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PRCI PR-201-9324/201-927
- Cyclic Pressure Fatigue Life of Pipelines with Plain Dents, Dents with Gouges, and Dents with Welds (Volume A & B)
- Report / Survey by Pipeline Research Council International, 06/01/1994
- Publisher: PRCI
$375.00$749.00
L51705e
Stress Engineering Services, Inc.
Research has been conducted to study the effects of dents, gouges, and weld seams on pipelines under cyclic internal pressure loading. The work associated with this project has involved both experimental and finite element analysis on pipes with D/t ratios from 19 to 94 experimentally and 18 to 100 theoretically. In support of this research, operators were surveyed regarding the expected dent shapes and failures that had occurred as a result of pipeline dents. The experimental portion of the work involved pipes (one 24" and several 12" NPS pipes) with controlled dents which were combined with welds and gouges. All specimens were subjected to cyclic internal pressures to study behavior in terms of fatigue. Elastic and plastic finite element analyses were conducted to determine stress concentration factors due to dents so that a fatigue analysis could be performed.
Both the experimental and theoretical research indicated that plain smooth dents with depths less than 5% of the diameter should not be a problem (regardless of the D/t ratio) unless the cyclic pressure service is very severe. Experimental results demonstrated that gouge depth has a significant impact on fatigue life. Unground gouges whose depth is more than 10% of the wall cannot be counted on to have any fatigue life. The process of grinding out the gouges was found to be an excellent method of repair, even when considering gouge depths as large as 15% of the pipe wall thickness. The position of the dents relative to the longitudinal welds was not found to be a determining factor when considering reduction in fatigue life; however, dents which were placed on girth welds had considerably shorter lives than dents which were off of these welds. Classification of the gouge depths in terms of wall thickness (d/t) was found to be the most effective means for categorizing these types of defects. An analytical procedure was developed for predicting fatigue life of a pipe with plain dents subjected to cyclic pressure loading. These results were compared to experimentally obtained values.
Stress Engineering Services, Inc.
Research has been conducted to study the effects of dents, gouges, and weld seams on pipelines under cyclic internal pressure loading. The work associated with this project has involved both experimental and finite element analysis on pipes with D/t ratios from 19 to 94 experimentally and 18 to 100 theoretically. In support of this research, operators were surveyed regarding the expected dent shapes and failures that had occurred as a result of pipeline dents. The experimental portion of the work involved pipes (one 24" and several 12" NPS pipes) with controlled dents which were combined with welds and gouges. All specimens were subjected to cyclic internal pressures to study behavior in terms of fatigue. Elastic and plastic finite element analyses were conducted to determine stress concentration factors due to dents so that a fatigue analysis could be performed.
Both the experimental and theoretical research indicated that plain smooth dents with depths less than 5% of the diameter should not be a problem (regardless of the D/t ratio) unless the cyclic pressure service is very severe. Experimental results demonstrated that gouge depth has a significant impact on fatigue life. Unground gouges whose depth is more than 10% of the wall cannot be counted on to have any fatigue life. The process of grinding out the gouges was found to be an excellent method of repair, even when considering gouge depths as large as 15% of the pipe wall thickness. The position of the dents relative to the longitudinal welds was not found to be a determining factor when considering reduction in fatigue life; however, dents which were placed on girth welds had considerably shorter lives than dents which were off of these welds. Classification of the gouge depths in terms of wall thickness (d/t) was found to be the most effective means for categorizing these types of defects. An analytical procedure was developed for predicting fatigue life of a pipe with plain dents subjected to cyclic pressure loading. These results were compared to experimentally obtained values.
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