This document is a peer review of two recent reports from PRCI Project IM-1-08, which proposes new minimum fracture toughness requirements to comply with PHMSA Mega Rule RIN1 -- 192.712. The original reports present practical recommendations for Charpy V-Notch (CVN) toughness values for vintage and modern pipeline material categories, offering some relief from the exceedingly conservative default toughness mandates in 49CFR192.712. However, these re-ports contain a controversial recommendation that the authors believe run counter to the consensus of published literature.
Specifically, the authors...
Specifically, the authors take issue with proposed toughness adjustments in IM-1-08, in which fracture toughness is assumed to decrease monotonically with relative crack depth, at, down to zero a/t at=0.9. Empirical data for vintage pipe joints, both burst tests and prior failures, show no evidence of a significant drop in toughness for deep cracks. Accordingly, the present authors conclude that the IM-1-08 recommendations concerning crack depth effects on fracture toughness lack technical justification.
The present authors also investigated the influence of pipe metal temperature on the pressure capacity of LF-ERW pipe within the range of 0 to 70°F. The study incorporated Monte Carlo simulations that accounted for variability in fracture toughness (including constraint effects), tensile properties, flaw dimensions, and flaw location (i.e., bond line versus heat-affected zone).
The target audience for this report includes pipeline operators, regulators, subject matter experts, and researchers with an interest in the crack threat. The original PHMSA Mega Rule RIN1 – 192.712 has a number of well-documented shortcomings, so there is a very strong need to modify this regulation. The present report is an important companion to the original IM-1-08 reports because it presents a different perspective on toughness rules and offers improvements on the original authors’ recommendations.