Manufacturing and Properties of Closure Head Forging Integrated With Flange for PWR Reactor Pressure Vessel

Closure head forging (SA508, Gr.3 Cl.1) integrated with flange for PWR reactor pressure vessel has been developed. This is intended to enhance structural integrity of closure head resulted in elimination of ISI, by eliminating weld joint between closure head and flange in the conventional design. Manufacturing procedures have been established so that homogeneity and isotropy of the material properties can be assured in the closure head forging integrated with flange. Acceptance tensile and impact test specimens are taken and tested regarding the closure head forging integrated with flange as very thick and complex forgings. This paper describes the manufacturing technologies and material properties of the closure head forging integrated with flange.

Experimental Program to Monitor the Irradiation Induced Embrittlement of the French Reactor Pressure Vessel Steels

By monitoring the irradiation-induced embrittlement of materials, the Pressure Vessel Surveillance Program (PVSP) contributes to the RPV integrity and lifetime assessments. This program is implemented on each PWR Unit in France; it is mainly based on Charpy tests, which are widely used in the nuclear industry to characterize the mechanical properties of the materials. Moreover, toughness tests are also carried out to check the conservatism of the PVSP methodology. This paper first describes the procedure followed for the Pressure Vessel Surveillance Program. It presents the irradiation capsules: the samples materials (low alloy Mn, Ni, Mo vessel steel including base metals, heat affected zones, welds and a reference material) and the mechanical tests performed. Then it draws up a synthesis of the analysis of about 180 capsules removed from the reactors at fluence levels up to 7.1019 n/cm2 (E > 1 MeV). This database gathers the results of more than 10,000 Charpy tests and 250 toughness tests. The experimental results confirm the conservatism of the Code-based methodology applied to the toughness assessment.

Remote Monitoring Systems for Detection of Contact by Unauthorized Construction Equipment and the Cathodic Protection Condition on Buried Pipelines

It is necessary to avoid spreading damage to the pipe when it is struck by construction equipment. It is difficult to install indirect methods (e.g. fiber optic sensors) for detection of construction equipment in heavy traffic areas. Therefore, remote monitoring systems, which can detect contact between such equipment and the steel of polyethylene-lined pipe, were developed and installed on a gas transmission pipeline (φ 600 mm, Length 9.4 km). Detection uses the change in pipe-to-earth resistance which is derived from inner pipe current and pipe to soil potential when contact occurs. Old and new data of pipe-to-earth resistance are continuously compared. If equipment contacts the steel pipe, pipe-to-earth resistance will drop below 100 Ω. The detection systems include maximal length sequence signal (pseudo-random signal) processing. This signal processing is superior for noise reduction. These systems also have remote monitoring of the cathodic protection condition (pipe to soil potential, current of coupons (probes), and transformer rectifier output voltage and current). From the office, pipeline lining and cathodic protection conditions are monitored at all times.

FEM Stress Analysis and the Sealing Performance Evaluation in Stainless Steel Elbow and Tee Fittings Under Internal Pressure: Case Where Internal Fluid is Liquid

Stainless steel fittings such as elbows, tees, nipples and so on have been widely used in mechanical structures and chemical plants, it is well known that the leakage in the fittings used sealing tapes is less than that without the sealing tapes. In a practical design, it is necessary to examine the stress states and the leakage in the fittings under internal pressure and external loads such as tensile loads, bending moments and so on. This paper deals with the FEM stress analysis of the fittings subjected to internal pressure. In the FEM calculations, the engaged screw threads are taken into consideration as helical threads in the three-dimension. The leakage tests for the fittings under internal pressure were also conducted by using liquid (oil). Using the results of the leakage tests and the calculated stress states in the fittings, the sealing performance of the fittings under internal pressure was evaluated and the effect of the tightening torque was clarified on the sealing performance. In addition, the numerical results were compared with the experimental results. As the result, the effects of the sealing tapes on the contact stress distributions were also clarified.

Global Assessment System for Structural Safety in Large Size Storage Tanks

Considering long term stable supply of oil fuel, the world largest long-term storage system of crude oil has been installed in Japan. In order to ensure safety of large size above ground storage tanks, global assessment system for structural integrity of tank considering risk level and shut down inspection interval has been developed on Risk Based Inspection, RBI and Fitness-For-Service, FFS for storage tanks of crude oil for national security reserve.

