A unified European approach to high temperature defect assessment code and its incorporation in a knowledge base system

Abstract

The background to high temperature defect assessment methodologies is investigated and similarities and differences are highlighted. It is clear that Europe is a leader in this developing field. Comparison of the existing European high temperature life assessment codes [1][2][3][4][5][6][7][8][9] lead to the conclusion that crack initiation is dealt with in different ways by the codes whereas creep and creep/fatigue crack growth are considered using the same models for analysis. At the same time whilst increasing sophistication is implemented in the analysis at the deterministic level insufficient emphasis is placed on the effects of the sensitivity and applicable bounds of the various parameters and material properties. The survey showed that for the same methods of analysis, widely different results can be derived depending on the choice of material properties, method for calculating K, reference stress σ ref and C*. The reason for the differences and the sensitivity to them is highlighted in this paper. The resulting conclusions suggest a methodology based on an expert system using both deterministic and probabilistic techniques would be beneficial. An outline of a defect assessment code structure, taking account of the major European codes, is presented which allows flexibility in terms of input of material data as well as the models used. The structure and the further development of the HIDA Knowledge Based System (KBS) is based on the concepts presented.Keyword: life assessment, creep, fatigue, power generation, knowledge based system Introduction Components in the power generation and petro-chemical industry operating at high temperatures are almost invariably submitted to static and/or combined loading. They may fail by crack growth, net section rupture or a combination of both. The present paper considers the defect assessment regime of failure. Figure 1 shows a schematic diagram of the range of crack initiation and growth bahaviour that a cracked component might show. A number of defect assessment procedures (e.g. the British Energy R5 and the French A16, BS-7910 [1-6] and the German FBH and two-criteria method) [7][8] based on experimental and analytical models are available to assess crack initiation and growth and to determine the remaining useful life of such components.

An R5 Based Creep-Fatigue Critical Flaw Assessment of an In-Service Reformer Piping Tee Using Finite Element Analysis

“…In this case, the predictions from R5 were in good agreement with experimental flaw propagation. A comprehensive comparison of existing European high-temperature codes (including R5) is presented by Nikbin [15]. Differences and sensitivity to specific analysis techniques is provided and a methodology based on deterministic and probabilistic techniques is suggested.…”

Creep/fatigue crack growth testing standardisation assessment and validation for specimens containing weld mismatch

“…Usually at short times the stress intensity factor K, or the elastic-plastic parameter J, is employed to describe the stress and strain distributions at a crack tip whereas at long times, when steady state conditions have been reached, the creep fracture mechanics term C* is used. 8,[16][17][18][19][20] During the intervening stage damage formation and stress redistribution is occurring at the crack tip. The parameters are validated by the right usage of parameters to describe creep brittle and creep ductile crack growth.…”

“…[16][17][18][19][20] The derivation for C* which is analogous to J is well documented 16,17 and will not be detailed in this paper. Once a steady state distribution of stress and creep damage has been developed ahead of a crack tip, it is usually found that creep crack growth rate can be described by an expression of form [16][17][18][19][20] …”

Ontology driven certification of pressure equipments

“…To assess the compliance to safety conditions, in the recent past, the verification of process plants has been improved through the application of KB technologies. In two works [4, 5], both originated from the research carried out in the European project HIDA [6], the authors apply KB technologies to the assessment of cracks in plant components, underlining the benefits deriving from the incorporation of defect checking code into a KB system. In the project TTF 2,6 which is supported by the European Pressure Equipment Research Council and is aimed at promoting the use of High Strength Steels, the integration of a new analysis method with appropriate material data into a KB system is proposed.…”