Stress testing special considerations

Piping joints shall be selected to suit the piping material, with consideration of joint tightness and mechanical strength under expected service and test conditions of pressure, temperature, and external loading. Layout of piping should, insofar as possible, minimize stress on joints, giving special consideration to stresses due to thermal expansion and operation of valves (particularly a valve at a free end). 

Stress intensification factors for branch connections are based on tests with at least two diameters of straight run pipe on each side of the branch centerline. More closely loaded branches may require special consideration. 

Those spots where three media meet, namely, the electrode, the insulation material, and the helium, are indicated in Fig. 1 by a circle in dashed lines. Those spots appeared to be particularly critical. Special consideration was given to improvements to relieve those spots of the electric stress as far as possible. Because of a simpler test arrangement, these experiments were performed at first in liquid nitrogen. The particularly proper insulators were tested in helium. It was found that a conductive layer on the inner surface of the insulator contacting the inner electrode resulted in significant improvement of the flashover behavior. The reason for this is probably that the insulator and... 

Whereas roller bottles and shake flasks are used for screening tests or for the cultivation of precultures, on production scale mainly stirred tanks, bubble columns, and in a few cases, also loop reactors are used (see Table 5). The stress in these reactors is therefore also of special significance and should be given particular consideration. 

Interim blood sampling of rats may not be necessary when the dose levels are similar in the short- and longer-duration studies. The sample timings in the guidelines refer to the core tests, but some specialized tests require samples to be collected at times in relation to the toxic injury in acute studies (e.g., cardiac biomarkers) or to expected peaks in the circadian or reproductive cycle rhythms. Additional times for blood sampling should be avoided if the procedures could compromise the health of the animals. In all procedures, consideration should be given to the possible stress effects of the sample collection procedures and the amount of blood collected in relation to the total blood volume. 

Process fluids may be used for hydrostatic testing in some special cases, but water is the almost universal choice. The quality of the water is an important consideration. Residues from hydrostatic testing often lead to corrosion. Chloride ions in the water are frequently a problem in apparatus or piping that is vulnerable to stress corrosion. Scrupulous removal of test water may be important for this reason or may be necessary because of interactions of water or rusted surfaces with process fluids. 

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