Service condition tests

Since the corrosion resistance of anodic films on aluminium is markedly dependent on the efficacy of sealing (provided the film thickness is adequate for the service conditions), tests for sealing quality are frequently employed as an index of potential resistance to corrosion. While it is admitted that an unequivocal evaluation of corrosion behaviour can only be obtained by protracted field tests in service, accelerated corrosion tests under closely controlled conditions can also provide useful information in a shorter time within the limitations of the particular test environment employed. 

To simulate service conditions tests may be needed with exposure being on one side of the test piece only, which can achieved by using a simple jig in which the test piece forms one end of a cylindrical container. If immersion under pressure is needed a special jig would have to be developed. The standard does not include cases of partial immersion nor immersion under pressure. 

The useful life of a practical primary battery is determined principally by the nature of its discharge pattern. Thus the best way of assessing a system for some particular application is to subject it to a discharge which simulates the service conditions. Tests have therefore been developed which recognize the principal function of various types of battery and specify the generation of intermittent or continuous currents of appropriate levels. Such procedures have been standardized for batteries of uniform size and cell configuration by bodies such as the International Electrotechnical Commission (IEC) and the American National Standards Institute (ANSI). New test routines are continually being devised to keep pace... 

The destructive effect of the weather varies with geographic location, season, time of day, cloud cover, and exposiue orientation because of variations in the critical weather factors with these conditions. Different weather conditions can also be encoimtered in individual years. Therefore, outdoor tests in one location dining a specific time interval cannot be expected to provide information on either absolute diuabiUties or stability rankings of materials under various service conditions. Tests are commonly carried out in environments that have the most... 

During a hydrotest the additional weight of the water superimposes the normal operational stress by steam pressure. The big advantage of the pneumatic test is now, that it is the best imitation of the normal service condition. 

Non-Desfructive testing can be apph ed widely in all industrial organisations during construction and after construction to determine, in first case, whether flaws have been introduced due to manufacturing process or in the second case, whether flaws have developed dtie to service conditions. NDT is therefore used to inspect... 

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

Table 8 indicates the compatibiUty of magnesium with a variety of chemicals and common substances. Because the presence of even small amounts of impurities in a chemical substance may result in significantly altered performance, a positive response in the table only means that tests under the actual service conditions are warranted (132). Other factors which may significantly alter magnesium compatibiUty include the presence of galvanic couples, variations in operating temperatures, alloy composition, or humidity levels. 

Resistance is iadicated by yes, ie, laboratory tests have shown enough promise to warrant test under actual service conditions. 

Special Tests. Even though the American Society for Testing and Materials offers a wide range of test methods, there are other special tests that are imposed upon the manufacturer by consumers, the military, the U.S. Government, and ia some cases local or municipal governments. These tests are generally very specific and are oriented toward particular service conditions. In many iastances, the producers develop special tests within thek laboratories to solve customer problems or predict product or production performance. Many of these tests subsequentiy are adopted by ASTM. 

Small variations in service conditions may appreciably affect corrosion resistance. Choice of materials is tlierefore guided wherever possible by a combination of experience and laboratory and site tests. 

Here Acto is the cyclic stress range for failure in Nf cycles under zero mean stress, and Acr m is the same thing for a mean stress of a .) Goodman s Rule is empirical, and does not always work - then tests simulating service conditions must be carried out, and the results used for the final design. But preliminary designs are usually based on this rule. 

Here is the number of cycles to fracture under the stress cycle in region i, and Nj/Nf is the fraction of the lifetime used up after N, cycles in that region. Failure occurs when the sum of the fractions is unity (eqn. (15.4)). This rule, too, is an empirical one. It is widely used in design against fatigue failure but if the component is a critical one. Miner s Rule should be checked by tests simulating service conditions. 

In order to choose the type of coating and determine the necessary coating thickness, many practice-oriented tests would have to be carried out in which the evaluation of damage areas and choice of service conditions are not always comparable [42-44]. However, information on the various thickness ranges of the PE coating in Ref. 4 was deduced from such experiments. 

