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Title: Surface analysis of TFTR vacuum vessel samples subjected to the post-weld heat treatment

Abstract

To ensure the dimensional stability of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel, it is necessary to perform a post-weld heat treatment (PWHT). This process consists of heating the vessel segments to approx. 450/sup 0/C for 1.5 h. The large size of the segments precludes a vacuum bake previous to installation. Effects of the PWHT on the vacuum vessel surface were studied using small samples of vessel material which were subjected to a variety of PWHT procedures, including inert gas purges and different oven designs. Changes in topography and near-surface chemistry were investigated with SEM and sputter-Auger electron spectroscopy. These samples were compared with the surface properties of non-baked UHV-quality stainless steel. The primary difference noted between the PWHT samples and the non-baked control was the thickness of the passivation oxide layer. The thickness of this mixed oxide (FeO/Cr/sub 2/O/sub 3//NiO) on the control sample was less than or equal to 100 A. The thickness of the oxide layer on the heat-treated samples ranged between 230 to 350 A, depending on the method of the PWHT. The effect of hydrogen glow discharge cleaning on these thicker oxide layers, and the consequences of such heat treatment procedure relative to oxygenmore » impurity production in fusion devices are discussed.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Princeton Univ., NJ (USA). Plasma Physics Lab.
OSTI Identifier:
7090436
Report Number(s):
PPPL-1722
TRN: 81-002502
DOE Contract Number:
AM02-76CH03073
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; TFTR REACTORS; PRESSURE VESSELS; AUGER ELECTRON SPECTROSCOPY; STABILITY; SURFACE PROPERTIES; CONTAINERS; ELECTRON SPECTROSCOPY; SPECTROSCOPY; THERMONUCLEAR REACTORS; TOKAMAK TYPE REACTORS; 700209* - Fusion Power Plant Technology- Component Development & Materials Testing

Citation Formats

Moore, R.L., Cohen, S.A., Cecchi, J.L., and Dylla, H.F.. Surface analysis of TFTR vacuum vessel samples subjected to the post-weld heat treatment. United States: N. p., 1980. Web. doi:10.2172/7090436.
Moore, R.L., Cohen, S.A., Cecchi, J.L., & Dylla, H.F.. Surface analysis of TFTR vacuum vessel samples subjected to the post-weld heat treatment. United States. doi:10.2172/7090436.
Moore, R.L., Cohen, S.A., Cecchi, J.L., and Dylla, H.F.. 1980. "Surface analysis of TFTR vacuum vessel samples subjected to the post-weld heat treatment". United States. doi:10.2172/7090436. https://www.osti.gov/servlets/purl/7090436.
@article{osti_7090436,
title = {Surface analysis of TFTR vacuum vessel samples subjected to the post-weld heat treatment},
author = {Moore, R.L. and Cohen, S.A. and Cecchi, J.L. and Dylla, H.F.},
abstractNote = {To ensure the dimensional stability of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel, it is necessary to perform a post-weld heat treatment (PWHT). This process consists of heating the vessel segments to approx. 450/sup 0/C for 1.5 h. The large size of the segments precludes a vacuum bake previous to installation. Effects of the PWHT on the vacuum vessel surface were studied using small samples of vessel material which were subjected to a variety of PWHT procedures, including inert gas purges and different oven designs. Changes in topography and near-surface chemistry were investigated with SEM and sputter-Auger electron spectroscopy. These samples were compared with the surface properties of non-baked UHV-quality stainless steel. The primary difference noted between the PWHT samples and the non-baked control was the thickness of the passivation oxide layer. The thickness of this mixed oxide (FeO/Cr/sub 2/O/sub 3//NiO) on the control sample was less than or equal to 100 A. The thickness of the oxide layer on the heat-treated samples ranged between 230 to 350 A, depending on the method of the PWHT. The effect of hydrogen glow discharge cleaning on these thicker oxide layers, and the consequences of such heat treatment procedure relative to oxygen impurity production in fusion devices are discussed.},
doi = {10.2172/7090436},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1980,
month =
}

