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이규영,배동호 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.12
In the area of heavy construction, welding processes are vital in the production and maintenance of pipelines and power plants. Welding processes happen to produce residual stresses and change the metal structure as a result of the large nonlinear thermal loading that is created by a moving heat source. The fusion welding process generates formidable welding residual stresses and metallurgical change, which increase the crack driving force and reduce the resistance to the brittle fracture as well as the environmental fracture. This is a serious problem with many alloys as well as the A106 Gr B steel pipe. This pipe that is used in petrochemical and heavy chemical plants either degrades due to corrosive environments, e.g., chlorides and sulfides, and/or become damaged during service due to the various corrosion damage mechanisms. Thus, in this study, after numerically and experimentally analyzing the welding residual stress of a multi-pass welded A106 Gr B steel pipe, the sulfide stress corrosion cracking (SSCC) characteristics were assessed in a 3.5 wt.% NaCl solution that was saturated with H₂S gas at room temperature on the basis of NACE TM 0177-90. The specimens used are of two kinds: un-notched and notched. Then, the sulfide corrosion fatigue (SCF) strength for the un-notched specimen was assessed below the low SSCC limit that was previously obtained from the SSCC tests for the notched specimen. From the results, in terms of the SSCC and SCF, all the specimens failed at the heat-affected zone, where a high welding residual stress is distributed. It was found that the low SSCC limit of un-notched specimens (σSSCCun-notched) was 46% (230 MPa) of the ultimate tensile strength (σU=502 MPa) of a multi-pass welded A106 Gr B steel pipe, and the notched specimens (σSSCCnotched) had 40% (200 MPa) of the ultimate tensile strength. Thus, it was determined that σSSCCun-notched was 13% lower than σSSCCnotched. Further, the sulfide corrosion fatigue limit (σSCFun-notched) was 32% (160 MPa) of the ultimate tensile strength of welded specimens. This σSCF un-notched was 20% lower than σSSCCnotched.
실측 둔화직선을 이용한 SB41 강의 J<SUB>IC</SUB> 평가에 관한 연구
허정원(C. W. Hue),오세욱(S. W. Oh),유재환(J. H. Yu),김득진(D. J. Kim),차귀준(G. J. Cha) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.2
The method of JSME S001-83 and ASTM E813-87 have been adapted for evaluation of the elastic-plastic fracture toughness J<SUB>IC</SUB> of SB41 steel. This SB41 steel have the characteristics of low-stength CT specimens. The test results obtained have been considered and compared on the basis of resulted data from two kinds of methods(JSME S001-83, ASTM E813-87) and two kinds of specimen configurations(smooth, side-grooved)<br/> On the basis of results from consideration and comparison, the difficulties for its application were presented in case when the standard ASTM E813-87 method was employed for the measurement of J<SUB>IC</SUB> in SB41 steel.<br/> A modified method was applied for measuring J<SUB>IC</SUB> in SB41 steel that it used the blunting line real-measured by experiment instead of the standard blunting line theoretically determined. and the result from that procedure was analyzed and the usefulness of that method was examined and considered.
STS304강의 순수 및 외팔보형 굽힘피로에 대한 파괴확률특성
노성국,정순억 경상대학교 해양산업연구소 2002 해양산업연구소보 Vol.15 No.-
Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frenquently. Therefore many people are suffering harm of property. The destruction cause of macaine components is almost accused by fatigue. This study is test for STS304 specimen by using pure and cantilever bending state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress the fatigue life of the test specimen was higher than low speed at high speed.
高溫下 304 스테인리스鋼의 크리프-疲勞相互作用下의 미소표면균열에 관한 파괴거동
서창민(Chang-Min Suh),이상돈(Sang-Don Lee),조일현(Il-Hyun Cho) 한국해양공학회 1988 韓國海洋工學會誌 Vol.2 No.2
This paper deals with the micro-surface-cracks behavior on the unnotched smooth specimens of Type 304 stainless steel at 593℃ in air under creep and creep-fatigue conditions that have 10 min and 1 min load holding times respectively. The behaviors of the micro-surface-cracks have been visualized by means of surface replica method and optical micro-photography. The quantitative characteristics of initiation, growth and coalescence of micro-surface-cracks have been investigated by observing and measuring the crack growth behaviors.<br/> Some of the important results are as follows:<br/> Main crack initiates at grain boundary in the early stage(10 to 20%) of its life time and grows through coalescence and finally leads to fracture. The distribution of micro-surface-crack length, 2a, can be plotted against the composite Weibull distribution. The growth rate of the main crack can be plotted against the stress intensity factor, crack tip opening displacement and J integral.