Inhibitors corrosion detection

Molybdate - [COLORANTS FORPLASTICS] (Vol 6) -lead detection [LEAD] (Vol 15) -role m H202 decomposition [HYDROGEN PEROXIDE] (Vol 13) -use as corrosion inhibitor [CORROSION AND CORROSION CONTROL] (Vol 7)... 

Measurements of the adsorption of inhibitors on corroding metals are best carried out using the direct methods of radio-tracer detection and solution depletion measurements . These methods provide unambiguous information on uptake, whereas the corrosion reactions may interfere with the indirect methods of adsorption determination, such as double layer capacity measurements", coulometry", ellipsometry and reflectivity Nevertheless, double layer capacity measurements have been widely used for the determination of inhibitor adsorption on corroding metals, with apparently consistent results, though the interpretation may not be straightforward in some cases. 

An electrical resistance methods which directly measures loss of metal from a probe installed in the corrosive system under study is described in Section 19.3. It is reported that corrosion equivalent to a thickness loss of as little as 2-5 X 10 cm can be detected . This technique is most useful as a means of monitoring steps taken to reduce corrosion, e.g. by inhibitors, or to detect changes in the corrosivity of process streams. Electrical methods of determining corrosion rates are considered subsequently. 

In a similar study, Gray et al. (60) investigated the possible formation of N-nitrosamines in heated chicken frankfurters which been prepared with various levels of nitrite (0-156 mg/kg). As expected, apparent N-nitrosamine levels increased with increasing concentrations of nitrite, but did not exceed 4 yg/kg except for two samples which contained 8 and II yg/kg of NMOR. The presence of these relatively high levels of NMOR was confirmed by mass spectrometry and raised the question as to its mode of formation. It was shown to be due to the morpholine present in the steam entering the smokehouse, as this amine is commonly used as a corrosion inhibitor in steam process equipment ( ). The detectable levels of NMOR in the Canadian study ( ) were also attributed in part to the use of morpholine as an anti-corrosion agent in the steam supply (62). 

The classic method for the determination of corrosion inhibitors in oil field brines is the dye transfer method. This method is basically sensitive to amines. Within this method, there are many variations that the analyst may use to determine the amount of corrosion inhibitor in either water or crude oil. Unfortunately these methods detect all amines present as corrosion inhibitors [1174]. 

Improved high-pressure liquid chromatography (HPLC) methods have been developed for the analysis of quaternary salt type corrosion inhibitors in brine waters [400]. However, these methods are not suitable for imidazolines and amido-amines. A method based on fluorescence detection has been described for the quantitative analysis of the imidazoline- and amido-amine-type corrosion inhibitors in both oil field water and crude oil samples by HPLC [1174]. 

UV spectroscopy can be used to detect low levels of organic corrosion inhibitors in produced water. An analytic method has been developed using a diode array UV spectrophotometer [630]. 

E. Buck, M. C. Allen, B. Sudbury, and B. Skjellerudsveen. Corrosion inhibitor detection by thin layer chromatography Development of the technique. In Proceedings Volume. Annu NACE Corrosion Conf (Corrosion 93) (New Orleans, LA, 3/7-3/12), 1993. 

Hydrazine compounds are widely used as fuels, corrosion inhibitors, catalysts, and dyes. However, such compounds are recognized as toxic agents consequently, their detection and processing are of much concern. Only a few recent papers pertain to the catalytic oxidation of hydrazine [148-150], with special emphasis... 

Morpholine is a synthetic organic liquid used mainly as an intermediate in the production of rubber chemicals and optical brighteners, as a corrosion inhibitor in steam condensate systems, as an ingredient in waxes and polishes and as a component of protective coatings on fresh fruits and vegetables. Occupational exposure may occur during the production of morpholine and in its various uses, but data on exposure levels are sparse. It has been detected in samples of foodstuffs and beverages (lARC, 1989). 

Since HtS dissolved in water is very corrosive to carbon 4 steel, a comprehensive corrosion-control program is being conducted. In the field, each well is treated once per month by displacing inhibitor down to the perfora-. tions with stock tank oil. Corrosion coupons in the flow-lines are inspected every 6 months Little corrosion has been detected in the field. In the plants, corrosion in-hibitor is added daily to the gas-sweetening solvent, the salt water system, and the stabilizer overhead. Inhibitor is -Jj also added to bulk chemicals as received. Numerous corrosion coupons and probes are installed in each facility and are pulled for inspection every 1 to 3 months Corrosion rates have been low (less than I mil/year) asY result of the inhibitor injection program. 

The various simple chromate anions including chromate, Cr042-, dichromate, Cr2072, and bichromate, HCr04, have all been reported to be potent corrosion inhibitors when they are present as soluble species in solution. Chromate is an effective inhibitor for Al, Fe, Mg, Cd, Sn, and many other metals and alloys. The specific form of the anion present in solution depends on its concentration and solution pH (21). Because evidence of corrosion inhibition has been detected over very wide ranges of soluble Cr(VI) ion concentration and pH, each of these species appears to possess inhibiting properties. 

Use Dyestuff manufacture, detection of nitrite, textile developing agent, laboratory reagent, vulcanizing agent, ion-exchange resins, block polymers, corrosion inhibitors, photography. 

As discussed earlier, it is important that corrosion inhibitors are transportable through the resin matrix and therefore this transport was investigated using radiochemical, spectroscopic and conductimetric methods on dry and water immersed resin, different detection techniques being applicable to different inhibitor species. In all cases it was found that diffusion was negligible in dry samples but that diffusing water could "pick up inhibitor species and transport them sufficiently well to compensate for any small amount of depletion of inhibitor at the chip surface. 

Alkanolamine-hased inhibitors have been tested in similar conditions. For ongoing chloride-induced corrosion with a chloride level of about 1-2 % by mass of cement, in mortar specimens no reduction in corrosion rate was found (Figure 13.6) except at low chloride concentrations. This is confirmed by two other studies [1,11,14] pre-corroded rebars in mortar (w/c 0.75, cover thickness 25 mm) did not show any detectable effect on the corrosion rate of embedded steel once active corrosion had been initiated, despite the fact that the specimens had low cover and porous mortar [14]. It seems that for penetrating or migrating inhibitors the favourable effects found in solution do not occur when applied to hardened mortar or concrete laboratory specimens with ongoing steel corrosion. It is thus necessary to look for information regarding the transport of inhibitor blends in mortar or concrete. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

A system must be carefully examined before a program of corrosion inhibition can be planned effectively. The examination mnst include a survey of any adverse effects an inhibitor may have on the process in which it is to be nsed and an analysis to detect the presence of interfering substances. 

One issue with corrosion inhibitors is to determine how effective they are. There are two aspects to this, can they be detected and levels measured quantitatively in the concrete and at the rebar surface Are they effectively suppressing the corrosion rate ... 

Detection is obviously specific to a particular active inhibiting chemical. Some tests are expensive and difficult. Much work has gone on to develop a test for aminoalcohols, with mixed results so far. As stated earlier, it is far easier to carry out test on admixed inhibitors than for those applied to hardened concrete. There can be dangers with under dosing inhibitors, in that corrosion may occur very aggressively in small anodic pits. It is therefore important that the risk of pitting and under dosing is fully understood. 

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