Technical Report:

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  • The TFTR vacuum vessel is to be protected with tungsten plates from the effects of neutral beam impingement. A thermal analysis is performed to determine the maximum allowable beam intensity (power per unit area) under normal and faulted operating conditions. In order to permit a faulted pulse, or unattenuated injection, to occur after normal pulse series, the maximum neutral beam energy flux should be below 10 kW/cm/sup 2/ depending on the beam design configuration, to prevent the melting of the plates. The analyses were performed using an injection time of 0.5 second and a cycle time of 300 seconds.
  • A structural evaluation of the TFTR Device Vacuum Vessel components was undertaken in order to verify the vessel adequacy in the prescribed operating environment. The products of this investigation appearing in this report include; (1) An evaluation of the required vessel wall thickness for the vessel design operating environment of one atmosphere external pressure and 93/sup 0/C (200/sup 0/F) uniform temperature. (2) A verification of vessel integrity to preclude a fatigue type failure for reactor startup and shutdown cyclic life in the design environment. (3) A verification of stiffening ring structural integrity. (4) A discussion of the design guidelines tomore » be used in providing adequate penetration reinforcement when the desired penetration spacing has been defined.« less
  • A structural evaluation of the bellows and bellows cover sections was undertaken in order to confirm the structural integrity of these TFTR vacuum vessel components in the prescribed operating environment. The evaluations investigate component stability, stress, and deflection behavior. The products of this investigation appearing in this report include; (1) Structural verification of the vacuum bellows as currently defined in an operating environment of one atmosphere external pressure and 93/sup 0/C (200/sup 0/F) uniform temperature. (2) The establishment of a structurally adequate design configuration for the bellows cover section. (3) The presentation of a parametric study which indicates the effectsmore » of varying some bellows cover section parameters in order to obtain acceptable variations of this design configuration. (4) A verification of bellows and bellows cover section integrity to preclude a fatigue type failure for reactor startup and shutdown cyclic life in the design environment.« less
  • The lithium corrosion resistance of the regular grade of 2 1/4 Cr-1 Mo steel can be vastly improved with a proper postweld heat treatment, but even greater improvements are needed. Results indicate that if weldments were tempered sufficiently long at 760C to remove all Mo/sub 2/C from the microstructure, even greater resistance to attack by low nitrogen lithium could be achieved. Corrosion tests should eventually be performed on regular grade 2 1/4 Cr-1 Mo steel weldments which have been given a long-term (> 25 h) post-weld temper at 760C. Lithium corrosion resistance of regular grade 2 1/4 Cr-1 Mo steelmore » may also be improved by employing a quench and temper heat treatment. Quenched microstructures have more homogenous distribution of carbides than isothermally annealed microstructures, and if properly tempered, should provide excellent lithium corrosion resistance. Furthermore, the toughness of such a lower bainite microstructure should be better than that of the ferrite-bainitic microstructure created by an isothermal anneal. Numerous parameters, all potentially deleterious to the lithium corrosion resistance of 2 1/4 Cr-1 Mo steel, remain to be investigated; two such variables are velocity effects and lead content in the lithium.« less
  • This project will conduct a systematic metallurgical study on the effect of post-weld heat treatment (PWHT) on the creep rupture properties of P91 heavy section welds. The objective is to develop a technical guide for selecting PWHT parameters, and to predict expected creep-rupture life based on the selection of heat treatment parameters. The project consists of four interdependent tasks: Experimentally and numerically characterize the temperature fields of typical post-weld heat treatment procedures for various weld and joint configurations to be used in Gen IV systems. Characterize the microstructure of various regions, including the weld fusion zone, coarse-grain heat-affected zone, andmore » fine-grain heat affected zone, in the welds that underwent the various welding and PWHT thermal histories. Conduct creep and creep-rupture testing of coupons extracted from actual and physically simulated welds. Establish the relationship among PWHT parameters, thermal histories, microstructure, creep, and creep-rupture properties.« less