• 제목/요약/키워드: corrosion fatigue crack

Search Result 160, Processing Time 0.024 seconds

Failure Analysis of Stress Reliever in Heat-Transport Pipe of District Heating System

  • Cho, Jeongmin;Chae, Hobyung;Kim, Heesan;Kim, Jung-Gu;Kim, Woo Cheol;Lee, Soo Yeol
    • Corrosion Science and Technology
    • /
    • v.21 no.4
    • /
    • pp.243-249
    • /
    • 2022
  • The objective of the present study was to perform failure analysis of double-layered bellow (expansion joint), a core part of stress reliever, used to relieve axial stresses induced by thermal expansion of heat-transport pipes in a district heating system. The bellow underwent tensile or compressive stresses due to its structure in terms of position. A leaked position sufferred a fatigue with a tensile component for decades. A cracked bellow contained a higher fraction of martensitic phase because of manufacturing and usage histories, which induced more brittleness on the component. Inclusions in the inner layer of the bellow acted as a site of stress concentration, from which cracks initiated and then propagated along the hoop direction from the inner surface of the inner layer under fatigue loading conditions. As the crack reached critical thickness, the crack propagated to the outer surface at a higher rate, resulting in leakage of the stress reliever.

Prediction of stress intensity factor range for API 5L grade X65 steel by using GPR and MPMR

  • Murthy, A. Ramachandra;Vishnuvardhan, S.;Saravanan, M.;Gandhi, P.
    • Structural Engineering and Mechanics
    • /
    • v.81 no.5
    • /
    • pp.565-574
    • /
    • 2022
  • The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

Prediction of Remaining Life Time and Determination of Inspection Cycle Considering Critical Crack in Tension Bar of Continuous Ship Unloader (연속식 하역기 텐션바의 임계 균열을 고려한 잔존수명 예측 및 검사 주기 선정)

  • Park, S.;Chung, J.Y.;Song, J.I.;Kim, D.J.;Seok, Chang Sung
    • Journal of the Korean Society of Safety
    • /
    • v.33 no.6
    • /
    • pp.1-7
    • /
    • 2018
  • The Continuous Ship Unloader (CSU) is an equipment that unloads freight from the ship docked in the port to the land. And the design target life time is designed to be 30 to 50 years, and it is classified as a semi-permanent large facility. However, cracks may occur due to structural defects, abnormal loads, and corrosion, and fatigue failure may occur before the design life is reached. In this study, we predicted the remaining life time of the main component of the CSU considering crack. And also proposed inspection cycle for maintenance of CSU based on the results of the remaining life time prediction. For this purpose, the structure, operational stresses of the CSU were analyzed and main members were selected. And tensile tests and fatigue crack propagation tests were performed with SM490YA and SM570TMC, which are used as main materials for CSU.

A Study on the Fatigue Crack Growth Under Variable Loading of Titanium Alloy (티탄합금의 변동하중하의 피로균열진전거동)

  • Lee, Jong-Hyung;Lee, Sang-Young;Yi, Chang-Heon;Kim, Yun-Gon;Lim, Chun-Kyoo;Lee, Chun-Kon;Kwon, Yung-Shin
    • Journal of the Korean Society of Industry Convergence
    • /
    • v.10 no.4
    • /
    • pp.201-206
    • /
    • 2007
  • Most of the fatigue fractures of various machine structures start at discontinuities or small defects. In this study property of crack growth of titanium alloy was also analyzed to investigate the difference compared with the carbon steel. Titanium alloy has very high specific strength, and the material is widely utilized in advanced engineering fields such as aerospace, atomic energy and ocean development because of its excellence in corrosion and heat resistance. Generally the machine structures experience irregular loadings rather than periodic forces. The prediction of the fatigue life therefore has been analyzed to provide fundamentals of the design and estimation of the machine structures under irregular loading conditions.

