Analysis of the plasticity characteristics of progressively drawn steel wires

Changes in the plasticity characteristics in air and in a hydrogenating environment of prestressing steel wires due to cold drawing process are investigated on the basis of slow strain rate tests on smooth specimens. The tested pearlitic steel is highly susceptible to hydrogen embrittlement at all stages of cold drawing. The inconsistency is revealed between the changes of two plasticity characteristics: reduction in area and uniform elongation. The obtained results are analysed distinguishing the contribution of resistance to crack initiation and crack propagation. Susceptibility to crack initiation increases as a result of cold drawing with simultaneous improvement of the crack propagation resistance.За результатами механічних випроб на повільний розтяг гладких зразків досліджено зміну характеристик пластичності у повітрі та наводнювальному середовищі прутків з перлітної сталі внаслідок холодного волочіння. Сталь високочутлива до водневого окрихчення на усіх етапах обробки. Виявлено невідповідність між змінами відносних звуження та рівномірного видовження. Отримані результати проаналізовано з виокремленням вкладу опору зародженню і поширенню тріщини. Внаслідок холодного волочіння підвищується чутливість до тріщиноутворення, при цьому опір поширенню тріщини дещо зростає.На основании результатов механических испытаний на медленное растяжение гладких образцов исследовано изменение характеристик пластичности на воздухе и в наводороживающей среде прутков из перлитной стали после холодного волочения. Сталь высокочувствительна к водородному охрупчиванию на всех этапах обработки. Обнаружено несоответствие между относительным сужением и равномерным удлинением. Полученные результаты проанализировали, выделяя отдельно сопротивление зарождению и распространению трещины. Вследствие холодного волочения повышается чувствительность к трещинообразованию, при этом сопротивление распространению трещины повышается

Stress corrosion cracking of gas pipeline steels of different strength

AbstractWith the development of the natural gas industry, gas transmission pipelines have been developed rapidly in terms of safety, economy and efficiency. Our recent studies have shown that an important factor of main pipelines serviceability loss under their long-term service is the in-bulk metal degradation of the pipe wall. This leads to the loss of the initial mechanical properties, primarily, resistance to brittle fracture, which were set in engineering calculations at the pipeline design stage. At the same time stress corrosion cracking has been identified as one of the predominant failures in pipeline steels in humid environments, which causes rupture of high-pressure gas transmission pipes as well as serious economic losses and disasters.In the present work the low-carbon pipeline steels with different strength levels from the point of view of their susceptibility to stress corrosion cracking in the as-received state and after in-laboratory accelerated degradation under environmental conditions similar to those of an acidic soil were investigated. The main objectives of this study were to determine whether the development of higher strength materials led to greater susceptibility to stress corrosion cracking and whether degraded pipeline steels became more susceptible to stress corrosion cracking than in the as-received state. The procedure of accelerated degradation of pipeline steels was developed and introduced in laboratory under the combined action of axial loading and hydrogen charging. It proved to be reliable and useful to performed laboratory simulation of in-service degradation of pipeline steels with different strength. The in-laboratory degraded 17H1S and X60 pipeline steels tested in the NS4 solution saturated with CO2 under open circuit potential revealed the susceptibility to stress corrosion cracking, reflected in the degradation of mechanical properties, and at the same time the degraded X60 steel showed higher resistance to stress corrosion cracking than the degraded 17H1S steel. Fractographic observation confirmed the pipeline steels hydrogen embrittlement caused by the permeated hydrogen