Corrosion loss

Aromaticity is the most important property of a carbon black feedstock. It is generally measured by the Bureau of Mines Correlation Index (BMCI) and is an indication of the carbon-to-hydrogen ratio. The sulfur content is limited to reduce corrosion, loss of yield, and sulfur in the product. It may be limited in certain locations for environmental reasons. The boiling range must be low enough so that it will be completely volatilized under furnace time—temperature conditions. Alkane insolubles or asphaltenes must be kept below critical levels in order to maintain product quaUty. Excessive asphaltene content results in a loss of reinforcement and poor treadwear in tire appHcations. 

Visual examination of external surfaces revealed grooves and general metal loss (Figs. 7.24 and 7.25). Metal loss was caused by erosion-corrosion. However, the corrosive loss was more important than erosive loss, since metal loss was also substantial in low-flow regions. 

The modern procedure to minimise corrosion losses on underground structures is to use protective coatings between the metal and soil and to apply cathodic protection to the metal structure (see Chapter 11). In this situation, soils influence the operation in a somewhat different manner than is the case with unprotected bare metal. A soil with moderately high salts content (low resistivity) is desirable for the location of the anodes. If the impressed potential is from a sacrificial metal, the effective potential and current available will depend upon soil properties such as pH, soluble salts and moisture present. When rectifiers are used as the source of the cathodic potential, soils of low electrical resistance are desirable for the location of the anode beds. A protective coating free from holidays and of uniformly high insulation value causes the electrical conducting properties of the soil to become of less significance in relation to corrosion rates (Section 15.8). 

Fig. 2.32 Corrosion losses for stainless steels exposed to flowing sodium at differing oxygen...

Fig. 3.6 Corrosion losses of steels exposed vertically, facing different compass directions...

Chemical reaction This involves the formation of distinct compounds by reaction between the solid metal and the fused metal or salt. If such compounds form an adherent, continuous layer at the interface they tend to inhibit continuation of the reaction. If, however, they are non-adherent or soluble in the molten phase, no protection will be offered. In some instances, the compounds form in the matrix of the alloy, for example as grain-boundary intermetallic compound, and result in harmful liquid metal embrittlement (LME) although no corrosion loss can be observed. 

Static test results may be evaluated by measurement of change of mass or section thickness, but metallographic and X-ray examination to determine the nature and extent of attack are of greater value because difficulty can be encountered in removing adherent layers of solidified corrodent from the surface of the specimen on completion of the exposure, particularly where irregular attack has occurred. Changes in the corrodent, ascertained by chemical analysis, are often of considerable value also. In view of the low solubility of many construction materials in liquid metals and salts, changes in mass or section thickness should be evaluated cautiously. A limited volume of liquid metal could become saturated early in the test and the reaction would thus be stifled when only a small corrosion loss... 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

A qualitative measure of the corrosion rate can be obtained from the slope of the curves in Fig. 2. Z INT is given in units of s ohm" . Owing to the presence of the uncompensated ohmic resistance and lack of values for Tafel slopes [Eq. (2)], data in Fig. 2 should be viewed as indicative of significant changes in corrosion rates. Corrosion loss remained low during the first 2 months, followed by a large increase for both flushed samples and controls. The corrosion rate increased when the surface pH reached values of 1 or less. Total corrosion loss as determined from integrated Rp data was less for the control than for the flushed sample. 

Figure 2. Cumulative corrosion loss Y. INT for mild steel sensors embedded in concrete and exposed to a sewer bypass (a) control sample, (b) flushed sample. (Reprinted from Ref 6 with permission from NACE International.)...

The NDE in some alloys was found to be larger than in pure aluminum, but in others (with In) to be reduced to very small values, leading to a corrosive loss of the metal of only 0.5% (cf. Fig. 25). 

Fig. 14. Ternary diagram similar to that in Figure 4 showing the distribution of compositions of corroded metallic particles from an LWR fuel sample. Corrosive loss of Mo makes the average composition more Pd-rich.

Some nf ihe means used to combat corrosion losses include ... 

Figure 4.7 Corrosion loss-time curve for zinc specimens exposed at different times of the year93...

Figure 6.18 shows the corrosion of iron. It represents a section of the pit and a growing pit inside the metal. The pitting factor = P/d considers the deepest pit compared with the uniform corrosion loss (Figure 6.19). However to characterise the pitting phenomenon statistically, it is recommended to take the average of the deepest 10 pits as recommended in ASTM G48 4...

