Kyoung-Sik Bang

Optimization of GTAW Parameters for Horizontal Welding of a STS316L Pipe

In this study, it was tried to analyze the effects of welding parameters on the weld penetration and aspect ratio when a STS316L pipe was welded in a horizontal position by GTAW. Experiments were systematically designed using a L18 orthogonal array, and the effects of welding parameters were statistically analyzed by ANOVA(Analysis of Variance). The shielding gas type has the largest effect on both the penetration and aspect ratio. The welding current type and shielding gas flow rate have a little effect on the penetration, whereas the electrode tip angle has a little effect on the aspect ratio. When welded at a selected welding condition, which is composed of He shielding gas, pulse current of 300/45 A, electrode tip angle of 90o, and shielding gas flow rate of 30 l/min, the estimated interval at least 95 % confidence was 1.99 ± 0.18 mm for the penetration and 0.31 ± 0.04 for the aspect ratio. From the confirmation experiments, the average penetration and aspect ratio were well agreed with the estimation as 1.96 mm and 0.30, respectively. Additionally, the effects of the welding speed and welding current on the penetration and aspect ratio were experimented and analyzed by linear regression. The penetration was linearly increased with the decrease of the welding speed and with the increase of the welding current, but the aspect ratio showed a tendency to a little decrease with the increase of both the welding speed and current.

Evaluation of Cumulative Damage From Drop to Puncture Conditions

During safety assessments of transport packages, cumulative damages are naturally accumulated for assessments performed using physical tests specimens. However, the cumulative damages are not as easily accounted when assessments are by numerical simulations. While analysts are comfortable with simulating packages for single events, it is not yet common practice to incorporate the effect handed over from a former event to the next, in a series of sequential load events. Thus, many numerical simulations in SAR (Safety Analysis Report) represent just a single event in the series of sequential event comprising the required accident condition. These single event numerical simulations are then based on initial conditions different from the analogous physical test specimen, which could contribute to a growing disparity in results between assessments by physically testing compared to numerical simulation. The reason why analyses do not consider the cumulative damage is difficulties in delivering the final result of the previous analysis to the current analysis.The hypothetical accident conditions described in the IAEA regulations include drop, puncture, fire, and water immersion conditions, which should be sequentially simulated. There can be cumulative damage between two accident conditions, such as drop and puncture, puncture and fire, and so forth. In this study, as the first step to consider cumulative damage, an analysis technology to perform a puncture analysis incorporating the final response field from a prior drop analysis is proposed. The necessity and validity of the proposed analysis technology are evaluated by a comparison with the results obtained by performing each analysis independently.Copyright

Evaluation of Structural Integrity for a Dry Storage System With Spacer Disks in a Scale Model Drop Test

A new type of dry storage system has been developed in Korea. The dry storage cask under development consists of a cask body, a canister, and an in-canister structure. The in-canister structure is a complicated structure with many baskets and spacer disks. The spacer disks are originally designed to dissipate the heat from the baskets but they also influence the structural behavior. To evaluate a spacer disks’ influence on the overall structure behavior, especially on the characteristics when it is under a drop test, analyses and tests were conducted. Based on the analysis result, the sensor location and type is determined. Test result is utilized to validate the analysis result. After the drop tests, some strain gauges were detached from the original positions since the relative displacement between a basket and a disk removed the cable from the sensor. Thus, careful attention has to be paid when installing the sensors and cabling inside the in-canister structure. By means of these analyses and tests, the availability of the sensor and cabling arrangement is evaluated and a test procedure is established.Copyright