HIDA activity on P91 steel

The 9%-12% Cr-steels are strategic materials for new power plant and for component substitution for plant life extension. One of these steels, P 91 was included in the project BE-1702 (HIDA) to provide crack initiation and growth data for the improvement and validation of procedures for high-temperature defect assessment. The paper presents an outline of the testing programme and the initial results for P 91. In addition to uniaxial and static/cyclic creep crack growth tests on standard fracture mechanics geometries, feature tests are also included in the experimental programme. These consist of internally pressurised pipe welds, pipe bends and 4-point bend pipes, and C-shaped specimens. The majority of these tests are still ongoing. The static and cyclic loading conditions are being employed to consider the range of creep/fatigue interaction in this alloy. All tests are being conducted at 625°C.     

Creep properties and damage behaviour of component-like tubes of Vm12-materials

Abstract

The gap in the energy supply between current availability and the rising demand for electricity worldwide has to be closed primarily by using modern steam and gas power stations with an increased degree of efficiency and decreased CO₂ emissions. Target values for reaching a high degree of efficiency of ≥50% demand increase the steam parameters. The modern creep-resistant steels and their weldments have to have both high creep rupture strength and corrosion resistance.

Within the European research programme COST 536, between 2005 and 2009 research and development work in the field of power plant steels had been carried out for conventional applications. The project was focused on the development of appropriate materials, coatings and surface treatments for components in steam power plants with steam inlet temperatures in the turbine of up to 650°C.

In framework COST 536, Siempelkamp Pruef- und Gutachter-Gesellschaft mbH (SPG) performed component-like creep tests at pressurized tubes made of martensitic steel VM12. This steel was developed by Vallourec & Mannesmann Tubes with the aim of reaching both sufficient creep strength and increased oxidation resistance and is already used for boiler application in new power plants in Germany.

In this paper, the experimental results of uniaxial creep tests, component-like creep tests on tubes with inner pressure and axial loading, metallographic examination and damage characterisation are presented. The tubes are equipped with capacitive high temperature strain gauges for on-line monitoring of strain. All testing data will be implemented as inputs for the numeric FE analysis. The effect of multiaxiality and stress redistribution will be discussed.     

HIDA activity on 2¼ Cr1Mo steel

Historically, the 2¼CrlMo steel is one of the first type of low alloy steels used in high temperature plant. The objective of the present study is to test uniaxial, standard fracture mechanics and feature specimens from the same batch of material as well as test welded and ex-service materials and samples with mechanically induced residual stress. The creep and creep/fatigue crack initiation and growth results using fracture mechanics modelling techniques will then be used to validate the ‘HIDA’ procedure for high-temperature defect assessment. This paper presents an outline of the testing programme. The initial results for this steel from both static and cyclic loading conditions are presented for the test temperature of 565°C. The feature tests, simulating actual components, consist of three industrially relevant pipe types which are pre-notched and internally pressurised. In addition some of these pipes are being tested under four point bending. Early results of the X-ray and magnetic measurements to characterise creep damage are also presented. Initial results of short term laboratory data derived from uniaxial tests as well as compact tension specimens are presented.     

Scatter bands in creep and fatigue crack growth rates in high temperature plant materials data

As a part of the European Commission supported project BE 1702: ‘HIDA’ Creep, creep-fatigue and high temperature fatigue crack growth data for five high temperature plant steels were accessed from a number of published and unpublished sources. These large sets of data were reviewed, and re-analysed where necessary, and plotted in terms of various crack growth rate correlating parameters. Thus limits of scatter bands and mean and upper 95% confidence limit creep and fatigue crack growth correlations are proposed. The present work covers a wide range of variables such as test specimen geometries, sizes, loading conditions and temperatures. Therefore, the correlations proposed are considered universal. However, it is envisaged that these correlations will be refined in future by enlarging the database and exploring the effect of the variables described above. The five materials studied are AISI 316 stainless, 2.25CrlMo, P91, 1CrMoV (forged), and 1CrMoV (cast) steel.     

