2000 Hook-up Book

Steam Tracing

Clip On Tracers The simplest form of tracer is one that is clipped or wired on to the main product line. Maximum heat flow is achieved when the tracer is in tight contact with the product line. The securing clips should be no further apart than 12" to 18" on 3/8" tracers, 18" to 24 on 1/2", and 24" to 36" on 3/4" and larger. The tracer pipes can be liter ally wired on, but to maintain close contact it is better to use either galvanized or stainless steel bands, about 1/2" wide and 18 to 20 gauge thickness. One very practical method is to use a packing case banding machine. Where tracers are carried around bends particular care should be taken to ensure that good contact is maintained by using three or more bands as in Fig. 8. Where it is not possible to use bands as at valve bodies, soft annealed stainless steel wire 18 gauge thick is a useful alternative. Once again, any special needs to avoid external corrosion or elec trolytic action may lead to these suggestions being varied. Welded Tracers Where the temperature differ ence between the tracer and the product is low, the tracer may be welded to the product line. This can be done either by short run welds as Fig. 10a or by a contin uous weld as Fig. 10b for maximum heat transfer.

Insulation The insulation must cover both the product line and the tracer but it is important that the air space remains clear. This can be achieved in more than one way. 1. The product line and tracer can first be wrapped with alu minum foil, or by galvanized steel sheet, held on by wiring and the insulation is then applied outside this sheet. Alternatively, small mesh gal vanized wire netting can be used in the same way as metal sheet Fig. 11a. 2. Sectional insulation, pre formed to one or two sizes larger than the product main, can be used. This has the disadvantage that it can eas ily be crushed Fig. 11b. 3. Preformed sectional insula tion designed to cover both product line and tracer can be used, as Fig. 11c. Preformed sectional insula tion is usually preferred to plastic material, because being rigid it retains better thickness and effi ciency. In all cases, the insulation should be properly finished with waterproof covering. Most insula tion is porous and becomes useless as heat conserving mate rial if it is allowed to absorb water. Adequate steps may also be needed to protect the insulation from mechanical damage.

In these cases the tracer is sometimes laid along the top of the pipe rather than at the bot tom, which greatly simplifies the welding procedure. Advocates of this method claim that this loca tion does not adversely affect the heat transfer rates. Heat Conducting Paste For maximum heat transfer, it can be an advantage to use a heat conducting paste to fill the normal hot air gap as in Fig. 10c. The paste can be used to improve heat transfer with any of the clip ping methods described, but it is essential that the surfaces are wirebrushed clean before apply ing the paste. Spacer Tracing The product being carried in the line can be sensitive to tempera ture in some cases and it is then important to avoid any local hot spots on the pipe such as could occur with direct contact between the tracer and the line. This is done by introducing a strip of insulating material between the tracer and the prod uct pipe such as fiberglass, mineral wool, or packing blocks of an inert material.

SYSTEM DESIGN

Lagging

Lagging

Lagging

Product

Product

Product

Aluminum Foil

Tracer

Tracer

Tracer

Wire Netting

11a

11b

11c

Figure 11 Insulating Tracer and Product Lines

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