Materials Science Forum Vol. 850

Abstract: Oil and gas long-distance pipelines which are buried under ground often have to be closely laid in the narrow area with the high voltage electric-power line. The earth electrode of the electric tower seriously impacts the cathodic protection system of the pipeline when it discharges electricity into the earth. Sometimes the cathodic protection system may even lose its efficacy and the pipe being corroded. Under this condition, fiber reinforced plastics (FRP) has been paid more and more attention as the alterative of the steel pipe because of its outstanding cathodic-resisting property. In this article, the property of FRP compared with the steel was analyzed. The advantages and shortcomings of FRP as the material of oil and gas long-distance pipeline were introduced. Furthermore the feasibility of FRP pipeline was discussed.

Abstract: The width of 36mm of inner surface layer was formed by Ni625 welding wires in the ends of glass-lined 20# metal pipe, and the metal tubes were welded. The microstructure and the distribution of the main alloying elements of the weld joints were analyzed by optical microscope (OM) and electron probe microscope analysis (EPMA). The mechanical property and nondestructive inspection tests of the welded joints were carried out. The results show that the welded joints were divided into three layers including root layer, transition layer and cap layer. The microstructure in root layer was characterized by the cellular-dendrite structure. The transition layer contained martensite and retained austenite. The capping layer included acicular ferrite and pearlite. The defect free joint was produced and performed well. The concentration of nickel and chromium element in weld root were higher than inner surface layer which proves that welding wire of transition layer protects the major alloying elements in welding root.

Abstract: Crack tip opening displacement (CTOD) tests were conducted on the weld and heat affected zone (HAZ) of L415MS/N08825 bimetallic composite pipe welded joint according to BS7448, ISO12135(2002) and ISO15653(2010) standards at room temperature. The fracture toughness of weld and HAZ were studied and analyzed. The fracture surface and inclusions were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS), respectively. The results showed that the average CTOD value of the weld was less than HAZ, CTOD values of HAZ exhibited larger discrete, which was mainly caused by Pop-in effect in P-V curve of HAZ samples. CTOD value of sample with Pop-in effect dropped several times than sample without Pop-in effect. The fracture surfaces of the weld and HAZ showed tough fracture to a certain extent, and the fracture surface of HAZ sample with Pop-in effect exhibited significant quasi-cleavage feature.

Abstract: In this paper, the effect of ferrous ion on the corrosion behavior of 410 martensitic stainless (410SS) steel was investigated by corrosion tests, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion tests were conducted in brine solution saturated with H₂S and two type of iron compounds (FeS and FeSO₄). The reults revealed that there exists apparent difference between piting resistence of FeSO₄ and FeS addition for 410SS. The corrosion rates of specimens in FeSO₄ solution was much higher than that of FeS, and the corrosion rate reached a maximum of 1.299 mm/year when the concentration was about 0.15 mol/L. The SEM results showed that without FeS (indissolvable) and FeSO₄, steel suffered slight corrosion, meanwhile several pittings appeared after 42 h. Compared with that of FeS, much more pittings grew on the specimens with FeSO₄. The corrosion product was mainly mackinawite.

Abstract: The microstructure and mechanical property of X90 parent material and weld were studied after the heat process of tempering (560°C) and quench (1000°C) + tempering (560°C), respectively. By the comparison of two different heat treatment processes, the effect of heat treatment for the microstructure and mechanical property of X90 parent material and weld was discussed. The results shown that the weld and heat-affected zone (HAZ) microstructure was improved after the heat process of quench (1000°C) + tempering (560°C), and the microstructure of HAZ was refined, which make the microstructure and mechanical property of X90 bend pipe parent and weld more similar, effectively. In addition, this paper also proved that the entire heating mode can effectively reduce the deterioration of microstructure and mechanical property caused by the bending process.