Shinobu Kawaguchi

Full-scale burst tests of ultra-high pressured rich-gas pipelines under buried and unburied conditions

The results of four full-scale burst tests conducted at the test site in Denmark were reported and the required fracture toughness for arrest was discussed for the X80 pipeline used for rich-gas transmission under ultra-high pressure (defined as greater than a 15 MPa internal pressure). The ductile crack arrest behavior was evaluated for buried using well-compacted sand and unburied conditions. The initial internal pressure of the tests was approximately 18.4 and 16.2 MPa corresponding to hoop stress of 400 and 350 MPa (72% SMYS and 64% SMYS), respectively. Natural gas that consisting of 89∼90 mol % methane and the balance being heavier hydrocarbons that give the rich-gas compositions was used for the burst tests. The outer diameters of the tested pipes were 762 mm (30-inch) and 610 mm (24-inch). The velocities of the propagated ductile cracks and the rich-gas decompression were determined from the data measured at the sampling rate of 25 kHz. Based on these test results, the required Charpy v-notch impact energy (vE energy) was used as a measure of the fracture resistance for arrest of the ductile propagating cracks evaluated under different backfill depth conditions. The applicability of the Battelle Two-Curve (BTC) approach was also investigated.Copyright

Modified Equation To Predict Leak/Rupture Criteria For Axially Through-Wall Notched X80 and X100 Linepipes Having a Higher Charpy Energy

A method of predicting the leak/rupture criteria for API 5L X80 and X100 line pipes was evaluated based on the results of hydrostatic full-scale tests for X60, X65, X80, and X100 line pipes with an axially through-wall (TW) notch. The TW notch test results defined the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The defined leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner, Maxey et al. This comparison revealed that the CVN-based equation was not applicable to the pipes having both a CVN energy greater than 120 or 130 J and flow. stress greater than the level of X65. In order to predict the leak/rupture criteria for these line pipes, the static absorbed energy for ductile cracking, (C us ) i , was introduced as representing the fracture toughness of a pipe material. The (C vs ) i value was determined from the microscopic observation of the cut and polished Charpy V-notch specimens after static three-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, (C v ) eq , which was defined as follows: (C v ) eq =4.5 (C vs ) i . The leak/rupture criteria for the X80 and X100 line pipes with higher CVN energies were reasonably predicted by the modified equation using the (C vs ) i value.

Evaluation of Leak/Rupture Limit for Axially Through-Wall Notched Line Pipes Using J-Integral Resistance Curve

This paper investigated the applicability of the differential function of J-integral Resistance (J-R) curves, that is, dJ/da to predict the leak/rupture limit on X65 and X80 line pipes. The leak/rupture limit depended on the J-R curves of line pipes and was estimable using the dJ/da approach irrespective of the levels of the Charpy impact energy. It is noted that the dJ/da approach enables us to evaluate the leak/rupture limit of pipelines having a high Charpy impact energy, to which the Charpy impact energy-based equation is inapplicable.Copyright

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

Abstract For two types of API 5L X65 linepipes, the critical conditions for ductile cracking of the linepipe steel and their applicability to the evaluation of the ductile cracking of an axially notched linepipe were investigated. Static three point bending tests and finite element (FE) analyses for a Charpy V notch specimen were conducted to evaluate the critical conditions for ductile cracking from the notch tip. At the position of ductile cracking for the Charpy specimen, the calculated stress triaxiality was almost constant for both linepipe steels; however, the equivalent plastic strain for each linepipe steel was different. Hydrostatic burst tests were then conducted for internally patched linepipes with an axial through wall notch. The results of FE analyses for the hydrostatic burst tests indicated that the maximum equivalent plastic strain value within the wall thickness was almost the same as that obtained from the three point bending test in the Charpy V notch specimen. It was therefore ascertained that the critical conditions for ductile cracking of linepipes with an actual notch can be predicted from the results of a small scale test and FE analysis, which are used to evaluate the relationship between the stress triaxiality and the equivalent plastic strain.

