Weep test

Weep test. In this test, unbraided samples of the tube are pressurized by filling them with a military fuel (MIL-S-3136, Type III and MIL-H-25579) consisting of 70% isooctane and 30% toluene. A 15 cm length of the tube is filled with the fuel with a small amount of red dye added to it to improve the visibility of the leak. The tube is pressurized to an initial pressure calculated from Eq. (5.2).00... 

Weep Test - This is a test to determine the integrity of a high pressure hose. In this procedure (MIL-S-3136, type III and MIL-H-25579) unbraided samples of the tube are pressurized by filling with a specified fuel (70% i-octane + 30% toluene) to a calculated initial pressure. Pressure is incrementally (0.035 MPa) increased until seepage occurs. This pressure is recorded as weep pressure. 

Figure 42 Storage and loss inoduluses ((/" and O ") of glutenin (30% moisture content) in a temperature weep test (0,5 K min heating rate 0.5% strain 1 Hz frequency) carried out with a pressure rheometer (modified from [258]).

Tests have indicated that the hydraulic gradient is negligible or very small for most tray designs. Ustial design practice is to omit its effect unle.ss the alue o( A is expected to be greater than 0.75 in. If hydraulic gradient is appreciable, then tbe holes nearer to the tray inlet (liquid) will tend to weep before those nearer the tiay outlet. 

Sentinel holes are used as a simple form of thickness testing. A small hole of about I - 6 mm diameter is drilled from the outer wall of the piece of equipment to within a distance from the inner wall (in contact with the corrodent) equal to the corrosion allowance on the equipment (Fig. 9.11). The technique has been used even in cases where the corrodent spontaneously ignites on contact with the atmosphere. The philosophy is that it is better to have a little fire than a big one which would follow a major leak from corrosion through the wall. When the sentinel hole begins to weep fluid a tapered plug is hammered into the hole and remedial maintenance planned. Siting the sentinel holes is somewhat speculative although erosion at the outside of a pipe bend is often monitored in this way. 

The weep point or strain-to-first-crack in a wall for filament-wound pipe constructed using isophthalic plastic is currently found to be not less than 0.009 in./in. This has been repeatedly demonstrated by careful coupon testing and burst testing of pipes with strain gauge instrumentation attached. 

Safety valves are normally manually tested at periods between 1 and 6 months and pressure-tested every 12 months. Boiler operating pressures are typically 5 to 10% less than safety valve set pressures to avoid valve weeping. 

Tests by Lockett and Banik (loc. cit.) show that weeping is often nonuniform, with some hydraulic conditions favoring weeping from the tray inlet and others from the tray outlet. Weeping from the tray inlet is particularly detrimental to tray efficiency because the weeping liquid bypasses two trays. 

Some cadmium-plated bolts and nuts were purchased and installed as a test in the plant. More bolts were purchased and eventually some of the cadmium-plated bolts were installed on the outlet piping flanges of a cracking furnace. The high temperature outlet flanges on the furnace started to weep a bit. An experienced, intelligent pipefitter attempted to snug up a few bolts and the nuts crumbled. (The cause of the failure was later determined to be due to corrosion phenomena called liquid metal embrittlement. )... 

Weep rste prediction. Lockett and Banik (56) and Hsieh and McNulty (63) proposed correlations for predicting weep rates from sieve trays. Both correlations are based on pilot scale deta, mainly with the air-water system. The Hsieh and McNulty correlation is based on a broader data bank, which includes the experimental data by Lockett and Banik. Hsieh and McNulty used an even wider, non-air-water, proprietary deta bank for testing some of their predicted trende. 

Tests by Banik (72) and Zhang et al. (70) show that weeping from valve trays is nonuniform. In Banik s 4 ft x 2 ft rectangular simulator, most of the weep issued from the inlet half of the tray at low liquid rates (< 3 gpm/in of outlet weir) and from the outlet half of the tray ax high liquid rates (>10 gpm/in of outlet weir). The nonuniformity appeared to escalate as weir height increased. This pattern of nonuniformity is similar to that observed by Banik and Lockett (56) on sieve trays. In Zhang et al. s (70) 5 ft x 1 ft rectangular simulator. 

A 79-year-old man developed a weeping dermatitis of the perianal skin, buttocks, and proximal thighs (32). In the previous 3 weeks, he had used Proctosedyl cream which contains cinchocaine (dibucaine). Patch tests were positive with Proctosedyl cream and 5% cinchocaine in petrolatum, while benzocaine, lidocaine, and clioquinol were negative. 

Sieve tray weeping may be expected to increase with tilting, but tests have shown that this effect is only important when the column operates at liquid flow rates [<5 gpm per inch of weir (250)]. 

To ensure practically no leakage, a leakage test is commonly conducted upon installation. In this test, the weep holes are plugged and the trays are filled with water to the top of the weir. The rate of fall of water level is then measvu ed. It has been recommended that this rate should not exceed 1 in per 20 minutes (48, 86, 257, 371, 409). If the leakage is not critical, a more liberal tolerance can be adopted (48). This test is not always conclusive, because a tray that leaks badly under test conditions may perform satisfactorily at the design temperature and vice versa. 

Occupational contact dermatitis was reported in an atopic worker routinely exposed to yucca Yucca aloifolia) leaves, weeping fig Ficus benjantina), and spathe flower Spathiphyllum wallisii). Skin prick tests were positive to all three plants, and IgE antibodies were found to weeping fig and spathe flower (Kanerva et al. 2001). 

RTR pipe designers also use a S-S curve but instead of a yield point, they use the point of first crack (empirical weep point) as shown in Figure 8.11. Either the ASTM hydrostatic or coupon test determines it. The weep point is the point at which the RTR matrix (resin) 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... 

Nine experimental determinations of velocities.were made in the 56 reflector pieces selected for study at pressure drops ranging from 17.5 to 33 7 psi. After two runs it was seen that flow in. .the reflector was considerably in excess of that- anticipated. An unsuccessful attempt was made to reduce the flow by plugging weep holes in the lower support casting and filling some open area at the "A piece end box sockets. Mean velocities in various types of channels for a typical test at 33.6 psi, after reducing the open area in the lower support casting, are shown in Table A4.A. 

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