Residual Stress Assessment in Japanese FFS Code for Pressure Equipment, HPIS Z101

2006 ◽  
Author(s):  
Yoshio Takagi ◽  
Shinji Konosu ◽  
Masataka Yatomi
Keyword(s):  
Residual Stress ◽  
Structural Integrity ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Current Version ◽  
Technical Literature ◽  
Stress Assessment ◽  
Weld Residual Stress ◽  
Level 1 ◽  
Level 2

The High Pressure Institute of Japan published the first edition of Fitness for Service Assessment Procedure in 2001, HPIS Z101. Z101 is currently being revised and updated including the addition of Level 2 Assessment which involves more detailed evaluation regarding the structural integrity of cracked pressure vessels or piping systems than Level 1 Assessment. One of the notable revisions of Level 1 and the additions in Level 2 are the weld residual stress assessment of welded components. In the Level 1 assessment, the simplified residual stress distribution was defined in the current version. After publishing the current version, the committee has made an additional investigation into the residual stress assessment in existing FFS codes such as R6 and API 579 and has also compared the data in the technical literature on residual stress. The existent FFS code contains a certain degree of safety in residual stress assessment by making conservative structural integrity assessments for cracked pressure vessels and piping to prevent unexpected failure. However, the definition of residual stress profiles on the surface is controversial. In addition, some simplified definitions in the FFS codes do not always evaluate the measured weld residual stress safely. In this paper, the contradictions and controversial issues regarding weld residual stress distributions are discussed. Furthermore, the draft of revised Z101 is explained.

Assessments of Residual Stress Due to Weld-Overlay Cladding and Structural Integrity of Reactor Pressure Vessel

2010 ◽  
Author(s):  
Jinya Katsuyama ◽  
Hiroyuki Nishikawa ◽  
Makoto Udagawa ◽  
Mitsuyuki Nakamura ◽  
Kunio Onizawa
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Stress Distribution ◽  
Structural Integrity ◽  
Base Material ◽  
Pressure Vessels ◽  
Residual Stress Distribution ◽  
Weld Overlay ◽  
Weld Residual Stress ◽  
Reactor Pressure

Austenitic stainless steel is cladded on the inner surface of ferritic low alloy steel of reactor pressure vessels (RPVs) for protecting the vessel walls against the corrosion. After the manufacturing process of the RPVs including weld-overlay cladding and post-weld heat treatments (PWHT), the residual stress still remain in such dissimilar welds. The residual stresses generated within the cladding and base material were measured as-welded and PWHT conditions using the sectioning and deep-hole-drilling (DHD) techniques. Thermal-elastic-plastic-creep analyses considering the phase transformation in heat affected zone using finite element method were also performed to evaluate the weld residual stress produced by weld overlay cladding and PWHT. By comparing analytical results with those measured ones, it was shown that there was a good agreement of residual stress distribution within the cladding and base material. Tensile residual stress in cladding is mostly due to the difference between the thermal expansions of cladding and base materials. It was also shown that taking the phase transformation during welding into account is important to improve the accuracy of weld residual stress analysis. Using the calculated residual stress distribution, fracture mechanics analysis for a postulated flaw during pressurized thermal shock (PTS) events have been performed. The effect of weld residual stress on the structural integrity of RPV was evaluated through some case studies. The result indicates that consideration of weld residual stress produced by weld-overlay cladding and PWHT is important for assessing the structural integrity of RPVs.

Neutron Diffraction Evaluation of Residual Stress for Several Welding Arrangements and Comparison With Fitness-for-Purpose Assessments

2006 ◽  
Author(s):  
Anna M. Paradowska ◽  
John W. H. Price ◽  
Raafat Ibrahim ◽  
Trevor Finlayson ◽  
Richard Blevins ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Assessment Procedure ◽  
Stress Distributions ◽  
Fitness For Purpose ◽  
Single Bead ◽  
Level 1 ◽  
Number Of Passes ◽  
Neutron Diffraction Technique ◽  
Level 2

In this research the neutron diffraction technique was used to investigate and compare the residual stress characteristics in a several weld arrangements. This research has focused on the effects on residual stress of: • restraint condition applied during welding, • the start and end of the weld for a single bead, and • increasing the number of passes. The measured residual stress distributions are normalized by the yield strength of the material and compared with distribution provided in fitness-for-purpose procedures. It is found that the current safety assessment procedure BS 7910 and R6 Level 1 are significantly conservative. For a less conservative assessment R6 Level 2 is recommended, however even this assessment is often conservative, in particular for transverse residual stresses.

