In this paper, a ring form electronic resistance (ER) sensor system was developed for the study of under-deposit corrosion (UDC) caused by mineral deposit in pipeline conditions. The corrosion status of different locations along the pipeline circle direction and the galvanic current between the deposit-covered area and the bare steel area were monitored by the conjunction of the ER method and electrochemical noise technique. The performance of inhibitor ethylene diamine tetra methylene phosphonic acid sodium (EDTMPS) on UDC was studied by both the electrochemical method and the ring form ER sensor system. The measurement results demonstrated that the inhomogeneous distribution of the rust layer will cause heterogeneous corrosion patterns in the pipeline. Though EDTMPS showed an excellent inhibition effect for the corrosion of both deposit-covered steel and bare steel in electrochemical tests, it failed for the inhibition of UDC in the pipeline working conditions and serious localised corrosion beneath the...

The monitoring of galvanic corrosion behaviour caused by mineral deposit in pipeline working conditions using ring form electronic resistance sensor system

Purpose




In this study the aim was to investigate under-deposit corrosion (UDC) behavior and the action effects of amino trimethylene phosphonic acid (ATMP) in the oxygen-contained solution.




Design/methodology/approach




Electrochemical methods and wire beam electrode techniques were used for the study of ATMP action effect for X65 steel under silica sand and CaCO3 particle deposit. Electronic coupon technique was used for the study of galvanic effect caused by the deposits and the action effect of ATMP.




Findings




ATMP would cause localized corrosion for the silica sand-covered steel. However, it could inhibit the localized corrosion of the steel beneath CaCO3 particle deposit. Galvanic effect test showed that the galvanic effect caused by the deposits was an important factor for the acceleration of UDC. ATMP had an obvious promotion effect for the galvanic current between bare coupon and silica sand covered coupon and different degrees of localized corrosion were observed beneath both deposits.




Originality/value




The authors believe that the paper may be of particular interest to the readers of the journal as the measurement methods for the UDC of X65 pipeline steel. The experiment they did in the laboratory found that the inhibitor ATMP has a good inhibition effect for bare steel, but it would accelerate the UDC. Different kinds of deposits would have different influences for the UDC behavior with inhibitor added.

Experimental study on under-deposit corrosion and its inhibition using electrochemical methods and electronic coupon technique

This paper investigated the effect of additional sulfide and thiosulfate on Q235 carbon steel corrosion in alkaline solutions. Weight loss method, scanning electron microscopy (SEM) equipped with EDS, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were used in this study to show the corrosion behavior and electrochemistry of Q235 carbon steel. Results indicate that the synergistic corrosion rate of Q235 carbon steel in alkaline solution containing sulfide and thiosulfate is larger than that of sulfide and thiosulfate alone, which could be due to redox reaction of sulfide and thiosulfate. The surface cracks and pitting characteristics of the specimens after corrosion were carefully examined and the corrosion products film is flake grains and defective. The main corrosion products of specimen induced by S2− and S2 are FeS, FeS2, Fe3O4, and FeOOH. The present study shows that the corrosion mechanism of S2− and S2 is different for the corrosion of Q235 carbon steel.

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Effect of Additional Sulfide and Thiosulfate on Corrosion of Q235 Carbon Steel in Alkaline Solutions

The effect of HCO 3 − and Cl − on the corrosion behavior of Q345 carbon steel in soil simulated solutions was investigated through electrochemical and surface characterizations. The results show that the sample behaves with active dissolution state in low concentration of Cl − solution while pseudo passivation of sample is observed in high concentration of Cl − solution. However, in solutions containing low concentration of HCO 3 − , the addition of high concentration Cl − does not result in the pseudo passivation of sample due to the formation of discontinuous film, which increases the corrosion rate. In addition, in solution containing high concentration of HCO 3 − , the addition of high concentration Cl − leads to much higher increase of corrosion rate. The deep corrosion pit is observed on the matrix due to the rapid rupture of FeCO 3 film and the sufficient development of pitting. 

Corrosion behavior on carbon steel in a simulated soil solution under the interaction effect of chloride and bicarbonate ions

Dynamic direct current (DC) may cause severe electrochemical corrosion on buried steel pipelines near urban rail transits. In this paper, the corrosion behavior of Q235B steel under dynamic DC interference was carried out in NS4 simulated soil solution (NS4 solution) including potassium chloride (KCl), sodium bicarbonate (NaHCO 3 ), calcium chloride (CaCl 2 ), Magnesium sulfate heptahydrate (MgSO 4 .7 H 2 O) and deionized water . The electrochemical corrosion behaviors of Q235B steel in NS4 solution were studied by means of potentiodynamic polarization (Tafel curve) and electrochemical impedance spectroscopy (EIS) techniques. Dynamic DC was simulated by four types of applied current according to the leakage current rule of rail trains arriving at and departing from the platform. The results of Tafel curves showed that Q235B steel exhibits a decrease in corrosion resistance with increasing applied current density, and anodic reaction exhibited active dissolution controlled by charge transfer. EIS results indicated that Nyquist plots of samples included double capacitive arcs and exhibited Warburg impedance characteristics caused by the concentration gradient . Weightlessness measurement showed that the average corrosion rates of four types of samples were 1.0, 1.4, 2.0, and 2.5 g.cm −2 . d −1 , respectively. In addition, the corrosion morphology indicated that samples featured in pitting corrosion, which was correlated to applied dynamic DC values and counts, and corrosion products were Fe 3 O 4 and Fe (OH) 3 . Finally, the study shows that corrosion of buried steel pipelines is related to rail train arriving types and counts. 

Corrosion Mechanism and Damage Characteristic of Q235B Steel Under the Effect of Stray Current in NS4 Simulated Soil Solution

In this work, corrosion of a 16Mn line pipe steel was investigated in a simulated soil solution by weight-loss test, electrochemical measurement, and surface analysis techniques. Moreover, the implication on the pipeline integrity was analyzed. It was found that a layer of corrosion product, i.e., ferrous and ferric oxides, would form on the steel surface to inhibit the further corrosion of the steel. The structure of the corrosion product layer would change with time, resulting in the steel corrosion experiencing a mechanistic alteration. The effects of oxygen and temperature on the steel corrosion were determined. Moreover, the uniform corrosion rate of the steel is within the acceptable range, and thus does not affect the pipeline integrity.

Zhenxing Yin

Papers

Corrosion of 16Mn Line Pipe Steel in a Simulated Soil Solution and the Implication on Its Long-Term Corrosion Behavior