Effect of Grade on Ductile Fracture Arrest Criteria for Gas Pipelines

2006 ◽  
Author(s):  
G. Wilkowski ◽  
D. Rudland ◽  
H. Xu ◽  
N. Sanderson
Keyword(s):  
Ductile Fracture ◽  
Correction Factor ◽  
Grade Level ◽  
Full Scale ◽  
Statistical Analyses ◽  
Background Information ◽  
Gas Pipelines ◽  
Charpy Test ◽  
Energy Value ◽  
Fracture Arrest

Several different criteria have been proposed over the years to predict the minimum toughness for arrest of an axial propagating crack for natural gas pipelines. The initial ones were empirically based. The Battelle Two-Curve Method (TCM) was subsequently developed and was somewhat less empirical. The TCM is still used frequently today. Nevertheless, all of these criteria use the Charpy energy as a measure of the material’s ductile fracture resistance. As higher-grade steels have been developed, it has been found from full-scale tests that a multiplier was needed on the predicted minimum Charpy arrest energy value as calculated from the original TCM. Several researchers have also suggested that a correction factor was needed on the Charpy energy as the Charpy energy value increased above a certain level. This was a nonlinear correction factor that essentially showed that as the Charpy energy value surpassed a certain level, the effective energy for ductile fracture arrest is less than the total energy from the Charpy test. This paper presents background information on several of these toughness correction factors, as well as statistical analyses of full-scale pipe burst tests on 186 lengths of X60 to X100 grade pipes using these methods. The results show the effects of grade level on not only the original TCM predictions, but also several other modifications for high Charpy energy levels. Additionally, a method has also been developed where the DWTT energy was used instead of the Charpy energy in the Battelle TCM. The results of the statistical analyses showed that all the Charpy-energy-based criteria required an increasing correction factor as the grade level increased. The one DWTT energy criterion was statistically constant with grade level. This difference between the Charpy criteria and the DWTT criterion was traced back to a changing relationship between the Charpy and DWTT energy values as the grade of the steel increases.

Mechanical and Metallurgical Aspects of the Resistance to Ductile Fracture Propagation in the New Generation of Gas Pipelines

2014 ◽  
Author(s):  
Igor Pyshmintsev ◽  
Alexey Gervasyev ◽  
Victor Carretero Olalla ◽  
Roumen Petrov ◽  
Andrey Arabey
Keyword(s):  
Ductile Fracture ◽  
Mechanical Test ◽  
Fracture Propagation ◽  
Rolling Plane ◽  
Full Scale ◽  
Charpy Test ◽  
Line Pipe ◽  
Surface Separation ◽  
Fracture Arrest ◽  
New Generation

The microstructure and fracture behavior of the base metal of different X80 steel line pipe lots from several pipeline projects were analyzed. The resistance of the pipes to ductile fracture propagation was determined by the full-scale burst tests. The high intensity of fracture surface separation (secondary brittle cracks parallel to the rolling plane of the plate) appeared to be the main factor reducing the specific fracture energy of ductile crack propagation. A method for quantitative analysis of microstructure allowing estimation of the steel’s tendency to form separations is proposed. The procedure is based on the EBSD data processing and results in Cleavage Morphology Clustering (CMC) parameter evaluation which correlates with full-scale and laboratory mechanical test results. Two special laboratory mechanical test types utilizing SENT and Charpy test concepts for prediction of ductile fracture arrest/propagation in a pipe were developed and included into Gazprom specifications.

The Application of the Battelle “Short Formula” to the Determination of Ductile Fracture Arrest Toughness in Gas Pipelines

2000 ◽  
Author(s):  
A. B. Rothwell
Keyword(s):  
Ductile Fracture ◽  
Original Description ◽  
Gas Pipelines ◽  
Research Committee ◽  
Original Intent ◽  
Decompression Wave ◽  
Wide Range ◽  
Fracture Arrest ◽  
Fracture Velocity

Many models and formulae have been put forward, over the years, for the determination of the toughness necessary for the arrest of propagating ductile fracture in gas pipelines. One of the first, and most prominent, was that developed by Battelle Columbus Laboratories for the Pipeline Research Committee of the American Gas Association. As originally embodied, the model involved the comparison of curves expressing the variation of fracture velocity and of decompression wave velocity with pressure (the “two-curve model” — TCM). To aid in analysis, at a time long before a computer was available on every desk, a “short formula” (SF) was developed that provided a good fit to the results of the TCM for a substantial matrix of conditions. This SF has subsequently been adopted by several standards bodies and used widely in the analysis of the results of full-scale burst tests. Since the original description of the derivation of the SF is to be found only in a report to the PRC dating back to the Seventies, many in the pipeline industry today are left without a full appreciation of its range of validity. The present paper briefly discusses the original intent of the SF as a substitute for the TCM, and presents the results of extensive calculations comparing the results of the two. It can be concluded that the SF provides an excellent estimate of the results of the TCM over a very wide range of design and operating parameters, within the limitations inherent in the method.