Determination of Conditional Probability of Dynamic Ductile Axial Crack Arrest for Conventionally-Rolled, Lower-Toughness Linepipe Materials

This paper presents an analytical procedure to predict the conditional probability of dynamic ductile axial crack arrest within one pipe joint length for pipeline materials operating at temperature above the brittle-to-ductile transition temperature. The analysis assumes there is an event to initiate a rupture with probability of one, so that the probability of a fracture event occurring is the probability of the rupture event (i.e., from mechanical damage) times the conditional probability of arrest within one pipe joint. The underlying deterministic model centers on the Battelle Two-Curve approach with a correction to predict the arrest length given the actual material toughness relative to the minimum arrest toughness. Past full-scale experimental results were used to develop statistical parameters that were used with the deterministic model in a Monte Carlo analysis. This model was calibrated for linepipe materials with a toughness less than 150J and a grade less than X65. Example cases are presented to demonstrate the variation of the probability of arrest with the pipeline operating conditions.

Determination of Conditional Probability of Dynamic Axial Crack Arrest for Conventionally-Rolled, Lower-Toughness Linepipe Materials

This paper presents an analysis procedure to predict the conditional probability of dynamic ductile axial crack arrest within one pipe joint length for pipeline materials operating at temperature above the brittle-to-ductile transition temperature. These analyses assume there is an event to initiate a rupture with probability of one, so that the absolute probability of a fracture event occurring is the probability of the rupture event (i.e., from mechanical damage) times the conditional probability of arrest within one pipe joint. The underlying deterministic model centers on the Battelle Two-Curve approach with a correction to predict the arrest length given the actual material toughness relative to the minimum arrest toughness. Past full-scale experimental results were used to develop statistical parameters that were used with the deterministic model in a Monte-Carlo analysis. This model was calibrated for low-toughness (<150J) and low-grade (<X65) linepipe materials. Example cases are presented to demonstrate the variation of the conditional probability of arrest with the pipeline operating conditions.Copyright

Modified Equation to Predict Leak/Rupture Criteria for Axially Through-Wall Notched X80 and X100 Linepipes Having Higher Charpy Energy

A method of predicting the leak/rupture criteria for API 5L X80 and X100 linepipes was evaluated, based on the results of hydrostatic full-scale tests for X60, X65, X80 and X100 linepipes with an axially through-wall (TW) notch. The TW notch test results clarified the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The obtained leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner et al. The comparison revealed that the CVN-based equation was not applicable to the pipes having a CVN energy (Cv ) greater than 130 J and flow stress greater than X65. In order to predict the leak/rupture criteria for these linepipes, the static absorbed energy for ductile cracking, (Cvs )i , was introduced as representing the fracture toughness of a pipe material. The (Cvs )i value was determined from the microscopic observation of the cut and buffed Charpy V-notch specimens after static 3-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, (Cv )eq’ which was defined as follows: (Cv )eq = 4.5 (Cvs )i . The leak/rupture criteria for the X80 and X100 linepipes with higher CVN energies were reasonably predicted by the modified equation using the (Cvs )i value.Copyright

Experimental Evaluation of Leak-Before-Break (LBB) Behavior for High-Grade Line Pipes With an Axial Through-Wall Flaw

Leak-before-break (LBB) behavior was evaluated for two series of conventional line pipes (X65) and three series of high-grade line pipes (X80) with various fracture toughness value. Full-scale hydrostatic burst tests were conducted for the line pipes with an axial through-wall flaw to determine hoop stress for LBB. The experimental results were then compared to the estimation using a Charpy V-notched impact energy (CVN)–based equation by Battelle. The present study clarified that the CVN-based equation was applicable to the pipes with CVN energy less than 130 J. On the contrary, the equation was not applicable to the pipes with CVN energy grater than 130 J. The results of instrumented Charpy tests showed that the load versus load-point displacement response for the high CVN energy pipes was different from that for the low CVN energy pipes. Therefore, the applicability of the CVN-based equation was dependent on the load versus load-point displacement response. This result suggested that the CVN-based equation should be modified to evaluate the LBB criterion for the pipes with relatively high toughness.Copyright