Control of ductile fracture propagation in modern gas pipelines

Abstract

Problem statement. The control of destruction  expansion is important aspect of exploitation safety supporting of the modern high-pressure gas pipelines. The technology of such control is most important for prevention extended ductile destruction of gas pipelines, that can make serious damage for economy and environment. The counterstand of running fracture extension is material property, which determine its ability of extended destruction arrest. The index of this ability is minimal absorbed energy of ductile fracture arrest, which is estimated by the results of full-sized burst tests. These tests are cumbersome and expensive enough. That is why Batelle Two Curv Method (BTCM) was proposed for definition running fracture arrest energy. In this test arrest energy is expressed by absorbed Charpy-V energy. BTCM was invented at  the beginning of 70s XX century and it was successfully used for steels with strength categories before X65, which have low or medium ductility.  After that new  high-ductile tube steels appeared in the industry, which were made with thermomechanical rolling method. It was discovered, that for this steels immediate  measurement Charpy-V energy is not reliable index of destruction arrest. That is why it was decided to determine  Charpy-V energy by the value of absorbed DWTT energy with using equalizations of correlation Charpy-V energy and DWTT energy. The range of such equalizations is already known. However, as it was shown in the analysis, all of them have crucial issues and disadvantages, which need characterization of correct and effective using these equalizations for determination running ductile fracture arrest energy with BTCM method in high-ductile tube steels, which have different strengths and thickness. Purpose. The characterization of accordance absorbed energy  Charpy-V and Drop Weight Tear Test (DWTT) correlation equalizations with real (experimental) correlation these indexes of researched high-ductile tube steels. Material and methodology. The high-ductile steels for gas pipelines, which have strength categories X80, X70,X65 and different thickness, were chosen as materials for research. Drop weight tear tests (DWTT)  were realized with using Zwick firm vertical drop machine. Full-sized samples with pressured cut were assayed in automatic registration curves force-moving mode. Full absorbed energy of destruction, energy of fracture genesis and running were determined . The quantity of ductile component in full-sized DWTT samples was estimated in accordance with standard 
APIRP5L3-96 (2007) and standard BSEN 10274:1999. Charpy-V energy was determined in accordance with standard  ГОСТ 9454-78 on the samples type H. Results. It was gotten real (experimental) correlation of absorbed Charpy-V and DWTT energy in modern high-ductile tube steels, which are extensively used in gas pipelines building. Scientific novelty. It was analysed  the modern condition of the problem with characterization destruction arrest in high-ductile  tube steels for high-pressure gas-pipelines. It was shown, that Wilkowski linear equalization for hot-rolled and normalized steels with strength categories before X65 fully accords with real correlation absorbed DWTT energy-absorbed Charpy-V energy in high-ductile steels with thickness before 25 mm, which were treated with thermomechanical rolling. If the steel has big thickness, no one of considered correlation equalizations will not accord with real correlation DWTT energy and Charpy-V energy. It is necessary to use real correlation of absorbed DWTT energy and Charpy-V energy  for high-ductile steels with such thickness or develop calculation methods to the way of  immediate using DWTT energy instead of  calculated with correlation equalizations Charpy-V energy. Practical value. It were specified the conditions of using BTCM method in accordance with half-ampirical correlation equalizations of absorbed  Charpy-V energy and DWTT energy, and real correlation of these variables during running ductile fracture arrest energy determination  in gas pipelines, that are made from modern high-ductile steels.