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[en] Thermally treated Alloy 690 is proposed as the most reliable steam generator tubing material. Compared with Alloy 600, Alloy 800 or Duplex stainless steel, Alloy 690 has a lower corrosion rate and metal release. EDF have selected Alloy 690, thermally treated, for future nuclear power plants

[en] This paper deals with the results found by completing a study work aimed at giving due consideration to the variables controlling the microstructure variation in modeling the alloy 800 fatigue-stress relaxation behaviour along with their effect on the fracturing process. The related push-pull cycles were performed in forced strain condition and the relaxing operation was carried out with the material exhibiting its maximum tension strained condition. Microstructure investigations and behaviour modeling are presented. (orig./RF)

[en] The chemical and electrochemical characteristics of synthetic solutions similar to those inside the occluded cell corrosion - OCC (pitting, cracks from stress corrosion) of incoloy 800, 25⁰C are studied. (E.G.)

[en] The alloy 800 used for the steam generators in the Super Phenix breeder reactor undergoes γ' [Ni₃ (Ti Al)] hardening. This paper attempts to take these microstructure effects into account in the formulation of the constitutive law for this material. Low cycle fatigue tests were carried out to imposed deformation. The mean diameters of the precipitates were determined by small angle neutron scattering and transmission electron microscopy. (orig./WL)

[en] To investigate the crack growth behaviour under combined creep-fatigue loading, CT 25 mm-specimens of X10NiCrAlTi 32 20 (Alloy 800) have been tested in experiments with cyclic loadings and hold times, with static loadings and short stress rekief interrupts, with ramp type loadings and with sequences of separate fatigue and creep crack growth periods. The test temperature of 700deg C was selected because only in this temperature range this alloy provides similar amounts of crack growth under creep and fatigue conditions due to equivalent stress levels. For the estimation of crack growth under combined loading conditions a linear accumulation of increase in crack length was proved using the crack growth laws of pure creep and fatigue crack growth. Hold time and ramp loadings lead to a higher crack growth rate compared with pure creep or pure fatigue crack growth tests. In hold time experiments the crack growth rate is higher than ramp tests of the same period time. The results of hold time tests can be fairly enough predicted by linear damage accumulation rules. (orig.)

[en] The present study served to investigate creep crack growth experiments for a tube with a 180deg surface crack in circumferential direction. The tube had an outer diameter of 197 mm and a wall thickness of 23.5 mm. It was loaded with four-point bending at 700deg C. No solutions for calculation of the C^*-integral were available in the literature for this testing geometry, so new approaches had to be found. An approximation method, the so-called limit analysis technique was used for this purpose. It requires the plastic limit load of a specimen and the displacement rate of the load application points as the experimental input parameters. Before the limit analysis technique was applied to the tube under bending, results from earlier creep crack growth experiments were used to verify this technique. The C^* values determined from the limit analysis were compared with values based on the numerical calculations of the EPRI handbook. A good agreement was found for both calculation methods. It therefore seems justified to apply the limit load procedure also to the tube loaded in bending. The calculation on the basis of the limit analysis was performed in two ways, which differed by the type of crack front modelling. The simpler model yielded results that were too conservative in comparison with the experimental results of CT specimens. The application of the second model, which better covers the true crack front, provides values for da/dt versus C^* which are actually within the scatter band of CT specimen results. This procedure therefore permits the transfer of standard specimen results to components. (orig.)

[en] Susceptibility to pitting corrosion of Incoloy 800 in 0.1M sodium chloride solution, at room temperature, was studied as a function of pH. In order to determine the pitting potentials (E_p), potentiokinetic and galvanostatic techniques were applied. The results obtained by both techniques indicate that there is no noticeable change of E_p values in the 3 to 11 pH range, and that E_p increases at pH 12. E_p values obtained by the galvanostatic method were lower than those measured using the potentiokinetic technique. The number and size of pits decreases as the pH increases. The morphology of pitting belongs to the crystallographic type. (Author)

[en] The creep rupture properties of high temperature alloys are being determined as part of the materials programme for the development of the high temperature, gas-cooled reactor (HTGR) as a source of nuclear process heat, especially for the gasification of lignite and coal. INCOLOY 800H AND INCONEL 617 have been tested in the temperature range from 1073 K to 1223 K in air as well as in helium with HTGR specific impurities. The static and dynamic creep behaviour of INCONEL 617 have been determined in constant load creep tests, relaxation tests and stress reduction tests. The results have been interpreted using the internal stress on the applied stress and test temperature was determined. In a few experiments the influence of cold deformation prior to the creep test on the magnitude of the internal stress was also investigated. (Author)

[en] Published in summary form only