Integrity Assessment of Pressure Components Operating with Creep Regime

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Copyright: Mahmood, Tahir
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Abstract
Efficient and cost effective design of pressure components at high temperature depend upon the availability of creep design methods that can be used by design engineers for accurately predicting the creep life. Quite a few creep design methods have been developed over the years but none of these methods can be regarded as the best reliable yet simple to apply for variety of problems. Some methods give better results for certain cases while are totally inaccurate for some other cases. Similarly, the practising engineers have developed the affinity with one method or the other. Also, there is no model that can be regarded as accurate for both elastic-creep and/or elastic-plastic-creep case. The thesis proposes two new creep life prediction methods that are quite easy to apply and give very accurate results. Proposed creep life prediction methods are based on strain energy density which is a scalar quantity and quite easy to calculate. The proposed methods assume that the damage induced in the material is directly related to the internal energy density absorbed at critically loaded regions in the material. Consequently, the proposed methods take into account both internal forces (stresses) and deformations (strains) yet they are simple to use in practice due to the scalar nature of internal energy density. The proposed methods have superiority over some of the existing methods that are based on only stress or only strain as these quantities are directional and hard to calculate. General philosophy for design of pressure components below creep range is to develop uniaxial material properties that are used for design with certain safety factors. A Similar approach has been used for creep design but only for elastic-creep problems. Problems involving elastic-plastic-creep are complex and no accurate methodology exists for such cases. Two methods proposed were investigated for accuracy by applying them to a range of pressure components including thin wall pressure pipe, thick wall pressure pipe & thick wall pressure pipe with circumferential weld. Notched bars were also analysed to investigate the relationship of multi-axiality parameter to notch radius. Proposed methods predicted life with error of less than 10%.
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Author(s)
Mahmood, Tahir
Supervisor(s)
Kanapathipillai, Kana
Chowdhury, Mahiuddin
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Publication Year
2014
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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