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Creep crack growth in service-exposed weld metal of 2.25Cr1Mo
KTH, Superseded Departments, Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
2001 (English)In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, Vol. 78, no 11-12, 749-755 p.Article in journal (Refereed) Published
Abstract [en]

Creep crack growth (CCG) has been studied for ex-service weld metal of 2.25Cr1Mo (P22). The testing was conducted at a temperature of 550degreesC and prior to testing, the material had been exposed to high temperature service for 110 000 h at 530 C. The results show a marked effect of the service exposure on the CCG properties of the material when compared to similar testing performed on a new material. The CCG rate was higher by a factor 3.1 in the service-exposed material, which should be compared to the model value of 3.2 based on the relations between the elongation values. The consumed deformation capacity was also estimated with the omega model for tertiary creep. In this case, an enhanced growth rate of 2.4 was obtained. Within a distance of about 10 mm in front of the propagating cracks, the number of creep cavities was significantly higher than in the surrounding material. The variation of the density of cavities as a function of distance from the crack tip was successfully modelled. (C) 2002 Published by Elsevier Science Ltd.

Place, publisher, year, edition, pages
2001. Vol. 78, no 11-12, 749-755 p.
Keyword [en]
creep crack growth, CrMo-steel, P22, ex-service, creep cavity, STRAIN
URN: urn:nbn:se:kth:diva-12072DOI: 10.1016/S0308-0161(01)00086-2ISI: 000174338300004OAI: diva2:300977
QC20100719Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2010-07-19Bibliographically approved
In thesis
1. Mechanical Properties of Welds at Creep Activation Temperatures
Open this publication in new window or tab >>Mechanical Properties of Welds at Creep Activation Temperatures
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Welds in materials intended for service at temperatures above the creep activation temperature often develop damage before the base metal. The weld is a discontinuity in the material and stresses and strains often accumulate in the weld. Knowledge of the properties of the weld is essential to the safe operation of the component containing the weld. The work in this thesis has been aimed at the study of welds in service at high temperatures: The work is divided into two main chapters. The first chapter deals with welds in stainlesssteels and dissimilar metal welds and includes three papers, and the second chapter dealswith welds in copper intended for nuclear waste disposal, also including three papers. Common to both parts is that the temperature is high enough for most of the damage in the welds to result from creep.

In the first part the role of the weld microstructure on the creep crack propagation properties has been studied. Experiments using compact tension specimens have been performed on service exposed, low alloyed heat resistant steels. The results show good correlation with the crack tip parameter, C*, during steady state creep crack growth. The test methodology has also been reviewed and sensitive test parameters have been identified. The results from the creep crack propagation tests on service exposed material has been modeled using uniaxial creep data on both new and ex-service material. The development of the weld microstructure in a dissimilar metal weld between two heat resistant steels has also been investigated. A weld was made between one ferritic and one martensitic steel and the development of the microstructure during welding and post-weldheat treatments has been studied. The results show that the carbon depleted zone that develops near the weld metal in the lower alloyed steel depends on the formation and dissolution of the M23C6-carbide. Variations of the weld parameters and the post-weld heat treatment affect the size and shape of this zone. The process has been successfully modeled by computer simulation.

The second part focuses on oxygen free copper intended for nuclear waste disposal containers. The containers are made with an inner core of cast nodular iron and an outer core of copper for corrosion protection. The copper shell has to be welded and two weld methods has been tested, electron beam welding and friction stir welding. Creep specimens taken from both weld types have been tested as have base metal specimens. The technical specifications of the waste canisters demand that the creep ductility of both the copper shell and the welds has to be as high as possible. The creep test results show that base material doped with at least 30 ppm phosphorus has high creep ductility, and friction stir welds made from this material has almost as high creep strength and creep ductility. Copper without phosphorus does not exhibit the same ductility. The creep properties evaluated from testing has been modeled and extrapolated for the intended purpose

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 69 p.
creep, creep crack propagation, OFHC copper, welds, nuclear waste disposal, creep modeling
National Category
Materials Engineering
urn:nbn:se:kth:diva-12077 (URN)978-91-7415-567-9 (ISBN)
Public defence
2010-03-05, Sal E3, Lindstedtsvägen 3, KTH, Stockholm, 10:00 (English)
QC20100719Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2010-07-19Bibliographically approved

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