Leak methods

Thermal conductivity and flexural strength and volume resistivity are as good as conventional LTCC material. Because fine leak rate by helium gas through this material is less than 1 x 10 Pam /s, it is possible to measure the hermeticity of the package by fine leak method. Dielectric constant and loss tangent were determined by dielectric resonator method using an HP 8757C network... 

In many cases faults will only restrict fluid flow, or they may be open i.e. non-sealing. Despite considerable efforts to predict the probability of fault sealing potential, a reliable method to do so has not yet emerged. Fault seal modelling is further complicated by the fact that some faults may leak fluids or pressures at a very small rate, thus effectively acting as seal on a production time scale of only a couple of years. As a result, the simulation of reservoir behaviour in densely faulted fields is difficult and predictions should be regarded as crude approximations only. 

Leaking fi om process flows may pose operational risks and cause environmental problems as well as economic losses. Two examples of tracer methods for testing, localising and quantifying leaks are given below. 

Fluorine in the atmosphere can be detected by chemical methods involving the displacement of halogens from haUdes. Dilute fluorine leaks are easily detected by passing a damp piece of starch iodide paper around the suspected area. The paper should be held with metal tongs or forceps to avoid contact with the gas stream and immediately darkens when fluorine is present. 

Superfluid helium can pass easily through openings so small that they caimot be detected by conventional leak detection methods. Such leaks, permeable only to helium II, are called supedeaks. They can be a source of fmstrating difficulties in the constmction of apparatus for use with helium II. 

Different combinations of stable xenon isotopes have been sealed into each of the fuel elements in fission reactors as tags so that should one of the elements later develop a leak, it could be identified by analyzing the xenon isotope pattern in the reactor s cover gas (4). Historically, the sensitive helium mass spectrometer devices for leak detection were developed as a cmcial part of building the gas-diffusion plant for uranium isotope separation at Oak Ridge, Tennessee (129), and heHum leak detection equipment is stiU an essential tool ia auclear technology (see Diffusion separation methods). 

Waste Treatment. Environmental concerns have increased the need to treat Hquid discharges from all types of industrial processes, as well as mnoffs where toxic substances appear as a result of leaks or following solubilization (see Wastes, industrial). One method of treatment consists of an ion-exchange system to remove the objectionable components only. Another involves complete or partial elimination of Hquid discharges by recycling streams within the plant. This method is unacceptable unless a cycHc increase in the impurities is eliminated by removing all constituents prior to recycling. 

Various coupling designs are available to transmit torque from the driver, eg, electric motor, to a pump. In order to contain the pumped fluid inside the pump and prevent the pumpage from leaking, several types of sealing methods are used. A few options are described herein. 

Spill Prevention and Detection. It is far better to prevent a leak or a spik than to clean one. The fundamental rule of leak and spik prevention is to reduce the possibkity for contamination by directing resources as close to the source as possible (Fig. 11). In addition to increasing the effectiveness of a spik and leak prevention program, the costs are lower if the focus is placed on preventing the occurrence in the first place. Regulatory trend, however, is to requite methods that respond to leaks after they occur. In addition to being more costly, this type of requirement is often a disincentive to prevent the leaks in the first place, because of the additional cost. 

Out-of-tank leak detection ground penetrating radar and inventory methods... 

Le kDetection. Leak detection methods may be subclassified according to whether or not they are on the tank. On-tank leak detection systems operate immediately upon leakage. 

Precision mass and volumetric methods use very precise measurements of pressure and/or level in the tank to detect leaks. The tank must be closed so that no Hquid enters or leaves the tank. The threshold of detection and fuimel required to perform a rehable test become greater as tank size increases. 

Tracer methods involving chemical markers injected into the contents of the tank may be used. Instmmentation capable of picking up the chemical marker can then determine the presence of a leak caused by seepage of the tracer into the ground. This, like the hydrocarbon sensing method, is genericaUy referred to as soil vapor monitoring. This method suffers the same weaknesses that have to do with undertank soil permeabUities. 

Use of Liners. The use of impermeable liners and membranes, often called release prevention barriers (RPBs) under tanks, may be the most effective leak detection and prevention method. On new tanks, it is relatively easy to install these systems, and large numbers of tanks are being built with this type of system in the 1990s. For existing tanks, however, it would be very costiy if not impractical to install liners. For existing tanks, the combination of other methods as well as an effective inspection program can be more effective as a substitute for a release prevention barrier. 

Piping required to have a sensitive leak test shall be tested by the gas- and bubble-formation testing method specified in Art. 10, Sec. V of the ASME Code or by another method demonstrated to have equal or greater sensitivity. The sensitivity of the test shall be at least (100 Pa mL)/s [(10 atm mL)/s] under test conditions. If a hydrostatic pressure test is used, it shall be carried out after the sensitive leak test. 

The hydrostatic test is, in one sense, a method of examination of a vessel. It can reveal gross flaws, inadequate design, and flange leaks. Many beheve that a hydrostatic test guarantees the safety of a vessel. This is not necessarily so. A vessel that has passed a hydrostatic test is probably safer than one that has not been tested. It can, however, stiU fail in service, even on the next appheation of pressure. Care in material selection, examination, and fabrication do more to guarantee vessel integrity than the hydrostatic test. 

The constant-molar-overflow assumption represents several prior assumptions. The most important one is equal molar heats of vaporization for the two components. The other assumptions are adiabatic operation (no heat leaks) and no heat of mixing or sensible heat effects. These assumptions are most closely approximated for close-boiling isomers. The result of these assumptions on the calculation method can be illustrated with Fig. 13-28, vdiich shows two material-balance envelopes cutting through the top section (above the top feed stream or sidestream) of the column. If L + i is assumed to be identical to L 1 in rate, then 9 and the component material balance... 

Safer Storage Conditions The hazards associated with storage facihties can often be reduced significantly by changing storage con(i-tions. The primary objective is to reduce the driving force available to transport the hazardous material into the atmosphere in case of a leak (Hendershot, 1988). Some methods to accomplish this follow. 

FIG. 26-32 Methods of diking for flammable hqiiids (a) traditional diking method allows leaks to accumulate around the tank. In case of fire, the tank will he exposed to flames that can he supplied hy fuel from the tank and will he hard to control, (h) In the more desirable method, leaks are directed away from the tank. In case of fire, the tank wiU he shielded from most flames and fire wiU he easier to fight. (From Englund, in Advances in Chemical Engineering, vol. 15, Academic Press, San Diego, 1.9.90, pp. 73—135, hy permission. )... 

Air is usually the basic load component to an ejector, and the quantities of water vapor and/or condensable vapor are usually directly proportional to the air load. Unfortunately, no reliable method exists for determining precisely the optimum basic air capacity of ejectors. It is desirable to select a capacity which minimizes the total costs of removing the noncondensable gases which accumulate in a process vacuum system. An oversized ejector costs more and uses unnecessarily large quantities of steam and cooling water. If an ejector is undersized, constant monitoring of air leaks is required to avoid costly upsets. 

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