Cyclic pressure fatigue life of pipelines with plain dents, dents with gouges, and dents with welds

Technical Report · Wed Jun 01 04:00:00 EDT 1994

OSTI ID:10169583

Fowler, J R; Alexander, C R; Kovach, P J; Connelly, L M ^[1]

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1. Stress Engineering Services, Inc., Houston, TX (United States)

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 inch and several 12 inch 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 unless the cyclic pressure service is very severe. 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.

• Research Organization: American Gas Association, Inc., Arlington, VA (United States); Stress Engineering Services, Inc., Houston, TX (United States)
• Sponsoring Organization: American Gas Association, Inc., Arlington, VA (United States)
• OSTI ID: 10169583
• Report Number(s): AGA--94015627; ON: UN94015627
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
022000
03 NATURAL GAS
032000
36 MATERIALS SCIENCE
360103
DEFORMATION
DIMENSIONS
EXPERIMENTAL DATA
FATIGUE
MATERIALS TESTING
MECHANICAL PROPERTIES
NATURAL GAS
PETROLEUM
PIPELINES
PRESSURIZATION
SERVICE LIFE
STRESS ANALYSIS
THICKNESS
TRANSPORT
TRANSPORT, HANDLING, AND STORAGE
WELDED JOINTS