Development of a Residual Stress Simulation Benchmark for a Single Bead-on-Plate Weldment

2006 ◽  
Author(s):  
Peter J. Bouchard ◽  
Lyndon Edwards ◽  
Anastasius G. Youtsos ◽  
Roger Dennis
Keyword(s):  
Residual Stress ◽  
Assessment Procedure ◽  
Defect Assessment ◽  
Best Estimate ◽  
Weld Residual Stress ◽  
Single Bead ◽  
Stress Prediction ◽  
Stainless Steel Bead ◽  
Stress Simulation ◽  
Network Project

Finite element weld residual stress modelling procedures involve complex non-linear analyses where many assumptions and approximations have to be made by the analyst. Weld modelling guidelines for inclusion in the R6 defect assessment procedure are in preparation and will be accompanied by a series of validation benchmarks that can be used to evaluate the accuracy of weld modelling procedures and assess their suitability for use in fracture assessments. It is intended to base one of the benchmarks on a stainless steel bead-on-plate weldment that has been extensively studied by members of Task Group 1 of the NeT European Network project. This paper uses round robin residual stress measurements from the NeT project to derive a statistically based ‘best estimate’ distribution of transverse stress passing through the wall-section at mid-length of the bead-on-plate weldment. The accuracy of a state-of-the-art residual stress prediction is benchmarked against the best estimate measurements using a root mean square error analysis and comparisons of decomposed components of stress. The appropriateness of using the predicted residual stresses in fracture assessments is assessed by comparing stress intensity factors based on the measured and predicted distributions of stress. The results from these studies will be used to help establish accuracy targets and acceptance criteria for the welding benchmark.

Integrity Assessment of Pressure Components With Local Hot Spots

2005 ◽  
Vol 127 (2) ◽  
pp. 137-142 ◽  
Author(s):  
R. Seshadri
Keyword(s):  
Hot Spots ◽  
Structural Integrity ◽  
Refractory Lining ◽  
Assessment Method ◽  
Pressure Vessels ◽  
Industrial Processes ◽  
Integrity Assessment ◽  
Piping Systems ◽  
Further Development ◽  
Level 2

Local hot spots can occur in some pressure vessels and piping systems used in industrial processes. The hot spots could be a result of, for instance, localized loss of refractory lining on the inside of pressure components or due to a maldistribution of process flow within vessels containing catalysts. The consequences of these hot spots on the structural integrity of pressure components are of considerable importance to plant operators. The paper addresses structural integrity issues in the context of codes and standards design framework. Interaction of hot spots, as is the case when multiple hot spots occur, is addressed. An assessment method, suitable for further development of a Level 2 “Fitness-for-Service” methodology, is discussed and applied to a commonly used pressure component configuration.

Estimation of Through-Wall Cracking Frequency of RPV Under PTS Events Using PFM Analysis Method for Identifying Conservatism Included in Current Japanese Code

2014 ◽  
Author(s):  
Kazuya Osakabe ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Genshichiro Katsumata ◽  
Kunio Onizawa
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Analysis Method ◽  
Integrity Assessment ◽  
The U.S

To assess the structural integrity of reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events, the deterministic fracture mechanics approach prescribed in Japanese code JEAC 4206-2007 [1] has been used in Japan. The structural integrity is judged to be maintained if the stress intensity factor (SIF) at the crack tip during PTS events is smaller than fracture toughness KIc. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of pressure components has become attractive recently because uncertainties related to influence parameters can be incorporated rationally. A probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. According to the PFM analysis method in the U.S., through-wall cracking frequencies (TWCFs) are estimated taking frequencies of event occurrence and crack arrest after crack initiation into consideration. In this study, in order to identify the conservatism in the current RPV integrity assessment procedure in the code, probabilistic analyses on TWCF have been performed for certain model of RPVs. The result shows that the current assumption in JEAC 4206-2007, that a semi-elliptic axial crack is postulated on the inside surface of RPV wall, is conservative as compared with realistic conditions. Effects of variation of PTS transients on crack initiation frequency and TWCF have been also discussed.

Investigation Into Residual Stresses in a Small Bore Pipe Weld With Stacked Stop/Start Locations

2020 ◽  
Author(s):  
Ben Pellereau ◽  
Simon Walter ◽  
Paul Pembury
Keyword(s):  
Residual Stress ◽  
Welding Process ◽  
3D Models ◽  
Defect Tolerance ◽  
Horizontal Pipe ◽  
Weld Residual Stress ◽  
High Fatigue ◽  
Fracture Assessment ◽  
Peak Location ◽  
Level 1

