European Code of Practice for Creep Crack Initiation and Growth Testing of Industrially Relevant Specimens

Abstract

The integrity and residual life assessment of high temperature components require information obtained from the material's mechanical, uniaxial creep, creep crack initiation (CCI), and growth (CCG) properties. The information derived from these material tests needs to be validated and harmonized following a Code of Practice (CoP) so that variability in data as well as in the analysis can be optimized between different institutions. The paper describes a CoP for creep crack growth testing of industrially relevant specimens, which was developed within the framework of the partially European Commission (EC) funded project called “CRETE.” Novel aspects of the CoP include advice for testing different specimen geometries, which differ from the standard Compact Tension (C(T)) specimen proposed in the only available CCG testing standard ASTM E 1457. Recommendations for required number of tests, techniques for testing, treatment of test records, reduction of test data, and data analysis are presented. Associated specimen selection guidelines for industrial creep crack initiation and growth testing are also described. Validation tests carried out within the project on Type 316H steel at 550°C and a C-Mn steel at 400°C using relevant specimen geometries are also briefly described. The CoP contains recommended K and C* solutions, Y functions, and η factors, which are used to determine values of the fracture parameters K and C* for the specimen geometries considered, and these are summarized in this paper. Information from these new tests, together with a review of previous creep crack growth tests on nonstandard geometries, have been used in recommending the best method of analysis for the creep crack initiation (CCI) and creep crack growth (CCG) data for a range of creep brittle to creep ductile materials.

Predicting creep crack initiation in austenitic and ferritic steels using the creep toughness parameter and time‐dependent failure assessment diagram

“…4 Components are often welded and the application of the TDFAD approach for weldments has been considered. [12][13][14][15][16] However, a number of complications arise when considering weldments such as material mismatch effects that may require consideration.…”

“…The primary and secondary creep constants in Eqs. (14) and (15) are given in Table 1 for 316H stainless steel at 550 • C and P22 steel at 565 • C. For a particular time, the total strain at any stress level is given by the sum of the elastic and plastic strain and the total creep strain accumulated in that time, i.e.…”

Creep fracture parameter C* solutions for semi‐elliptical surface cracks in plates under tensile and bending loads

“…In addition, for the non-steady-state conditions, fracture parameter C t was proposed by Saxena to characterize creep crack growth (CCG). 21,22 And a large number of studies [23][24][25][26][27][28][29] indicated that the CCG rate can be well correlated with C*, which means that C* can be applied to predict and assess creep life of cracked components and devices under high temperature conditions.…”