Results of the Test Method

Despite strenuous efforts, duphcating field conditions may be difficult or impossible, this objective being subject to the additional difficulty that conditions actually are unknown. Many times, an evaluation test may be altered to develop a more corrosive condition or to accelerate the test. 

In such cases, the combination of corrodents should remain the same, but it may be necessary to increase concentrations. The question then arises concerning interpretation of data. If the test is accelerated, the absolute corrosion rates may be higher than those resulting under field conditions. 

However, it must be assumed that the same corrosion mechanism is taking place and if an inhibitor is effective at high corrosion rates, it will also be effective under milder conditions. Testing using comparative data under accelerated conditions will permit identification of the better inhibitors. Then, under field conditions, the actual dosage of the inhibitor may have to be determined in some other manner. 

In a laboratory test, the question always arises as to when an inhibitor is effective. Must the corrosion rate be stopped completely or can it be slowed to some degree and stiU be effective In the field, the decisive factor will be whether the inhibitor eliminates failures. 

A complicating factor in both laboratory and field is the fact that corrosion products (or other surface-active particles) wiU adsorb the inhibitor and either keep it from the metal surface or lower its available concentration. StiU another factor to consider in interpreting data is the wide statistical band over which test results will vary until a minimum necessary concentration of inhibitor is exceeded. 

---

Corrosion tests provide the basis for the practical control of corrosion and therefore deserve a more exhaustive discussion than limitations of space will permit. A detailed description of all the procedures and devices that have been employed in corrosion studies in many countries will not be attempted. Instead, attention will be directed principally to underlying principles and to comments on the significance and limitations of the results of the test methods that are considered. Further details may be obtained from the references and from the comprehensive works by Champion and Ailor ... 

The bias determined in the validation referred to the difference between average results of the test method and average results of the independent reference method. However, it was recognized that other sources of bias, e.g. some interferences, may increase the true bias of the method in some unique field situations. 

When the operator has determined the totality of the uncertainty budget within the possibilities offered by his laboratory, the uncertainty due to the presence of (a) possible systematic error(s) or bias remains. Only one possibility exists to detect such a bias. It lies in external help. Comparing the results of the test method to another method developed in-house involves the risk of having an unknown laboratory bias, e g. biased primary calibrants etc. Therefore, it is more appropriate to look for external help. This can come from the comparison of results obtained on a reference sample with those obtained on the same sample by another laboratory or by analysing a certified reference material. Both possibilities will be dealt with in the next two chapters of this book. 

The paper discusses the application of dynamic indentation method and apparatus for the evaluation of viscoelastic properties of polymeric materials. The three-element model of viscoelastic material has been used to calculate the rigidity and the viscosity. Using a measurements of the indentation as a function of a current velocity change on impact with the material under test, the contact force and the displacement diagrams as a function of time are plotted. Experimental results of the testing of polyvinyl chloride cable coating by dynamic indentation method and data of the static tensile test are presented. 

Application of magnetic fluids in ultrasonic non-destructive testing [1-3] opens the real perspectives for automation of the testing methods, based on the surface waves. This report presents the results of investigations aimed at the creation of the transducer of the surface waves for the automated control. The basic attention is drawn to the analysis of the position of the front meniscus of the contact liquid when the surface waves excite through the slot gap. 

A number of standards exist for the determination of some of these parameters. BS 1377 Part 3 1990 refers to methods of tests for soils for civil engineering purposes, and Part 9 refers to these and corrosivity tests in situ. It is significant that the standard draws attention to the fact that the results of the tests that are described should be interpreted by a specialist. ASTM tests for pH and resistivity of soil used for corrosion testing are covered by G51 1977(R1984) and G57 1978 (R1984), respectively. 

In this test for transparent plastics, the loss of optical effects is measured when a specimen is exposed to the action of a special abrading wheel. In one type of test the amount of material lost by a specimen is determined when the specimen is exposed to falling abrasive particles or to the action of an abrasive belt. In another test, the loss of gloss due to the dropping of loose abrasive on the specimen is measured. The results produced by the different tests may be of value for research and development work when it is desired to improve a material with respect to one of the test methods. The variables that enter into tests of this type are... 

