Fitness for Service Evaluation of Ring Joint Groove Cracking

1999 ◽  
Vol 122 (1) ◽  
pp. 72-75
Author(s):  
R. G. Brown ◽  
G. M. Buchheim ◽  
D. A. Osage ◽  
J. L. Janelle
Keyword(s):  
Driving Force ◽  
High Stress ◽  
Service Evaluation ◽  
Small Sample ◽  
Crack Advance ◽  
Ring Groove ◽  
Stress Region ◽  
Fracture Assessment ◽  
Inherent Problem ◽  
Pressure Hydrogen

Cracking of ring joint style flanges has been a recurring problem in the petrochemical industry, particularly in high-pressure hydrogen processing vessels. The cracking of the ring joint groove region is an inherent problem with the design. The ring groove is subjected to high stresses from the wedging action of the gasket and the ring groove radii are not substantial enough to effectively reduce the stress concentrating effect. A fitness for service assessment was conducted for a hydrogen processing vessel containing cracks in the ring groove radius region of a ring joint style flange. The flange was forged 2-1/4Cr-1Mo material with a Type 347 SS overlay. Results of an elastic-plastic numerical fracture mechanics assessment showed that the driving force for crack propagation was high for a very localized region near the ring groove radius. However, the driving force decreased significantly for deeper cracks as the crack tip became removed from the very localized high stress region of the ring groove. The assessment also showed that the highest stresses occurred during the bolt-up operation. Metallurgical tests were performed on a small sample removed from the flange. The chemistry, grain size, microstructure, and hardness of the material indicated that the probability that this material had very low resistance to hydrogen-assisted crack growth during downtime was quite small and that the resistance to crack advance during service was good. Therefore, the combined results of the fracture assessment and metallurgical testing were used to justify continued operation without repair of the cracks present in the flange. [S0094-9930(00)01901-6]

The Crack Arrest Capability of 9-Percent Ni Steels (ASTM 553, Type 1) LNG Storage Tanks

1991 ◽  
Vol 113 (3) ◽  
pp. 380-384
Author(s):  
P. B. Crosley ◽  
E. J. Ripling
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
High Stress ◽  
Crack Arrest ◽  
Storage Tanks ◽  
Membrane Stress ◽  
High Stress Region ◽  
Fast Running ◽  
Stress Region

Safety of structures can be assured, even if cracks initiate in localized regions of abnormally low toughness, and/or abnormally high stress (LT/HS), if the materials from which they are fabricated have a high enough crack arrest fracture toughness. When this requirement is met, fast-running cracks that initiate in LT/HS regions arrest when their tip encounters material having normal toughness and stresses. The work described in this paper was carried out to determine the crack arrest capability of LNG storage tanks by determining the longest LT/HS region in which a crack could initiate and still arrest when it leaves this region. The determination consisted of relating a fracture analysis with the measured full-thickness crack arrest fracture toughness of three 9-percent Ni plates which were reported in reference [1]. The calculations used a residual stress pattern, produced by welding, superimposed on a typical membrane stress. The residual stress was selected as an example of a localized high stress region. It was found that tanks built from the poorest of the three tested plates could arrest cracks about 3/4 m long, while tanks built from the two tougher plates could arrest cracks almost 2 m long.

Further Development of a Model for Predicting Corrosion Fatigue Crack Growth in Reactor Pressure Vessel Steels

1987 ◽  
Vol 109 (3) ◽  
pp. 340-346 ◽  
Author(s):  
J. D. Gilman
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Alloy Steel ◽  
High Stress ◽  
Time Dependent ◽  
Crack Advance ◽  
Low Alloy Steel ◽  
Time Rate ◽  
Paris Law

Analysis of fatigue crack growth data for low-alloy steel shows that the influence of cyclic frequency in simulated LWR environments can be interpreted as the superposition of a time-dependent, corrosion-assisted crack growth rate upon an increment predicted by a Paris law. The time-dependent component increases monotonically to a maximum of about 6×10−5 mm/s as stress cycling becomes more aggressive. A useful measure of aggressiveness is the average time rate of crack advance due to the Paris law component alone; i.e., AΔKn × frequency. The result suggests that current ASME Code methods for flaw assessment are highly conservative in some regimes of stress and frequency, but there is a possibility of growth rates well above the ASME XI, Appendix A curves in a very low-frequency, high-stress regime. An upper bound to the time rate of corrosion-assisted crack growth in low-alloy steel is well supported by the data. The threshold conditions for the onset of this high rate are less well defined and require further investigation.

