In the 1980s, studying the effect of neutron irradiation and temper embrittlement on structural materials for the fusion and fission programmes was a major challenge. In this context the development of small specimen test techniques began, allowing the characterization of structural materials for nuclear applications with small amounts of material. The small punch technique is of one these small specimen test approaches. It is widely used for the development and monitoring of structural materials, however there is currently no comprehensive international standard for small punch testing. An EN standard on small punch testing is currently being developed under the auspices of ECISS/TC101/WG1. Besides describing the apparatus, procedures, and specimens, it will include recommendations for the estimation of tensile, fracture and creep properties from small punch testing as well as machine readable formats for representing and transferring test data. This paper describes the current status of the standard and highlights some of the changes with regard to the current CWA 15672 (2007).

European Standard on Small Punch Testing of Metallic Materials

Creep damage and expected creep life for welded 9-11% Cr steels

Small Punch Test (SPT) is an evolving small specimen test technique which has the potential to extract the mechanical properties from small volume specimens. This test method is used to determine the in situ mechanical properties of components in service for measuring the structural integrity and residual life. The pre-requisite for using this test is to establish correlations between SPT and conventional tests in priori. A number of correlations have been developed between traditional tests and SPT results for determining mechanical properties. The validity of these correlations have to be examined, as these are developed from a specified set of materials and testing conditions. To evaluate SPT and the developed correlations, it is crucial to understand the fundamentals of this test method, the different regimes of deformation experienced by the specimen and its sensitivity for various testing parameters. The attempt of this work is to relook the SPT as a whole and its potential to measure the different mechanical properties. This work lists the various SPT configurations, materials used in literature and the correlations developed. In addition, the influence of test parameters on SPT response, the viability of empirical or analytical relations used to extract mechanical properties and the general issues in SPT is discussed.

Overview of Small Punch Test

Experience on in-service damage in power plant components

Tensile, creep and fracture testing of prospective Fe-Al-based alloys using miniature specimens

A new standard is currently being developed under the auspices of ECISS/TC 101 WG1 for the small punch testing technique for the estimation of both tensile and creep properties. Annex G of the new standard is covering the assessment and evaluation of small punch creep (SPC) data. The main challenge for estimating uniaxial creep properties from SPC data is the force to equivalent stress conversion between SPC and uniaxial creep tests. In this work a range of SPC assessment methodologies, benchmarked for the standard, are compared for verifying the best practice used in the standard. The estimated equivalent stresses for SPC are compared to uniaxial creep stresses at equal rupture times, using three alternative models. In-depth analyses are performed on SPC and uniaxial creep data for P92, F92 and 316 L steel tested within an inter-laboratory round robin. The formulation for SPC equivalent creep strain rate in the standard is also assessed.

Creep strength and minimum strain rate estimation from Small Punch Creep tests

Creep damage and long term life modelling of an X20 steam line component

Structures operating in the creep regime will consume their creep life at a greater rate in locations where the stress state is aggravated by triaxiality constraints. Many structures, such as the welded steam mixer studied here, also have multiple material zones differing in microstructure and material properties. The 3-dimensional structure as such in addition to interacting material zones is a great challenge for finite element analysis (FEA), even to accurately pinpoint the critical locations where damage will be found. The studied steam mixer, made of 10CrMo 9-10 steel (P22), has after 100 000 hours of service developed severe creep damage in the several saddle point positions adjacent to nozzle welds. FE-simulation of long term behaviour of this structure has been performed taking developing triaxiality constraints, material zones and primary to tertiary creep regimes into account. The creep strain rate formulation is based on the logistic creep strain prediction (LCSP) model implemented to ABAQUS, including primary, secondary and tertiary creep. The results are presented using a filtering technique utilising the formulation of rigid plastic deformation for describing and quantifying the developing “creep exhaustion”.Copyright © 2008 by ASME

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Juhani Rantala

Papers

Creep strength and minimum strain rate estimation from Small Punch Creep tests

Creep damage and long term life modelling of an X20 steam line component

Modeling and Verification of Creep Strain and Exhaustion in a Welded Steam Mixer

Modelling the development of creep damage: The licon experience

Relaxation of OFP copper