In TPE, the hard domains can act both as filler and intermolecular tie points thus, the toughness results from the inhibition of catastrophic failure from slow crack growth. Hard domains are effective fillers above a volume fraction of 0.2 and a size <100 nm [200]. The fracture energy of TPE is characteristic of the materials and independent of the test methods as observed for rubbers. It is, however, not a single-valued property and depends on the rate of tearing and test temperature [201]. The stress-strain properties of most TPEs have been described by the empirical Mooney-Rivlin equation... 

The ISO guide is particularly concerned with the establishment of reference materials which contain the analyte as a small, or even trace, quantity in a complex matrix. These reference materials serve as measurement benchmarks when applying an appropriate analytical procedure for the determination of an analyte in the sample. The value attributed to the reference material is usually the mean of residts obtained from a variety of methods and laboratories. Thus, the value attributed to the substance may have a high degree of uncertainty. A particular reference material is subjected to the same procedure as the test samples so that greater confidence can be given to the results of the test samples provided that the value found for the reference material falls within the given uncertainty. 

For cases where equation (4.17) is true, the change from the nominal to the alternative level is significant. However, the results of the test will be misleading if the factors investigated are not independent. Such a study may be used to set the level of control that should be applied at particular stages of the method, e.g. adjust the pH to 6.5 0.2. It is also possible to study the effect of potential interferences by using this approach. 

The problem of toxic subjects detection in the tested objects can be solved by two options chemical analysis, for revealing separate toxics, or their products, and biotesting with the result of the tested samples toxicity degree indication without identification of the agent. Qualitative and quantitative chrmical/analytical methods allow with the higher accuracy and, in some cases, rapidly detect presence of the separate toxics or their products in the tested objects. It is important for the regular detection of the different pollutions of any agents in the tested objects. 

It might be interesting to note how far the results of accelerated test methods agree with full-length outdoor exposure and the effect of natural daylight. The correlation between outdoor or daylight exposure, including factors such as location,... 

Most of the test methods used to assess the anaerobic biodegradability of organic chemicals have been screening level tests based upon measuring the increase in gas volume or pressure resulting from the conversion of a test material to carbon dioxide (C02) and methane (CH4), such as the ECETOC-28 test [3,4],... 

The compendium contains a note in <711> that requires that air bubbles be removed if they change the results of the test. The suggested method found as a footnote in <711> uses heat followed by filtration under vacuum. There is a plethora of methods for deaeration (14), an earlier method was to boil and cool the medium. There are also several varieties of automated deaeration equipment. The mechan-... 

The purpose of die tests described on the paper of Missouri School of Mines (Ref 7) is to help in predicting expl performance in rock from performance in water. Four expls were tested both in water and in rock so that direct comparison of the results of the two methods of testing could be made. The rock tests were made at a granite quarry operated by the Consolidated Quarries Division of the Georgia Marble Co, near Lithonia, Ga. The rock was uniform with sp gr ca 2.6 and propagation velocity of about 18000 ft/sec. The underwater tests were made in a deep pond at the Armour Foundation test facility near Coal Ciry, Illinois. Water had sp gr 1.0 and propagation velocity 5000 ft/sec... 

Attempts to reduce the uncertainty of particular aspects of the risk assessment process do not succeed in decreasing the uncertainty attached to the overall assessment. For example, great efforts are put into standardizing methods of testing, so that a test will produce the same result time after time, from laboratory to laboratory.4 This increases the certainty as to whether a chemical has a particular hazardous property or not and enables the concentration at which it has an adverse effect to be precisely defined. However, precision and certainty are only achieved because the property is defined in relation to the very particular conditions under which the test is carried out it is doubtful that these conditions are representative of the situations that are of concern, in which heterogeneous wild animal or human populations are exposed to chemicals. We may be sure of the result of the test, but very uncertain as to its relevance with respect to the risks we are trying to assess. 