Abstract Small bore austenitic stainless steel pipework is used in a number of nuclear plant systems. Many of these locations are subjected to large thermal shocks and therefore have high fatigue usage factors. Their justification therefore often includes a fatigue crack growth and fracture assessment, for which a key input is the residual stress associated with the welding process, in UK assessments these are typically taken from the R6 compendium. A common process used for these welds is manual tungsten inert gas welding, due to access difficulties each pass is usually completed in two halves. The stop-start locations for each weld run are sometimes stacked, especially in horizontal pipe runs where each weld operation starts at the bottom of the pipe and progresses upwards. The stack up of stop-start locations is likely to lead to considerable circumferential variation in weld residual stress, potentially resulting in stresses that locally exceed the R6 profiles. This paper presents results from a series of FE models for a single small bore pipe weld. The simulated weld is a 3-pass manual TIG weld with an EB insert in a 2 inch (50 mm) nominal diameter pipe. Both 2D and 3D models were run. The results of the modelling are then compared with measurements of weld mock-ups of the same weld (both with and without the stop-start stack-up). The results show that, local to the assumed stop location the predicted stresses do exceed even the R6 level 1 profile (a membrane stress equal to the 1% proof stress of the material). However, the locally enhanced stresses drop off quickly away from the peak location, so for defects of a size that may be a concern for a defect tolerance assessment, the R6 Level 1 and 2 profiles remains appropriate or bounding.

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.

Integral Mean of Yield Concept Applied to Thermal Hot Spots: Validation of a Level 2 Damage Assessment Method

2018 ◽  
Author(s):  
Henry Kwok ◽  
Simon Yuen ◽  
Jorge Penso
Keyword(s):  
Hot Spots ◽  
Damage Assessment ◽  
Hot Spot ◽  
Load Capacity ◽  
Assessment Method ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Level 3 ◽  
Level 2

The overall framework for a Level 2 assessment of local thermal hot spot in pressure vessels was first developed by Seshadri [1]. The assessment procedure invokes the concept of integral mean of yield and the concept on a reference volume to determine the reduction of load capacity caused by hot spot damage. This paper investigates the accuracy of this assessment by comparing the results of the Level 2 assessment with a Level 3 assessment (inelastic finite element analysis). Three examples with varying pressure component and hot spot sizes are considered. The comparison yielded a low variance between the Level 2 and Level 3 assessments with the Level 2 assessment being more conservative.

Study on Weld Residual Stress and Crack Propagation Evaluations for a Saddle-Shaped Weld Joint

2013 ◽  
Author(s):  
Jinya Katsuyama ◽  
Koichi Masaki ◽  
Kunio Onizawa
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Weld Joint ◽  
Power Plants ◽  
Structural Integrity ◽  
Piping System ◽  
Stress Distributions ◽  
Analysis Model ◽  
Element Analysis ◽  
Weld Residual Stress

Stress corrosion cracking (SCC) have been observed in reactor coolant pressure boundary piping system at nuclear power plants. When an SCC is found, the structural integrity of piping should be assessed according to a fitness-for-service rule. However, the rule stipulates the assessment procedures for crack growth and failure only for a simple structure such as cylindrical or plate-wise structure. At the present, the methodology even of an SCC growth evaluation for a geometrically complicated piping such as saddle-shaped weld joints has not been established yet. This may be because analyses on the weld residual stress distribution which affects the SCC growth behavior around such portion are difficult to conduct. In this study, we established a finite element analysis model for a saddle-shaped weld joint of pipes. The residual stress distributions produced by the tungsten inert gas (TIG) welding were calculated based on thermal-elastic-plastic analysis with moving and simultaneous heat source models. Analysis results showed complicated weld residual stress distributions, i.e., residual stresses in both hoop and radial directions were tensile at the inner surface near the nozzle corner in branching pipe. SCC growth simulation based on S-version finite element method (S-FEM) using the weld residual stress distributions in saddle-shaped weld joint was also performed. We confirmed an applicability and the accuracy of S-FEM to saddle-shaped weld joint.

Neutron Diffraction Evaluation of Residual Stress for Several Welding Arrangements and Comparison With Fitness-for-Purpose Assessments

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Anna M. Pardowska ◽  
John W. H. Price ◽  
Raafat Ibrahim ◽  
Trevor R. Finlayson
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Assessment Procedure ◽  
Stress Distributions ◽  
Fitness For Purpose ◽  
Single Bead ◽  
Surface Measurements ◽  
Number Of Passes ◽  
Neutron Diffraction Technique ◽  
Level 2

In this research, the neutron diffraction technique was used to investigate and compare the residual stress characteristics in several weld arrangements. This research has focused on the effects on residual stress of restraint condition applied during welding, the start and end of the weld for a single bead, and increasing the number of passes. The measured residual stress distributions are normalized by the yield strength of the material and compared with distribution provided in fitness-for-purpose procedures. It is found that the current safety assessment procedure BS 7910 and R6 Level 1 significantly conservative for longitudinal stresses outside the weld and heat affected zone, and for transverse residual stress across the weldment for surface measurements. For a less conservative assessment, R6 Level 2 is recommended, however, even if this assessment is often conservative, in particular, for transverse residual stresses.

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