Modeling and Simulation of Creep Crack Growth in High Chromium Steels

2014 ◽  
Author(s):  
Nicola Bonora ◽  
Luca Esposito ◽  
Simone Dichiaro ◽  
Paolo Folgarait
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Chromium Steel ◽  
Creep Model ◽  
Model Parameters ◽  
Approximate Methods ◽  
High Chromium ◽  
Creep Crack ◽  
Wide Range

Safe and accurate methods to predict creep crack growth (CCG) are required in order to assess the reliability of power generation plants components. With advances in finite element (FE) methods, more complex models incorporating damage can be applied in the study of CCG where simple analytical solutions or approximate methods are no longer applicable. The possibility to accurately simulate CCG depends not only on the damage formulation but also on the creep model since stress relaxation, occurring in the near tip region, controls the resulting creep rate and, therefore, crack initiation and growth. In this perspective, primary and tertiary creep regimes, usually neglected in simplified creep models, plays a relevant role and need to be taken into account. In this paper, an advanced multiaxial creep model [1], which incorporates damage effects, has been used to predict CCG in P91 high chromium steel. The model parameters have been determined based on uniaxial and multiaxial (round notched bar) creep data over a wide range of stress and temperature. Successively, the creep crack growth in standard compact tension sample was predicted and compared with available experimental data.

Creep Crack Growth of P92 Welds

2008 ◽  
Author(s):  
Masataka Yatomi ◽  
Akio Fuji ◽  
Ken-ichi I. Kobayashi ◽  
Masaaki Tabuchi ◽  
Takeo Yokobori ◽  
...  
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Creep Model ◽  
Element Analysis ◽  
Creep Properties ◽  
Creep Crack ◽  
Type Iv ◽  
Growth Properties ◽  
Power Law Creep

This paper represents creep properties and creep crack growth properties for P92 welds. The CCG tests were carried out using cross-welded compact tension (C (T) specimens at several temperatures. The crack front was located at HAZ region to simulate Type IV crack. Finite element analysis was conducted to simulate multiaxiality in welded joints and compare the experimental results. The constitutive behaviour for these materials is described by a power law creep model.

Virtual Methods in Creep Crack Growth Predictions in 316H Stainless Steels

2007 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Stainless Steels ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Creep Model ◽  
Elastic Plastic ◽  
Creep Crack ◽  
Plastic Creep ◽  
Plane Strain Crack

The paper discusses numerically based virtual techniques of creep crack growth predictions in a fracture mechanics component. The material properties used are for 316H stainless steels and the constitutive behaviour of the steel is described by a power law creep model. A damage-based approach is used to predict the crack propagation rate in compact tension (C(T)) specimens and the data are correlated against an independently determined C* parameter. Elastic-plastic-creep analyses are performed using two different crack growth criteria to predict crack extension under plane stress and plane strain conditions. The NSW and NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions. The plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model, for values of C* within the limits of the present creep crack growth testing standards. At higher loads and C* values, the plane strain crack growth rates, predicted using an elastic-plastic-creep material response, approach is considered and compared to the plane strain NSW-MOD model.

The Influence of Specimen Geometry and Test Times on High Temperature Crack Growth Behaviour in Parent and Welded 316H Stainless Steel

2008 ◽  
Author(s):  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
Masaakai Tabuchi ◽  
David W. Dean ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Large Fraction ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Parent Material ◽  
Test Duration ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Order Of Magnitude ◽  
Fracture Specimens

Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens including sections taken from a 316 steel weldment. These specimens include the compact tension, C(T), and circumferentially cracked notched bar, CCB, geometries of various sizes. Results are presented from two creep crack growth (CCG) tests on a large and a small CCB weldment specimen. The creep crack initiation (CCI) and growth (CCG) behavior of the CCB weldments has been compared to that of homogeneous parent material (PM) CCB and C(T) specimens and to C(T) weldment specimen data. The data has been analyzed in terms of the C* parameter. The initiation period is found to occupy a large fraction of the test duration for weldments. The CCG rates in the larger CCB weldment test is on the order of six times faster, for a given value of C*, compared to the smaller specimen, indicating a specimen size effect. The CCI times are around an order of magnitude greater for the CCB weldment specimens compared to C(T) weldment data and are higher than that of the PM CCB data. It is recommended that further testing on weldment specimens is performed to affirm the apparent trends.

Characterizations of creep crack growth in 1 per cent Cr Mo V steel

1981 ◽  
Vol 16 (2) ◽  
pp. 137-143 ◽  
Author(s):  
D J Smith ◽  
G A Webster
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Growth Data ◽  
Creep Crack ◽  
Test Pieces ◽  
Reference Stress ◽  
Collapse Mode ◽  
Two Parameters ◽  
Creep Deformations

Estimates of stress intensity factor, K, reference stress, σref, and creep parameter, C∗, have been made for compact tension (CT) and double cantilever beam (DCB) test-pieces containing side grooves. Limit analysis techniques were used to determine the latter two parameters. It is shown that the expressions developed for σref are sensitive to the collapse mode proposed, whereas those for C∗ are largely independent. Comparisons of predictions of creep crack growth data on CT and DCB specimens of a 1 per cent CrMoV steel in terms of K and σref have revealed different dependences for the two geometries, suggesting that neither parameter gives satisfactory correlations. Better overall agreement is obtained with the C∗ parameter, even though gross creep deformations were not observed. It is suggested that further improvement may be gained with this parameter if more accurate estimates of C∗, which allow the inclusion of elastic terms, are used.

