Corrosion Rate Of Pipeline Steel Research Articles

The Influence of CaCO3 Scale Formation on AC Corrosion Rates of Pipeline Steel Under Cathodic Protection

In this paper, the influence of CaCO3 scale formation on the AC corrosion rate of pipeline steel under cathodic protection was investigated. The CaCO3 layer was deposited on X65 steel electrochemically and then studied in a soil simulant. A method for determining the fractional surface coverage of the scale based on either deposition current or electrochemical impedance spectroscopy data is presented. After the deposition process, samples were exposed to 3 V root mean square (RMS) AC potential at 60 Hz and varying degrees of cathodic protection at DC potentials of −770, −700, −650, and −600 mV vs. saturated calomel electrode. It was demonstrated that the scale acts as a simple barrier and the corrosion rate of steel, exposed at the base of pores in the scale, is equal to that of boldly exposed samples. These results are discussed in the light of the previously developed theoretical model for AC corrosion.

Corrosion Behavior of Pipeline Carbon Steel under Different Iron Oxide Deposits in the District Heating System

The corrosion behavior of pipeline steel covered by iron oxides (α-FeOOH; Fe3O4 and Fe2O3) was investigated in simulated district heating water. In potentiodynamic polarization tests; the corrosion rate of pipeline steel is increased under the iron oxide but the increaseing rate is different due to the differnet chemical reactions of the covered iron oxides. Pitting corrosion was only observed on the α-FeOOH-covered specimen; which is caused by the crevice corrosion under the α-FeOOH. From Mott-Schottky and X-ray diffraction results; the surface reaction and oxide layer were dependent on the kind of iron oxides. The iron oxides deposit increases the failure risk of the pipeline and localized corrosion can be occurred under the α-FeOOH-covered region of the pipeline. Thus, prevention methods for the iron oxide deposit in the district pipeline system such as filtering or periodic chemical cleaning are needed.

Experimental research on the corrosion of X series pipeline steels under alternating current interference

Abstract Many buried oil and gas pipelines are parallel to the high-voltage transmission lines and electrified railways in a long distance. Alternating current (AC) corrosion of these pipelines are very significant in such cases, and might lead to leakage even serious accidents. Laboratory experiment was carried out through weight-loss method in a simulated soil solution at various AC densities from 0 to 200 A/m2 and frequencies from 10 to 200 Hz. The results indicated that the corrosion rate increased with the increasing of AC current density. Furthermore, with the increase of AC interference frequency, the AC current involved in the electrode reaction process is decrescent, which caused a lower corrosion rate of pipeline steel. Morphology and corrosion product investigations explained that a better anti-corrosion behavior of X80 than that for X60 and X70 under AC interference. The investigation results are benefit to provide a new strategy to forecast and evaluate of the AC-induced corrosion, and design of the buried X series oil/gas pipelines.

Electrochemical studies of the galvanic coupling zinc/pipeline steel in the presence of an applied alternating current

The effects of alternating current on the galvanic coupling zinc/pipeline steel were investigated in 4 g/L Na2SO4 simulated backfill solution by weight‐loss measurements for 96 hr, electrochemical measurements, and surface examinations. Alternating current accelerates the dissolution of zinc significantly but reduces the corrosion rate of pipeline steel. Under an applied alternating current, zinc DC potential shifts negatively while the DC potential shift direction of pipeline steel is closely related to the value of alternating current density. When the alternating current density is low the DC potential shifts negatively. It, however, shifts positively under higher alternating current density. Besides, the coupling current increases with alternating current density.

Effect of soil particle size on the corrosion behavior of natural gas pipeline

In this study, the effect of soil particle size (0.1–0.25mm, 0.6–1.0mm) on the corrosion behavior of natural gas pipeline was investigated by electrochemical technology. The results indicated that the polarization resistance of pipeline steel decreased with decreasing particle size. For all polarization curves, the right shift of cathodic branch with decreasing particle size, suggests that the cathode oxygen reduction process is accelerated. The corrosion of steel is controlled by the process of cathode diffusion and oxygen reduction. This can be attributed to the effect of gas/liquid/solid three-phase boundary (TPB) zone on cathodic process of pipeline steel, and the corrosion rate is mainly determined by the cathodic reaction. The corrosion rate of pipeline steel increased with decreasing particle size.

Corrosion of X-65 Pipeline Steel Under a Simulated Cathodic Protection Shielding Coating Disbondment

Pipeline corrosion is a common problem for polyethylene (PE) tape-coated oil and gas transmission pipes buried under ground. It is often seen under cathodic protection (CP) shielding coating disbondments, where a wrinkle filled with ground water could be formed. This study investigates corrosion of X-65 pipeline steel under a simulated CP shielding coating disbondment with a gap size of 1 cm. Results showed that the corrosion rate of pipeline steel under the CP shielding coating disbondments is a function of carbon dioxide (CO2) and level of CP at the holiday of the coating disbondment, and could be significantly different to that in bulk environments.

A mechanistic model for pipeline steel corrosion in supercritical CO2–SO2–O2–H2O environments

A mechanistic model was established to predict uniform corrosion rate and investigate the corrosion mechanisms of pipeline steel in supercritical CO2–SO2–O2–H2O environments. A six-region division (SIWDES: Supercritical CO2, Interface, Water film, Deposition, Electrodic, and Solid) was applied to mathematically describe the model. The modified three-characteristic-parameter correlation model was used to calculate the ion activity coefficients, which calculates the activity coefficients of ions in thin water film with high ionic strength. The model can reasonably predict the corrosion rate of pipeline steel for the primary variables, determine the concentration distribution of each component in the water and product films, and also reflect the impact of corrosion product film on corrosion rate. A comparative analysis between the model and the experimental results showed that the model reasonably predicted the effects of the main factors on corrosion rate.

Modeling Pipeline Corrosion under a Disbonded Coating Under the Influence of Underneath Flow

Abstract Laboratory and field experience revealed an increased corrosion rate of pipeline steel under disbonded coatings when aerated water flows underneath. The quantitative effect of the flow vel...

Corrosion Characteristics of Rigid Polyurethane Thermally Insulated Pipeline with Insulation Defects

Abstract Electrochemical tests were conducted to study the external corrosion of a steel pipeline beneath the disbonded insulation with a holiday in synthetic groundwater. The corrosion rate of pipeline steel under the insulated condition was much lower than that under the uninsulated condition. The better corrosion property of the insulated steel was attributable to the formation of a protective rust layer under the insulation. This is mainly because the mass transfer or the thickness loss rate through the insulation was small compared to the convective mass transfer directly to the electrolyte without insulation. Breaks or holidays in insulation exposed the pipeline steel to possible galvanic corrosion. Galvanic corrosion occurred on the insulated and uninsulated steels. Galvanic corrosion at the cracked insulation developed because the uninsulated steel (cracked) was active to the insulated steel (crack-free) and galvanic attack is concentrated in a small cracked area by a large cathode (crack-free)/an...

Influence of Moisture on Corrosion of Pipeline Steel in Soils UsingIn SituImpedance Spectroscopy

Abstract The interrelationships between the corrosion rate of pipeline steel and soil parameters have been investigated under both controlled laboratory and natural outdoor conditions. Both defect-...