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If flow is likely to be stopped,the designer may want Examination of equation(1)or(2)shows that for any or to provide a.means to drain the pipeline partially or given set of thermal conditions an increase in AY will completely. If,for some unforeseen reason,the increase L and vice versa.Increasing AY and L to the Driscopipe pipeline should plug and freeze,the maximum will reduce the number of anchor points pipeline will not be damaged.The frozen fluid may needed but may increase wear on the pipe from swell the diameter of the pipe but it will return to movement and may increase the possibility of kinking nominal size as the fluid thaws.Due to the nature of the tine if lateral movement does not occur uniformly. polyethylene pipe,a flame(such as a propane or One practical approach to design is to calculate L acetylene torch)cannot be used to thaw a frozen using formula(3)for strain(s)in the pipe wall equal to section of pipe.Other methods must be used. 1%and(e)equal to 5%.The L value at 5%strain will The toughness and excellent abrasion resistance of give the shortest distance between anchor points and Driscopipe will take the abuse of movement across should be considered maximum for strain(s)and minimum spacing for L.The spacing for L should be sand and soil without detrimental effects on its to targe a possible considering other installation strength or service life.However,in rocky areas, sharp rocks which could cut the pipe should be location factors,such as available right-of-way,slope removed and may be replaced with a bed of sand of the ground,etc.Higher values for L mean less or soil strain(s)and fewer anchor points and,consequently, lower costs,generally. Lateral Deflection Due to Thermal Movement in Overland Pipelines. Type 3:Buried Pipelines L Introduction: When pipelines are buried,they are { subjected to external loads.The effect of external pressure on flexible Driscopipe is more complex than {�Y LAY the effect of internal pressure only.For design Pipe Anchor purposes,a distinction is usually made between rigid and flexible pipes.A rigid pipeline(such as concrete) The following formulae will allow the designer to is considered to be the total structure and must be —� calculate lateral deflection of the pipeline and anchor designed to sustain all external toads as well as point spacing. internal pressure.But,Driscopipe is a flexible pipe AY = L .56a T (1) and is considered to be only one component of the "pipe-soil'system,as described more fully on L s AY page 35. 50 ATAT (2) Thus,in a buried situation,the SDR of the pipe and (3) the-strength of the soil envelope must be specified in L D= _96,AT order to keep the three burial design parameters(wall C crushing,wall buckling and ring deflection)within Where: AY =Lateral deflection(inches) acceptable limits.The pipe and soil envelope L =Length of pipe between become one system.The mutual interaction and anchors(inches) strength contribution of the pipe to the soil and the a =Coefficient of thermal expansion soil to the pipe result in a highly successful integral (irvireq structure.Corfect design centers around two points: AT =Change in temperature(`F) a)matching the proper wall-thickness to the external e =Strain(incheslnch) soil pressure and b)the analysis of how Driscopipe 'D =Pipe outside dia.(inches) and the soil surrounding the pipe accept the backfill earthloadmg and transfer it to the undisturbed walls SAY of the ditch or trench such that the pipeline will deflect 7RRadius slightly into static equilibrium with the soil. R_4AY2+L2 8AY 34