Creep rupture testing of alloy 617 and A508/533 base metals and weldments.

Technical Report · Tue Jan 17 00:00:00 EST 2012

DOI:https://doi.org/10.2172/1033487· OSTI ID:1033487

Natesan, K; Li, M; Soppet, W K; Rink, D L ^[1]

---

1. Nuclear Engineering Division

The NGNP, which is an advanced HTGR concept with emphasis on both electricity and hydrogen production, involves helium as the coolant and a closed-cycle gas turbine for power generation with a core outlet/gas turbine inlet temperature of 750-1000 C. Alloy 617 is a prime candidate for VHTR structural components such as reactor internals, piping, and heat exchangers in view of its resistance to oxidation and elevated temperature strength. However, lack of adequate data on the performance of the alloy in welded condition prompted to initiate a creep test program at Argonne National Laboratory. In addition, Testing has been initiated to evaluate the creep rupture properties of the pressure vessel steel A508/533 in air and in helium environments. The program, which began in December 2009, was certified for quality assurance NQA-1 requirements during January and February 2010. Specimens were designed and fabricated during March and the tests were initiated in April 2010. During the past year, several creep tests were conducted in air on Alloy 617 base metal and weldment specimens at temperatures of 750, 850, and 950 C. Idaho National Laboratory, using gas tungsten arc welding method with Alloy 617 weld wire, fabricated the weldment specimens. Eight tests were conducted on Alloy 617 base metal specimens and nine were on Alloy 617 weldments. The creep rupture times for the base alloy and weldment tests were up to {approx}3900 and {approx}4500 h, respectively. The results showed that the creep rupture lives of weld specimens are much longer than those for the base alloy, when tested under identical test conditions. The test results also showed that the creep strain at fracture is in the range of 7-18% for weldment samples and were much lower than those for the base alloy, under similar test conditions. In general, the weldment specimens showed more of a flat or constant creep rate region than the base metal specimens. The base alloy and the weldment exhibited tertiary creep after 50-60% of the rupture life, irrespective of test temperature in the range of 750-950 C. The results showed that the stress dependence of the creep rate followed a power law for both base alloy and weldments. The data also showed that the stress exponent for creep is the same and one can infer that the same mechanism is operative in both base metal and weldments in the temperature range of the current study. SEM fractography analysis indicated that both base metal and weldment showed combined fracture modes consisting of dimple rupture and intergranular cracking. Intergranular cracking was more evident in the weldment specimens, which is consistent with the observation of lower creep ductility in the weldment than in the base metal.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: NE; INL
• DOE Contract Number: DE-AC02-06CH11357
• OSTI ID: 1033487
• Report Number(s): ANL/EXT-11/46; TRN: US201202%%897
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
08 HYDROGEN
ALLOYS
COOLANTS
CREEP
DUCTILITY
ELECTRICITY
FRACTOGRAPHY
FRACTURES
GAS TUNGSTEN-ARC WELDING
GAS TURBINES
HEAT EXCHANGERS
HELIUM
HYDROGEN PRODUCTION
IDAHO NATIONAL LABORATORY
OXIDATION
POWER GENERATION
PRESSURE VESSELS
QUALITY ASSURANCE
REACTOR COMPONENTS
RUPTURES
STEELS
STRAINS
TESTING
TURBINES