Temperature and Design Pressure

Temperature
Operating service temperature for Driscoplex® 6400 may be between –30°F and up to 140°F. The system operating temperature will affect the allowable design parameters of Driscoplex® 6400 systems. Detailed temperature rating information is provided in the “Design Pressure” section below. Driscoplex® 6400 can handle conditions of freezing water much better than traditional metal piping. In the event that water does freeze inside Driscoplex® 6400, the line should be carefully and fully thawed before placing it back in service. To prevent freezing, the line may be insulated and may be heat traced if necessary. Heat tracing equipment should not exceed 120°F (49°C). Exposure to the sun increases operating temperatures, especially during summer months. This may reduce the Design (Working) Pressure capability of the system.

Design Pressure
The following formula given in API 15LE Section 5.1.5 is used to compute the design pressures in Driscoplex® 6400 piping systems for operating temperatures up to but not over 140°F (60°C). For operating temperatures below 73°F (23°C), use 73°F (23°C) Design Pressures.

(Equation 1)          PR=2×HDS×FSF×TSF
                            ((DR-1))

Where:
PR = Pressure Rating, psi
HDS = Hydrostatic Design Stress, Table 3
FSF = Fluid Service Factor
TSF = Temperature Service Factor
DR = Dimension Ratio for OD Controlled Pipe

(Equation2)                DR = OD
                                   t

Where:
OD = Outside Diameter
t = Pipe Minimum Wall Thickness, in

Operating Pressures (psig)
Tables 5 & 6 provide maximum allowable operating pressures (MAOP) for PE4710 pipes. PE pipes of the same DR and Material Designation Code, but different outside diameters have the same Design (Working) Pressure Ratings. Pressure ratings are calculated using Equation 1 above. A check should be made to determine if these pressures apply under the state and/or local codes governing the specific application. Use 80°F pressure ratings for operating temperatures below 80°F (27°C).

Pressure Surge Capacity
System pressures due to frequently occurring surges or water hammer events of up to 1-1/2 times the rated system operating pressure are well within the limits of the Driscoplex® 6400 piping system. System pressures of twice the rated operating pressure can be tolerated occasionally. For moderate flow velocity systems, i.e. 5 ft/sec or less, it is generally unnecessary to include a surge allowance within the pressure rating of the system. For lines operating at higher velocities, the allowance will be reduced.

Cold Bending Radius
The allowable cold bending radius for Driscoplex® 6400 pipe is dependent upon the pipe OD, DR and the presence of fittings in the bend. See Performance Pipe’s Technical Note PP-819-TN Field Bending of Driscoplex® Pipe. Table 8 provides the cold bend radius that can be used for long term applications.

Special Considerations for Plowing and Planting
Plowing and planting involve cutting a narrow trench and feeding the pipe into the trench through a shoe or chute fitted just behind the trench cutting equipment. The shoe or chute feeds the pipe into the bottom of the cut. The minimum bend radius of the pipe through the shoe may be tighter than the minimum bend radius of the pipe used for a permanent long-term installation, but it must not be so tight that the pipe kinks. Table 9 presents the minimum short-term bend ratio for applications such as plowing and planting. The pipe’s path through the shoe or chute should be as friction-free as practicable to reduce additional outer-fiber tensile stresses. Generally plowing and planting is limited to 12” and smaller pipes.