Protective sheaths

Thermocouples in chemical plants are usually found in sheaths. These sheaths protect the thermocouple and also allow the thermocouple to be removed and replaced without shutting down the process. One chemical plant had some thermocouples that did not have sheaths, although they looked like the sheathed type. This led to an accidental release of toxic and flammable material. Can you explain why ... 

Assists in growth and repair of body tissues and maintenance of myelin sheaths protecting nerve cells Necessary for formation of tooth enamel and elastin and collagen... 

Bakharevich (Ref 4) enclosed in a rigid casing (sheath) of compressed KC1 and asphalt binder (1.5%), Ammonits and Pobedits to obtain expls, known as Metanits, which did not ignite methane-air mixts and had deton rates of 46204900m/sec. The sheath protected the expls from dynamic compression, Another expl described by Bakharevich was Miporit... 

High output emf—useful for low temperature sensitivity. Requires good sheath protection in sulphur-bearing or reducing atmospheres. 

Requires good sheath protection for sulphur-bearing or reducing atmospheres. 

Are cables and leads protected from damage by sheathing, protective enclosures or by positioning away from causes of damage ... 

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

The nonbonding electron clouds of the attached fluorine atoms tend to repel the oncoming fluorine molecules as they approach the carbon skeleton. This reduces the number of effective coUisions, making it possible to increase the total number of coUisions and stiU not accelerate the reaction rate as the reaction proceeds toward completion. This protective sheath of fluorine atoms provides the inertness of Teflon and other fluorocarbons. It also explains the fact that greater success in direct fluorination processes has been reported when the hydrocarbon to be fluorinated had already been partiaUy fluorinated by some other process or was prechlorinated, ie, the protective sheath of halogens reduced the number of reactive coUisions and aUowed reactions to occur without excessive cleavage of carbon—carbon bonds or mnaway exothermic processes. 

These foams are used for board stock in commercial and industrial buildings as insulation for internal cavity and external walls, roof, floor, and foundations. Spray-appHed foam, covered subsequently with one of a variety of protective coatings, is widely used for large roofing appHcations and has limited use as external walls. Eor residential buildings, the principal use is as external sheathing board. 

Elame-spread and smoke-density values, and the less often reported fuel-contributed semiquantitive results of the ASTM E84 test and the limited oxygen index (LOI) laboratory test, are more often used to compare fire performance of ceUular plastics. AH building codes requite that ceUular plastics be protected by inner or outer sheathings or be housed in systems aH with a specified minimum total fire resistance. Absolute incombustibHity cannot be attained in practice and often is not requited. The system approach to protecting the more combustible materials affords adequate safety in the buildings by aHowing the occupant sufficient time to evacuate before combustion of the protected ceUular plastic. 

Wool fibers consist of cells, where battened ovedapping cuticle cells form a protective sheath around cortical cells. In some coarser fibers, a central vacuolated medullary cell type may be present. 

Copper is a galvanic metal and causes corrosion, in the presence of moisture, in nearby metals, such as cable sheathes, steel structure and water, gas or drain pipes, buried in its vicinity. With all such metafs. it forms a complete electrolytic circuit and corrodes them. Tinning may give protection against its galvanic effects but this is ati expensive proposition... 

Fig. 1-8 Constructional drawing of the Sammarang, which was the first ship to make a sea voyage to Nova Scotia from March 1824 to January 1825 with cathodic protection of the copper sheathing.

In soil, anodes are connected by cables to the object to be protected. The cable must be low resistance in order not to reduce the current delivery. Therefore with long lines, the cable cross-section must be proportionately large. A cable with NYM sheathing with 2.5 mm Cu is mostly sufficient. Occasionally stronger cables and special insulation are required, e.g., NYY 4 mm Cu. Power supply cable buried in soil should have a noticeably light color. For use in seawater, occasionally temperature, oil and seawater-resistant cable is demanded, e.g., HOVRN. ... 

A single or multicored plastic-coated cable of the type NYY or NYY-O is used as the connecting cable between a protected object and an anode in soils and fresh water, and particularly in seawater, medium heavy or heavy rubber-sheathed connections of an NSHou or NSSHou type are used. Heavy welded connections of type NSLFSou are used for severe mechanical loading. In addition to these, for ships, marine cable of type MGCG or watertight cables must be considered. 

In the cathodic protection of asymmetrically connected communication cables, distortions are coupled into the transmission lines coming from the ripple of the sheath current. In this case also, limiting the residual ripple to 5% is usually sufficient. 

For several years now, cable ducts have been manufactured from plastic pipes, which are watertight and form a continuous run of piping. In laying the ducts, low points can occur in which condensed water or water penetrating from the ends can collect. In many cases this water has led to corrosion damage in lead-sheathed cables. Lead-sheathed cables must therefore only be used in such ducts with an additional PE sheath of type A-PM2Y. Cathodic protection of these cables is not possible because of their complete insulation by the plastic pipe. 

Cables with a copper sheathing are used only seldom. The protective cover is the same as with a corrugated steel-sheathed cable. If a cable with copper sheathing is connected to a lead-sheathed cable (A-PMbc) (see Table 13-1), the copper sheathing acts as a cathode in a galvanic cell and is therefore cathodically protected. 

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