A review on welding of high strength oil and gas pipeline steels

Pipeline failures in corrosive environments – A conceptual analysis of trends and effects

Stress Corrosion Cracking of Pipelines

This study focuses on the influence of reinforcements in microstructure, mechanical and tribological properties when compared to the base material (Al 7075). Boron carbide (B4C) and cow dung ash (CDA) were reinforcements by varying the weight percentage from 0 to 10 using two stage stir casting technique. Micro structural analysis and phase identification were investigated by optical microscope, SEM with EDX and XRD respectively. Mechanical and tribological testing was carried out and fracture mechanisms for tensile, impact and wear were analysed. Micro structural images reveal uniform distribution of reinforcements in matrix and XRD confirms the presence of reinforced B4C - CDA particles in the samples. It is concluded that the mechanical and tribological properties have increased while adding B4C - CDA reinforcements yet impact strength has slightly reduced. Dimples, transgranular cleavage facets, cracks and micro ploughing, micro cuttings are revealed from the fractured specimens of tensile, impact and wear respectively.

Studies on micro structural characteristics, mechanical and tribological behaviours of boron carbide and cow dung ash reinforced aluminium (Al 7075) hybrid metal matrix composite

Effect of heat treatment on H2S corrosion of a micro-alloyed C―Mn steel

The corrosion resistance of commercial aluminium alloy (2024) and binary Al–Cu
 x
 and Al–Mg
 x
 alloys reinforced with TiC particles using a pressureless infiltration method has been evaluated in 3.5% NaCl solution using potentiodynamic polarization curves and linear polarization resistance measurements. The TiC preforms were sintered at 1250, 1350 and 1450 °C and infiltrated in the range of 900–1200 °C under argon atmosphere. Some specimens were heat treated at 530 °C for 150 min, water quenched and subsequently artificially aged at 190 °C for 12 h in an argon atmosphere and naturally aged at room temperature for 96 h, respectively. The corrosion resistance of the composites was evaluated as a function of the addition of Cu and Mg into the aluminium. In all cases pitting corrosion was observed with or without additions of Cu or Mg, but these elements increased the anodic corrosion current. However, it was found that addition of TiC particles in the composite without heat treatment reduced the anodic current density and the number and size of pits in the Al-2024 alloy. When the heat treatment was applied to the composite, either artificially or naturally aged, the anodic current density of the Al-2024 alloy increased.

Corrosion behaviour of aluminium metal matrix composites reinforced with TiC processed by pressureless melt infiltration

The Stress Corrosion Cracking (SCC) is a local corrosion process which is characterized by the initiation and propagation of cracks. It takes place under the simultaneous action of sustained tensile stresses and specific corrosive environment on a susceptible material. The formation of SCC occurs below the yield strength of the material and typically below the design stress and fatigue limit of an engineering structure. Since the first discovery of SCC on the exterior surface of a buried high pressure natural gas transmission pipeline in 1965 (Leis & Eiber, 1997), SCC has continued to make a significant contribution to the number of leaks and ruptures in pipelines. Two forms of SCC can exist on buried steel pipelines (Beavers & Harle, 2001). The first discovered form of SCC propagates intergranularly and is associated with a concentrated alkaline electrolyte in contact with the steel surface, commonly called as high pH-SCC or classical SCC. A second form of SCC was discovered in Canada in the early 1980. This form of SCC propagates transgranularly and is associated with a dilute neutral pH electrolyte in contact with the steel surface, commonly called as low pH-SCC, non-classical, or near neutral pH-SCC. Currently, there are some mechanisms proposed to explain the SCC occurrence including the following: (1) a role for hydrogen in enhancing crack tip dissolution; (2) a possible synergistic growth by fatigue and corrosion. For high pH-SCC it is observed that the mechanism involves anodic dissolution for crack initiation and propagation. In contrast, for low pH-SCC is associated with the dissolution of the crack tip and sides, accompanied by the ingress of hydrogen in the steel. Steels with high tensile strength are more susceptible to SCC. Cracks propagate as a result of anodic dissolution in front of their tip in SCC process, due to the embrittlement of their tip by hydrogen based mechanism. It was revealed that cracking behavior of pipeline steel in the soil environment depends of the cathodic protection applied. Applying different potentials levels the dominance of SCC process changes. At relatively low potential, the steel cracking is based primarily on the anodic dissolution mechanism. When the applied potential increases negatively, hydrogen is involved in the cracking process, resulting in a transgranular cracking mode (Liu et al, 2008).

