Hydrostatic test. See

Connections welded to the casing shall meet or exceed the material requirements of the casing, including impact values, rather than the requirements of the connected piping. All connection welding shall be completed before the casing is hydrostatically tested (see 7.3.2). 

Casing, stuffing box, cover or seal chamber, and jackets shaU be designed to wiUistand a hydrostatic test at 1.5 times die maximum design pressure for the pardcular component and material of construction used (see para. 5.2.1). 

In addition to hydrostatic testing of cylinders at the time of manufacture, DOT requires the owner or his authorized agent to fulfill periodic requalification requirements for his cylinders. See 49 CFR 173.34(e) [9]. Hydrostatic retest or visual inspection under certain conditions are the accepted methods for requalifying cylinders. Requalifying periods and test pressures for cylinders in ammonia service are shown in Table 6. 

RTR pipe designers also use a stress-strain curve similar to that used by steel pipe designers. However, instead of a yield point, they use what is called an empirical weep point, or the point of first crack (see Fig. 5-30). It is determined by either coupon or hydrostatic tests. The weep point is the point at which the matrix becomes excessively strained so that minute fractures begin to appear in the structural wall. At this point it is probable that in time even a more elastic liner will be damaged and allow water or whatever else the pipe is carrying to ooze or weep through the wall. As is the case with the yield point of steep pipe, reaching the weep point is not necessarily cataclysmic. The pipe can still continue to withstand quite a bit of additional load before it reaches the point of ultimate strain and failure. 

Regardless of the type of hydrostatic testing method used, DOT and TC regulations both specify that the periodic retest must include an external and internal visual examination of the cylinder. It is recommended that these inspections be conducted prior to the hydrostatic retest in accordance with the applicable Compressed Gas Association standards. See references [13] through [16] and [20]. External and internal inspection considerations were discussed more thoroughly in previous sections of this chapter. 

If, as a result of hydrostatic tests, a cylinder leaks or shows a permanent expansion which exceeds 10 percent of the total expansion, it must be condemned. Except for TC/ DOT-3AL aluminum cylinders approved for ammonia service, cylinders condemned because of excessive permanent expansion may be requalified if heat-treated and then hydrostatically retested. See 49 CFR 173.34(e)(4). [9]... 

B. A second and also successful method accounts to a certain extent for the aeration effect, based on test data from many references. This method is not quite as conservative when estimating total tower pressure. This follows the effective head concept of Hughmark et al. [31]. Effective head, hg, is the sum of the hydrostatic head plus the head to form the bubbles and to force them through the aerated mixture. Figure 8-130 is the correlation for hg plotted against submergence, hji [31]. See Dynamic Liquid Seal. ... 

The saturation pressure seems to be proportional to the elastic modulus of the propellant (Figure 10). Although there is no solid experimental evidence, it is suspected that the positive hydrostatic pressure acts as a retardation parameter in cavitation or in debonding of particles from the polymeric matrix, as described by Gent and co-workers. Qualitatively, the effect of applied pressure during a tensile test is believed to delay the occurrence of vacuoles and to decrease their number. This assumption may be sustained by simultaneous volume-expansion measurements taken during tensile tests under different pressures. For an increase in pressure, the relative measured volume decreases (see Figure 11). 

The flow cup is a relative-capillary viscosimeter. The outlet nozzle is a very short capillary, and the propulsive force is the hydrostatic pressure of the liquid, which during the tests flows under its own weight from the central outlet nozzle on the bottom of the cup. The flow cup has a defined geometry with a given volume for the sample liquid. For the measurement, the nozzle is closed, the cup is filled with the sample liquid and then the time is measured that the Uquid takes to completely drain out of the cup. From that efflux time, the kinematic viscosity v is calculated. Up to this day many different flow cups are used around the world (see Fig. 3.3). 

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