Background The radiation budget represents the balance between incoming energy from the Sun and outgoing thermal (longwave) and reflected (shortwave) energy from the Earth. In the 1970's, NASA recognized the importance of improving our understanding of the radiation budget and its effects on the Earth's climate. Langley Research Center was charged with developing a new generation of instrumentation to make accurate regional and global measurements of the components of the radiation budget. The Goddard Space Flight Center built the Earth Radiation Budget Satellite (ERBS) which carried the first ERBE instruments. ERBS was deployed from the Space Shuttle Challenger in October 1984 by NASA Astronaut Sally Ride and launched into a 57 degree inclination precessing orbit with a period of approximately 72 days. In addition to the ERBE scanning and nonscanning instruments, the satellite also carried the Stratospheric Aerosol Gas Experiment (SAGE II). ERBE instruments were also launched on two National Oceanic and Atmospheric Administration weather monitoring satellites, the NOAA-9 satellite in January 1985 and the NOAA-10 satellite in October 1986. Science Team An international team of scientists was selected from proposals to an Announcement of Opportunity in 1978 to participate in the design and development of ERBE. Dr Bruce Barkstrom, of the Radiation Sciences Branch of Langley's Atmospheric Sciences Competency, was selected as the ERBE Principal Investigator. He led the team through 30 meetings to guide the development of the instrumentation and the ground processing software for analyzing the data, including algorithm development and data validation activities. Instrument Development Langley formed a team of electronic, thermal, and mechanical experts to develop the ERBE instruments. Led by Jack Cooper, Experiment Manager, and Glenn Taylor, Instrument Manager, this team developed the specifications for two types of instruments. TRW, of Redondo Beach, California, was selected to build the instruments, calibrate them in a unique thermal/vacuum radiometric calibration facility, and help integrate the instruments with the ERBS and NOAA satellite platforms.
Service induced cracking in Alloy 600 has been known for a long time, having been first observed in the 1980’s in steam generator tubing and small bore piping, and later, in 1991, in reactor vessel control rod drive mechanism (CRDM) head penetrations. Other than steam generator tubing, which cracked within a few years of operation, the first Alloy 600 cracking was in base metal of Combustion Engineering small bore piping, followed closely by CE pressurizer heater sleeves. The first reactor vessel CRDM penetrations (base metal) to crack were in France, US plants found CRDM cracking several years later. Three plants have discovered weld metal cracking at the outlet nozzle to pipe weld region. This was the first known weld metal cracking. This paper will chronicle the development of service-induced cracking in these components, and compare the behavior of welds as opposed to base metal, from the standpoint of time to crack initiation, growth rate of cracks, and their impact on structural integrity. In addition, a discussion of potential future trends will be provided.
Surveillance materials consisting of a SA-508 Class 2 forging, a Mn–Mo–Ni Linde 80 submerged-arc weld, and an SA-533, Grade B, Class 1, correlation monitor material were thermally aged on a commercial reactor pressure vessel. The materials were exposed to a thermal environment of 260°C for 209000h. This temperature is below the range (minimum of 370°C) where the effects of long-term thermal aging are typically considered relevant. Charpy impact, master curve transition temperature, upper-shelf fracture toughness, and tensile testing were conducted to evaluate the long-term thermal aging changes in material properties. Small changes in the impact properties were observed for all the materials, but were generally within the 95 % confidence bounds for typical Charpy data. Upper-shelf energy also showed small variations, but a general decrease for all materials was not seen. Fracture toughness testing at the upper shelf indicated that the upper-shelf toughness had increased, however the data is scattered. Master curve T0 testing in the transition region showed little change in the forging and plate results; however an improvement in the transition temperature of the weld metal was measured.
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