Weld Residual Stress and Fracture Behavior of NASA Layered Pressure Vessels

2019 ◽  
Author(s):  
F. W. Brust ◽  
R. H. Dodds ◽  
J. Hobbs ◽  
B. Stoltz ◽  
D. Wells
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Fracture Behavior ◽  
Service Evaluation ◽  
Pressure Vessels ◽  
Weld Residual Stress ◽  
Proof Testing ◽  
Fracture Assessment ◽  
High Level ◽  
Initial Results

Abstract NASA has hundreds of non-code layered pressure vessel (LPV) tanks that hold various gases at pressure. Many of the NASA tanks were fabricated in the 1950s and 1960s and are still in use. An agency wide effort is in progress to assess the fitness for continued service of these vessels. Layered tanks typically consist of an inner liner/shell (often about 12.5 mm thick) with different layers of thinner shells surrounding the inner liner each with thickness of about 6.25-mm. The layers serve as crack arrestors for crack growth through the thickness. The number of thinner layers required depends on the thickness required for the complete vessel with most tanks having between 4 and 20 layers. Cylindrical layers are welded longitudinally with staggering so that the weld heat affected zones do not overlap. The built-up shells are then circumferentially welded together or welded to a header to complete the tank construction. This paper presents some initial results which consider weld residual stress and fracture assessment of some layered pressure vessels and is a small part of the much larger fitness for service evaluation of these tanks. This effort considers the effect of weld residual stresses on fracture for an inner layer longitudinal weld. All fabrication steps are modeled, and the high-level proof testing of the vessels has an important effect on the final WRS state. Finally, cracks are introduced, and service loading applied to determine the effects of WRS on fracture.

scholarly journals Intermediate-Temperature Creep Deformation and Microstructural Evolution of an Equiatomic FCC-Structured CoCrFeNiMn High-Entropy Alloy

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 960 ◽  
Author(s):  
Chengming Cao ◽  
Jianxin Fu ◽  
Tongwei Tong ◽  
Yuxiao Hao ◽  
Ping Gu ◽  
...  
Keyword(s):  
Activation Energy ◽  
Dynamic Recrystallization ◽  
Creep Deformation ◽  
High Stress ◽  
Intermediate Temperature ◽  
Tensile Creep ◽  
High Entropy Alloy ◽  
High Entropy ◽  
Stress Region ◽  
Stress Dependent

The tensile creep behavior of an equiatomic CoCrFeNiMn high-entropy alloy was systematically investigated over an intermediate temperature range (500–600 °C) and applied stress (140–400 MPa). The alloy exhibited a stress-dependent transition from a low-stress region (LSR-region I) to a high-stress region (HSR-region II). The LSR was characterized by a stress exponent of 5 to 6 and an average activation energy of 268 kJ mol−1, whereas the HSR showed much higher corresponding values of 8.9–14 and 380 kJ mol−1. Microstructural examinations on the deformed samples revealed remarkable dynamic recrystallization at higher stress levels. Dislocation jogging and tangling configurations were frequently observed in LSR and HSR at 550 and 600 °C, respectively. Moreover, dynamic precipitates identified as M23C6 or a Cr-rich σ phase were formed along grain boundaries in HSR. The diffusion-compensated strain rate versus modulus-compensated stress data analysis implied that the creep deformation in both stress regions was dominated by stress-assisted dislocation climb controlled by lattice diffusion. Nevertheless, the abnormally high stress exponents in HSR were ascribed to the coordinative contributions of dynamic recrystallization and dynamic precipitation. Simultaneously, the barriers imposed by these precipitates and severe initial deformation were referred to so as to increase the activation energy for creep deformation.

Creep and Fracture Mechanisms in an Oxide-Dispersion Strengthened Ni3Al-Based Alloy Between 649°C and 982°C

1994 ◽  
Vol 364 ◽  
Author(s):  
Ralph P. Mason ◽  
Nicholas J. Grant
Keyword(s):  
Stress Exponent ◽  
High Stress ◽  
Oxide Dispersion Strengthened ◽  
Fracture Mechanisms ◽  
Oxide Dispersion ◽  
Creep Tests ◽  
Creep Mechanisms ◽  
Stress Region ◽  
Power Law Creep ◽  
Reported Data

AbstractAn oxide-dispersion strengthened (ODS) Ni3Al-based alloy has been fabricated and creep tested. Previously reported data for minimum creep rate as a function of stress indicated that two creep mechanisms operate at intermediate temperatures of 732 and 816°C [1]. This paper reports the results of recent interrupted creep tests and fractographic studies which serve to identify the two creep mechanisms. Creep at low stresses or low creep-rates occurs by constrained growth of cavities on transverse grain boundaries. In this low stress region an apparent stress exponent of 5.1 is observed. Creep at high stresses or high creep-rates results from the bulk deformation of grains by power law creep with a much smaller contribution due to grain boundary cavitation. The stress exponents of 13 and 22 observed in this high stress region are typical of ODS alloys. In both regions fracture is observed to be mixed mode with a large transgranular component due to the high grain aspect ratio developed in this material. Limited data at 982°C indicate the occurrence of only one mechanism which can be described by a stress exponent of 9.1. It was not possible, based on fractographic studies, to associate the creep mechanism at 982°C with either of those observed at the intermediate temperatures. No fractographic studies were performed at 649°C due to lack of valid specimens; however, the stress exponent of 13.5 observed at 649°C suggests that creep occurs by deformation of the grains.

