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DR/SCOPIPE . If flow is likely to be stopped, the designer may want to provide a means to drain the pipeline partially or completely. If, for some unforeseen reason, the Driscopipe pipeline should plug and freeze, the pipeline will not be damaged. The frozen fluid may swell the diameter of the pipe but it will return to nominal size as the fluid thaws. Due to the nature of polyethylene pipe, a flame (such as a propane or acetylene torch) cannot be used to thaw a frozen section of pipe. Other methods must be used. The toughness and excellent abrasion resistance of Driscopipe will take the abuse of movement across sand and soil without detrimental effects on its strength or service life. However, in rocky areas, sharp rocks which could cut the pipe should be removed and may be replaced with a bed of sand or soil. Lateral Deflection Due to Thermal Movement in Overland Pipelines. L L i LAYLAY Pipe Anchor The following formulae will allow the designer to calculate lateral deflection of the pipeline and anchor point spacing. AY = L.50 AT (1) L = AY 50aA (2) D 96 ATAT (3) L= e Where: AY = Lateral deflection (inches) L = Length of pipe between anchors (inches) a = Coefficient of thermal expansion (inlin/°F) AT = Change in temperature (°F) s = Strain (inches/inch) D = Pipe outside dia. (inches) FAY Lf R = Radius R _ 4AY2+12 8AY 34 Examination of equation (1) or (2) shows that for any given set of thermal conditions an increase in AY will increase L and vice versa. Increasing AY and L to the maximum will reduce the number of anchor points needed but may increase wear on the pipe from movement and may increase the possibility of kinking the line if lateral movement does not occur uniformly. One practical approach to design is to calculate L using formula (3) for strain (s) in the pipe wall equal to 1 % and (E) equal to 5%. The L value at 5% strain will give the shortest distance between anchor points and should be considered maximum for strain (e) and minimum spacing for L. The spacing for L should be as large as possible considering other installation location factors, such as available right-of-way, slope of the ground, etc. Higher values for L mean less strain (s) and fewer anchor points and, consequently, lower costs, generally. Type 3: Buried Pipelines Infroducfion. When pipelines are buried, they are subjected to external loads. The effect of external pressure on flexible Driscopipe is more complex than the effect of internal pressure only. For design purposes, a distinction is usually made between rigid and flexible pipes. A rigid pipeline (such as concrete) is considered to be the total structure and must be designed to sustain all external loads as well as internal pressure. But, Driscopipe is a flexible pipe and is considered to be only one component of the "pipe -soil" system, as described more fully on page 35. Thus, in a buried situation, the SDR of the pipe and the strength of the soil envelope must be specified in order to keep the three burial design parameters (wall crushing, wall buckling and ring deflection) within acceptable limits. The pipe and soil envelope become one system. The mutual interaction and strength contribution of the pipe to the soil and the soil to the pipe result in a highly successful integral structure. Correct design centers around two points: a) matching the proper wall thickness to the external soil pressure and b) the analysis of how Driscopipe and the soil surrounding the pipe accept the backfill earthloading and transfer it to the undisturbed walls of the ditch or trench such that the pipeline will deflect slightly into static equilibrium with the soil.