Flaw Tolerance Evaluation of CASS Piping Materials

2009 ◽  
Author(s):  
Timothy J. Griesbach ◽  
Vikram Marthandam ◽  
Haiyang Qian ◽  
Patrick O’Regan
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Thermal Aging ◽  
Prolonged Exposure ◽  
Delta Ferrite ◽  
Acceptance Criteria ◽  
Centrifugally Cast ◽  
Reactor Coolant ◽  
Flaw Tolerance ◽  
Asme Code

Prolonged exposure of cast austenitic stainless steels (CASS) to reactor coolant operating temperatures has been shown to lead to some degree of thermal aging embrittlement (reduction in fracture toughness of the material as a function of time). The fracture toughness data for the most severely aged CASS materials were found to be similar to those reported for some austenitic stainless steel weld metal, in particular weld metal from submerged arc welds (SAW). Such similarity offers the possibility for applying periodic inservice inspection flaw acceptance criteria, currently referenced in the ASME Code Section XI, Subsection IWB, for SAW and shielded metal arc weld (SMAW), to CASS component inservice inspection results. This paper presents the data to support both the proposed screening criteria (based on J-R crack growth resistance) for evaluation of the potential significance of the effects of thermal aging embrittlement for Class 1 reactor coolant system and primary pressure boundary CASS components, for those situations where the effects of thermal aging embrittlement are found to be potentially significant. The fitness for continued service is based on the comparison of the limiting fracture toughness data for Type 316 SAW welds and the lower-bound fracture toughness data reported for high-molybdenum, high delta-ferrite, statically and centrifugally-cast CASS materials. These comparisons and the associated flaw acceptance criteria can be used to justify exemptions from current ASME Code Section XI inservice inspection requirements through flaw tolerance evaluation (e.g., see ASME Nuclear Code Case N-481).

scholarly journals Fracture Resistance of Cast Austenitic Stainless Steels

2016 ◽  
Author(s):  
Y. Chen ◽  
W-Y. Chen ◽  
A. S. Rao ◽  
Z. Li ◽  
Y. Yang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Growth Rate ◽  
Corrosion Resistance ◽  
Neutron Irradiation ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Light Water Reactor ◽  
Delta Ferrite ◽  
Light Water

Cast austenitic stainless steels (CASS) possess excellent corrosion resistance and mechanical properties and are used alongside with wrought stainless steels (SS) in light water reactors for primary pressure boundaries and reactor core internal components. In contrast to the fully austenitic microstructure of wrought SS, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite. The delta ferrite is critical for the service performance since it improves the strength, weldability, corrosion resistance, and soundness of CASS alloys. On the other hand, the delta ferrite is also vulnerable to embrittlement when exposed to reactor service temperatures and fast neutron irradiations. In this study, the combined effect of thermal aging and neutron irradiation on the degradation of CASS alloys was investigated. Neutron-irradiated CASS specimens with and without prior thermal aging were tested in simulated light water reactor environments for crack growth rate and fracture toughness. Miniature compact-tension specimens of CF-3 and CF-8 alloys were tested to evaluate the extent of embrittlement resulting from thermal aging and neutron irradiation. The materials used are static casts containing more than 23% delta ferrite. Some specimens were thermally aged at 400 °C for 10,000 hours prior to the neutron irradiation to simulate thermal aging embrittlement. Both the unaged and aged specimens were irradiated at ∼320°C to a low displacement damage dose of 0.08 dpa. Crack growth rate and fracture toughness J-integral resistance curve tests were carried out on the irradiated and unirradiated control samples in simulated light water reactor environments with low corrosion potentials. While no elevated crack propagation rates were detected in the test environments, significant reductions in fracture toughness were observed after either thermal aging or neutron irradiation. The loss of fracture toughness due to neutron irradiation seemed more evident in the samples without prior thermal aging. Transmission electron microscope (TEM) examination was carried out on the thermally aged and neutron irradiated specimens. The result showed that both neutron irradiation and thermal aging can induce significant changes in the delta ferrite. A high density of G-phase precipitates was observed with TEM in the thermally aged specimens, consistent with previous results. Similar precipitate microstructures were also observed in the neutron-irradiated specimens with or without prior thermal aging. A more extensive precipitate microstructure can be seen in the samples subjected to both thermal aging and neutron irradiation. The similar precipitate microstructures resulting from thermal aging and neutron irradiation are consistent with the fracture toughness results, suggesting a common microstructural origin of the observed embrittlement after thermal aging and neutron irradiation.