High temperature creep behaviour of single crystal oxides

The creep resistance of several single crystal oxides is evaluated on the basis of creep data from different sources using a Larson-Miller (L-M) method. The possible creep mechanisms involved in high temperature creep deformation of single crystal oxides are discussed by comparing the collected creep data with theoretical creep models. The high temperature creep of single crystal oxides is generally considered as a diffusion-controlled process: dislocation climb controlled by the lattice diffusion of the slowest moving species (power law) at moderately high stresses, Harper-Dorn creep at low stresses, and power law breakdown at high stresses. The relative comparison of the creep data from different sources using the L-M method and the general analysis about the high temperature creep behaviour indicate that single crystal oxides with a precise stoichiometric composition, complex crystal structure and selected orientation such as [111] oriented YAG (Y₃Al₅O₁₂),c-axis Al₂O₃, [110] oriented MgAl₂O₄ are potential candidates as reinforcements for very high temperature structural applications.     

Creep fatigue behaviour of Type 321 stainless steel at 650°C

Abstract

Type 321 austenitic stainless steel has been used in the UK’s advanced gas cooled reactors for a wide variety of thin section components which are within the concrete pressure vessel. These components operate at typically 650°C and experience very low primary stresses. However, temperature cycling can give rise to a creep fatigue loading and the life assessment of these cycles is calculated using the R5 procedure. In order to provide materials property models and to validate creep fatigue damage predictions, the available uniaxial creep, fatigue and creep fatigue data for Type 321 have been collated and analysed. The analyses of these data have provided evolutionary models for the cyclic stress strain and the stress relaxation behaviour of Type 321 at 650°C. In addition, different methods for predicting creep fatigue damage have been compared and it has been found that the stress modified ductility exhaustion approach for calculating creep damage gave the most reliable predictions of failure in the uniaxial creep fatigue tests. Following this, validation of the new R5 methods for calculating creep and fatigue damage in weldments has been provided using the results of reversed bend fatigue and creep fatigue tests on Type 321 welded plates at 650°C in conjunction with the materials properties that were determined from the uniaxial test data.     

Predicting effect of upward temperature excursions on long-term creep of an austenitic steel

Abstract

A procedure was demonstrated for predicting the effect of upward temperature excursions on the long-term creep of a type 316 steel. The procedure exploits the existence of regimes of stable creep at 600–750°C, from which creep rates can be used to predict long-term strain accumulation or rupture, without the problems associated with the history dependence of creep rupture data for solution treated steel. Pre-aging can be used to remove the potential for transient metallurgical strengthening and ensure stable creep. The excursion tests were run under the relevant conditions and the overall creep rate determined for a few cycles, for comparison with isothermal behaviour. Creep strains caused by the 1 h excursions were consistent with stable creep at the excursion temperature. Thus, the transient increased strain rate observed after excursions must have been compensated by a transient depression of strain rate on reaching the excursion temperature.

MST/580     

Effect of niobium on creep and creep crack growth of cast Ni–Cr austenitic steel

Abstract

An investigation of the effect of Nb on creep properties and creep crack growth rate in a 25Cr–35Ni–0·4C (wt-%) cast steel at 871 and 950°C was carried out. Tensile tests were also carried out at room temperature, 871, and 950°C. The tensile strength and elongation increased with an increase in Nb content at high temperatures. There existed an optimum Nb content for the creep properties and creep crack growth rate. Creep crack growth is controlled by creep deformation.

MST/1222     

Physical significance and reliability of Larson–Miller and Manson–Haferd parameters

Abstract

Both the Larson–Miller and the Manson–Haferd parameters are used to extrapolate rupture data from high temperature creep. The first of these is in agreement with the theoretical equation for low temperature deformation only, and cannot describe the high temperature properties accurately. The second parameter has no physical basis. Starting from data taken from a theoretical stress–rupture time diagram, both extrapolation methods are tested. At the lower stresses the Larson–Miller method considerably overestimates the resistance of the material to rupture. Despite the lack of physical significance, the Manson–Haferd parameter coincidentally describes to some extent the complex deformation patterns due to the different deformation mechanisms, and is more reliable for high temperature predictions.

MST/1882     

A survey of European industrial experience within the HIDA project

This paper describes the activity performed within one of the main tasks of the HIDA project, i.e. to collate and analyse cases of component cracking in high temperature plant. This work involved collecting and processing a large body of information, contributed from both HIDA Consortium partners and external industrial organisations. This exercise resulted in a large sample of collated data from the power and petrochemical plant in Europe. This work showed that high temperature cracking is a major problem, the occurrence of which is expected to increase in the near future. Most cracks affect welds, the assessment of which is largely complicated by the simultaneous presence of different materials, with different deformation and cracking behaviours. Thus, a tool suitable to assess high temperature defects must be able to deal with welds.     

