Inhibitors field testing

This method is by far the most widely used around the world and generally relies on the direct analytical determination of a key inhibitor component species, such as C1O4, Zn, Mo, PO4, SiC>3, or phosphonate. The degree of control is a function of the frequency and method of analysis, plus the variability in cooling system operation. If inhibitor and other testing is only carried out infrequently (say every 2 to 3 weeks) and only simple field test kits are employed for all analyses, it is unlikely that good long-term control can be satisfactorily achieved. 

Unless the cooling system operation is particularly stable, inhibitor reserve testing should be carried out daily, using the best type of field equipment that can be afforded. A portable colorimeter or spectrophotometer is recommended. The results should be graphed for easy viewing and data interpretation. 

The Messoyakha field has been produced through both inhibitor injection and depressurization, as well as combinations of the two. The inhibitor injection tests, presented in Table 7.14 from the combined results by Sumetz (1974) and Makogon (1981, p. 174), frequently gave dramatic short-term increases in production rates, due to hydrate dissociation in the vicinity of each injected well bore. In the table, methanol and mixtures of methanol and calcium chloride were injected under pressure, using a cement aggregate. For long-term dissociation of hydrates, depressurization was used. 

A field test was conducted to evaluate the valve train wear in a 2.3 L OHC (over-head cam) engine with new technology crankcase lubricants these oils also passed the V-D test (Haris and Zakalka, 1983). Oils formulated with secondary alkyl zinc dithiophosphate (ZDDP) wear inhibitor provided significantly better wear protection than two different primary alkyl ZDDPs. Secondary alkyl ZDDP demonstrated good wear protection at a phosphorus content as low as 0.07 (wt%). 

The hose is formed from a non-plasticized polymer and is brought into contact with the inhibitor liquid (Fig. 2.5e). Such films have a structure similar to that shown in Fig. 2.6b. The pore-free layer functions as a barrier, while the porous one is the Cl carrier. The porous layer comprises about 25-50% of the film thickness, which is in part dependent on the contact time of the hose and the liquid. According to field tests, the degree of thermal-diffusive filling of the polymer with a 50% solution of Cl (M-1) in dioctyl phthalate PI increments in the course of blowing by 3 to 5.5% as the solution degree over the mandrel rises from 1 to 3.5 cm. 

Rust-inhibition efficiency of VCI depends largely on their pressure and vapor saturation. The higher the saturated vapor pressure, the more reliably the inhibitor protects the article, especially in the initial period of preservation. To keep the article in a passive state for longer, the ambient VCI concentration should be maintained at the required level. This concentration can be defined accurately only in experiments via prolonged field tests [16]. 

Another problem arises because often only one, the most volatile, component of the inhibitor blend can be analysed using an amine electrode as in the case of proprietary migrating corrosion inhibitors [1,9]. In this way, the diffusion of the volatile part of the inhibitor blend can be measured but no information on the diffusion of the non-volatile fraction can be obtained. Both components of an inhibitor blend are needed at the steel surface to get an inhibiting effect (Figure 13.3). However, only the volatile component diffuses easily through the porous concrete. This may explain the discrepancy between solution experiments and mortar or field tests [1,9,11]. It has also been reported that the volatile component of organic inhibitor blends evaporates [1,9]. 

Field Tests and Experience with Corrosion Inhibitors... 

Only calcium nitrite, introduced more than thirty years ago, has a long and proven track record as a corrosion inhibitor for reinforced concrete [1,4]. MFP and alkano-lamine-based organic inhibitor blends are increasingly used but unfortunately most of the commercial apphcations lack rigorous control of the inhibitor effect. One of the very few comparative field tests on chloride-contaminated concrete studied MFP and a proprietary alkanolamine inhibitor added in the side-walls of a tunnel (16). The inhibitors were applied by the producers. The measurements of macrocell currents and half-cell potential mapping revealed that both inhibitors were virtually ineffective at the chloride concentrations of 1-2 % by mass of cement present [16]. 