Basis for ASME Section XI Code Case for Flaw Tolerance Evaluation of CASS Piping

2013 ◽  
Author(s):  
Timothy J. Griesbach ◽  
David O. Harris ◽  
Nathaniel G. Cofie ◽  
Alan Chockie ◽  
Dilip Dedhia
Keyword(s):  
Stainless Steel ◽  
Ultrasonic Inspection ◽  
The United States ◽  
Primary System ◽  
Delta Ferrite ◽  
Centrifugally Cast ◽  
Flaw Tolerance ◽  
Piping Systems ◽  
Effects Of Aging ◽  
Renewal Period

Thermal aging of cast austenitic stainless steel (CASS) piping is a concern for long term operation of nuclear power plants. The effects of aging in susceptible (i.e., high delta ferrite) CASS piping and components must be managed through the license renewal period. In the United States, utilities must follow the guidance for managing age-related degradation in the Generic Aging Lessons Learned (GALL) report, and this may include analyses or inspections to demonstrate that the piping systems remain flaw tolerant. The duplex structure and large grain size of the CASS materials poses challenges with non-destructive examinations (NDE) using ultrasonic inspection (UT) techniques of the CASS components which further complicates the ability to demonstrate that any existing flaws would not compromise piping integrity. Recent analytical studies of fully aged CF8M piping have resulted in a probabilistic fracture mechanics (PFM) model that has been used to develop allowable flaw sizes based on various levels of probability of failure. This model has been utilized extensively to generate a series of flaw acceptance limits that could be equated to the service levels in the ASME Code. A proposed ASME Section XI Code Case has been developed based on this PFM methodology for flaw tolerance evaluation of CASS piping components considering the effects of aging and uncertainties in material properties. The Code Case is currently under review by the ASME Working Group on Pipe Flaw Evaluation. This paper outlines the proposed Code Case and presents a technical basis for the flaw tolerance evaluation of CASS piping components. The ultimate objective of the flaw tolerance evaluation is to determine allowable flaw sizes in CASS components and determine target flaw sizes for NDE that will ensure safe operation with these components considering possible flaw growth. The flaw tolerance evaluation could be applied for a range of piping systems including pressurizer surge lines and primary system piping made from either statically or centrifugally cast stainless steel.

Tempering Response in Type 410 Stainless Steel Welds for Petrochemical Application

2020 ◽  
Author(s):  
Takuya Kusunoki ◽  
Boian Alexandrov ◽  
Benjamin Lawson ◽  
Jorge Penso ◽  
Joe Bundy
Keyword(s):  
Stainless Steel ◽  
Weld Metal ◽  
Low Cost ◽  
Postweld Heat Treatment ◽  
Base Metals ◽  
Delta Ferrite ◽  
Asme Code ◽  
Fresh Martensite ◽  
Steel Welds ◽  
Welding Consumables

