Pc calculated in accordance with ISO 13478 Table 3 - Results of FS and S4

critical pressure (Pc) tests at 0[degrees]C on DRISCOPLEX[R] 6500 MDPE Pipe Nominal Outside Measured Measured Diameter FS [P.sub.c] S4 [P.sub.c] (mm) SDR (bars) (1) (bars) 219 11 8.5 1.10 219 17 8.5 (3) 0.90 168 11 9.5 1.15 168 17 8.5 1.08 Nominal S4-to-FS Measured Outside Converted S4-to-FS Diameter [P.sub.c] (2) Correlation (mm) SDR (bars) Factor 219 11 6.56 4.5 219 17 5.84 5.0 (3) 168 11 6.74 4.9 168 17 6.49 4.6 1.

As the pressure decreases there comes a point at which the pressure of the fluid becomes smaller than the

critical pressure of C[O.sub.2].

Figure 2 gives the isobaric plots near the critical point of [P.sub.c]] = 0.0006631 and Figure 3 displays the effects of YM charge and BI parameter on the

critical pressures. On T-[r.sub.+] plot of Figure 2, just as the case of [beta] [right arrow] [infinity], P > [P.sub.c] isobar describes the "ideal gas" phase.

Davis (24) proposed, "the

critical pressure must therefore counteract this closing moment before providing a sufficiently high crack driving force for propagation." By applying simple beam theory to a semi-circular section of pipe geometry and Castigliano's first theorem.

This indicates that x = [r.sub.c]/[r.sub.+] is fixed; however the critical effective temperature, critical volume, and

critical pressure are dependent on the value of [r.sub.c].

Its Small Scale Steady State

critical pressure of over 10 bar (145 psig) is equivalent to a full-scale

critical pressure of over 650 psi, which is equivalent to the PE 100+ materials used internationally."

If the pressure in the pipe is above the

critical pressure [CP] and the temperature is below the CT the crack will propagate to the end of the pipe at a very high speed.

* Added rapid crack propagation (RCP) required value of a full-scale

critical pressure greater than 1.5 times the maximum operating pressure for polyethylene (PE) materials.

We call this shear rate and the corresponding pressure drop the critical shear rate and the

critical pressure drop.

For example, for modern PE pipe RCP

critical pressure limitations, using formulas in the current standards, are underestimated by 1.5 to 2 times.