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Title: Factors limiting the in-service lifetime of CrMoV steels and weldments for pressure equipment
Author: Manna, G.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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This research project addresses the factors limiting the lifetime of industrial components for pressure equipment used in particular in the petrochemical industry but also strongly linked conventional energy production plants. Hydrogen attack, and the combined effect of both creep and hydrogen attack, are the key phenomena forming the object of study. These are frequently the cause of damage and catastrophic failures, with huge economic impact on the affected plants. As the study is of industrial relevance, tests representative of the industrial reality have been carried out under simulated conditions. Three steels have been selected: the standard 2.25Cr-lMo steel, which is the conventional commercial steel used for the construction of pressure vessels for petrochemical plants; the V-modified 2.25 Cr-lMo steels, which represents the steel of new generation pressurized equipment; and the V-modified 3Cr-lMo, which is also a newly designed alloy for pressure equipment use. Each of these materials was supplied with an industrial scale weldment and each test piece contained weld material. The experimental part of the thesis, which included, among the others, tests on tubular specimens pressurized with high-temperature hydrogen or argon, has been realized using the unique hydrogen creep facilities available at the Institute for Energy of the Joint Research Centre. Moreover, interrupted creep tests, mainly carried out in hydrogen, allowed to gain more insight into the evolution of the damage in the different metallurgical zones of the chosen weldments. The tested specimens underwent extended microstructural characterization by means of optical microscope, scanning electron and transmission electron microscopes. Whilst the sample made of V-modified 3Cr-lMo steel failed in the base metal, those made with standard 2.25Cr-lMo steel, or with its V-modified grade, exhibited Type IV failure, in both hydrogen and air. Based on the synergies between hydrogen attack and creep, conclusions on the evolution of the damage and the steps leading to failure are drawn. Hydrogen attack, however limited for more resistant steels, is still expected to contribute to premature failure in the weldments, and great care should be taken when introducing even improved steels into hydrogen bearing environments.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available