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Research Papers: Design and Analysis

Study on the Effects of Switching Temperature on the Thermal Fatigue Life of the Shell-to-Skirt Junction of Coke Drum

[+] Author and Article Information
Masaaki Oka

Department of Mechanical Systems of Engineering,  Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan;  S. H. I Examination and Inspection, Ltd., 1501 Imazaike, Saijo, Ehime 799-1393, Japan

Himsar Ambarita, Masashi Daimaruya, Hiroyuki Fujiki

Department of Mechanical Systems of Engineering,  Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan; Faculty of Engineering, Mechanical Engineering Department,  Sumatera Utara University, Jl. Almamater 20155 Medan, Indonesia

J. Pressure Vessel Technol 133(6), 061210 (Oct 31, 2011) (11 pages) doi:10.1115/1.4004564 History: Received May 04, 2010; Accepted March 29, 2011; Published October 31, 2011; Online October 31, 2011

In spite of the fact that coke drums are subjected to cyclic thermal and mechanical loads, generally, they are not designed for cyclic loads. Thus, their operational life is much shorter than other pressure equipment in refineries. Due to information developed from surveys, it was determined that the major typical location of failure due to thermal fatigue in coke drums is the shell-to-skirt junction area. This paper focuses on temperature and stress characteristics and also the thermal fatigue life of the junction area. The main objective of this paper was to explore effect of the switching temperature on thermal fatigue life of the junction area. Four coke drums, currently in service have been considered in the analyses, named drums A, B, C, and D, identical in dimensions and with an operating cycle period of 48 h. Operational temperatures and strains have been measured and collected every minute. The number of measured cycles of coke drum A, B, C, and D were 52, 53, 53, and 54 cycles, respectively. Thus, a total of 212 cycles have been analyzed. The operational temperatures and strains were examined. Finite Element Method (FEM) analyses have been performed on the selected cycles in order to find the most severe location in the junction area. The strain history and FEM results were used to assess thermal fatigue life. The thermal fatigue lives were calculated based on low cycle fatigue properties using engineering steels for high temperature components issued by National Institute for Materials Sciences (NIMS) in Japan. The number of cycle to fracture versus switching temperature for the coke drums was then plotted. The curve best fitting criteria was then used to develop an equation relating the number of cycle to fracture as a function of switching temperature. The results show that the switching temperature strongly affects the number of cycle to fracture. These results can be used to provide the necessary information to operate coke drums safely in order to extend their useful lives.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Dimensions of the considered coke drums and measured locations

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Figure 2

Typical operational temperatures at the area shell-to-skirt junction of coke drum

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Figure 3

Typical temperatures variations in hoop directions for one cycle

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Figure 4

Typical temperatures at inner surfaces of the heat box and upper part of the skirt for one cycle

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Figure 5

Typical axial and hoop strains at the shell-to-skirt junction area

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Figure 6

Effects of the different injection time on maximum axial strains

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Figure 7

Maximum and minimum strains at location T5 for all coke drums

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Figure 8

FEM model and structural boundary conditions

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Figure 9

Typical measured and numerical axial strains comparison

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Figure 10

Typical axial strain distributions in the junction area in the preheating stage

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Figure 11

Numerical axial strains history for one cycle at some locations

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Figure 12

Comparison of axial strains at inner and outer surface of the upper part of the skirt

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Figure 13

Maximum and minimum strains at location 5i for all coke drums

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Figure 14

Effect of the switching temperature on thermal fatigue life

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