Tomoya Kawabata

DIFFERENCE BETWEEN ASTM E1290 AND BS 7448 CTOD ESTIMATION PROCEDURES

Since the British Standards Institution (BSI) standardized BS 5762 in 1979, a popular way of calculating the Crack Tip Opening Displacement (CTOD) has been the use of the plastic hinge model with an assumed rotational centre. The American Society for Testing and Materials (ASTM) previously accepted the plastic hinge model and standardized E1290 in 1989. However, ASTM revised E1290 in 2002, and has proposed a fracture parameter conversion from the J-integral to CTOD. These two different CTOD calculations probably lead to confusion for Fitness-for-Service (FFS). The Fracture Toughness Study Committee of the Japan Welding Engineering Society (JWES) organized a working group, and the effects of CTOD testing methodology on CTOD values were investigated. In this paper, the results of CTOD round-robin tests in the working group are summarized, and the difference between the critical CTOD values obtained by ASTM E1290–02 and those by BS 7448, which involves the plastic hinge model, is described.

Development of 7%Ni-TMCP Steel Plate for LNG Storage Tanks

Demand of natural gas continues to increase in the recent years due to the rise of environmental issue and the drastic increase of crude oil price. These events led to the increase of constructions of Liquefied Natural Gas (LNG) storage tanks worldwide. The inner tank material for above ground LNG storage tanks have mostly been made of a 9% nickel steel plate over the last 50 years as it has excellent mechanical properties under the cryogenic temperature of −160deg-C. During this period, the LNG storage tanks made of 9%Ni steel plate have been operated safely at the many LNG export and import terminals in the world. Meanwhile, technologies of steel making, refinement, design, analysis, welding and inspection have been improved significantly and enabled enlarging volumetric capacity of the tank 2–3 times. There was a tendency for nickel price to increase in recent years. In such a circumstance lowering Ni content has focused attention on the 9%Ni steel as nickel is an expensive and valuable rare metal and a 7%Ni steel plate was eventually researched and developed by optimizing the chemical compositions and applying Thermo-Mechanical Controlled Process (TMCP). As a result, it was demonstrated that 7%Ni-TMCP steel plate had excellent physical and mechanical properties equivalent to those of 9%Ni steel plate. In order to evaluate fitness of the 7%Ni-TMCP steel plate and its weld for LNG storage tanks a series of testing was conducted. Several different plate thicknesses, i.e. 6,10,25,40 and 50 mm, were chosen to run large scale fracture toughness tests including duplex ESSO tests, cruciform wide plate tests as well as small scale tests. It was concluded that the 7%Ni-TMCP steel plate warrants serious consideration for use in LNG storage tanks. This paper reports details of the research and development of the 7%Ni-TMCP steel plate.Copyright

Consideration on the Toughness Requirement to the Austenitic Weld Metal in the LNG Storage Tanks Subjected to a Partial Height Hydro Test

PD7777 published by British Standard Institute in 2000 proposes an additional fracture requirement to the main steel components of the low temperatures storage tank where a partial height hydrostatic test is allowed instead of the full height hydrostatic test required in BS 7777. In the PD7777 a high level (75J) of fracture toughness is required for the austenitic weld metal in 9%Ni steel plate to prevent the re-initiation of ductile fracture from the arrested brittle crack in the weld. This is to report a study that the J-Cv correlation of austenitic weld metal is determined by the experimental data obtained from the actual weld joints in 9%Ni steel plate in order to assess a rational toughness requirement to the austenitic weld metal employed in the 9% Ni made LNG storage tanks. From this study it is concluded that fracture toughness of 75J is too conservative and 50J is adequate. Further some FEM analyses were performed to verify the validity of the weld surrounded by the large amount of heterogeneous base metal in the yield strength distribution.

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

ABSTRACT By using the six sets of interatomic potentials for face-centred cubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The simulations were performed at 100, 300 and 600 K, with a primary knock-on atom energy of 50 keV. The number of residual defects is not dependent on the SFE at all the temperatures. For clusters of self-interstitial atoms (SIAs), their clustering behaviour does not depend on the SFE, either. However, the ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature. Because most large vacancy clusters have stacking fault structures, they preferentially form at lower SFE; however, it is observed only at the lowest temperature, where the mean size increases with decreasing SFE. At higher temperatures, because of their extremely low number density, the vacancy clustering behaviour does not depend on the SFEs.

Critical Condition of the Branching Behaviour of Running Brittle Cracks in Steels

In this paper, using the devised under-matched welded joint to change the volume of high stress areas near the crack tip, the mechanism of crack propagation is investigated by experiments and the dynamic finite element method (FEM) analysis in which the rational shape of the crack front line are assumed. For evaluating the crack running behaviour, ESSO tests were performed under -100deg.C and several stress conditions and strain gauges and crack gauges were instrumented in measuring the crack propagation velocity which is used for input data of FEM analysis. The results of experiments show that the crack propagation velocity tends to be a little higher in the material with soft welded joint in which the expansion of high plastic strain region is significantly concentrated in the softer material and consequently the exceedingly-high stress region over 4-5 times σy0 (yield strength at ambient temperature and in static) is widely distributed than in the homogeneous material. Interestingly crack bifurcations were observed in both specimens at low crack velocity position (around 800 m/s), contrary to the findings of the elastic dynamic fracture mechanics. Further, the soft welded joint tends to branch in a shorter distance. This is also thought to be due to the high stress concentration in the vicinity of the crack tip in soft welded joint. The triaxiality situations were computed by FEM analysis and the result shows agreement with the above estimate.

Effect of specimen size, applied stress and temperature gradient on brittle crack arrest toughness test

Temperature gradient type ESSO test is one of the most popular test methods for evaluating the brittle crack arrest toughness,

Effect of Undermatched Weld on Deformation and Brittle Fracture Behaviors in High-Tensile Strength Steel Plate Welded Joint

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Investigation on Enhancement of Uniform Elongation in 780 MPa Class High Tensile Strength Steel Plate-Studies of Safety Against Fracture on 780 MPa Class High Tensile Strength Steel Plate after Prestrain (Report 2)-

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