The Practical Application of 36% Ni Steel Piping in LNG Plants

Conventionally, 18-8 stainless steel has been used for the facility of cryogenic service in LNG plant because of the excellent toughness. Although 18-8 stainless steel piping requires pipe looping to relax thermal expansion in the cryogenic piping of LNG plant, 36% Ni steel (generally called as Invar) piping does not require pipe looping due to its low coefficient of linear expansion of about one-tenth of that of 18-8 stainless steel. Elimination of pipe looping makes significant reduction of the piping cost by reducing the number of elbows, welding points and adoption of small diameter of piping. Furthermore, it is possible to reduce the tunnel diameter, when the piping is installed in a tunnel. However, conventionally, it has been known that there is a difficulty in adopting the material from the viewpoint of weldability, which is reheat cracking at the weld metal in multi-layer welding. So, we have developed an excellent welding technology for 36% Ni steel with a new welding consumable. In order to adopt 36% Ni steel to the cryogenic piping in LNG plant, comprehensive experiments to find out the properties such as mechanical properties, corrosion resistance, weldability, nondestructive inspection and thermal stress analysis were conducted. By using the results the appropriate welding procedures were established and 36% Ni steel was used for the Ohgishima LNG receiving terminal of Tokyo Gas Company.

Assessment of U.S. Embrittlement Trend Equations Considering the Latest Available Surveillance Data

The mechanistically-guided embrittlement correlation model adopted in ASTM E 900-02 was based on a database of U.S. surveillance results current through calendar year 1998. There exists now an extensive amount of new surveillance data that includes a large amount of boiling water reactor (BWR) results from an integrated, supplemental surveillance program designed to augment the plant-specific BWR surveillance programs. These recent data allow a statistical test of the ASTM E 900-02 embrittlement correlation, as well as the NRC correlation model currently being used in the pressurized thermal shock (PTS) re-evaluation effort and the older Regulatory Guide 1.99, Revision 2 correlation. Even though the ASTM E 900-02 embrittlement correlation is a simplified version of the NRC model, a comparison of the two embrittlement correlation models utilizing the new database has proven to be revealing. Based on the new BWR data, both models are inadequate in their ability to predict BWR results; this inadequacy has even more significance for extrapolation outside of the database for BWR heat-up and cool-down curves, as well as some pressurized water reactor (PWR) heat-up curves. Other aspects of the two models, as revealed from this preliminary look at the new data, are presented.

Irradiation Hardening of Austenitic Stainless Steels: From Field Experience to Modeling

Materials for the core internals of Pressurized Water Reactors (austenitic stainless steels) are submitted to neutron irradiation. To understand the ageing mechanisms associated to irradiation and propose life predictions of the component, a multi step iterative approach consisting in particular in modeling the evolution of the hardening has been undertaken. Combination of characterization and modeling of simplified situations and field expertise is proposed.

Structural Integrity Assessment for Various Failure Modes Using a Risk-Based Maintenance Method

In this paper, a newly developed system called RBM (Risk-Based Maintenance) is presented. The system is used to describe the structural integrity of buried pipeline based on the index of risk that is defined in the product of the failure frequency and the consequence. Various failure modes corresponding to each degradation mechanism are included, and the estimation of failure probability that the external load exceeds the structure resistance is carried out. As the result of trial evaluation compared with the past earthquake incident, it is in good agreement with actual damage of pipeline subjected to liquefaction and large ground deformation. Furthermore, the system enables operators to maintain the structural integrity for service life by providing the most optimized maintenance plan according to the risk level. The features of the quantitative risk evaluation approach and the benefits of the developed RBM system as a means of structural integrity assessment are also discussed.

Stress Corrosion Cracking of Cold Worked Austenitic Stainless Steels in Laboratory Primary PWR Environment

Austenitic Stainless Steels (ASS) are widespread in primary and auxiliary circuits of Pressurized Water Reactors (PWRs). Moreover, some components suffer stress corrosion cracking (SCC) under neutron irradiation. This degradation could be the result of the increase of hardness and / or the modification of chemical composition at the grain boundary by irradiation. In order to avoid complex and costly corrosion facilities, the effects of radiation hardening on the material are commonly simulated by applying a pre-strain on non-irradiated material prior to stress corrosion cracking tests. The typical features of the cracking process in primary environment at 360°C during CERTs included an initiation stage (composed of a true initiation time and a slow propagation regime leading to a crack depth lower than 50 μm), then a “rapid” propagation stage before mechanical failure. Pre-straining increased significantly CGRs and the mode of pre-straining could strongly modify the crack path. No significant cracking (< 50 μm) was obtained under a pure static loading. A dynamic loading (CERT or cyclic) was required and various thresholds (hardness, elongation, stress) for the occurrence of SCC were determined. An important R&D program is in progress to develop initiation and propagation models for SCC of austenitic SS in primary environment.