Pipelines corrosion rate

It is visualized that the proposed coal slurry pipelines could be used as biological plug flow reactors under aerobic conditions. The laboratory corrosion studies under dynamic test conditions show that use of a corrosion inhibitor will limit the pipeline corrosion rate to acceptable levels. 

About 80% pyritic sulfur removal has been achieved by microbial desulfurization of Illinois 6 and Indiana 3 coals using T. ferrooxidans in laboratory shake-flask experiments and in a two-inch pipeline loop. The 10 to 25 wt% coal/water slurry was recirculated at 6-7 ft/sec for 7 to 12 days at 70-90°F. Results also show that the rates of bacterial desulfurization are higher in the pipeline loop under turbulent flow conditions for particle sizes, 43 to 200/m as compared to the shake-flask experiments. It is visualized that the proposed coal slurry pipelines could be used as biological plug flow reactors under aerobic conditions. The laboratory corrosion studies show that use of a corrosion inhibitor will limit the pipeline corrosion rates to acceptable levels. 

Corrosion likelihood describes the expected corrosion rates or the expected extent of corrosion effects over a planned useful life [14]. Accurate predictions of corrosion rates are not possible, due to the incomplete knowledge of the parameters of the system and, most of all, to the stochastic nature of local corrosion. Figure 4-3 gives schematic information on the different states of corrosion of extended objects (e.g., buried pipelines) according to the concepts in Ref. 15. The arrows represent the current densities of the anode and cathode partial reactions at a particular instant. It must be assumed that two narrowly separated arrows interchange with each other periodically in such a way that they exist at both fracture locations for the same amount of time. The result is a continuous corrosion attack along the surface. 

Cooling water pipes are essential for the operation of power stations and must not cease to function. Pipelines for fire fighting are also important for safety reasons. Such steel pipelines are usually well coated. At areas of unavoidable damage to the pipe coating, there is an increased danger due to cell formation between steel and concrete where local corrosion rates of >1 mm a are to be expected [4], Damage to pipelines for fire fighting has frequently been observed after only a few years in service. 

The rotating disc and rotating cylinder have been successfully applied in the laboratory to study the effect of flow on corrosion rates and are much easier to use than actual pipelines and other real geometries. The results of these tests can now be correlated to geometries likely to be found in pipes, pumps, bends, etc. in plant by use of dimensionless group analysis. There-... 

The development of soil corrosivity assessment techniques has largely been due to the pipeline industry s requirements for better corrosion risk assessment and the reduction of pipeline failures. Corrosion in soil is a complex process and over the years several parameters have been identified as having a significant effect on the corrosion rate in a given soil. 

The NACE corrosion scale is a visual rating of surface rusting from 0% to 100%. Most refiners, product pipeline companies, and marketers of fuel require an NACE surface rust rating of 5% or less. The NACE corrosion rating scale is outlined in TABLE 7-1. 

Most microbial desulfurization studies have been conducted in the laboratory shake-flask type experiments, and the major drawback cited against such a process has been that the rates of pyritic sulfur removal were not high enough to reduce the reactor size to a reasonable capacity (2,6). In this study an attempt has been made to determine the effectiveness of T. ferrooxidans under simulated pipeline conditions for pyritic sulfur removal. Since the microbial desulfurization process is conducted under acidic environment, an attempt has been made to determine the corrosion rates under dynamic conditions using Illinois //6 and Indiana 3 bituminous coals and to investigate the effectiveness of a commercial corrosion inhibitor for controlling the corrosivity. 

The addition of T. ferrooxidans in salt medium at the desired concentration to the coal/water slurry increased the corrosion rates for both the coals tested. The corrosion rates for the 72-hour and 500-hour experiments in the presence of T. ferrooxidans in salt medium with 10 wt% slurry of Illinois //6 ranged from 4.2 X 10 3 ipy to 1.41 X 10 ipy, respectively. However,the introduction of up to 10 ppm of a commercial corrosion inhibitor, Calgon T G-10, inhibited the corrosion rates with Illinois 6 and Indiana 3 coals to very low levels approaching those obtained with the deionized water. Balck Mesa pipeline has used this corrosion inhibitor on a regular basis with very satisfactory results. 

