Papers by Keyword: Slow Strain Rate Testing (SSRT)

Abstract: Hydrogen evolution behavior of an Al-Mg-Si alloy affected by hydrogen embrittlement was investigated using a tensile testing machine equipped with quadruple mass spectrometer in an ultrahigh vacuum chamber. Plate type test pieces were solutionized at 540°C for 1h, quenched in water and then aged at 175°C for 8h or 240h. Some of the aged test pieces were pre-deformed in air with a relative humidity of 90% at a slow strain rate of 8.3x10-7s-1 to introduce hydrogen from the testing atmosphere. As a result of the tensile test with mass spectrometry, it was shown that hydrogen was highly evolved at the moment of fracture. The area fraction of intergranular fracture decreased when the aging condition was changed from peak-aged to over-aged, which was in agreement with the decrease in the amount of hydrogen evolved at the moment of fracture.

Abstract: Stress corrosion cracking (SCC) of austenitic stainless steel serviced in aggressive environment often occurs in power, petrochemical industry, and leads to premature equipment failure and great economic loss. This paper focuses on the problem of the SCC on the 304L stainless steel nozzle of a hydrogenation reactor, which is caused due to on-line alkali cleaning. Susceptibility for SCC was evaluated by Slow Strain Rate Test (SSRT) for as-rolled and sensitized 304L stainless steel in low concentration sodium hydroxide solution with high temperature. The effects of different strain rates, different concentration of sodium hydroxide and different solution temperatures on SCC were investigated. On the basis of this, the contrast tests were also performed in high temperature pure water. After SSRT, fractograph of the fractured specimens was analyzed by using scanning electron microscopy (SEM).

Abstract: JIS-SPV50Q high strength steel is often employed in construction of liquid petroleum gas (LPG) spherical tanks due to its high strength and good ductility. In general, post weld heat treatment is not performed after welding of SPV50Q high strength steel and welding residual stress will be retained in weldment. Service experience and inspection indicate that higher H2S concentration and welding residual stress result in the environmental failure, such as blistering or hydrogen induced cracking (HIC), sulfide stress corrosion cracking (SSCC) and stress oriented hydrogen induced cracking (SOHIC). In the present paper, the cracking behavior of SPV50Q high strength steel weldment by manual electric arc welding has been investigated in various saturate solutions with different concentrations of H2S. The results of slow strain rate testing, performed at a strain of 1×10-6s-1, reveal the presence of SSCC and HIC in the base metal adjacent to HAZ. The ffects of the different temperatures of post weld heat treatment on cracking are discussed. The suitable post weld heat treatment could increase the resistance of SPV50Q weldment on SSCC or HIC and does not decrease the mechanical properties of SPV50Q weldment.

Abstract: A possible approach to describe the role of the environment in the phenomena behind crack initiation and crack propagation in stress corrosion cracking (SCC) is to assume that the transport of species through the oxide film on the material surface is one of the rate-controlling factors. The transport rates of ionic and electronic defects through the oxide film are, in addition to the environment, also affected by the stress and strain applied to the bulk material. In this paper, the surface oxide film formed on AISI 316L steel in slow strain rate tests (SSRT) in simulated BWR condition has been analyzed by using Electron Spectroscopy for Chemical Analysis (ESCA). The obtained film composition and structure have been combined with in-situ contact electric resistance (CER) measurements in order to evaluate the changes in oxide film electric properties during straining in the above environment. The results show that oxide film resistance of the strained part exhibits a maximum at around 2% of strain, which seems to correlate with a maximum in the Cr(III) concentration in the inner layer of the oxide. The implications of these results to SCC are discussed based on Mixed-Conduction Model (MCM).