Trends in High Temperature Structural Integrity Assessment

2009 ◽  
pp. 3-3-18
Author(s):  
George A. Webster
Keyword(s):  
High Temperature ◽  
Structural Integrity ◽  
Integrity Assessment

The Influence of AGR Gas Carburisation on the Creep and Fracture Properties of Type 316H Stainless Steel

2016 ◽  
Author(s):  
Mustafa Nasser ◽  
Catrin M. Davies ◽  
Kamran Nikbin
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Structural Integrity ◽  
Substantial Reduction ◽  
Creep Crack Growth ◽  
Creep Rupture ◽  
Rupture Time ◽  
Metallographic Examination ◽  
Fracture Properties ◽  
Integrity Assessment

Defects in the UK’s AGR nuclear reactors have been historically found in superheater regions of the boilers. These components are fabricated from type 316H austenitic stainless steel and operate in carbon dioxide gas coolant environments under creep conditions, at temperatures up to 550°C. As a result, some components maybe carburised throughout their life resulting in the formation of a hardened outer surface layer. This layer results from interstitial carbon diffusion and is thought to impact on the creep, creep-fatigue and fracture properties of 316H. Carburisation is currently unaccounted for within high temperature structural integrity assessment procedures. It is essential that carburisation and resulting damage mechanisms are well understood in order to accurately predict the failure of components. This paper aims to investigate the effect of AGR gas carburisation on the creep and fracture properties of type 316H stainless steel. Specimens have been preconditioned within a simulated AGR gas environment. The presence of carburisation has been confirmed through metallographic examination, hardness testing and surface analysis techniques. A series of constant load high-temperature creep tests have been conducted on preconditioned specimens. Compared to as-received material, carburised specimens displayed a significant reduction in creep rupture time with cracking of the outer carburised layer initiating creep crack growth. This phenomenon is seen to occur at very low strains and has been confirmed through interrupted creep testing. The substantial reduction in creep rupture time is postulated to result from embrittlement of the carburised material owing to strong precipitation of carbides along grain boundaries. It is concluded that carburisation can lead to a severe reduction in creep rupture life in test conditions; the possible implications of this with regards to plant conditions are discussed.

The Formulation of Material Characteristics of Austenitic Stainless Steels at Extremely High Temperature

2017 ◽  
Author(s):  
Kenta Shimomura ◽  
Takashi Onizawa ◽  
Shoichi Kato ◽  
Masanori Ando ◽  
Takashi Wakai
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Structural Integrity ◽  
Austenitic Stainless Steels ◽  
Severe Accident ◽  
Integrity Assessment ◽  
Severe Accidents ◽  
Material Characteristics

This paper describes the formulation of material characteristics of austenitic stainless steels at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants. After the severe accident in Fukushima dai-ichi nuclear power plants, it has been supposed to be very important not only to prevent the occurrence of abnormal conditions, i.e. from the first to the third layer safety, but also to prevent the expansion of the accident conditions, i.e. the fourth layer safety[1] [2]. In order to evaluate the structural integrity under the severe accident condition, material characteristics which can be used in the numerical analyses, such as finite element analysis, were required [3] [4]. However, there were no material characteristics applicable to the structural integrity assessment at extremely high temperature. Therefore, a series of tensile and creep tests was performed for austenitic stainless at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants, namely up to 1000 °C. Based on the acquired data from the tests, monotonic stress-strain equation and creep rupture equation applicable to the structural analysis at extremely high temperature, up to 1000 °C were formulated. As a result, these formulae make it possible to conduct the structural integrity assessment using numerical analysis techniques, such as finite element method.

Structural Integrity Assessment of Weldments at High Temperature: A Proposed New Approach for R5

2008 ◽  
Author(s):  
N. G. Smith ◽  
D. W. Dean ◽  
M. P. O’Donnell
Keyword(s):  
High Temperature ◽  
Fatigue Damage ◽  
Structural Integrity ◽  
Fatigue Crack Initiation ◽  
Current Approach ◽  
Assessment Procedure ◽  
New Approach ◽  
Integrity Assessment ◽  
Creep Fatigue ◽  
Match Effect