Amongst the factors that will influence service performance are the effect of additives and impurities, temperature, detailed geometric size and shape, orientation and morphology, surface condition, energy and speed of any impacting blow, the shape of the impacting instrument, the environment, and strains in the article due to external loads. For this reason it is desirable, but not always feasible, to test prototype articles under conditions as close to service conditions as possible. 

The glass-fibre nylons have a resistance to creep at least three times as great as unfilled polymers. In the case of impact strength the situation is complex since unfilled nylons tend to break showing tough fracture whereas the filled polymers break with a brittle fracture. On the other hand the glass-filled polymers are less notch sensitive and in some tests and service conditions the glass-filled nylons may prove the more satisfactory. 

Cold Differential Test Pressure - The cold differential test pressure (in kPa gage) is the pressure at which the valve is adjusted to open on the test stand. This cold differential test pressure includes the corrections for service conditions of back pressure and/or temperature. 

Fortunately the situation in practice is not quite as complex as it might seem. In general, very acceptable designs are achieved by using impact data obtained under conditions which relate as closely as possible to the service conditions. Impact strength values available in the literature may be used for the initial selection of a material on the basis of a desired level of toughness. Then, wherever possible this should be backed up by tests on the plastic article, or a specimen cut from it, to ensure that the material, as moulded, is in a satisfactory state to perform its function. 

Each item of apparatus tested, all flexible cords, switches, fuses, plugs and socket outlets are in good serviceable condition except as stated. There is no sign of overloading of conductors or accessories except as stated. Apparatus tested includesjdoes not include Portable Appliances. 

Oxidation tests on Nimonic 90A, in which sodium chloride was introduced into the atmosphere, showed that this constituent produces a significant deterioration in the protective nature of the normally adherent film. Although under certain service conditions the presence of sodium chloride is likely, this is not always so, and thus the general applicability of the results of laboratory tests in sodium sulphate and mixtures involving sodium chloride may be questioned. Test procedures for hot-salt corrosion have been reviewed by Saunders and Nicholls who concluded that burner rig testing is the most appropriate procedure provided contaminant flux rates similar to those found in an operating turbine are used in the rig. 

Most of the early work carried out in relation to these aspects of the problem used nitrates as the cracking environment where low-strength steels have been the objects of interest. Consequently most of what follows refers to cracking in boiling concentrated nitrate solutions except where otherwise stated. The medium and higher strength steels, such as involved in sour oil well equipment and other applications, are more frequently tested in chloride- or sulphide-containing environments related to service conditions, but the failure of these steels is dealt with elsewhere (see Section 8.4). 

The practical result of epitaxy is a very high degree of adhesion between coating and substrate. The force needed to separate the interface is similar to that needed to break the metals on either side. Where a true metallic bond forms at an epitaxial interface it is only possible to measure adhesion if the bond is the weakest of the three near the interface. An adhesion test based on breaking the joint indicates only which of the three is weakest. For practical purposes any epitaxial joint will have a strength more than adequate for service conditions. 

All testing has to be related to environmental conditions whose characteristics must be defined. The relation of accelerated corrosion test condition to real service conditions is one aspect while another is defining classes of environment and relating them to characteristic corrosion performance in order to produce useful specification guidelines. BS5493 1977 is an attempt to do this using four categories appropriate primarily to the UK (Table 13.2). Such a classification is clearly an over-simplification, but represents an important step in this particular direction. 

Henthorne , in considering the corrosion testing of weldments, points out that the test will also give high rates due to (a) end-grain attack, which is particularly prevalent in resulphurised or heavily cold-worked material and (d) dissolution of Ti(C, N) such as occurs in Type S2J weldments and leads to knife-line attack. Since most service conditions do not cause attack on the alloy in these conditions the test can be misleading. 

---