Testing of Inhibitors

The properties such as gel time and exotherm peak temperature, mechanical properties, that is, tensile strength and percent elongation, bond strength with 

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Tests in waters and soils should ordinarily be allowed to run for extended periods in excess of 3 years, with removals of specimens in groups after different time intervals. A desirable schedule for any extended test in a natural environment is one in which the interval between successive removals is doubled each time. For example, the first removal would be after 1 year, the second after 3 years, and the third after 7 years, and so on. On the other hand, test periods should not be significantly longer than the process or exposure time of the end-use requirement. The testing of inhibitors for use if pickling or cleaning treatments should be of a period commensurate with the practical requirement which may be for only a few minutes. 

The three types of test procedure discussed in this chapter may often be identified in testing of inhibitors or inhibited products. The testing of inhibited engine coolants provides a suitable example. 

The testing of inhibitors for use in oil and gas production, transport and processing normally involves two-phase oil-water fluids with, sometimes, a... 

Prepare 20 mM inhibitor stock solutions in DMSO, which will allow testing of inhibitors in cells at up to 40 pM at the non-toxic concentration of 0.2 % DMSO. Store stock solutions as small... 

Ancillary testing of inhibitor/resin properties e.g. solubility of inhibitor in resin and diffusion rates of inhibitor in resin. 

Larger sacle testing of inhibitors in transfer moulding compounds prior to practical use of the idea. 

Ancillary Testing of Inhibitor Resin Properties. It was found that inhibitor could be introduced fairly readily in the two part liquid system either by direct dissolution in the resin or hardener or, for some of the less soluble inhibitors, as a fine dispersion in the resin. Introduction in powder transfer moulding resins was achieved by ball milling the inhibitor with the powder. Subsequent analysis of samples of powder showed that the inhibitor had been uniformly dispersed. 

Larger Scale Testing of Inhibitors in Transfer Moulding Resins. 

A recirculating dynamic test method can be used when it is desired to simulate fleld flow or operational conditions. Some of the parameters that should be controlled are the velocity of the corrosive medium, the oihwater ratio (in case of oil-field inhibitors), temperature, and dissolved gas and/or air concentration. Variables that can be imposed are the type of corrosive medium, the concentration of inhibitor, the effect of precorrosion of the test specimen, and the type of inhibitor treatment. This type of flow test provides a more severe test of inhibitor film life than the static bottle test. It furnishes a useful technique for the study of variables affecting inhibitor performance. Correlation between laboratory tests and field use of inhibitors is better using this technique than it is using data from the static test. 

Chloro-oxazolo[4,5-/i]quinoline-2-carboxylic acid methyl ester was the most active compound in tests for inhibitors of antigen-induced release of histamine in vitro from rat peritoneal mast cells (IC50 of 0.3 p,M) and as inhibitors of IgE-mediated passive cutaneous anaphylaxis in the rat (ED50 (intraperitoneal) of 0.1 mg/kg in dose 0.5 mg/kg as an inhibitor of the test)—10 times and 60 times more potent, respectively, than the disodium salt of cromoglycic acid (85JMC1255). 

Viewed in perspective, evidence of failure in service has been rare and the practical hazard is certainly very much lower than would appear from the results of laboratory tests. In chlorinated hydrocarbons the effect can be controlled by the addition of inhibitors, and, for example, the appropriate commercial degreasants containing these inhibitors are specified in a British detence standard. ... 

Aluminium coatings exposed as sprayed show remarkable protective properties and in many cases the only evidence of age is the appearance of small hard nodules of aluminium oxide, and these do not appear to be deleterious. However, the dead white of the sprayed surface soon becomes discoloured by dirt and so a paint covering is usual. A chromate inhibitor is not essential and two coats of a simple vinyl-based sealing paint have given remarkable results in the tests of the American Welding Society over periods of 12 and 15 years. 

Composition of the liquid environment The ionic composition, arising from dissolved salts and gases, has a considerable influence on the performance of inhibitors. In near-neutral aqueous systems the presence of certain ions tends to oppose the action of inhibitors. Chlorides and sulphates are the most common examples of these aggressive ions, but other ions, e.g. halides, sulphides, nitrates, etc. exert similar effects. The concentration of inhibitor required for protection will depend on the concentrations of these aggressive ions. Laboratory tests " have given some quantitative relationships... 

An exception to the lone pair or donor electron requirement of organic inhibitors is provided by the quaternary ammonium compounds. Meakins reports the effectiveness of tetra-alkyl ammonium bromides with the alkyl group having C 10. Comparative laboratory tests of commercial inhibitors of this type have been described . The inhibiting action of tetra-butyl ammonium sulphate for iron in H S-saturated sulphuric acid has been described, better results being achieved than with mono-, di- or tri-butylamines . 

Temperature effects may also be used in test methods and notably for assessing the effects of inhibitors in acid solutions. The technique is based on that first proposed by Mylius which records the temperature-time behaviour associated with the exothermic reaction resulting from the initial contact of a metal with a corrosive acid solution. The effectiveness of inhibitors may then be determined from their effects on the temperaturetime behaviour. ... 

Laboratory tests used in the development of inhibitors can be of various types and are often associated with a particular laboratory. Thus, in one case simple test specimens, either alone or as bimetallic couples, are immersed in inhibited solutions in a relatively simple apparatus, as illustrated in Fig. 19.34. Sometimes the test may involve heat transfer, and a simple test arrangement is shown in Fig. 19.35. Tests of these types have been described in the literatureHowever, national standards also exist for this type of test approach. BSl and ASTM documents describe laboratory test procedures and in some cases provide recommended pass or fail criteria (BS 5117 Part 2 Section 2.2 1985 BS 6580 1985 ASTM 01384 1987). Laboratory testing may involve a recirculating rig test in which the intention is to assess the performance of an inhibited coolant in the simulated flow conditions of an engine cooling system. Although test procedures have been developed (BS 5177 Part 2 Section 2.3 1985 ASTM 02570 1985), problems of reproducibility and repeatability exist, and it is difficult to quote numerical pass or fail criteria. 

The testing of vapour phase inhibitors, usually referred to as volatile corrosion inhibitors, is essentially a matter of placing a test specimen in the vapour space of a closed vessel containing an aggressive atmosphere — frequently water vapour, perhaps with SO2 present—and a quantity of the inhibitor. Variations on the basic technique include provision for circulation of the vapour, the use of paper impregnated with inhibitor, provision for temperature cycling, etc. 

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)... 

These same diamine materials find further application in, for example, formulations for mussel and barnacle control in large once-through, condenser cooling systems, as corrosion inhibitors and biostats for hydrostatic testing of oil and gas pipelines, and as corrosion inhibitors in food industry retort cookers. 

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