PROTECTION OF PIPELINE FOR PUMPING HYDROGEN-CONTAINING GAS UNDER PRESSURE AGAINST LOW-TEMPERATURE HYDROGEN CORROSION

One of the causes of pipeline corrosion and a way to solve it are considered

Criteria of Material Failure in Relation to Hydrogen Saturation

A steadily rising interest which specialists in various fields show towards the problem of hydrogen affecting metallic materials and causing their failure is connected to all-increasing requirements set on the durability of machines and equipment in operation. Metallic structures are most often surrounded by such environment which contains hydrogenous components or hydrogen itself (in chemical industry, power engineering, etc). And it leads to various types of degradation in metals (hydrogen embrittlement, hydrogen corrosion, and so on), which, in its turn, could cause catastrophic results. Ultimate strength is considered to be a representative parameter of the process of hydrogen degradation in steels. The authors cite the results of testing conducted on hydrogen-saturated specimens made of A516-55 steel which register a significant decrease in the ultimate strength. It is proposed to use a diagram which describes a fall in metal strength and transition of structural materials into their brittle states following an increase in hydrogen concentration. Discussion is made on criteria for hydrogen-saturated materials of metallic structures failing when a momentary overload occurs under default working conditions.

Study of the effect of tensile stresses on hydrogen absorption upon cathodic protection of steel in sea water

When using cathodic protection of steel in sea water, hydrogen can be accumulated on the cathode surface and penetrate deep into the metal. This rather dangerous phenomenon of hydrogen corrosion can lead to hydrogen embrittlement, i.e., to destruction of the metal. We present the results of studying the impact of the temperature and external tensile stresses on the hydrogenation of cathodically protected steel in calm and mobile Baltic sea water. Dependence of the inhibitory hydrogenation on the temperature and applied load under the action of benzenesulfapyridine chloride as an inhibitor was analyzed. An MIP-102 machine (wire samples) and special equipment (half-ring and plate lamellar samples) were used to provide smooth control of the applied load set by the deflection and controlled by dynamometers (lamellar samples were tested under constant deformation). When studying the effect of temperature on steel hydrogenation, the working cell was thermostatically controlled. The wire and plate samples were polarized for 96 h, and half-ring samples for 1 h. The potential was measured with respect to the silver chloride reference electrode. The layered distribution of absorbed hydrogen in the metal was determined using anodic dissolution. It is shown that external tensile stresses increase the hydrogen content in the surface layers of steel. Hydrogen absorbed by a metal changes the potential of the steel surface (the more absorbed hydrogen, the stronger change). It is also shown that hydrogen is absorbed by the metal more actively in moving seawater than in calm water, and an increase in the load contributes to an increase in hydrogen content in the metal both in calm and mobile seawater. However, the load did not affect the hydrogen absorption with the inhibitor present, thus providing reduction of the hydrogen content in the metal under loading.

Effect of Hydrogen and Absence of Passive Layer on Corrosive Properties of Aluminum Alloys

This paper reports the results of research on the effect of hydrogen permeation and the absence of passive layers on the variations in the corrosive properties of aluminum alloys. The study demonstrated that such variations contribute to the deterioration of corrosive properties, which in turn contributes to shortening the reliability time associated with the operation of aluminum alloy structures. The analysis involved structural aluminum alloys: EN AW-1050A, EN AW-5754, and EN AW-6060. It was demonstrated that the absorption of hydrogen by the analyzed alloys led to the shift of the electrode potential to the negative side. The built hydrogen corrosion cells demonstrate in each case the formation of electromotive force (EMF) cells. The initial EMF value of the cell and its duration depends on the duration of hydrogenation. As a result of removing the passive layers, the electrode potential also changes to the negative side. Following the removal of the passive layer from one of the electrodes, the cells also generated a galvanic (metal) cell. The duration of such a cell is equivalent to the time of restoration of the passive layer. The formation of such hydrogen and metal galvanic cells changes the electrochemical properties of aluminum alloys, therefore deteriorates the corrosive properties of aluminum alloys.

Investigation of the Hydrogen Stratification of the Metal of the Active Gas Pipeline

One of the most common types of metal destruction in the oil and gas industry is hydrogen embrittlement. Hydrogen corrosion is a complex of negative effects of hydrogen on steel, leading to the destruction of metal structures. Hydrogen passes through a defect-free metal, without lingering in it. In the presence of defects, hydrogen is retained in the metal forming a brittle solid solution, metal stratification along the segregation streamer, blistering. Studies of the metal of a gas pipeline made of steel 09G2S are presented in the article. The sample was selected from the local zone of destruction in the condensate collector, the metal of the pipe had typical for hydrogen corrosion stratifications. The scope of the study was identification of the most dangerous part of hydrogen corrosion on the sample taken from the local zone of destruction. Studies on the chemical composition and mechanical properties of 09G2S steel were also carried out. Stress-related characteristics of the metal microstructure of the failed gas pipeline were obtained and the character of the destruction progress was revealed. The presence of sulfides cluster in the metal of studied pipe was determined applying metallographic method for determining nonmetallic inclusions.