Abstract

When designing systems for the transportation and distribution of gas, safety is one of the main issues to be considered. In order to minimize potential hazards, this subject is treated in international regulations. Manufacturing characteristics of gas pipes and their typical defects are described in the first part of this work. Safety concerns related to the presence of real and potential crack type defects in gas pipes are presented. An actual gas pipeline, which has been feeding natural gas to the city of Córdoba (Argentina) for more than forty years, is considered as a study case. In order to determine the properties of this gas pipeline, mechanical tests from material samples were carried out. The stress state associated with “plane” type defects is determined using a model that is based on the material toughness of the pipe, which is appropriate for studying the behavior of cracks. This model allows computing, depending on the dimensions of the pipe, the transition pressure which separates possible defects into two categories: defects which cause failure by breakage of the pipe and defects which only cause gas leaks. The pipe failure pressure for passing and non-passing defects can also be determined using this model. The system safety conditions are defined considering the size of the defects and the work pressure. The range of lengths of possible defects, the size of the defects that are critical, and the size of the defects which are tolerable for a fixed safety coefficient, are determined. Finally, the problem of determining in a quick way, the reduced pressure acceptable for the safe operation until repairs, of a system under the presence of a crack of “non-tolerable size”, is addressed.  

Abstract

When designing systems for the transportation and distribution of gas, safety is one of the main issues to be considered.  In order to minimize potential hazards, this subject is treated in international regulations. Safety concerns related to the presence of real and potential corrosion type defects in gas pipes are presented. An actual gas pipeline, which has been feeding natural gas to the city of Córdoba (Argentina) for more than forty years, is considered as a study case. In order to determine the properties of this gas pipeline, mechanical tests from material samples were carried out. The stress state associated with “volumetric” type defects is determined using a model that is based on the flux stress of the material of the pipe, which is appropriate for studying the behavior of corroded pipelines. This model allows computing, depending on the dimensions of the pipe and the length of the defect, the transition pressure which separates possible defects into two categories: those which cause failure by breakage of the pipe and those which only cause gas leaks. The pipe failure pressure for passing and non-passing defects can also be determined using this model. The system safety conditions are defined considering the size of the defects and the work pressure. The range of lengths of possible defects, the size of the defects that are critical, and the size of the defects which are tolerable for a fixed safety coefficient, are determined. Finally, the problem of determining in a quick way, the reduced pressure acceptable for the safe operation until repairs, of a system under the presence of flaws of “non-tolerable size”, is addressed.