Effect of natural aging on the microstructural regions, mechanical properties, corrosion resistance and fracture in welded joints on API5L X52 steel pipeline

Abstract

A characterization study was done to analyze how microstructural regions affect the mechanical properties, corrosion and fractography of the Heat Affected Zone (HAZ), weld bead and base metal for pipe naturally aged for 21 years at 30 °C. Results showed that microstructures exhibited damage and consequently decrease in properties, resulting in over-aged due to service. SEM analysis showed that base metal presented coarse ferrite grain. Tensile test indicated that microstructures showed discontinuous yield. Higher tensile strength was obtained for weld bead, which exhibited a lower impact energy in comparison to that of HAZ and base metal associated with brittle fracture by trans-granular cleavage. The degradation of properties was associated with the coarsening of nano-carbides observed through TEM images analysis, which was confirmed by SEM fractography of tensile and impact fracture surfaces. The weld bead reached the largest void density and highest susceptibility to corrosion in H 2 S media when compared to those of the HAZ and base metal. RESUMEN:Efecto del envejecimiento natural sobre la microestructura, propiedades mecánicas, resistencia a corrosión y fractura en uniones soldadas de acero para tubería API5L X52. Se realizó un estudio de caracterización para analizar cómo la microestructura afecta a las propiedades mecánicas, corrosión y fractura de la zona afectada por calor (ZAC), soldadura y metal base para tubería envejecida naturalmente durante 21 años a 30 °C. Los resultados indicaron que las microestructuras presentaron daño y consecuentemente reducción en propiedades mecánicas, como consecuencia del envejecimiento por servicio. El estudio mediante MEB mostró que el metal base presenta grano ferrítico grueso. La prueba de tensión indicó que las microestructuras mostraron fluencia discontinua. La mayor resistencia a la tracción se presentó en la soldadura, la cual alcanzó menor energía de impacto en comparación con la ZAC y metal base asociado con fractura frágil por clivaje transgranular. La degradación de las propriedades está en relación con el engrosamiento de nanocarburos observados a través del análisis de imágenes por MET, lo que se confirmó mediante fractografía por MEB de superfícies de fractura bajo tensión e impacto. La soldadura alcanzó la mayor densidad de microhuecos y la mayor susceptibilidad a la corrosión en un medio conteniendo H 2 S que cuando se compara con la ZAC y metal base.

Numerical Analysis Of The Harmfulness Of The Fatigue-Corrosion Defect In A Metal Pipe Under Internal Pressure

“…To analyze the effect of corrosion on the harmfulness of cracks in pipes, the action of two fluids that have a corrosive effect on X52 steel pipes is studied in the present paper. The numerical model of the pipe is identical to the model used in a previous study led by authors [9][10][11][12][13][14][15][16][17][18][19][20][21]. This model is used in the current study with the aim of measuring the reduction in service life imposed by the action of each fluid.…”

“…The stress corrosion curve parameters are presented in Table 3 which provides information on corrosion in two different media. Several cases of cracks were studied in the previous study, in particular, those likely to exist in pipes welded longitudinally and located on the base material [9][10][11][12][13][14][15][16][17][18][19][20][21]. The results of this study showed that the most harmful type of crack is the longitudinal crack located in the inner surface of the pipe.…”

Fractographic Analysis of GTAW Robotic Welded Joints Fractured under Stress in Experimental HSLA Cr-Ni Steel

“…A study on tensile fracture in welded joints in API-5L-X52 line pipe steel, by means of an artificially aged double pass SAW process, showed the existence of micro-voids associated with micro-cavities present in the morphology of the ductile fracture, which was characterized with stress testing, microscopy and SEM [9]. In subsequent research on the aforementioned welded joints in API-5L-X52 pipes, the authors [10] used digital processing in fractographic images by segmentation and "Top-Hat" transform; finding more number of micro hollows in the ductile failure (equivalent to 2µm).…”

The Mechanical and Brittle Properties of Gas Pipeline in Service

“…The yield point, then, increases and reaches values close to the brit- * corresponding author; e-mail: maria.hagarova@tuke.sk † paper contributed to the 11th Polish-Japanese Joint Seminar on Micro and Nano Analysis, Gniew, Poland, September 11-14, 2016 tle strength. The notch sensitivity also increases and transition temperature of notch toughness shifts toward positive values [5][6][7].…”