Experimental Investigation of Constraint Effects on Creep Crack Growth

2002 ◽  
Author(s):  
Adam D. Bettinson ◽  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
George A. Webster
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Growth Data ◽  
Creep Crack ◽  
Low Constraint ◽  
Constraint Effects ◽  
Crack Growth Model ◽  
Crack Growth Rates

In this work the effects of specimen size and type on creep crack growth rates in stainless steel are examined. Experiments have been carried out on high constraint compact tension specimens (CT) and low constraint centre cracked panels (CCP) of ex-service 316H stainless steel. All testing was carried out at 550°C. Constraint effects have been observed in the data, with the large CT specimens having the fastest crack growth rate and the small CCP specimens the slowest. These trends are consistent with those that would be predicted from two parameter (C*–Q) theories. However, it is found that a constraint dependent creep crack growth model based on ductility exhaustion overpredicts the constraint dependence of the crack growth data.

Specimen Orientation and Constraint Effects on the Creep Crack Growth Behaviour of 316H Stainless Steel

2012 ◽  
Author(s):  
A. Mehmanparast ◽  
C. M. Davies ◽  
D. W. Dean ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Uniaxial Creep ◽  
Microstructural Effects ◽  
Specimen Orientation ◽  
Constraint Effects

Pre-compression (PC) is found to have strong effects on the tensile, uniaxial creep rupture and creep crack growth (CCG) behaviour of type 316H stainless steel at 550 °C. In this work, blocks of 316H steel have been pre-compressed to 8% plastic strain at room temperature and compact tension, C(T), specimens are extracted from the pre-strained blocks with loading directions parallel and normal to the PC axis. The influence of specimen orientation and thickness on the CCG behaviour of the PC material is examined. The results are compared to short term and long term CCG behaviour of 316H steel at the same temperature. Higher CCG rates and shorter CCI times have been found in PC material with a loading direction normal to the PC axis compared to that parallel to the PC axis. These observations are discussed with respect to the microstructural effects.

Influence of Prior Deformation on Creep Crack Growth Behaviour of 316H Austenitic Steels

2012 ◽  
Author(s):  
Hamed Yazdani Nezhad ◽  
Noel P. O’Dowd ◽  
Catrin M. Davies ◽  
Ali N. Mehmanparast ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Fe Analysis ◽  
Austenitic Steels ◽  
Creep Data ◽  
Growth Behaviour ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Good Agreement

The influence of pre-strain and pre-stress on creep crack growth behaviour of 316H austenitic steels is studied experimentally and numerically in this paper. Compact tension, C(T), specimens (25mm thickness) have been extracted from two steam headers, one as-received and one uniformly compressed to the strain value of 8%. The C(T) specimen extracted from the as-received header was compressed, introducing a non-uniform strain field. Creep crack growth (CCG) tests were performed at 550°C. Comparisons have been provided with the results from as-received C(T) specimens. Finite element (FE) analysis has been carried out to simulate the CCG behaviour of the C(T) specimens. By choosing the problem parameters appropriately, good agreement may be achieved between the FE predictions and the creep data.

Comparison Between Crack Growth in Fracture Mechanics Specimens and Feature Component Tests Carried Out in a Low-Alloy Steel

1999 ◽  
Vol 122 (1) ◽  
pp. 40-44 ◽  
Author(s):  
Kamran Nikbin
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Growth Data ◽  
Good Correspondence ◽  
Creep Crack ◽  
Growth Properties ◽  
Circumferential Defects ◽  
Testing Condition

In both power generation plants and the chemical industries, there is a need to assess the significance of defects which may exist in high-temperature equipment operating in the creep range. This paper examines the methods of analysis used in laboratory creep crack growth data and their relevance to crack growth data derived from feature component tests which best simulate actual components under controlled testing condition. The material examined was a 214 Cr 1 Mo steel in the new condition at 550 and 600°C. The creep crack growth properties were determined on compact tension specimens. The data were compared with representative crack growth data from feature test components. These consisted of cracked rings, thick-walled cylinders, and thin-walled tubes containing axial or circumferential defects under combinations of axial and internal pressure loading. Little influence of size or temperature on the measured crack propagation rates was observed when the results were plotted against the creep fracture mechanics parameter C*. This is shown to be because the relevant condition had little effect on the appropriate crack tip creep ductilities of the material. Good correspondence was observed between the compact tension and the feature component tests, suggesting the feasibility of the C* method for predicting short-term laboratory tests using different geometries. [S0094-9930(00)01001-5]

Sign in / Sign up

Export Citation Format

Share Document