Rotor Welding: TVA Experience

2008 ◽  
Author(s):  
H. G. Best ◽  
M. E. Koss
Keyword(s):  
High Stress ◽  
Base Material ◽  
Turbine Rotor ◽  
Third Party ◽  
Fossil Plant ◽  
Weld Repair ◽  
Stress Region ◽  
Turbine Rotors ◽  
Additional Base ◽  
Single Flow

TVA has a fleet of 59 units with 187 large steam fossil turbine rotors, 68 fossil generators, and 27 auxiliary turbine rotors, in-service. The original equipment manufacturers (OEM) rotors have three designs some welded, others are shrunk on disk, but the majority of the rotors are mono-block. TVA has worked with OEM’s, third parties, and with-in TVA to perform weld repairs on rotors. Rotor Problems requiring welding: 1. Journal/gland damage due to lubrication failure and/or wear. 2. Attachment area damage due to cracks or distortion. 3. Attachment area due to changes in design. In the TVA fleet there are approximately 20 rotors that have been welded. Most of these have been successfully operated, but there have been 3 failures of welded rotors that will be discussed. Allen Fossil Plant Unit 3 Intermediate Pressure–Low Pressure Single Flow Turbine Rotor: In 1992 this rotor had a failure of the Curtis Stage. The decision was made to have the rotor welded and change the number of blades. Westinghouse (the OEM) performed the design and weld repair. In 2000 the unit experienced vibration, the unit was disassembled, and the weld repair had failed at the fusion line. An investigation of the failure revealed the weld had not been located at the designed location and the actual location of the weld was in a high stress area. Gallatin Fossil Plant Unit 4 High Pressure Turbine Rotor: TVA designed an upgrade to the Rateau Stage to change from axial entry to a tri-pin attachment. This required the welding of the disk. During welding, with a third party, cracks resulted that extended into the base material. This failed and additional base material was removed before welding. After 8 years of operation the rotor experienced vibration, the unit was inspected, and the weld was found with creep cracks in the heat affected zone (HAZ). An investigation of the failure revealed the expanded weld build-up relocated the HAZ into a high temperature, high stress region of the rotor. Widows Creek Fossil Plant Unit 7 Boiler Feed Pump Turbine Rotor: The rotor experienced stress corrosion cracking (SCC) of the fifth stage during operation in 2003. The rotor was weld repaired and returned to service in 2006. After 5 months of operation the rotor experienced vibration, was inspected, and the welded fifth stage and the sixth stage had experience SCC failures.

A-117 Strategic Memory and Advanced Reasoning Training for Rehabilitation of Warfighters with Mild Traumatic Brain Injury

2021 ◽  
Vol 36 (6) ◽  
pp. 1167-1167
Author(s):  
Jason Bailie ◽  
Paul Sargent ◽  
Sandi Chapman ◽  
Melissa Caswell ◽  
Juan Lopez ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Executive Functioning ◽  
Mild Traumatic Brain Injury ◽  
Cognitive Abilities ◽  
High Stress ◽  
Small Sample ◽  
Cognitive Complaints ◽  
Relevant Effect ◽  
Strategic Memory

Abstract Background Military personnel require a level of cognitive readiness that ensures they function safely and effectively in high-stress situations. Warfighters who experienced a mild traumatic brain injury (mTBI) often complain of persistent cognitive issues that may impact those abilities. This study presents preliminary data on the efficacy of a 4-week Strategic Memory Advanced Reasoning Training (SMART) for warfighter rehabilitation. SMART improves executive functioning in order to enhance overall cognitive abilities. Methods This is part of a randomized clinical trial (Validation of Cognitive Enhancement Therapy for mTBI). 22 Marines with prior mTBI and current cognitive complaints; 7 of whom completed SMART and were included in the analysis. Cognitive tests of interest included the Delis-Kaplan Executive Function System Color Word (CW) and Trail Making (TM). Results Improvements were observed on TM Number Sequencing (Pre: M = 9.71, SD = 2.06; Post: M = 11.86, SD = 1.35, p = 0.011, d = 1.37) and approached significance on Letter Sequencing (Pre: M = 10.29, SD = 1.81; Post: M = 12.57, SD = 1.13, p = 0.066, d = 1.26). Though non-significant, a large clinically-relevant effect size was found for Number-Letter Switching (Pre: M = 8.14, SD = 1.95; Post: M = 9.57, SD = 2.15, p = 0.106, d = 0.72). CW performance improved on Inhibition (Pre: M = 5.29, SD = 3.86; Post: M = 8.86, SD = 2.34, p = 0.034, d = 1.03) and Inhibition/Switching (Pre: M = 4.86, SD = 4.06; Post: M = 8.43, SD = 4.12, p = 0.015, d = 1.26). Conclusions The SMART program resulted in large improvements in the executive functioning of a small sample of warfighters with persistent cognitive complaints following a mTBI. The results support further examination of the efficacy of SMART for warfighter rehabilitation.

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