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This paper describes how a utility became interested in acoustic emission testing for the survey inspection of its buried gas pipelines. Several weld failures emphasized the need to develop inspection techniques to monitor these pipelines in order to locate weld flaws in high-stress regions to permit prompt weld repairs and assure system integrity. It was found that a weld must have a certain metallurgical flaw and must be located in a high-stress region in order to precipitate an inservice oxyacetylene weld failure in a pipeline. It was found that metallurgical flaws in high-stress regions can be located by acoustic emission tests.
This paper describes the field development of the acoustic emission testing technique and the correlation of the field results with the laboratory results. It was found that the stress levels imposed by either internal pressurization or by external loading in the field tests are sufficient to cause critical flaws to emit and be located. Then replacement or reparation of the critical flaws located in this manner would restore the integrity of the pipeline. Discussed in the paper are the other nondestructive correlations such as radiography and correlations through tension tests, hydrostatic tests, bend tests, and fatigue tests.
acoustics, emission, pipelines, nondestructive tests, crack propagation, gas pipes, residual stress
Research engineer, Philadelphia Electric Co., Philadelphia, Pa.