 
Training Courses from GF Piping Systems
Training courses for GF customers are available on request for the planning and design of plastic pipe systems. These courses are usually also CDP (Career Development Plan) supported and can offer practical as well as theory modules. Please enquire with your local GF expert for details.

The movement can be calculated accurately and needs to be calculated for each individual significantly long straight length of pipe. The movement , either expansion or contraction, can be compensated for in the pipe layouts quite easily. There are basically 2 methodologies to compensate for the movement ;

• Flexible sections
• Compensators

To reduce the amount of linear movement the pipe can be physically fixed , ie mechanically clamped or located to ensure movement of the pipe takes place either side of this point. This is known as a "fixed point". It is sually represented in engineering drawings with the symbol X. Mechanical flanges or Valves can easily be used as fixed points if the flange of valves is mechanically located at a set point.
When creating a fixed point in a length of pipe care should be taken not to mechanically distort or damage the pipe. Dependent on material there are various methods to create a fixed point. See below diagrams for recommended fixed point installations.

COOL-FIT consists of 3 layers (PE Outer Jacket – GFHE Insulation – PE Pressure Carrier Pipe) and to calculate the thermal movement of the complete pipe it is necessary to take into account several variables. 

The linear movement of the outer PE jacket is effected by the ambient maximum and minimum temperatures whilst the carrier pipe is influenced by the fluid maximum and minimum working temperatures. As well as these x4 temperature variables, it is also necessary to be aware of the installation temperature which effects the carrier pipe.

To ensure accuracy Gf offers a FOC digital tool to calculate expansion/contraction on COOL-FIT pipe and also flexible section lengths. (Lb).
After simple registration please download the GF COOLING Tool-Box for accurate calculation of COOL-FIT thermal linear movement.

Correct installation of a plastic pipe system allows the pipe to move laterally, either by using sliding brackets or simply supporting the pipe at the pipe clamp by use of a pipe clamp with an inside diameter larger then the outside diameter of the pipe. There are various 3rd party suppliers of such brackets and also GF has options available.

Fixed system: there may be no space to be able to plan in flexible sections, in this case it is possible for some systems and usually smaller dimensions to completely fix the system at each pipe bracket to prevent movement at every pipe bracket. Effectrively creating a fixed point at every pipe support. This is generally speaking an expensive solution and only to be used on plastic pipes when normal compensation is not possible. It needs detailed engineering calculations and can only be considered for smaller dimensions and only a limited amount of systems. Please consult GF for engineering support

GF has developed its own pipe bracketing system specifically designed to for thermoplastic pipe systems (ie: PVC, PE, PP-H, PVDF etc). The design ensures that no stress transfer to pipe caused by thermal expansion or seismic events. Standard pipe clamps and supports can be over-tightened such that the plastic pipe is deformed causing high local stresses. Over tightening of local pipe clamps should always be avoided. GF Stress Less is designed so that squeezing or deforming of the pipe cannot occur.

Outdoors: For pipe systems installed out-doors there is an influence of direct sunlight on the outside diameter of the pipe. This has the effect of increasing the outer surface temperature of the pipe quite significantly. For example in the Middle-East or southern Europe it is not uncommon for black PE pipe to have a surface temperature of +/- 70°C caused by the effect of direct sunlight. The effect this has on the expansion contraction of the pipe has been extensively tested and measured by GF Piping Systems. Follow the link below to "Outdoors Installations" for details. To summarise the effect is far less than one would expect as the heat increase is only on the surface of the pipe and also not even completely over the whole surface of the pipe (only approx. 40% of the outer surface of the pipe is effected by the sunlight and also not 24 hours a day and only on the surface of the pipe). The formulas and calculation tools recommended and supplied by GF Piping Systems have correction factors in-built for outdoor use.

Underground: Pipe systems laid underground require a completely different set of engineering calculations. The pipe cannot physically move and the temperature differences are less, however care should be taken to engineer properly the entry and exit points of the pipe system. PE pipe is ideal for underground use due to its high impact strength, UV resistance and high E-Modulus. The EN1610 specifies all parameters for laying of PE underground ie in trenches. GF also has a separate technical handbook for "Utility Systems" including design of underground pipes – please refer to the relevant handbooks for guidance.

In terms of mechanical compensation for linear movement there are
basically 2 types of solutions, namely either expansion joints / bellows
and/or flexible hose or pipe.

For expansion joints it is important to make the manufacturer aware that you are compensating for movement in a plastic pipe. The tensile strength of plastic pipes is a lot less than metallic pipes and this must be considered when deciding exactly which type of expansion joint is suitable. Effectively the expansion joint should move before the pipe distorts, hence it is important to inform the expansion joint manufacturer of the pipe system material properties.

Flexible hoses / pipes can offer a simple compensation methodology. The correct mechanical connection to the plastic pipe is necessary for long-term reliable functionality.