High-Cycle Analytical Thermal Fatigue Tests on Pipe Structures

2002 ◽  
Author(s):  
J. M. Stephan ◽  
F. Curtit
Keyword(s):  
Thermal Fatigue ◽  
Thermal Stresses ◽  
Heat Removal ◽  
Fatigue Tests ◽  
Bench Test ◽  
Surface Finishes ◽  
Water Sprays ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue ◽  
Non Destructive

In 1998, a leak occurred in the main mixing zone of the residual heat removal systems (RHR) of the EDF CIVAUX nuclear plant unit 1. The crack is attributed to high-cycle thermal fatigue due to the fluid thermal turbulences. An research and development (R&D) program is now being conducted at EDF to understand the incident and to assess the risks of cracks in other mixing zones. This program includes thermal-hydraulic tests on mock-ups and their numerical interpretation, material testing in high-cycle fatigue, structure tests on mock-ups submitted to high-cycle thermal stresses and their interpretations, and developments in non destructive evaluations in the presence of crazing zones (thermal striping). After a brief presentation of the R&D program, the paper presents a new high-cycle thermal fatigue bench test, named INTHERPOL, for pipe structures. The thermal cycles consist of periodic controlled cold shocks by water sprays and hot shocks by infrared radiations on the inner surface of part of the structure. The structure under test, the water spray devices and infrared modules are inserted into a tank to allow constant control of the environment. The types of pipe structures tested include plain or welded structures and various industrial surface finishes. The first tests results and their numerical interpretations are presented.

scholarly journals Experimental Facility for High Cycle Thermal Fatigue Tests Using Laser Shocks

2013 ◽  
Vol 66 ◽  
pp. 669-675 ◽  
Author(s):  
L. Vincent ◽  
M. Poncelet ◽  
S. Roux ◽  
F. Hild ◽  
D. Farcage
Keyword(s):  
Thermal Fatigue ◽  
Fatigue Tests ◽  
Experimental Facility ◽  
High Cycle Thermal Fatigue

High Cycle Thermal Fatigue Issues in RHRS Mixing Tees and Thermal Fatigue Test on a Representative 304 L Mixing Zone

2011 ◽  
Author(s):  
Jean Alain Le Duff ◽  
Bruno Tacchini ◽  
Jean Michel Stephan ◽  
Regis Tampigny ◽  
Antoine Fissolo ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Fatigue Test ◽  
Thermal Fatigue ◽  
Fatigue Cracks ◽  
Mixing Zone ◽  
Thermal Fatigue Test ◽  
Surface Finishes ◽  
Thermal Fatigue Cracks ◽  
High Cycle Thermal Fatigue

In May 1998, a leak (30 m3 / h) occurred in the reactor heat removal system (RHRS) of the CIVAUX 1 power plant (PWR type N4 – 1400 MWe) which was then in a hot shutdown situation. A 180 mm through-wall crack was found in a 304 L austenitic stainless steel elbow in a mixing area of high and low temperature fluids [1, 2]. All mixing zones of main (␀10″) and minimum flow lines (␀4″) of the four N4 plants were affected by cracking [3]. After metallurgical examinations of these austenitic stainless steel components and an analytical damage evaluation, the major root cause for cracking was identified as high cycle thermal fatigue. The cracks were found in the mixing tees and at the roots of welds in mixing areas. The presence of ground surface finishes and geometrical discontinuities (weld roots and tapers) were identified as amplifier of fatigue damage. For the new RHRS mixing zones of N4 plants, decision was taken to suppress welds or locate them away from mixing area and to improve the surface condition (remove the weld root singularity, remove striations due to machining by polishing and reduce residual stresses). For the other 54 French PWRs (900 & 1300 MWe) with different design of RHRS mixing zones, the inspections showed that they were also all damaged by thermal fatigue with generally small cracks less than 3 mm excepted for the PWRs of Saint Alban 2 (5 mm) [4]. To reproduce the thermal fatigue phenomenon occurring in mixing zones, a representative endurance thermal fatigue test named “FATHER” was performed by CEA under an EDF, CEA and AREVA NP agreement [5, 6]. The test lasted 300 hours. It was performed on a 304L stainless steel mixing zone of 7 mm thick and 6″ diameter with a temperature difference of 160°C between cold and hot fluids. Different internal surface finishes were introduced in the test mock-up: coarse and fine grinding, industrial polishing, as extruded surfaces and as welded or flushed joints. Numerous NDE were performed during and after the endurance fatigue test like ultrasonic examinations or dye liquid penetrant inspections. They lead to the observation of many small thermal fatigue cracks located near as welded joints, on ground surfaces and on unpolished flushed welds. Cracks were not observed on industrially polished surfaces reproduced in straight piping sections or in flushed plus polished welds. After the test of 300 hours, the mock-up was axially cut in two symmetric half parts and sampling plates containing thermal fatigue cracks were machined from each of the half mock-up to perform detailed metallographic examinations. More than 50 thermal fatigue cracks with depths of 100 to 1000 μm were observed. Cracks initiate mainly on geometrical discontinuities like weld toes or grinding striations. Test results have also allowed to improve and to validate methods and tools for predicting crack initiation in mixing zones. The “FATHER” experiment can be seen as a significant contribution for preventing the risk of HCF in PWR equipment.

