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® u if flow is likely to be stopped,the designer may want Examination of equation(t)or(2)shows that for any 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 t_and vice versa.Increasing V 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 line if lateral movement does not occur uniformly. polyethyte. e 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 sectio of pipe.Other methods must be used. 1%and(s)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 briscopipe 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 strength or service life.However.in rocky areas, as large as passible considering other installation d cut the pipe should be location factors,such as available right-of-way,slope sharp rocks which coul of the ground,etc.Higher values for L mean less re and may be replaced with a bed of sand strain(s)and fewer anchor pants and,consequently, or sal. lower costs,generally. ° Lateral Defection Due to Thermal Movement in Overland Type 3:Buried Pipelines Poelines. —4=t ----L �_ _ tntroducUon.: When pipelines are buried,they are i 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 �P'�pe 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 loads as well as pant spacing. internal pressure.But.Driscopipe is a flexible pipe AY= L V—.5()aAT (1) and is considered to be only one component of the "pipe-soil"system,as described more fully on L = ®Y page 35. (2) Thus,in a buried situation.the SDR of the pipe and the-strength of the soil envelope must be specified in D 9®T6 ®T6 (3) order to keep the three burial design parameters(wall L = e crushing.wall buckling and ring deflection)within Where: ®Y=Lateral deflection(inches) acceptable limits.The pipe and sal 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 CE =Coefficient of thermal expansion soil to the pipe result in a highly successful integral (infieF) structure.Correct design centers around two points: 4T =Change in temperature( F) a)matching the proper wall-thickness to the external s =Strain(inches/inch) soil pressure and b)the analysis of how Driscopipe D =Pipe outside dia.(inches) and the soil surrounding the pipe accept the backfin earthloading and transfer it to the undisturbed walls ®Y of the ditch or trench such that the pipeline will deflect slightly into static equilibrium with the soil. R=Radius R=4®Y2+L2 8AY 34