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Four soils were obtained from right of way (ROW) in South of Mexico, at 1.5 m depth close to pipelines. This work analyzed physicochemical effect of different types of Mexican clay soils in corrosion and stress corrosion cracking (SCC) behavior in contact with X60 and X65 steels. The parts with colonies of cracks were identified for emergencial replacement before the complete substitution scheduled for the near future. The lifetime expected for the pipeline was 30 years, and the old asphaltic coating was damaged in several points of the line, which is also a determinant factor for the occurrence of this type of failure.

The TGSCC occurs in near-neutral pH electrolytes, nucleating preferentially in external pits. The scanning electron microscopy analysis of colonies of cracks (circumferential and longitudinal) revealed that they were transgranular stress corrosion cracks (TGSCC), caused by soil. The toughness and tensile properties met the requirements of X65 and X70 grades. The microstructure and mechanical properties of the API 5L X65 steel, on which the pipe was fabricated, were characterized. In this work, longitudinal and circumferential colonies of cracks found in a 30 years old Brazilian gas pipeline were characterized. Stress corrosion cracking of gas pipelines is an important issue due to leak and explosion risks involved. Thousands of kilometers of gas pipelines are installed in different regions of the world. Gas pipelines are important and strategic systems for gas transportation across long distances.

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The model uses the analogy between the notch sensitivity behavior under fatigue and under EAC conditions, so it quantifies how the stress gradient around the notch tips affects the tolerance to mechanically short cracks that depart from there, considering the characteristics of the loading and of the notch geometry, as well as the basic material properties inside the given environment, expressed by its EAC resistances to crack initiation from a smooth surface This model can provide a powerful alternative design tool for the pass/nonpass criterion traditionally used to deal with such mechanical-chemical problems, since it properly considers and quantifies the stress analysis issues that affect them. Notch sensitivity effects under environmentally assisted cracking (EAC) conditions have been recently quantified considering the tolerance to short cracks that may start at their tips and become nonpropagating after growing for a while, a behavior that depends on the stress gradients ahead of the notch tips and on the basic material resistances to crack initiation and propagation inside an aggressive medium. The higher corrosion resistance of X60 steel is related to a more homogenous microstructure and higher content of elements, such as Ni and Cr, than those of X65 steel that decrease the corrosion rate. A highly corrosive soil, such as SV1, causes the formation of pits instead of cracks, which is attributed to the dissolution process however, lower SCC indexes were obtained for this system. SCC index obtained from SSRT indicates that X60 and X65 steels exhibited good resistance to SCC. After SSRT, the fracture surfaces were analyzed through scanning electron microscopy (SEM). SCC susceptibility was evaluated using slow strain rate tests (SSRT). Galvanic coupling between inclusions and the base metal and dissolution of the inclusions might have enhanced the nucleation of pits at these sites. Inclusions caused pitting in the gage section of X60 and X65 steels exposed to SV1 soil by anodic dissolution. Soils from SV1 and SV2 generated pitting, and soils from SO1 and SO2 produced general corrosion. Steels exposed to SV1 soil exhibited a higher corrosion rate related to a higher content of chlorides and acid pH than those seen in other soils, which resulted in the pitting of such steels.

Showed that soil with a higher index (SV1) has a higher corrosion rate.Įlectrochemical impedance spectroscopy (EIS) and polarization curves were performed and correlated to corrosion rate and SCC susceptibility of steels. Relationship with the corrosive tendency of soils, was estimated. Index (ratio between sand and silt + clay), which was seen to have a Observed that soil texture might be related to corrosivity. Physicochemical and textural analysis of soils was carried out andĬorrelated to SCC susceptibility and corrosion mechanism. SO2), and two others from the State of Veracruz (SV1 and SV2). Two soils were from the State of Oaxaca (SO1 and Four soils were obtainedįrom the right of way (ROW) land in Southern Mexico, at 1.5 m depthĬlose to pipelines. Mexican clay soils on corrosion and stress corrosion cracking (SCC)īehavior in contact with X60 and X65 steels. This work analyzed the physicochemical effect of different types of

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