The validation requirements are discussed as they apply to both the sample preparation and sample analysis aspects of a dissolution method. The focus of the discussion in this chapter is on the validation considerations that are unique to a dissolution method. Validation is the assessment of the performance of a defined test method. The result of any successful validation exercise is a comprehensive set of data that will support the suitability of the test method for its intended use. To this end, execution of a validation exercise without a clearly defined plan can lead to many difficulties, including an incomplete or flawed set of validation data. Planning for the validation exercise must include the following determination of what performance characteristics to assess (i.e., strategy), how to assess each characteristic (i.e., experimental), and what minimum standard of performance is expected (i.e., criteria). The preparation of a validation protocol is highly recommended to clearly define the experiments and associated criteria. Validation of a test method must include experiments to assess both the sample preparation (i.e., sample dissolution) and the sample analysis. ICH Q2A [1] provides guidance for the validation characteristics of the dissolution test and is summarized in Table 4.1. 

It becomes clear from the discussion of the previous sections that any test result is not absolute but is limited by a variety of factors. Before testing starts there are limitations arising from how the material was produced, how it was sampled and how the test pieces were formed. The results are further limited by the form of test piece, the selection of the test method and the exact test conditions adopted. The actual results obtained are then subject to uncertainty limits that arise from such factors as natural material variation, tolerances on the accuracy of test instruments and tolerances on test conditions. 

A fundamental point to be borne in mind when test methods are being devised, and when the results from various types of test are being considered, is that what is being tested is a bulk property and that in deducing this property from the results of the test a theory has to be used which applies to all the material in the test. This is not always taken into account, (although in many cases the finer points of the theory become irrelevant). For example, consider a simple tensile test in which a flat strip is gripped at each end and strained at a constant rate. 

Measurements of the desired property or properties (usually grouped together under the general title specifications) are expressed as numerical values therefore, the accuracy of these measurements is of the utmost importance. The measurements need to be sufficiently accurate so as to preclude negative scientific or economic consequences. In other words, the data resulting from the test methods used must fall within the recognized limits of error of the experimental procedure so that the numerical data can be taken as fixed absolute values and... 

Many of the test methods applied to coal analysis are empirical in nature, and strict adherence to the procedural guidelines is necessary to obtain repeatable and reproducible results. The type of analysis normally requested by the coal industry may be a proximate analysis (moisture, ash, volatile matter, and fixed carbon) or an ultimate analysis (carbon, hydrogen, sulfur, nitrogen, oxygen, and ash). 

Accuracy is often expressed inversely in terms of the standard deviation or variance and includes any systematic error or bias. Accuracy includes both the random error of precision and any systematic error. The effect of systematic error on the standard deviation is to inflate it. In the measurement of coal quality for commercial purposes, accuracy expressed in this manner is generally of less interest than is systematic error itself. When systematic error is reduced to a magnitude that is not of practical importance, accuracy and precision can become meaningful parameters for defining truly representative sampling and for interpretation of the results of various test methods. 

The measurement of systematic error is carried out by taking the differences of replicate results. From a statistical standpoint, to detect a systematic error, it is necessary to reduce the precision limits of the mean to a value less than some multiple of the standard deviation of the differences. To be classified as bias, systematic error must be of a magnitude that is of practical importance. Without proper experimental design, the systematic error may be of a magnitude that is of practical importance because of the various errors. These errors (errors of omission) render the data confusing or misleading and indicate the unreliability of the test method(s). 

The chief differences in the methods for the determination of volatile matter emanating from the thermal decomposition of coal are (1) variations in the size, weight, and materials of the crucibles used (2) the rate of temperature rise (3) the final temperature (4) the duration of heating and (5) any modifications that are required for coals which are known to decrepitate or which may lose particles as a result of the sudden release of moisture or other volatile materials. In essence, all of these variables are capable of markedly affecting the result of the tests, and it is, therefore, very necessary that the standard procedures be followed closely. 

---