Abstract Type 410 martensitic stainless steel is typically used in highly corrosive environments within petrochemical installations due to its resistance to halide stress corrosion cracking, hardenability, and low cost compared to austenitic stainless steel. However, the industry has experienced difficulties in meeting the ASME toughness, and NACE hardness requirements for wet sour services of Type 410 steel welds. Recent studies have shown that these problems are related to the wide compositional ranges of Type 410 base metals and welding consumables, leading to exceeding the A1 temperature during postweld heat treatment (PWHT) and formation of fresh martensite, and to retention of significant amount of delta ferrite in the final weld metal and heat affected zone microstructures. These studies have identified two Type 410 optimized weld metal compositions that met the specified hardness and toughness requirements. The objective of this work was to quantify the tempering response in one of the optimized welding consumables and in two Type 410 base metals. Samples of these materials were subjected to a series of PWHTs at temperatures corresponding to the lower and upper limits of the ASME code recommended temperature range (760 C and 800 °C) and at 10 °C below the A1 temperature of each material. The PWHT durations were 5 and 30 minutes, and 1, 2, and 4 hours. The hardness values related to all PWHTs performed below the corresponding A1 temperatures were used to generate Holloman–Jaffe type equations for all tested materials. As expected, the PWHTs performed above the A1 temperatures resulted in the formation of fresh martensite.

Fracture Toughness and Deformation Behavior of Cast Austenitic Stainless Steels After Thermal Aging

2017 ◽  
Author(s):  
Yiren Chen ◽  
Wei-Ying Chen ◽  
Chi Xu ◽  
Xuan Zhang ◽  
Zhangbo Li ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Cooling System ◽  
Austenitic Stainless Steels ◽  
Ferrite Content ◽  
Delta Ferrite ◽  
Light Water ◽  
Water Reactors ◽  
The Impact

Cast austenitic stainless steels (CASSs) are used in the cooling system of light water reactors (LWRs) for components with complex shapes, such as pump casings, valve bodies, coolant piping, etc. The CF grades of CASS alloys are the cast equivalents of 300-series stainless steels (SSs) and show excellent mechanical properties and corrosion resistance. In contrast to the fully austenitic microstructure of wrought SSs, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite and are vulnerable to thermal aging embrittlement. The service performance of CASS alloys is of concern after long-term exposure to high-temperature coolant. In this work, we studied the effects of thermal aging and ferrite content on the fracture resistance of CASS alloys. Crack growth rate and fracture toughness J–R curve tests were performed on aged and unaged CASS alloys in simulated light water reactor environments. The impact of thermal aging on the cracking susceptibility was investigated and the effect of ferrite content was evaluated. Significant embrittlement was observed in the CASS alloys after aging at 400°C. To understand the embrittlement mechanism, microstructural characterizations were performed with transmission electron microscope. The thermal aging produced G-phase precipitates and phase separation in the ferrite, but did not affect the microstructure of austenite. Consequently, the ferrite was hardened considerably after thermal aging while the hardness of austenite phase remained unchanged. The difference in hardness created a high incompatible strain at the interface between ferrite and austenite, leading to fracture at phase boundaries.

NIMROD 617KS

Alloy Digest ◽  
2002 ◽  
Vol 51 (5) ◽  
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Weld Metal ◽  
Tensile Properties ◽  
Base Metal ◽  
Heat Treating ◽  
Nominal Composition

Abstract Nimrod 617KS is an Inconel-type consumable with a nominal composition of nickel, 24% Cr,12% Co, and 9% Mo and is used to join UNS N06617 and Nicrofer 6023 to themselves. The alloy is designed for high-temperature service and is often used as the weld metal in dissimilar cases to ensure the weld is as strong as the base metal. This datasheet provides information on composition, hardness, and tensile properties as well as fracture toughness. It also includes information on heat treating and joining. Filing Code: Ni-583. Producer or source: Metrode Products Ltd.

UNIFLUX VCM 125

Alloy Digest ◽  
1978 ◽  
Vol 27 (1) ◽  
Keyword(s):  
Carbon Dioxide ◽  
Fracture Toughness ◽  
Weld Metal ◽  
Heat Treating ◽  
Carbon Steels ◽  
Low Alloy Steels ◽  
Electrode Wire ◽  
Molybdenum Steel ◽  
Alloy Steels ◽  
Welding Electrode

Abstract UNIFLUX VCM 125 is a continuous flux-cored welding electrode (wire) that is used to deposit 1 1/4% chromium-1/2% molybdenum steel for which it was developed. Welding is protected by a shielding atmosphere of 100% carbon dioxide. This electrode also may be used to weld other low-alloy steels and carbon steels; however, the weld metal may differ somewhat from 1 1/4% chromium-1/2% molybdenum because of weld-metal dilution. When Uniflux VCM 125 is used to weld 1 1/4% chromium-1/2% molybdenum steel, it provides 95,000 psi tensile strength at 70 F and 24 foot-pounds Charpy V-notch impact at 40 F. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as heat treating, machining, and joining. Filing Code: SA-340. Producer or source: Unicore Inc., United Nuclear Corporation.

