Expansion & Contraction
User Manual: Expansion & Contraction
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Expansion & Contraction Page Expansion & Contraction Introduction Change in length Allowing for expansion or contraction Bracket spacing 6.02 6.03 6.04 - 6.07 6.08 - 6.12 6 GEORGE FISCHER ‡ 6.01 Expansion and Contraction All materials expand or contract with the increase or decrease in temperature. The amount of this expansion or contraction is dependent on the coefficient of linear expansion α. This coefficient is very rarely linear for a material, however for most calculations a good average is used. ∆L = change in length L = pipe length Example How much will a 10m length of PB (INSTAFLEX) expand if the working temperature is 60°C and the installation temperature is 15°C? ∆t = working temperature installation temperature ∆t = 60°C –15°C ∆t = 45°C Therefore ∆L= 0.13 x 10 x 45 ∆L= 58.5mm The average linear expansion coefficient of polybutylene (PB): α = 0.013 mm/m°C Therefore ∆L = α x L x ∆t Important Please note that ∆t is the difference between the installation temperature and the working temperature. Where ∆L = change in length in mm α = coefficient of expansion L = original length in mm ∆t = temperature difference in °C Change in length ∆ L in mm for PB pipes Temperature difference ∆t in °C 10 20 30 40 50 60 70 80 0.1 0.2 0.3 0.4 0.5 0.1 0.3 0.4 0.5 0.6 0.3 0.5 0.8 1 .0 1 .3 0.4 0.8 1 .2 1 .6 2.0 0.5 1 .0 1 .6 2.1 2.6 0.7 2.0 2.0 2.6 3.3 0.8 2.3 2.3 3.1 3.9 0.9 2.7 2.7 3.6 4.6 1.0 3.1 3.1 4.2 5.2 0.6 0.7 0.8 0.9 1 .0 0.8 0.9 1 .0 1 .2 1 .3 1 .6 1 .8 2.1 2.3 2.6 2.3 2.7 3.1 3.5 3.9 3.1 3.6 4.2 4.7 5.2 3.9 4.6 5.2 5.9 6.5 4.7 5.5 6.2 7.0 7.8 5.5 6.4 7.3 8.2 9.1 6.2 7.3 8.3 9.4 10.4 2.0 3.0 4.0 5.0 6.0 2.6 3.9 5.2 6.5 7.8 5.2 7.8 10.4 13.0 15.6 7.8 11 .7 15.6 19.5 23.4 10.4 15.6 20.8 26.0 31 .2 13.0 19.5 26.0 32.5 39.0 15.6 23.4 31 .2 39.0 46.8 18.2 27.3 36.4 45.5 54.6 20.8 31 .2 41 .6 52.0 62.4 7.0 8.0 9.0 10.0 11 .0 12.0 9.1 10.4 11 .7 13.0 14.3 15.6 18.2 20.8 23.4 26.0 28.6 31 .2 27.3 31 .2 35.1 39.0 42.9 46.8 36.4 41 .6 46.8 52.0 57.2 62.4 45.5 52.0 58.5 65.0 71 .5 78.0 54.6 62.4 70.2 78.0 85.8 93.6 63.7 72.8 81 .9 91 .0 100.1 109.2 72.8 83.2 93.6 104.0 114.4 124.8 Pipe l. in m Example from table A 5m long pipe working at a temperature of 50°C will expand or contract by 32.5mm. 6.02 GEORGE FISCHER ‡ Change in length ∆ L in mm for PB pipes Temperature Difference ∆t in °C Pipe length L in m 6 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Change in length ∆L in mm GEORGE FISCHER ‡ 6.03 Allowing for Expansion or Contraction 1 . General Being a member of the thermoplastic family, INSTAFLEX PB is subject to greater thermal movement than metals. As all materials expand or contract and since the modulus of elasticity (E) of INSTAFLEX is very low, at 350N/mm2, overcoming the effects of expansion or contraction is generally easier than with metals. There are three principal methods to overcome the effects of thermal movement. Method 1 By optimising the flexibility of PB by using the changes of direction found in most installations or to install expansion loops. This method is most commonly used in places where the pipework is not visible, i.e. in ceiling voids or riser ducts. Flexible expansion leg Pipe lateral yielding in riser Expansion Fixed point bracket Sliding bracket Flexible Leg Expansion Loop Expansion Fixed point bracket Sliding bracket Sliding bracket Flexible Leg Fixed point bracket Flexible Leg Fixed point bracket 6.04 GEORGE FISCHER ‡ Method 2 Similar to Method 1 but using pipe carrier to continually support the pipe. The advantage of this approach is that pipe is continually supported and the bracket centers can be much further apart. Ideal for use in areas where the pipe is visible. Typical Pipe Carrier Pipe in Riser Carrier Pipe ties Pipe carrier Flexible Leg 6 Flexible Expansion Leg with carrier Pipe carrier Expansion ∆L Pipe ties Fixed point bracket Sliding bracket Flexible Leg GEORGE FISCHER ‡ Fixed point bracket 6.05 Method 3 This method utilises the unique feature of INSTAFLEX, namely its ability to absorb any thermal movement within itself without detriment to the material or system. This is achieved by rigidly Fixed point bracket Sliding bracket fixing the pipework to prevent any thermal movement. This system is commonly used where there are long pipe runs with laterals. Fixed point bracket Pipe carrier Pipe ties Calculating the Flexible Leg for Methods 1 and 2. a = k x √ ∆L x od where a = flexible leg in cm k = constant PB = 10 ∆L= Expansion or Contraction in cm Sliding Bracket “a” Fixed Point Bracket Flexible Leg Example How long should leg “a” be if the expansion ∆L is 3.25cm on a 6.3cm od pipe? a = 10 x √ 3.25 x 6.3 6.06 ~ 45cm GEORGE FISCHER ‡ Graphical method for Determining the Flexible Leg “a” For methods 1 and 2 110 1 . Control the direction and amount of thermal movement by careful positioning of fixed points. 