  • PDF

A Study on Influences of Crack Morphology Variables (균열형상변수의 영향 고찰)

  • Park, Won-Bae;Lee, Young-Shin
    • Proceedings of the KSME Conference
    • /
    • 2004.04a
    • /
    • pp.324-329
    • /
    • 2004
  • In this study, an application of crack morphology variables in the Leak-Before-Break(LBB) evaluation for nuclear piping systems is investigated, including influences on the leakage crack size and crack instability loads. The crack surface roughness and the number of flow turns as a function of the crack opening displacement are applied to LBB evaluations for KSNP pressurizer surge line, for which fatigue and stress corrosion cracking are considered as failure mechanisms. As a result, there would be a significant impact on safety margins to acceptance criteria for the surge line if crack morphology variables are applied additionally to the current regulatory guide without re-analyses for justification of safety factors being applied on the leakage crack size and piping loads for evaluations.

  • PDF

A Study on the Fatigue Crack Growth Characteristics of the Welded Part According to the Welding Method of Ship Structural Steel (선체구조용강의 용접방법에 따른 용접부의 피로균열전파특성 연구)

  • Park, Kyeong-Dong;Ki, Woo-Tae;Lee, Ju-Yeong
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.31 no.4
    • /
    • pp.385-393
    • /
    • 2007
  • The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.

A Study on the Fatigue Crack Grouth Charactionistic of carbon Steel in High Temperature Environment (고온환경하에서 탄소강의 피로균열진전 특성)

  • Lee, Jong-Hyung;Choi, Seong-Dae;Yang, Seong-Hyeon;Kim, Young-Moon
    • Journal of the Korean Society of Industry Convergence
    • /
    • v.7 no.4
    • /
    • pp.399-405
    • /
    • 2004
  • Currently, the use of carbon steel in a high temperature environment, such atomic reactor, increases. Test piece was heated in electric furnace and the prescribed temperature was controlled within ${\pm}1^{\circ}C$. Debris that falls apart from cracked section due to friction is accumulated inside. Then, as it causes fretting corrosion (formation of oxide layer), it contributes to crack closure.

  • PDF

A study on fatigue properties of GFRP in synthetic sea water (인공해수중 GFRP의 피로특성에 관한 연구)

  • 김연직;임재규
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.17 no.6
    • /
    • pp.1351-1360
    • /
    • 1993
  • The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.

Study on the Corrosion Charactristics and its Corrosion Protection of Steel Fishing Banks (강제어촌의 부식특성과 그 방식에 관한 연구)

  • Lim, Uh-Joh;Lee, Jong-Rark
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.28 no.2
    • /
    • pp.216-227
    • /
    • 1992
  • The corrosion rate, behavior of corrosion fatigue and characteristic of cathodic protection for SB41 were investigated by corrosion and corrosion control tests in seawater at laboratory and coast. The main result obtained are as the following; 1) The corrosion rate of base metal (BM) is about 28-37 mg/dm super(2) day in seawater of coast. 2) The correlation between the stress intensity factor range $\Delta$K and crack propagation rate da/dN for weldment follows paris' rule in seawater : da/dN=C($\Delta$K) super(m) where m is the slope of the correlation, and is 2.02 for BM and 1.75 for heat affected zone (HAZ) respectively. 3) The corrosion sensitivity of HAZ is more sensitive than that of BM under the low region of $\Delta$K. 4) With increase of bared surace area of cathode, cathodic protection potential is increased sharply.

  • PDF

Development of Assessment System for Pipeline Integrity (매설배관의 건전성 평가 시스템 개발)

  • 이억섭;윤해룡
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.20 no.8
    • /
    • pp.158-165
    • /
    • 2003
  • The object of this work is to develop an assessment system for pipeline integrity. The internal algorithm and the database of the system are described in this paper. The system consists of four module applications; the effect of corrosion in pipeline, crack, SCC (stress corrosion cracking) and fatigue module. The database of the system is separated to mainly four parts; geometry of pipeline, material properties, boundary condition and general properties. This system may give a guideline for maintenance and modifications.