Dynamic fracture toughness (JId) behavior of armor-grade Q&T steel weldments: Effect of weld metal composition and microstructure

2009 ◽  
Vol 15 (6) ◽  
pp. 1017-1026 ◽  
Author(s):  
Govindaraj Magudeeswaran ◽  
Visvalingam Balasubramanian ◽  
S. Sathyanarayanan ◽  
Gankidi Madhusudhan Reddy ◽  
A. Moitra ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Dynamic Fracture ◽  
Dynamic Fracture Toughness ◽  
Metal Composition ◽  
Weld Metal Composition

scholarly journals Microstructure and Fracture Toughness of Fe–Nb Dissimilar Welded Joints

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 86
Author(s):  
Qiaoling Chu ◽  
Lin Zhang ◽  
Tuo Xia ◽  
Peng Cheng ◽  
Jianming Zheng ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Weld Metal ◽  
Thermal Cycle ◽  
Peak Load ◽  
Local Phase ◽  
Weld Formation ◽  
Lamellar Structures ◽  
Average Hardness ◽  
Radial Cracks

The relation between the microstructure and mechanical properties of the Fe–Nb dissimilar joint were investigated using nanoindentation. The weld metal consists mainly of Fe2Nb, α-Fe + Fe2Nb, Nb (s,s) and Fe7Nb6 phases. Radial cracks initiate from the corners of the impressions on the Fe2Nb phase (~20.5 GPa) when subjected to a peak load of 300 mN, whereas the fine lamellar structures (α-Fe + Fe2Nb) with an average hardness of 6.5 GPa are free from cracks. The calculated fracture toughness of the Fe2Nb intermetallics is 1.41 ± 0.53 MPam1/2. A simplified scenario of weld formation together with the thermal cycle is proposed to elaborate the way local phase determined the mechanical properties.

Combining CaO–SiO2–TiO2 and CaO–SiO2–Al2O3 ternary phase systems for design of bimetallic welds

2021 ◽  
Vol 235 (8) ◽  
pp. 1271-1283
Author(s):  
Deepak Bhandari ◽  
Rahul Chhibber ◽  
Lochan Sharma ◽  
Navneet Arora ◽  
Rajeev Mehta
Keyword(s):  
Weld Metal ◽  
Power Plants ◽  
Ternary Phase ◽  
Desirability Function ◽  
Manganese Content ◽  
Research Work ◽  
Welding Process ◽  
Delta Ferrite ◽  
Electrode Coating ◽  
Phase Systems

The bimetallic welds are frequently utilized for pipeline transport system of the nuclear power plants. The occurrences of welding defects generally depend on the filler electrode as well as the electrode coatings during shielded metal arc welding process. This study involves the design of austenitic stainless steel welding electrodes for SS304L–SA516 bimetallic welds. The objective of research work includes the novel design of Al2O3–TiO2–CaO–SiO2 coatings by combining two ternary phase systems using extreme vertices mixture design methodology to analyze the effect of key coating constituents on the weld metal chemistry and mechanical properties of the welds. The significant effect of electrode coating constituent CaO on weld metal manganese content is observed which further improves the toughness of bimetallic weld joints. Various regression models have been developed for the weld responses and multi objective optimisation approach using composite desirability function has been adopted for identifying the optimized set of electrode coating compositions. The role of delta ferrite content in promoting the favourable solidification mode has been studied through microstructural examination.

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