2. Take care to ensure the pipe can move freely within the loose brackets. 3. Never create a fixed point by tightening the bracket to squeeze the pipe. 4. Ensure that the positioning of loose bracket does not inadvertently create a fixed point. d110 100 d90 90 d75 80 d63 d50 70 d40 60 d32 50 d25 45 Flexible Leg “a” General Guidelines 6 40 30 20 10 Change in length ∆L in cm 9 8 7 6 5 4 3 2 1 4 3 2 1 Temperature difference ∆t in °C 10 10 9 8 7 6 5 length of pipe run in m GEORGE FISCHER ‡ 6.07 Method 1 º Bracket Spacing Pipe bracket intervals in cm Pipe size d 20°C 30°C 40°C 50°C 60°C 80°C 16 20 25 32 40 50 63 75 90 110 70 75 80 90 105 115 130 140 155 190 70 80 80 90 100 115 130 140 150 190 65 75 80 90 100 110 125 135 150 180 65 75 75 90 95 110 120 130 145 180 60 70 75 85 95 105 120 130 140 170 60 70 70 80 90 100 110 120 130 160 The pipe bracket spacing may be increased by 30% in the case of vertical pipes. i.e. multiply the values given by 1 .3. The bracket spacings above are based on a maximum deflection of 0.25cm between the brackets. Method 2 º Loose Bracket Spacing with support tray Pipe size d 6.08 All Temperatures Tie Spacing 16 to 75mm 1 .5 to 2m maximum approx. every 30cm 90 & 110 No support tray 1 .5 to 2m maximum approx. every 30cm GEORGE FISCHER ‡ Pre-stressing An alternative solution for Methods 1 and 2 is to cut the pipe short by the amount that it is calculated that it will expand or contract, such that when it is at its normal operating temperature the expansion leg or loop is straight. Position at ambient temperature Position at operating temperature Note There must be a Flexible Leg “a” Flexible leg ‘a’ Fixed point assembly Method 3 º Bracket Spacing 6 Bracket distances for hot water pipes Pipe dim d mm 16 20 25 32 40 50 63 75 Fixed point distances L Loose bracket distances L1 Pipe binder distances L2 maximum 6m between fixed points 1 .5 to 2m max. approx every 30cm last fixed point brackets. For fixed installations the expansion force of the pipe is transferred to the expansion force Force on bracket = expansion force 2 GEORGE FISCHER ‡ Force on bracket =0 expansion force Force on bracket =0 expansion force Force on bracket = expansion force 2 6.09 Temp. Difference ∆t in °C. Expansion Forces generated by PB pipes for Temperature Differences Expansion Force FR in N To calculate the expansion force, the following formula may be used; FR = A x E x α x ∆t°C. 2 where A = (D2 - d2) π 4 A = pipe cross section area mm2 E = modulus of elasticity 350N/mm2 α = coefficient of linear expansion = 0.013mm/m°C ∆t = temperature difference °C FR = expansion force 2 Example What is the force acting on an end bracket for a 63 mm od pipe with a temperature difference of 50°C? FR = (63 2 - 51 .42) π x 350 x 0.013mm/°C x 50 4x2 FR = 1185 N 6.10 GEORGE FISCHER ‡ Forces due to expansion of various sizes of PB pipe which would be transferred to a fixed point pipe support clamp, can be read from the graph on page 11 . Depending on how far the centerline of the pipe needs to be from the supporting structure will effect the required diameter of the fastening rod used to hold the fixed point in place. This can be determined using the graph below and the expansion forces on page 11 . Hanger length H in cm Choosing the Diameter of the Fastening Rods for the Pipe Clamp and Bass Plate 6 Expansion Force Fz in N Calculating the Fixed Point Support Clamp D H L X FR FZ Diameter of the fastener rods Distance to ceiling or wall from the pipe Distance between screws Number of screws with tensile strength Fixed point forces (N) Screw or dowel retention force (N) 2-hole base plate x=1 4-hole base plate x=2 GEORGE FISCHER ‡ Fz = FR x H LxX [N] Example: Fz = 1200N x 20cm = 1000N 12cm x 2 Retention force per screw: Fz = 1000N 6.11 Fixed Point and Sliding Brackets Arrangement of fixed point support brackets Fixed points direct thermal expansion of the pipe in the desired direction. Fixed points should ideally be installed at a fitting and should support it on both sides or be installed in between the two fittings. Attention! Pipe brackets for fixed point and sliding support should be lined with suitable rubber inserts or of such a design to prevent any damage to the pipe. Elbow Tee Connecting socket Valve connection Typical fixed point assembly Sliding support brackets Sliding brackets allow an axial movement of the pipe. The bracket must be in line with the pipe. Sliding brackets should be lined with rubber inserts suitable for plastic pipe, or of such a design to prevent any damage to the pipe. All commercially available pipe clamps and fastening materials, which are suitable for plastic pipe installations can be used as fixed points or sliding pipe supports for INSTAFLEX. 6.12 GEORGE FISCHER ‡
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