Life assessment of welded joints operating within creep range

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open access
Embargoed until 2015-02-06
Copyright: Pramanik, Mridul Ashish
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Abstract
A large portion of the high temperature critical components, used in the power, petroleum, and chemical plants etc. of the world have been in operation for long time like 30 to 40 years, are welded. In comparison to the parent metal, the mechanical and structure characteristics and properties of as-welded and weld metal are different, i.e. Hardness values of weld metal are significantly larger. Moreover, the heat affected zone causes structural differences in the comparison to the unaffected parent metal. Therefore, it is very important to determine possible degradation processes occurring in the weld joint inducing the properties changes during long term service and study the behaviour of each zone of the weld joints in the service conditions, as if critical welded components can be replaced before their failure during in the long term operation of those plants. In this thesis, a new model has been introduced and implemented to predict the remaining life of weld joints subjected to creep failure at high temperature and compared with other existing models. This proposed model contains two independent methods, stress analysis approach and strain analysis approach, to predict the remaining life of welded joints. To calculate the creep life, at first finite element analysis of the experimental cases has been done on the basis of Norton s creep law and then numerical results have been used for further calculation according to the proposed model theory. Finite element analysis showed that strain energy density has its maximum value in the heat affected zone, so creep failure occurs there, which is similar to the experimental observations. A new creep parameter has been found during the implementation of the proposed model which is the function of temperature and material properties for both the approaches, independently. This parameter plays a significant role to control the margin of error of the proposed model. Furthermore, stress analysis approach of the proposed creep life model has more good accuracy than the strain analysis approach. The whole study showed that proposed model goes with excellent accuracy with the experimental cases than the other existing creep life prediction models.
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Author(s)
Pramanik, Mridul Ashish
Supervisor(s)
Kanapathipillai, Sangarapillai
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Publication Year
2013
Resource Type
Thesis
Degree Type
Masters Thesis
UNSW Faculty
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