Creep–fatigue crack development from short crack starters

Abstract

A series of isothermal strain controlled creep–fatigue tests on fully instrumented cylindrical specimens with shallow chordal crack starters has been conducted for an advanced 9%Cr turbine rotor steel at 600 and 625°C. Cyclic/hold wave shapes involving a dwell period at peak strain in tension or compression were also performed with crack development being monitored by means of electrical potential drop instrumentation. It is found that temperature, total strain range and hold period are the most influential factors on short creep–fatigue crack propagation rates and specimen life. In order to establish a reliable relationship to represent subcritical crack development for high temperature component integrity assessment, the effectiveness of candidate correlating parameters such as cyclic strain range, cyclic J integral and strain energy density factor have been evaluated. Their application to circumstances involving short crack development due to fatigue, and interacting and non-interacting creep loading are evaluated with reference to the evidence determined from post-test metallurgical examination.     

Effect of a temperature change from 20 to 50°C on the basic creep of HPC and HPFRC

This research was performed in order to study the basic creep of High Performance Concretes (HPC) under uniaxial compression at 20 and 50°C. The aim of this work is to contribute to a better understanding of the basic creep phenomena of HPC at moderate temperature and to provide experimental data which will be used in Thermo-Hydro-Mechanical models such as those necessary for the National project CEOS.FR (Sellier, Thermo hydro mechanical numerical modelling, invited paper at the CEOS International workshop on Control of cracking in R.C. structures: a major step towards serviceability, 2009). The article also presents the fitting of a model considering the effect of temperature via an Arrhenius law affecting its viscous modules (Sellier and Buffo-Lacarriere, Eur J Environ Civ Eng 10:1161–1182, 2009). The concretes are those envisioned for future storage structures of Intermediate Level Long-Life Nuclear Wastes. The research programme has been established with four HPC, two non fibrous and two fibrous; the kinetics and amplitude of basic creep under uniaxial compression are measured during several months at 50°C and compared to those obtained at 20°C for the same materials (Camps, PhD thesis, 2008). Experimental results show that the average creep at 50°C is about twice the creep at 20°C. Besides, results show that this amplification depends on the binder type; the sensitivity to the temperature rise is greater for blended cement based concretes than for OPC based ones. The creep increase due the temperature rise is higher for the HPC under study than for ordinary concretes inventoried in a literature survey. The creep amplitude of HPC seems correlated to their amount of secondary C–S–H. At last, the fitting of the model parameters on the experimental results shows that the values of activation energy are quite close to those obtained by other authors on ordinary concretes (Bazant et al., J Eng Mech ASCE 130(6): 691–699, 2004).     

A note on limitations of a certain creep function used in practice

The creep function of Aleksandrovskii, widely used in some parts of the world, is compared to long-range creep test data available in the literature, using computer optimization techniques. It is found that this creep function is inherently incapable of modeling creep for large creep durations and high ages at stress application.

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Résumé La fonction de fluage d'Aleksandrovskii largement utilisée dans certaines parties du monde est confrontée à l'aide des techniques d'optimisation informatisée aux résultats d'essais de fluage à long terme publiés. On établit que cette fonction de fluage ne peut se prêter à une mobilisation pour les études de fluage sur de grands intervalles de temps et sous des sollicitations appliquées à des ages avancés.

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This work has been carried out as part of a project sponsored by the U.S. National Science Foundation under Grant, No. ENG 75-14848 (A 00 and A 01).     

Development Pharmaceutics and process Validation

Abstract

A resume is presented of the guideline on the data required under Part I.A.4. of the Annex to European Directive 75/318/EEC covering the choice of composition of a medicinal product, supported by data on development pharmaceutics. The broad areas of development studies cover the function and compatibility of active ingredients and excipients, the development of liquid, semi-solid and solid dosage forms and the suitability of containers.

The guideline aims also to cover general aspects of process validation. The principles laid down in the Guideline are compared with those of FDA guideline on process validation which are much more detailed, but share the same overall aim.

One of the fundamental aims of the regulatory control of medicinal products is to ensure the correct purity, potency and consistency of manufacture of each product according to the quality appropriate for its intended use. While Good Manufacturing Practice is essential for quality assurance, other factors such as product design and development may also influence quality, and therefore must be studied and controlled. With this in mind, the Regulatory Authorities of the European Community have produced a guideline to the types of studies that should be undertaken in the development of a medicinal product, and which should be presented in support of application for marketing authorisation. A properly presented section on Development Pharmaceutics at the beginning of a dossier is extremely useful, if not essential, in explaining the rationale behind a particular product and giving the reviewer a clearer understanding of the data presented in support of product quality.

