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Title: Recent Research On Flaw Behavior During Hydrostatic Testing
Author: J. F. Kiefner, W. A. Maxey, R. J. Eiber, And A. R. Duffy Battelle Memorial Institute
Source: American Gas Association 1970
Year Published: 1970
Abstract: CONCERNING the subject of hydrostatic * testing, a vast amount of research and field experience has established firmly the immensely beneficial results that accrue from a hydrostatic proof test. Research in this field has been sponsored by the Pipeline Research Committee (Project NG-18) for a number of years. Summaries of this experience have been presented at prior Transmission Conferences in 1966(1) and 1968(2), and detailed publications dealing with the benefits of proof testing in pipelines(3) and in other types of structures(4,5,6) have been published. The studies presented in these references clearly have set forth by means of theory and experiment the following concepts wherein lies the value of proof testing. These are that hydrostatic proof testing removes defects the higher the test pressure, the smaller the remaining defects, and thus the testing of a pipeline (or other structure) to a stress level in excess of its operating stress level will remove defects which otherwise might fail when the structure is placed in service. None of this is new to those already familiar with hydrostatic testing. None of these concepts has been altered materially by subsequent findings. Yet one particular phenomenon which has been observed on occasion during hydrostatic tests(7) and which tends to be somewhat unsettling is that of a pressure reversal. the situation in which a defect survives a given test pressure level only to fail upon subsequent pressurization at a level below that of the previous test. It, is the current research of the phenomenon of pressure reversals and the implications with regard to hydrostatic tests that constitute the principal topics of this presentation. To provide background material with respect to pressure reversals, mathematical models of the behavior of defects in presstirized line pipe materials and the time-dependent nature of defect behavior are discussed. Then experimental findings concerning the nature of pressure image omitted reversals are presented. From these some logical conclusions about the nature of reversals can be drawn.

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