In areas where general corrosion is the expected form, a simple ultrasonic thickness gage can be utilized to determine the extent of corrosion, based on baseline readings made at installation or previous inspections. The entire unit need not be examined. Attention can be focused on those areas most likely to corrode, such as liquid levels, mixing zones, or areas of high turbulence. Corrosion probes, which can be placed in process equipment or pipelines, can monitor corrosion conditions by measuring an actual corrosion current, or other process parameters known to be related to general corrosion rates. These data can be constantly monitored and recorded to predict equipment wear, or as an alert to upset conditions. 

Chloride, sulfate, carbonate, and fluoride are among the principal anions of interest in water treatment programs. High chloride concentrations are of concern because of their tendency to accelerate the corrosion rates of pipelines and local water distribution systems. Sulfate at concentrations above 150 ppm can cause severe digestive upset, essentially the symptoms of diarrhea, especially in nonacclimatized people. The concentration of carbonate present has important consequences in relation to hardness, about which more is said later. Fluoride concentrations of ca. 1 ppm in water supplies are beneficial in... 

With respect to corrosion, the conventional classification of climates in marine, inland, industrial, etc. types is not sufficient. It should now be specified with respect to the actual chemical components in the atmosphere, as well as humidity and other factors. Recent research in this field has led to much more precise methods for estimating corrosion rates in polluted atmospheres (38). Economically, perhaps even more important problems are caused by the increased corrosion of water supply pipelines. Not only copper is dissolved, but also cadmium from soldered joints, and larger steel and cement pipelines may also be affected. 

The effectiveness of cathodic protection can be accomphshed by monitoring the pipeline potential using the close interval potential survey (CIPS) method or by using direct current voltage gradient (DCVG) or IR coupon techniques. Also, physical and electrochemical methods can be used to estimate the corrosion rates of a cathodicaUy protected system. 

The most widely used potential monitoring measurements are based on protection potential criteria. Despite improvements in these methods, they only indicate if the pipeline is protected, underprotected, or overprotected. These methods can only estimate the corrosion rates, but should not be used to predict the life expectancy of the system. A more advantageous solution would be the introduction of kinetic CP criterion that... 

L.I. Freiman, A theory and design of an insulating insert in a cathodicaUy protected underground water pipeline. II. The corrosion rate of anodic zones and effectiveness of the insert, Prot. Met. 38 (2002) 277-283 (Translation of Zashchita MetaUov). 

The determination of a corrosion rate, to be applied to a defect analysis in a pipeline fltness-for-service analysis, was undertaken by and described in a paper by Lawson (2005) where both deterministic and probabilistic approaches were used and the results compared. The paper concluded that the deterministic approach has the distinct advantage of simplicity. This of course is in direct relation to the volume and accuracy of data required. However, the inability to deal with uncertainties in the input data is a primary weakness. The probabilistic approach, on the other hand, has the advantage of facilitating quantification of failure probability on the bases of uncertain data. The disadvantages in this case are that it can be time consuming and rather complex. ... 

HjS level lower than 500 ppm), then the corrosion of a pipeline is affected by the concentration of both carbon dioxide and hydrogen sulfide. A small amount of HjS does not allow the formation of a stable carbonate layer. Figure 9.4 shows how corrosion rate varies as a function of carbon dioxide at various temperatures [5], and Figure 9.5 shows the same effect when H2S is present in the gas (see also Figure 9.6). 

In the case of oil pipelines, the rate of sweet corrosion is significantly high at the 6 o clock position because of the preferential separation of water layers at the bottom of the pipeline. In wet gas handling pipelines, the sweet corrosion may take place in the form of top-of-line corrosion. In this form, due to heat loss to the environment, the pipeline becomes cooler. This causes the condensation of water on the top surface of the pipeline. This prevents the formation of a protective carbonate scale and thereby corrodes the inner top surface of the pipeline. Sweet corrosion initiates at areas where the protective iron carbonate films are unstable. This instability could be due to existing pits on the metal surface or due to presence of surface impurities such as sulfide inclusions. This results in... 

It may also be defined as the destruction of metal by electrochemical action, and it cannot take place unless an electrolyte is present. These leakages are cansed primarily by corrosion as the result of the exposure of the inner surface of the pipeline to water. However, corrosion of the external surfaces of pipelines also occurs because the exposure to their external environment may influence the corrosion rate of pipelines [2]. 

Water entering a steel pipeline at the rate of 40 liters/min contains 5.50 mL O2 per liter (25 °C, latm). Water leaving the pipe contains 0.15mL O2 per liter. Assuming that all corrosion is concentrated at a heated section 30 m in area forming Fe203, what is the corrosion rate in gmd ... 

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