Specimen plant tests

In certain cases, it is necessary to choose materials for equipment to be used in a process developed in the laboratory and not yet in operation on a plant scale. Under such circumstances, it is obviously impossible to make plant tests. A good procedure in such cases is to construct a pilot plant, using either the cheapest materials available or some other materials selected on the basis of past experience or of laboratory tests. While the pilot plant is being operated to check on the process itself, specimens can be exposed in the operating equipment as a guide to the choice of materials for the large-scale plant or as a means of confirming the suitability of the materials chosen for the pilot plant. 

Test Specimens In carrying out plant tests it is necessary to install the test specimens so that they wih not come into contact with other metals and alloys this avoids having their normal behavior disturbed by galvanic effects. It is also desirable to protect the specimens from possible mechanical damage. 

Heat-flux corrosion rates can also be determined in plant tests using steam-heated tubular specimens which are weighed or callipered. 

Field and Plant Tests Field exposure of test panels offers the benefit of a high degree of control over surface preparation and application. Moreover, through standardised exposure conditions, broader comparisons between both paint systems and locations are possible. More importantly, since replicates may be removed and laboratory tested periodically, changes in properties can be followed in considerable detail. At least four replicates should be examined for each exposure period to minimise the effects of atypical specimens. 

The next step in the evaluation was to place a TMl testing machine in a plant and run duplicate tests on all types of products for a period of several months. Results of flexural strength tests are shown in Table 2. For clarity, only the averages are shown in this table, but standard deviations were calculated for each average and were very similar for the two machines. For example, on 12.7-mm ( / -in.) regular wallboard where 129 sets of specimens were tested, the standard deviations were as shown in Table 3. This again shows that the two... 

Incorporating suitable test specimens in test plants or existing production plants not yet optimally designed... 

Attempts to assess sensitization in Type 304 alloy by means of 5-15 min potentiostatic electrochemical tests in solutions that simulated exactly the plant conditions have been shown to be invalid [42]. This testing period is much too short for testing in simulated service conditions, i.e., the electrode potential applied to the specimen in the laboratory test, the solution compositions, and temperature were the same as those to be used in plant service. Thus, there was no accelerating factor in the laboratory test and it would have had to be just as long as a plant test, perhaps 3-12 months, to determine whether or not the material would be subject to intergranular attack in plant service. 

ASTM G 4 Standard Method for Conducting Corrosion Coupon Tests in Plant Equipment Provides guidelines for in-plant testing— weight loss coupons, specimen racks, reporting. 

Other plant test specimen designs and evaluation techniques are available. Some fit in restricted spaces and/or monitor electrochemical parameters. Examples of such fixtures, electrode polarization probes, appear in Fig. 4. These allow monitoring of the corrosion process and can detect changes in plant operation that cause excessive attack. 

Test Results The methods of cleaning specimens and evaluating results after plant corrosion tests are identical to those described earlier for laboratoiy tests. 

An alloy tie bar in a chemical plant has been designed to withstand a stress, ct, of 25 MN m at 620°C. Creep tests carried out on specimens of the alloy under... 

Inhibitor control can be effected by conventional methods of chemical analysis, inspection of test specimens or by instrumentation. The application of instrumental methods is becoming of increasing importance particularly for large systems. The techniques are based on the linear (resistance) polarisation method and the use of electrical resistance probes. They have the advantage that readings from widely separated areas of the plant can be brought together at a central control point. (See Section 18.1.)... 

Service tests, in which the test specimens —which may often take the form of manufactured components —are exposed to the particular conditions in which they are to be used, e.g. in process streams of chemical plant. 

Variations in solution composition throughout a test should be monitored and, if appropriate, corrected. Variations may occur as a result of reactions of one or more of the constituents of the solution with the test specimen, the atmosphere or the test vessel. Thus, it is important that the composition of the testing solution is what it is supposed to be. Carefully made-up solutions of pure chemicals may not act in the same way as nominally similar solutions encountered in practice, which may, and usually do, contain other compounds or impurities that may have major effects on corrosion. This applies particularly to artificial sea-water, which is usually less corrosive than natural sea-water. This subject is discussed in detail in a Special Technical Publication of ASTM, and tests with natural, transported and artificial sea-water have been described . Suspected impurities may be added to the pure solutions in appropriate concentrations or, better still, the testing solutions may be taken directly from plant processes whenever this is practical. 

ASTM G4 (latest revision) gives guidance for conducting plant corrosion tests, and in particular, for various methods for mounting specimens (coupons) in process plant. This standard evolved from ASTM and NACE Technical Committees. 

With respect to worker safety and re-entry studies, reference substances are necessary to assay the test substance (and, if applicable, any control substance) and determine its stability and for the analyses of specimens collected in the study. Specimens may include plant material (dislodgeable residues), adsorbent media (inhalation), or clothing/dosimeter materials collected during a worker safety study to assess exposure. If biomonitoring is involved, blood and/or urine specimens may be analyzed against reference substances of known purity. 

Three areas of methodolc stressed here are of special concern for the study of air pollution effects on v etation growth of the test organisms, exposure facilities, and instrumentation. First, to determine the effects of air pollutants on many plant species, one must have a good understanding of the best cultural conditions for a given test crop some results reflect the use of poor test specimens. Second, dynamic... 

Adhesion tests can be broken into two categories qualitative and quantitative. They vary from a simple Scotch tape test to a complicated flyer tape test, which requires precision-machined specimens and a very expensive testing facility. Quantitative (such as peeling) tests have been developed for coatings on plastics (12), but not to the same extent for metal-to-metal systems. The quantitative testing systems in limited use, mainly in the electronics industry, are not commonly present in production plants but have been used to aid in process development. For quality control purposes, qualitative tests for metal-to-metal adhesion (13) are usually adequate. The adhesion of some plated metal parts is improved with baking for 1 to 4 h at relatively low (120 to 320°C) temperatures. 

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