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Assessment of Stress Corrosion Cracking on Pipeline Steels Weldments Used in the Petroleum Industry by Slow Strain Rate Tests

Summary of the mechanical properties obtained from SSRT of X52 steel. Environment YS (MPa) RS (MPa) UTS (MPa) E (GPa) Strain (%) EL (mm) TF (h) RA(%) PE (%) Air 368 243 450 245 19.1 4.85 52.31 78.95 17NS4 pH 5 330 212 422 259 15.7 3.99 45.28 72.72 15NS4 pH 8 463 273 545 279 15.5 3.94 45.24 67.90 14NS4 pH 10 372 153 462 209 15.6 3.95 45.44 68.16 15 Table 4. SCC index obtained from mechanical properties of SSRT. Environment RA (%) RAR TF (h) TFR PE (%) PER ELR (mm) ELR Strain (%) SR Air 78.95 - 52.31 - 17 - 4.85 - 19.1 -NS4 pH 5 72.72 0.92 45.28 0.87 15 0.88 3.99 0.82 15.7 0.82NS4 pH 8 67.90 0.86 45.24 0.86 14 0.82 3.94 0.81 15.5 0.81NS4 pH 10 68.16 0.86 45.44 0.87 15 0.88 3.95 0.81 15.6 0.82 was not observed. However, a decreases in YS, UTS, EL and deformation was observed, which can be attributed to diffusion of hydrogen atoms into the steel generating hydrogen embrittlement. 3.4 Surface fracture analysis Figure 5 shows the SEM images of the fracture surfaces of the X52 pipeline steel after carried out the SSRT in air and in the synthetic soil solution (NS4 solution). Measurements of final diameter of fracture were carried out in order to calculate the reduction area (RA). The SSRT of the X52 steel in air presented a ductile fracture, and it is characterized by extensive plastic (permanent) deformation of the material (figure 5a). One mechanism of ductile fracture is known as microvoid coalescence

Electrochemical Noise for Detection of Stress Corrosion Cracking of Low Carbon Steel Exposed to Synthetic Soil Solution

One important challenge in the petroleum industry is reduce the problem produced by the corrosion of structures or pipeline steel caused by contact with the aggressive fluids, such as aqueous solution containing H2S or CO2. In this work, the corrosion of weldment of API X52 pipeline steel immersed in NACE solution saturated with H2S was studied. In the corrosion tests, the electrochemical techniques, polarisation curves and linear polarisation resistance were carried out in samples of API X52 pipeline steel focus in the three different zones of the weldment: heat affected zone, weld bead and base metal. In addition, a superficial analysis was made in order to identify the film of corrosion products. The temperature increment and the H2S dissolved in the NACE solution increase the corrosion rate of the three different zones. The heat affected zone was the more affected by the corrosion test and the phases mackinawite, troilite and pirrothite were identified in the film of corrosion products.

Corrosion kinetics of pipeline carbon steel weld immersed in aqueous solution containing H2S

The susceptibility of API X-60 and X-65 longitudinal weld beads to sulfide stress cracking (SSC) has been evaluated using slow strain rate tests (SSRT) in the NACE solution saturated with ...

M. Salazar

Papers

Corrosion behaviour of aluminium metal matrix composites reinforced with TiC processed by pressureless melt infiltration

Assessment of Stress Corrosion Cracking on Pipeline Steels Weldments Used in the Petroleum Industry by Slow Strain Rate Tests

Electrochemical Noise for Detection of Stress Corrosion Cracking of Low Carbon Steel Exposed to Synthetic Soil Solution

Corrosion kinetics of pipeline carbon steel weld immersed in aqueous solution containing H2S

Sulfide Stress Cracking Susceptibility of Welded X-60 and X-65 Pipeline Steels