THE GENESIS OF BUNDLES IN METAL PIPES: INFLUENCE ON DANGER OF THESE DEFECTS AND METHODS OF IDENTIFICATION

Abstract

Background For the rational planning and execution of repair work, it is accepted to be guided by the principle of objects servicing according to their technical condition. This principle has been used in the operation of oil and gas pipelines, however, an analysis of the approaches implemented in this case shows that it is often only formally observed. It can be clearly seen in the example of the bundles of metal pipes. Such defects are fairly common, but the existing standards for assessing the quality of pipes, in fact, do not recognize them as representing a real threat to the carrying capacity of the pipeline, at least if the stratification is flat. An analysis of existing studies of the genesis of the formation of metal bundles shows that at present it is customary to distinguish two types of similar defects: metallurgical and hydrogen. To extend these ideas, an assumption was made about the effect on the formation of stratification of the aging process of the metal. From a theoretical point of view, this is justified by the fact that aging, characterized by the segregation of carbides along grain boundaries, leads to metal embrittlement, which increases the likelihood of stratification. Aims and Objectives Establishing the causes of bundles formation and their effect on the risk of these defects. Methods Optical (microscope NIKON MA200) and electron microscope (Jeol JEM-200CX microscope) microscopy of various metal zones, standard mechanical tests of the templates being studied (InstronSI-1M coper, SHIMADZU EHF-EV200K2-040-1A X-ray spectroscopy of splitting zones (spectrometer JEOLJPS-9010MX). Results The article presents the results of complex experimental researches of pipe fragments with bundles. It is established that besides to the known types of bundles, caused by metallurgical liquation and hydrogen embrittlement, there is another one - caused by the aging process in metal, which, as the hydrogen type of bundles, leads to drop the performance properties of metal in the defective zone. Also was evaluated the possibility to identify of different types of bundles by non-destructive methods.