Evaluation of Leak-Before-Break (LBB) Behavior For Axially Notched X65 and X80 Line Pipes

Abstract

Leak-before-break (LBB) behavior was evaluated for two series of API 5L X65 line pipes and three series of X80 line pipes with various levels of Charpy V-notch (CVN) absorbed energy. Full-scale hydrostatic burst tests were conducted for the line pipes with an axial through-wall (TW) notch to determine LBB criteria, that is, the relationship between the axial TW notch length and hoop stress for LBB. The determined LBB criteria were verified by full-scale partial gas burst tests for line pipes with an axial part-through-wall (PTW) notch and were then compared to the estimation using the CVN energy-based equation that Kiefner et al. have proposed. The present study demonstrated that the estimation using the CVN-based equation was in good agreement with the experimental results for the pipes with a relatively low CVN energy of less than 130 J. On the contrary, the equation was not applicable to the pipes with a relatively high CVN energy of more than 130 J. The results of instrumented Charpy tests clarified that the load versus load-point displacement curves for Charpy specimens from the high CVN energy pipes were different from those from the low CVN energy pipes. Therefore, the applicability of the CVN-based equation was dependent on the load versus load-point displacement curve for a Charpy specimen.

Transferability of critical condition for ductile cracking in bent small scale specimen to evaluation of critical internal pressure for ductile cracking in axially notched linepipe

“…Kawaguchi et al 5 carried out similar hydrostatic burst tests for axially TW notched pipes and demonstrated, based on the experimental results, that the equation proposed by Kiefner et al is not applicable to some of the recent higher strength and higher toughness pipes. In other words, most previous studies evaluating the leakage or rupture criteria have been conducted solely on the basis of pipe test results; therefore, the dominant factor determining the failure behaviour of notched linepipes has not necessarily been elucidated by these studies.…”

“…Figure 7 shows the relationship between the stress triaxiality and the maximum equivalent plastic strain in the wall thickness during the three point Hydrostatic tests of the pipes with an axial TW notch machined in the base metal were performed at room temperature: three tests were carried out for pipe A and two tests for pipe B. 5 The lengths of the axial TW notches machined in the test pipes (2a 0 ) were 250, 300, and 400 mm for pipe A, and 250 and 350 mm for pipe B. As shown in the schematic view of the axial TW notch in Fig.…”

Development and validation of a leak before break criterion for cylindrical pressure vessels

“…The LBB design philosophy used for high pressure vessel and related energy plant equipment has been attracting much interest from a safety and economic point of view. 2 Kawaguchi et al 3 reported that LBB is one of the three fracture modes concerning burst behavior of notched gas pipelines. LBB concept is part of break preclusion (BP) concept in Germany.…”

Applicability of Existing Fracture Initiation Models to Modern Line Pipe Steels

“…Furthermore, by performing surface-cracked pipe tests (Case 1 and Case 2 in Fig. 1), it was demonstrated that pipe rupture could occur for cases where leak was predicted using the original criterion (7) . In addition, limited surface-cracked pipe tests (8) have…”

“…The start of ductile tearing, technically the "initiation of the fracture event", can occur Fig. 1 Leak/rupture analysis results for X80 line-pipe steel (7) at much lower pressures than the maximum failure pressure. In the 1960's and early 1970's when these original equations were developed, instrumentation techniques were not available to monitor the start of ductile tearing and stable crack growth up to the maximum pressure.…”