Fracture Propagation in Underwater Gas Pipelines

1986 ◽  
Vol 108 (1) ◽  
pp. 29-34 ◽  
Author(s):  
W. A. Maxey
Keyword(s):  
Ductile Fracture ◽  
Pipe Wall ◽  
Fracture Propagation ◽  
Full Scale ◽  
Gas Pipelines ◽  
Buried Pipelines ◽  
Nitrogen Gas ◽  
Line Pipe ◽  
Fracture Velocity

Two full-scale ductile fracture propagation experiments on segments of line pipe pressurized with nitrogen gas have been conducted underwater at a depth of 40 ft (12 m) to evaluate the ductile fracture phenomenon in underwater pipelines. The pipes were 22-in. (559-mm) diameter and 42-in. (1067-mm) diameter. Fracture velocities were measured and arrest conditions were observed. The overpressure in the water surrounding the pipe resulting from the release of the compressed nitrogen gas contained in the pipe was measured in both experiments. The overpressure in the water reduces the stress in the pipe wall and thus slows down the fracture. In addition, the water surrounding the pipe appears to be more effective than soil backfill in producing a slower fracture velocity. Both of these effects suggest a greater tendency toward arrest for a pipeline underwater than would be the case for the same pipeline buried in soil onshore. Further verification of this effect is planned and a modified version of the existing model for predicting ductile fracture in buried pipelines will be developed for underwater pipelines.

Applicability of Existing Models for Predicting Ductile Fracture Arrest in High Pressure Pipelines

2006 ◽  
Author(s):  
John Wolodko ◽  
Mark Stephens
Keyword(s):  
High Pressure ◽  
Ductile Fracture ◽  
High Pressures ◽  
Fracture Propagation ◽  
High Strength Steels ◽  
High Strength ◽  
Full Scale ◽  
Stage Of Development ◽  
Fracture Arrest ◽  
Arrest Toughness

The ductile fracture arrest capability of gas pipelines is seen as one of the most important factors in the future acceptance of new high strength pipeline steels for high pressure applications. It has been acknowledged for some time that the current methods for characterizing and predicting the arrest toughness for ductile fracture propagation in high strength steels are un-conservative. This observation is based on the inability of existing models to predict the required arrest toughness in full-scale ductile fracture propagation tests. While considerable effort is currently being applied to develop more accurate methods for predicting ductile facture arrest, the resulting models are still in a preliminary stage of development and are not immediately amenable for use by the general engineering community. As an interim solution, a number of authors have advocated the empirical adjustment or reformulation of the existing models for use with the newer, high strength pipe grades. While this approach does not address the fundamental issues surrounding the fracture arrest problem, it does provide methods that can be used in the near term for analysis and preliminary design. The desire to use these existing methods, however, is tempered by the uncertainty associated with their applicability in situations involving high pressures and/or high toughness materials. In an attempt to address some of these concerns, a statistical analysis was conducted to assess the accuracy of a number of available fracture arrest models by comparing predictions to actual values determined from full-scale fracture propagation experiments. From the results, correction factors were developed for determining the required toughness levels in high pressure applications that account for the uncertainty in the theoretical prediction methods.

Paper 10: The Influence of Moisture on the Efficiency of a One-Third Scale Model Low Pressure Steam Turbine

1965 ◽  
Vol 180 (15) ◽  
pp. 39-49
Author(s):  
A. Smith
Keyword(s):  
Steam Turbine ◽  
Correction Factor ◽  
Rotational Speed ◽  
Direct Injection ◽  
Maximum Level ◽  
Low Pressure ◽  
Full Scale ◽  
Scale Model ◽  
Supersaturation Ratio ◽  
Multi Stage

The rapid increase in blade-tip diameters and peripheral speeds of low pressure turbines in large 3000 rev/min turbo-generators has presented the designer with many difficult mechanical and aerodynamic problems. To assist in the aerodynamic development of such blading, design studies on an experimental low pressure (l.p.) turbine were started early in 1959. Economic and technical considerations limited the choice to a one-third scale model steam turbine capable of running at three times the normal rotational speed to preserve full-scale working Mach numbers on the blading. Overall output and steam consumption were measured on a hydraulic dynamometer and by volumetric tanking respectively. The inlet steam temperature was controlled by a direct injection desuperheater so that the expansion could be kept dry for traversing or reduced to design inlet temperatures for normal wet running. Three multi-stage sets with last row blade diameters corresponding to 90-in, 120-in, and 136-in full-scale turbines have now been tested in the experimental turbine and the wet performance of the largest forms the subject of this paper. The overall wetness losses on the model 136-in diameter turbine have been assessed from a series of seven tests in which the inlet superheat and rotational speed were varied whilst maintaining fixed inlet and outlet pressure levels. To isolate the stage moisture correction factor (α), however, where a stage-by-stage approach was adopted, in which the dry stage efficiencies were initially established from interstage traverses under dry steam conditions. Two wet steam analyses were made, the first assuming equilibrium and the second supersaturated expansion, but the choice seemed immaterial since the moisture correction factor was almost the same for both. In the case of the supersaturated expansion calculation, it was necessary to establish the point of reversion from supersaturated to near equilibrium expansion (the Wilson point) and supplementary water extraction results were used to establish the maximum supersaturation ratio. These suggest that the maximum level is nearer to 3 in the model turbine than to the value of 4–6 quoted for convergent-divergent nozzles.

Sign in / Sign up

Export Citation Format

Share Document