The majority of problems associated with the structural integrity of components, particularly those operating at high temperature, are associated with welds. The R5 procedures provide a comprehensive methodology for the assessment of structures operating within the high temperature creep regime. This includes advice on the modifications required to the basic procedure to account for weldments in creep-fatigue crack initiation assessments. The current approach is based on the use of a Fatigue Strength Reduction Factor (FSRF) which has a value according to the particular class of welded joint. The FSRF affects the calculation of creep and fatigue damage. However, the current approach can be excessively conservative for as-welded weldments which are the main type of weldments in plant. This paper outlines the proposed changes to R5, which seek to achieve the following objectives: • to simplify and clarify the current advice for creep-fatigue initiation assessments of weldments, whilst maintaining a conservative assessment procedure; • to have a robust procedure which can be applied to complex components and loading conditions. The new approach separates the FSRF into two components which are as follows: • the geometric strain enhancement due to the weldment geometry (if applicable) and the material mis-match effect between parent material and weld metal, which is called the Weld Strain Enhancement Factor (WSEF), and • the fatigue endurance reduction effect due to the presence of small imperfections (e.g. inclusions, porosity, etc.) in the weldment constituent materials, which is called the Weld Endurance Reduction (WER). The WSEF is used to determine the stress at the start of a dwell or hold period and, because it has a lower value than the FSRF (due to the removal of the WER), results in less conservative calculations of creep damage compared to the current procedure, which uses the full FSRF. For fatigue damage predictions, the modified route is broadly similar to the current route, since the combination of the WER and the WSEF in the modified route corresponds to the FSRF used in the current route. Assessments to demonstrate the improved endurance predictions using the proposed new approach have been performed on several creep-fatigue weldment features tests and examples are provided in this paper.

Advances in Research of Elevated and High-Temperature Structure Integrity of Process Pressure-Bearing Equipment in Chinese Petrochemical Industry

2008 ◽  
Author(s):  
Xuedong Chen ◽  
Shandong Tu ◽  
Zhichao Fan ◽  
Tiecheng Yang ◽  
Weihe Guan ◽  
...  
Keyword(s):  
High Temperature ◽  
Damage Assessment ◽  
Life Prediction ◽  
Structural Integrity ◽  
Early Stage ◽  
Research Work ◽  
Pressure Vessels ◽  
Temperature Structure ◽  
Integrity Assessment ◽  
Set Up

During 1995∼2000, investigations were carried out four times on the safety conditions of pressure-bearing equipments in petrochemical enterprises in China. As a result, it is found that many failure cases are related to elevated or high temperature environment. Because the service conditions of Chinese pressure vessels and process characteristics of petrochemical enterprises are somewhat different from those of the other countries, it is a challenge to set up Chinese standard for high-temperature structural integrity assessment, and these research work was started at 2000, namely the early stage of “10th five-year plan” (from 2000 to 2005), during which Hefei General Machinery Research Institute (HGMRI), East China University of Science and Technology, Zhejiang University, Zhejiang University of Technology, etc. have accumulated a lot of data on high-temperature performance of typical steels, set up various life prediction and damage assessment models, preliminarily formed the technical methods for defect safety assessment of high-temperature in-service pressure vessels, and thus lay a foundation for establishment of Chinese high-temperature defect assessment code. In this paper the present status, existing problems and future development direction of China are described in the aspect of non destructive test (NDT) of elevated and high-temperature defects, integrity assessment of defect-containing structures, life prediction and damage assessment etc.

Residual Strain Measurement of C/C-SiC Tubes at High Temperature

2006 ◽  
Vol 524-525 ◽  
pp. 665-670 ◽  
Author(s):  
Robert C. Wimpory ◽  
Carsten Ohms ◽  
P. Horňák ◽  
Dimitar Neov ◽  
Anastasius Youtsos
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
Residual Strain ◽  
Strain Measurement ◽  
Structural Integrity ◽  
Research Centre ◽  
Vacuum Furnace ◽  
Joint Research ◽  
Integrity Assessment ◽  
Residual Strains

As part of the European project “high and ultrahigh temperature heat exchangers” (HITHEX) the prediction and experimental assessment of the lifetime behaviour, characterisation and qualification of particular CMC materials, including carbon fibre reinforced carbonsiliconcarbides (C/C-SiC), has been executed. Part of the programme of the HITHEX project was the measurement of the strain development within the C/C-SiC tubular specimens from room to high temperature, the results of which are presented here. Residual strains have been determined in several specimens by neutron diffraction at the High Flux Reactor (HFR) of the Joint Research Centre in Petten, The Netherlands. At the HFR two facilities are available for residual strain investigations. Both instruments were utilised in the investigations. The first facility at beam tube HB5, the combined stress and powder diffractometer, employs a constant neutron wavelength of 0.257 nm, and the second facility at HB4, the Large Component Neutron diffraction facility, LCNDF, has a flexible wavelength. The installation of a vacuum furnace has enabled the residual strain measurement of specimens at high temperature on HB4. The furnace had to fulfil three main criteria for the investigation of these specimens; high-temperature, good neutron penetration and negligible oxidation of the specimens. The ceramic specimens, which have outer and inner diameters of 50 and 40 mm, respectively, and a length of 100 mm have been measured to temperatures of up to 1450°C. Measurements were carried out in two directions on the SiC phase of several specimens, i.e. in the radial and tangential (hoop) directions. The implications of these results with respect to the structural integrity assessment of these components at high temperatures are discussed.

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