Creep crack initiation and growth in thick section steel pipes under internal pressure

Abstract

In this study, creep crack growth in pre-cracked straight and bent pipes of a 9% Cr-steel, containing multiple cracks and tested at 625°C under static and slow cyclic pressure loading, is investigated. The results have been interpreted in terms of the creep fracture mechanics parameter C* and compared with data obtained on standard compact tension (CT) specimens of the same material and batch. In making the assessments, reference stress methods have been used to determine C* for the pipes. Several formulae can be employed for calculating reference stress depending on whether it is based on a 'global' or a 'local' collapse mechanism. When using this approach, it is shown that the values obtained for C* are sensitive to the material properties, geometric dimensions and crack lengths chosen in the analysis. However, it has been found that, the most satisfactory comparison of crack growth rates with standard CT specimen data is obtained when the 'global' reference stress solution is used in conjunction with the nominal thickness of a pipe and the mean parent uniaxial creep properties. Also, no difference has been observed between the crack growth rates measured in the straight and bent pipes. The main effect of the slow pressure cycling was to cause an acceleration in the early stages of cracking.

A Damage Tolerance Model for Plates with Surface Cracks Under Combined End Force and Bending

“…Therefore, when calculating crack propagation limit size, the mechanical properties of the material must be known and the analysis of stress state at the crack crosssection must be done. Stress state of the crack section is very complex, there are also a lot of description methods, and reference stress method is adopted in this paper, which can be divided into the global reference stress and the local reference stress [8]. Literature [8][9][10] has studied the relationship between the reference stress and the corresponding plastic collapse, the relationship between the reference stress and the elastic strain energy and the relationship between the reference stress and stress intensity factor.…”

“…Stress state of the crack section is very complex, there are also a lot of description methods, and reference stress method is adopted in this paper, which can be divided into the global reference stress and the local reference stress [8]. Literature [8][9][10] has studied the relationship between the reference stress and the corresponding plastic collapse, the relationship between the reference stress and the elastic strain energy and the relationship between the reference stress and stress intensity factor. They confirmed the elastic-plastic fracture mechanics parameter J and the creep fracture mechanics parameter C* for flawed components by local reference stress method.…”

“…Carter AJ studied the limit load of flawed components using the local reference stress [11]. The results of literature [12][13][14] show that local reference stress is too conservative in the calculation of the crack propagation and the global reference stress could better reflect the characteristics of crack propagation. In this paper, the global reference stress is adopted to analyze the limit crack size of cracked aluminum alloy plate under bending load, and crack closure effects are ignored during the calculation.…”

Probabilistic analysis of creep crack initiation and growth in pipe components

“…Previously it has been shown [21] that a 'Global' solution of reference stress [4] is most appropriate for cracked pipe components and therefore this solution is chosen in this paper to estimate C*. 'Global' solutions are based on collapse of the entire cross-section at the site of the defect.…”

Evaluación de la longitud de grietas por fatiga mediante la deformación plástica en muestras compactas de tracción empleando el ruido magnético de Barkhausen

“…Estos aceros han recibido gran parte de la atención de la comunidad científica a nivel internacional, debido a la importancia económica y social que requiere el estudio de su durabilidad; por ello, entre los principales ensayos que se llevan a cabo se encuentra el de velocidad de propagación de grietas a elevadas cargas y temperaturas, simulando las condiciones reales de explotación [6][7][8][9] .…”