DNV GL strongly advises the operators of PE gas pipe distribution systems to determine whether pipe materials used within their systems have been My tested to determine the RCP

critical pressure level.

It was shown in this work that both the FS and S4 Pc results for pipe of equal diameter and different wall thickness can exhibit lower critical pressures with decreasing pipe wall thickness.

S4 critical pressure tests at 0[degrees]C were performed by Chevron Phillips Chemical Company LP at their Research Center in Bartlesville, OK, in accordance with the ISO 13477 standard (2).

where CPFI is the critical pressure ratio, [D.sub.o] is the pipe outside diameter, SDR= t/[D.sub.o] is the standard dimension ratio, and t is the pipe wall thickness.

Relative to the S4 test, the FS tests yields higher values of critical pressure for pipes tested at the same temperatures.

The Irwin--Corten model (18) predicts RCP critical pressure by applying linear elastic fracture mechanics (LEFM) analysis to a pipe geometry.

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.

The crack front will be dragged back on the bore surface increasing the fracture resistance and thus increasing the critical pressure. Such a crack front shape arises for similar reasons in the double torsion test (25).

Also, as temperature increases, plane stress fracture resistance increases and more work is required to separate the ligament at the bore surface, which increases the critical pressure further.

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

The combination of this result with the slight decrease in the capillary pressure drop, leads to a decrease in the total critical pressure drop (or possibly a minimum at [Alpha] [approximately equal to] 30 [degrees]), as seen in Fig.

A three-dimensional collapse failure mechanism associated with the DOT shield tunnel was presented in the aim to calculate the

critical pressure. Exciting the rotational "horn" in the mechanism allows the slip surface to develop more freely than the mechanism composed of conical blocks.