A Sensitivity Study of Creep Crack Growth in Pipes

2002 ◽  
Author(s):  
K. Wasmer ◽  
K. M. Nikbin ◽  
G. A. Webster
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Sensitivity Study ◽  
Pressure Vessels ◽  
Materials Properties ◽  
Creep Crack ◽  
Piping Systems ◽  
Mechanics Concepts ◽  
Assessment Procedures

Failure of pressure vessels and piping systems that operate at high temperatures can occur by net section rupture, creep crack growth or a combination of both processes. Several design and assessment procedures are available for dealing with this situation. These include the ASME Pressure Vessel and Piping, French RCC-MR (Appendix 16) and British R5 and BS7910 codes. Each of these procedures uses a combination of continuum mechanics and fracture mechanics concepts to make an assessment. Although the procedures adopt the same basic principles, often different formulae are employed to make an assessment. The main parameters that are used are reference stress, σref, stress intensity factor, K, and the creep fracture mechanics term C*. In this paper, an analysis is performed to estimate the sensitivity of the predictions of creep crack growth in a pressurised pipe to the choice of formulae used and materials properties employed. It is shown that most sensitivity is obtained to choice of expression employed for calculating σref and to whether batch specific or more generic materials properties data are selected.

Assessment of Power Plant Components With Flaws and Defects Operating in the Long-Term Creep Range

2019 ◽  
Author(s):  
Magdalena Speicher ◽  
Thorben Bender ◽  
Andreas Klenk ◽  
Falk Mueller ◽  
Christian Kontermann ◽  
...  
Keyword(s):  
High Temperature ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Material Behavior ◽  
Critical Crack Length ◽  
Creep Crack ◽  
Combining Data ◽  
Crack Problems

Abstract Originating from defects and flaws in high temperature components crack initiation and crack propagation under service conditions can occur. Fracture mechanics data and procedures are needed to study crack problems and to support an advanced remnant life evaluation. During subsequent research in the past 35 years, data were determined for different high temperature materials. Methodologies and concepts taking into account the specific material behavior were developed in order to be able to describe crack initiation and crack growth and have appropriate assessment methods available. For creep crack initiation two criteria principles were used and for creep crack growth assessment based on the integral C* parameter were applied. Furthermore, a method for determination of critical crack length was developed allowing decisions whether modified stress analysis methods are sufficient or more complicated fracture mechanics methods are needed. To provide data and methodologies in a user-friendly way, a program system combining data and methods was implemented. The paper describes developed features and shows comparisons to other methods. The methods can be applied for design purposes as well as remnant life assessments.

A Creep Crack Growth Study of a Low Alloy Butt Weld Subject to Internal Pressure and System Moments Using R5 Assessment Procedures

2009 ◽  
Author(s):  
Jinhua Shi
Keyword(s):  
Internal Pressure ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Growth Study ◽  
Defect Depth ◽  
Butt Weld ◽  
Initial Defect ◽  
Creep Crack ◽  
Study Results ◽  
Assessment Procedures

Appropriate life predictions of components are essential to ensure safety operations of nuclear power plants, especially for welds operating at high temperatures where creep crack growth can be large and dominate their lives. In this paper, for a low alloy butt weld with a given set of loadings (temperature, internal pressure and system moments), a parametric creep crack growth study has been carried out using R5 assessment procedures as follows. • The plant has been operated for 209,200 hours and will be operating further for 47,300 hours; • Initial defect depths are 1, 2, 2.3, 3, 4 and 5 mm; • Crack aspect ratios (initial defect depth: defect half length) are 0.125, 0.2, 0.23, 0.3, 0.4 and 0.5. • Postulated defects are axial (internal and external) and circumferential (internal and external) semi-elliptical surface-breaking surface defects. The study results are presented by a series of graphs which show a minimum acceptable wall thickness for each initial defect depth and aspect ratio under the assessment conditions assumed. The graphs can be used for the plant life management to reduce the decision making time on these welds and to improve the plant power generation.

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