Corrosion Behavior Of Heat-affected Zone X90 Pipeline Steel In Acidic Medium

In the process of oil and gas storage and transportation,the production of pipeline steel,pipe network,and maintenance all require welding technology,so the quality of welded joints will directly affect the safety of oil and gas storage and transportation pipelines.With the improvement of the strength grade of pipeline steel,the research on its mechanical properties,toughness,etc.has been deepened,but the research on the corrosion-related properties of the welded heat affected zone is less and less comprehensive.Therefore,it is particularly important to fully study the corrosion performance of the high-grade pipeline heat affected zone.In this paper,different regions of the X90 pipeline steel heat affected zone were obtained by using a Gleeble 3500 thermal/force simulation machine.The corrosion characteristics of the X90 pipeline steel in the heat affected zone were studied by analyzing the microstructure,corrosion product composition,structure and morphology,and used.Electrochemical analysis technique explores the electrochemical corrosion behavior of different areas in heat affected zone in acidic media.Through the analysis of metallographic structure and product film morphology,it can be found that during the short-term etching process,the difference in metallographic structure is the key to the final degree of corrosion.The grain boundary area in the coarse-grained region and the critical coarse-grained region account for a relatively small amount,etching Corrosion resistance is best during the process;the corrosion protection film properties have a great influence on the corrosion characteristics at the later stage of the etching process.The X90pipeline steel base material and the critical region undergo grain refinement and the resulting corrosion product film is more etched than other structures.Solid and dense,the relative corrosion resistance is improved,and the product film in the coarse-grained region and the critical coarse-grained region has more microscopic defects,and the corrosion resistance decreases at the later stage of etching.The results of electrochemical experiments show that under the experimental conditions,the anodic reaction is controlled by activation,Tafel slope b_c>b_a,so the electrode reaction is controlled by the cathode.The Nyquist profile of heat-affected zone in X90 pipeline steel is divided into two cases.In the first case,the low-frequency zone is characterized by inductive resistance.At this time,the concentration of H~+or Cl~-in the solution is high,and the surface of the microstructure in the heat-affected zone is active and dissolved.In the state,there is no product precipitation.At this time,the degree of corrosion in the coarse-grained regions of the critical grains is the most serious.In the second case,the impedance spectrum shows only a single capacitive reactance characteristic.At this time,the concentration of H~+or Cl~-in the solution is low,reflecting the information generated on the corrosion product layer on the electrode surface.At this time,the coarse grained coarse grain region and the critical coarse grain region are resistant to poor corrosion.In this paper,the relationship between the organizational differences and the morphology and electrochemical characteristics of the product films is studied to provide theoretical guidance for the better production of X90 pipeline steel.It has certain reference value for the study of corrosion behavior of other different organizations.