Quality Assurance of every product must be demonstrated, and validation is the key to its demonstration, put simply, validation is the act of proving that a process works. Thus the manufacturing methods and controls specified in an application should follow on from the development studies, and be based on valid principles. Demonstration of the validity of the manufacturing process should be provided as should the validation of the analytical methods used to control the process and therefore the product. Thus process validation should be seen as being strongly supported on the one hand by development pharmaceutics, and on the other by analytical validation.     

Determination of creep properties of P91 by small punch testing

Abstract

Small punch creep testing was conducted to determine creep properties of P91 at 873 K. The procedure followed the European Code of Practice for Small Punch Tests. Results of small punch creep test and finite element analysis were compared and discussed. Based on the results, a practical method was proposed to determine the parameters of Norton creep law more conveniently for material which obey this law. The validity of the proposed method was verified and it is shown that the parameters of the Norton creep law can be determined from only one experimental curve directly.     

Degradation assessment of welded joints by X-ray diffraction technique

Abstract

X-ray diffraction technique has been recognized as a useful tool for the assessment of material degradation extent after a long-time service. Framework 5 project “XPECTION” was dealing with this task with respect to high-temperature creep degradation of boiler tube steels. This paper summarizes partial results of an experimental programme concentrated on mechanical properties degradation of base metals of steel and Al-alloy test specimens of welded components as a result of fatigue loading.     

Creep ductility of 1CrMoV rotor steel

Abstract

The creep ductility of 1CrMoV steels at a given temperature is high at high stresses responsible for high strain rates and ductile rupture, and low at lower stresses responsible for low strain rates and constrained cavity growth at grain boundaries. The magnitudes of ductility in the high and low stress regimes and the time to, and strain rate at, the transition between the two is determined by the chemical composition and the adopted quality heat treatment procedure of the steel. The basis for a material pedigree function forming part of a creep ductility model for 1CrMoV rotor steel is presented. Low ductility 1CrMoV steels are expected to be extremely notch sensitive. While this appears to be true for medium to high strength heats of the alloy, it is not necessarily the case for lower strength heats. There is not a simple inverse relationship between creep ductility and creep strength. Increasingly, creep-fatigue lifetime predictions for high temperature 1CrMoV power plant components subjected to thermo-mechanical transients employ a creep ductility exhaustion methodology to determine the creep damage accumulated per cycle. A creep ductility model of the type developed in the paper is suitable for forming the basis of such an approach.     

A new method for assessing high-temperature crack growth

Experimental creep crack growth (CCG) test data are obtained by following standards that characterize CCG rates using the C* parameter. Such data are then used in high‐temperature failure assessment procedures. An alternative approach to defect assessment at high‐temperature failure is an extension of the R6 failure assessment diagram (FAD). At high temperature, creep toughness, K^c_mat, can be estimated from CCG tests and replaces low‐temperature toughness in R6. This approach has the advantage that it is not necessary to establish a creep fracture regime, such as small‐scale, primary or widespread creep. Also, a new strain‐based FAD has been developed, potentially allowing variations of stress and temperature to be accommodated. In this paper, the results of a series of crack growth tests performed on ex‐service 316H stainless steel at 550 °C are examined in the light of the limitations imposed by ASTM for CCG testing. The results are then explored in terms of toughness and presented in FADs.     

First order reaction kinetics for transient creep in NiAl hardened austenitic steel

Abstract

Transient creep of an NiAl hardened austenitic steel was analysed in the temperature range of 823 to 923 K at stresses ranging from 150 to 450 MPa in the frame work of first order reaction kinetics. The present analysis is aimed: to correlate various transient creep parameters with steady state creep rate following first order reaction rate theory to obtain correlation constants; and to arrive at a unified equation to describe primary and steady state regimes of the creep curves in terms of correlation coefficients thus derived. Good correlation of transient creep parameters with steady state creep rate has been obtained over the test conditions studied indicating that the basic mechanism of deformation is the same for all the three stages of creep. Unified equation that fits the experimental creep strain time data for different test conditions over transient and steady state regimes has been obtained in terms of correlation coefficients.