The suitable stereochemistry, not focused herein, is described as playing an important role (22). As reported in patents of Firmenich S.A., the ring opening reaction of 18 (Eq. 15.2.7) was preferably carried out with the Lewis acidic homogeneous catalysts such as BF3-etherate (5), Mgl2 (21) or SnC14 (21) with almost complete yield at room temperature in toluene as solvent. These catalysts, however, imply a process limitation to discontinuous liquid phase conditions. Major drawbacks are given by a relatively complicated separation procedure of products and catalyst in addition to corrosion, loss of catalyst and environmental... 

Synthetic Slag (K2)-H20 H2 System. In order to extend the vapor transport conditions in slag systems to a reducing hydrous environment similar to that present in coal gasification, a series of TMS and KMS measurements were made using H2 or H2O as the initial reactant gas. With the TMS system, compositions of H2-N2-H2O up to 10 vol % H2 were attained prior to hydrogen-induced corrosive loss of the transpiration reactor. 

An allowance for corrosion loss of the metal may sometimes be necessary. An internal corrosion allowance is not necessary if a relatively impermeable lining such as a plastic or elastomeric membrane is to be installed before the vessel is to be lined. An external corrosion allowance may, however, be required, particularly if the vessel is installed without sufficient clearances on side or bottom to permit sandblasting and maintenance painting. 

Allowances for expected corrosion over the plant life or time between replacements must be added to the minimum vessel wall thicknesses calculated to comply with the ASME BPV Code. These corrosion allowances can be economically or mechanically prohibitive if the corrosion rate is high. Guidance on corrosion allowances is given in the ASME BPV Code Sec. VIII Div. 1 Non-mandatory Appendix E. The corrosion allowance should at least equal the expected corrosion loss during the desired life of the vessel. 

In order to prevent corrosion loss, it is very important to inspect the coating condition inside the ballast tank of ship, such as oil tankers, LNG ships and cargo ships. The current inspection standard defines that the ratio of paint defect surface area in the total surface is visually inspected every two or three years periodically. However, the current visual inspection has some problems, such as the dangerous and dark environment for inspectors, the inaccurate evaluation result depending on the inspector s skill and the time consuming and heavy labor required in order to inspect all the hundreds of tank compartments. In order to overcome these issues,... 

Dose-response functions describing the corrosion as function of SO and time of wetness are today available for steel and zinc. In extensive areas of the temperate climate zone the corrosion loss may be described by SO pollution solely. 

We have seen how consideration of theoretical deposition velocities has identified potential biases in economic assessments. An additional consideration is the relative uncertainties in the determination of theoretical vs. experimental deposition velocities. The heat transfer data on which the theoretical deposition velocities are based are generally very precise, within a few percent. In contrast, the damage functions developed by Lipfert et al. (3) for metals from extant corrosion test data are only capable of predicting corrosion losses at a given time and place within a factor of two, although the individual regression coefficients are much better than that. Most of the uncertainty in the experimental approach is felt to be in test site characterization rather than... 

The oil vapor and gases from the oxidizer pass to a tar separator where the heavier portions of the product are allowed to collect before the condenser is reached to prevent the formation of deposits in the condenser which would lower the thermal efficiency. A tubular condenser with tubes and tube sheets of aluminum is used to collect the oil vapors and oxidized products. The high proportions of organic acids in the product make it essential that aluminum or other resistant metal be used to prevent corrosion losses in equipment as well as contamination of product. Because of the low concentration of product in the nitrogen gas it is necessary to use a large condensing surface. A cooling surface of... 

Electrochemical corrosion A framework of opportunities is presented with respect to corrosion research and engineering, dissemination of information, and new control technology to reduce corrosion losses. 

Cycling weight loss = 115 g (19 g / cell) Grid corrosion loss = 36%... 

Cycling weight loss 240 g (40 g/cel) Grid corrosion loss 39%... 

The rate of corrosion (loss of metal) is proportional to the amount of current that flows in the corrosion cell. From Ohm s law we know that, for direct current,... 

Impurities of major significance in alkali silicates are iron, alumina, calcium and magnesium, chloride, sulfate, carbonate and titania. They may originate as impurities in raw materials, be added from the manufacturing equipment, or be absorbed from the atmosphere. The degradation of product quality may be manifested as undesirable color, turbidity in solution, corrosiveness, loss of alkalinity or altered reactivity of products made from the silicate (e.g., iron or sulfate may poison a silica-based catalyst manufactured from a silicate solution). 

Mansfeld and coworkers [44] used linear polarization to determine polarization resistance, i p, for mild steel sensors embedded in concrete exposed to a sewer environment. One concrete sample was periodically flushed with sewage to remove sulfuric acid produced by sulfur-oxidizing bacteria. Another sample was used as a control. A data logging system collected at 10-min intervals simultaneously for the two corrosion sensors and two additional pH electrodes placed at the concrete surface. Figure 7 [44] shows cumulative corrosion loss, S I NT... 

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