Numerical Investigation on Thermal Striping Phenomena in a T-Junction Piping System

2014 ◽  
Author(s):  
Masaaki Tanaka ◽  
Yasuhiro Miyake
Keyword(s):  
Numerical Simulation ◽  
Thermal Fatigue ◽  
Large Scale ◽  
Structural Integrity ◽  
Piping System ◽  
Simulation Code ◽  
Fine Mesh ◽  
Large Eddy ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

Thermal striping phenomena caused by mixing of fluids at different temperature is one of the most important issues in design of Fast Breeder Reactors (FBRs), because it may cause high-cycle thermal fatigue in structure and affect the structural integrity. A numerical simulation code MUGTHES has been developed to investigate thermal striping phenomena and to estimate high cycle thermal fatigue in FBRs. In this study, numerical simulation for the WATLON experiment which was the water experiment of a T-junction piping system (T-pipe) conducted in JAEA was carried out to validate the MUGTHES and to investigate the relation between the mechanism of temperature fluctuation generation and the unsteady motion of large eddy structures. In the numerical simulation, the large eddy simulation (LES) approach with standard Smagorinsky model was employed as eddy viscosity model to simulate large-scale eddy motion in the T-pipe. The mesh as the same with the previous study as reference, the finer mesh and the coarser mesh arrangements were employed to estimate the Grid Convergence Index (GCI) for uncertainty quantification in the validation process. The modified method of the GCI estimation based on the least squire version could successfully quantify uncertainty. Through the numerical simulations, it was indicated that the fine mesh arrangement could improve the temperature distribution in the wake. It could be found that the thermal mixing phenomena in the T-pipe were caused by the mutual interaction of the necklace-shaped vortex around the wake from in the front of the branch jet, the horseshoe-shaped vortex and the Karman’s vortex motions in the wake.

Numerical analysis of thermal striping induced high cycle thermal fatigue in a mixing tee

2009 ◽  
Vol 239 (5) ◽  
pp. 833-839 ◽  
Author(s):  
Jeong Ik Lee ◽  
Lin-wen Hu ◽  
Pradip Saha ◽  
Mujid S. Kazimi
Keyword(s):  
Numerical Analysis ◽  
Thermal Fatigue ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue

Some Advances on Understanding of High Cycle Thermal Fatigue Crazing

2006 ◽  
Vol 129 (3) ◽  
pp. 400-410 ◽  
Author(s):  
Said Taheri
Keyword(s):  
Fatigue Life ◽  
Beneficial Effect ◽  
Thermal Fatigue ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Residual Stress Field ◽  
Crack Network ◽  
Apparent Contradiction ◽  
Weld Residual Stress ◽  
High Cycle Thermal Fatigue

The aim of this paper is to improve the understanding of high cycle thermal fatigue crazing observed in some areas of residual heat removal (RHR) systems made of 304L stainless steel in PWR nuclear plants. High cycle thermal crazing and the absence of crazing under purely mechanical loading are explained through the arrest of cracks initiated at the surface in the thickness of the component for thermal fatigue. This arrest is due to high stress gradients in the case of thermal loading due to the high frequency of the thermal load. It is shown that close to the weld, the crack network configuration is related to the tensile weld residual stress field in accordance with the detrimental effect of tensile mean stress on fatigue life. However, these results are in apparent contradiction with the material uniaxial fatigue tests, where a beneficial effect of tensile mean stress is observed in load-controlled fatigue tests. Moreover, it is shown that near the weld, the absence of a crack network is related to the compressive weld residual stress field in accordance with the beneficial effect of compressive mean stress on fatigue life. This result is however, in apparent contradiction with the observation of crazing far from the weld under a highly compressive stress. These contradictions may be explained by the detrimental effect of prehardening in strain control and the beneficial effect of prehardening in stress control for stainless steels. From these results it is concluded that shot peening which is usually considered to be beneficial for ferritic steel may be detrimental in high cycle thermal fatigue for stainless steels. It may also be concluded that in high cycle thermal fatigue of stainless steel, improvement of fatigue life would be possible with heat treatment by reduction of strain-hardening rather than with shot peening.

Hydro-thermo-mechanical analysis on high cycle thermal fatigue induced by thermal striping in a T-junction

2013 ◽  
Vol 27 (10) ◽  
pp. 3087-3095 ◽  
Author(s):  
Sun-Hye Kim ◽  
Nam-Su Huh ◽  
Moon-Ki Kim ◽  
Dae-Geun Cho ◽  
Young-Hwan Choi ◽  
...  
Keyword(s):  
Thermal Fatigue ◽  
Mechanical Analysis ◽  
Thermal Striping ◽  
High Cycle Thermal Fatigue
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