Other field tests with proprietary vapour-phase inhibitors [17] in a parking garage with chloride-contaminated precast slabs did not show encouraging results. Corrosion-rate measurements showed a reduction of 60% in areas with initially intense corrosion but also an increase of corrosion rate in areas with low corrosion rates. On structures from 1960 with an admixed-chloride content higher than 1% by mass of cement, already featuring patch repairs, a three-year corrosion rate survey showed lower corrosion rates in the treated areas compared to untreated ones, but cracking and spalling increased also in the treated areas [18]. 

The use of corrosion inhibitors could be a promising technique in restoring reinforced concrete structures, offering benefits as reduced costs and inconvenience of repairs. It has, however, to be taken into account that the use of corrosion inhibitors in repair systems is far less well-established than their application as admixtures in new structures. The performance of proprietary corrosion inhibitors in repair systems marketed under different trade names is not yet sufficiently documented by independent research work, especially when considering field tests. 

Because of the complexity of real systems, inhibitor selection is by far not straightforward and requires testing by laboratory and field studies. Commercial formulations usually contain a combination of several active inhibitors, blended with a specific surfactant/solvent package, which controls the release of the inhibitors into the environment (i.e. the available inhibitor concentration). The protection of multimetal systems requires particular care, since efficient inhibitors for one metal may be ineffective or even corrosion-accelerating for another metal. In general, the performance of formulations depends on the system parameters and has to be evaluated by field tests to ensure protection. 

The world, however, is not unidimensional, and there are many more parameters that affect inhibitor performance, including their interactions. One parameter that has caused workers in this field much concern and consternation is the flowrate under which the inhibitors are tested. Table 1 below summarizes some results obtained under controlled constant pH and various degrees of agitation in Kettle Test arrangements. Even though the experimental design was not complete, the data show that with the exception of Inhibitor D the other three are either pH or flow sensitive or both. 

Recently migrating corrosion inhibitors have been proposed as surface applied liquids (Mader, 1994). It is claimed that the inhibitor will migrate both in the gas and in the liquid phase to the reinforcement. The results reported are conflicting a recent laboratory study on precorroded (both chloride induced and carbonated) mortar samples showed practically no effect in reducing the corrosion rate even after several immersion cycles in the inhibitor solution (Elsener et al., 1999b). Despite some field tests (Laamanen et al., 1996) and an increasing number of applications, very few documented and conclusive results exist on the inhibitor efficiency. A first field test with different surface applied inhibitors on a well characterized and instrumented side wall of a tunnel started in Switzerland in 1998. 

This KPI is a measure of the availability of corrosion inhibitors to provide protection against corrosive processes. The inhibitor efficiency itself should have been determined from a combination of previous laboratory and field testing to determine the optimum concentration... 

After initial selection of the inhibitor) s) by means of laboratory tests, operational or field tests should be conducted before final selection. Tests should be conducted in the field or plant by monitoring the corrosivity of the fluid of interest in the presence of the inhibitor(s) initially selected. This is normally accomplished by treating the medium and measuring the effectiveness of the inhibitor with the appropriate standard methods. The initially selected inhibitor(s) should pass an operational or field test of 90 days minimum duration. 

Z)-ll-Hexadecenal has been isolated from the female moth, Heliothis armigera, and is a potent olfactory stimulant for males in laboratory and field tests (657). The olfactometer response of laboratory-reared males of H. virescens to its pheromones, (Z)-ll-hexadecenal and (Z)-9-tetra-decenal and the inhibitor (Z)-9-tetradecen-l-ol formate has been studied 658). 

A totally different approach to increasing the efficiency of fertilizing is to slow down the rate of nitrification, and hence to reduce the water-borne losses of the nutrient. This has been possible since the early 1960s when nitrapyrin, the first nitrification inhibitor, became commercially available. Many inhibitors are now on the market—nitrapyrin and dicyandiamide are the two most popular choices—but their use is rather expensive, their performance is highly variable, results from field tests are often contradictory, and their applications have been restricted to just a few field crops (above all corn and root crops) and special climatic conditions. ... 

Britton, C. F., The Selection, Evaluation and Testing of Oil Field Corrosion Inhibitors , Seminar The Development and Use of Corrosion Inhibitors , Oyez Scientific and Technical Services Ltd., London (1983)... 

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