CCG PROFILES CRACK CRACK
The weld P91 material, which is also subject to damage could be the weakest link in the structure and would need to have validated laboratory data available in order to make meaningful life assessment predictions.Īlthough creep life of most components is characterised by a continuum damage mechanism CDM where failure is controlled by either creep rupture or creep strain failure mode, creep crack initiation (CCI) and growth (CCG) in some cases tend to dominate the total life of the component. Modified 9Cr-1Mo alloy, known as Grade P91 steel, has been extensively used for high pressure and high temperature piping and headers in conventional power plants mainly in the outlet section of the boiler such as final superheater and also main steam piping which are subject to the creep damage. Keywords: P91 Creep crack growth fracture mechanics, NSW NSW-MOD C* Introduction Design and assessment challenges that remain in treating P91 weld failures are then addressed in light of the analysis. Creep crack growth life is predicted based on short-term uniaxial creep crack growth (CCG) data. Particular areas where existing data are limited in the literature are highlighted. This paper provides a review and reanalysis of published information using properties quoted in codes of practice and from recent research data regarding the creep crack growth of P91 steel, and uses existing models to predict its behaviour.
Incidences of cracking in P91 welds have been reported in times significantly less than 100,000 hours leading to safety and reliability concerns worldwide.
However, evidence from premature weld failures in P91 steel suggests that design standards and guidelines may be non-conservative for P91 welded pressure vessels and piping. Since Grade P91 steel was introduced in the 1980s as enhanced ferritic steel, it has been used extensively in high temperature headers and steam piping systems in power generating plant. However, as the 9%Cr material is relatively new, there is relatively limited data available and understanding with respect to quantifying the effect of variables on life prediction of components fabricated from P91 is more difficult. Old grades of creep resistant materials such as P11 and P22 have been studied in depth and data and prediction models are available for design and fitness for service assessment of creep rupture, creep crack growth, thermo-mechanical fatigue, etc. Paper presented at WELDS 2009: Design, testing, assessement and safety of high-temperature welded structures. National Structural Integrity Research Centre.Structural Integrity Research Foundation.
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