Document YoQNZ53x6kEGKD63Ywd1M4Y0

. 114 CHAPTER 7 1962 Guide And Data Book or not, depending upon the load on the conduit. Drainage is provided by the drainage pockets filled with crushed stone or gravel and may be install*^ on either or both sides of the conduit. They conduct water from the top of the conduit to the drain below which is connected to the sewer or some other disposal facility. Variations of the concrete-box type have side walls constructed of hollow vitrified tile, concrete blocks, or other suitable materials, and covered with a re inforced concrete slab. The top and sides are sometimes covered with a waterproofing membrane of asphalt or hot pitch and roofing paper. The solid-pour construction, Conduit B, Fig. 1, is also usually madft with common materials and consists of poured structural concrete which is vibrated and tamped around a conventionally insulated steam line. If the insulation has a high compressive strength it can support the pipe, other wise, the pipe should be supported independently. Reinforc ing is sometimes used to prevent settlement. An eccentric space may be left around the pipe by using insulation larger than the outside diameter of the pipe to permit upward movement of the pipe during the warm-up periods. During, construction, pipe is suspended by wires. Precautions should be taken to prevent the pipe from floating. The top of the conduit should be coated with asphalt emulsion or tar to help seal shrinkage cracks. Anchor stresses are higher with this type of construction. Variations of this type include en closure of the pipe and insulation in tile, concrete, steel, or asbestos pipe and then pouring of concrete around outer pipe. This method provides .sp&oe for 'pipe supports, if needed. External drainage can be provided by methods similar to the concrete box type construction. Conduits constructed of common materials are often pre ferred by the district heating industry because of the condi tions imposed in congested street beds, heavy traffic loads, and drainage conditions or because of the ease of opening and closing tire conduit, for branch pipe connections. .Prefabricated conduits, C and D, Fig. 1, are commonly constructed in standard lengths. In some, as in C, the in. sulated pipe or pipes are placed within a corrosion-resistant helically-corrugated metal jacket which is protected with a heavy asphaltic coating. Similar casings are made of steel protected with an anti-corrosive compound. Both are of welded construction and can be tested under air .prepare. In conduit D the insulated pipe is placed concentrically within the corrosion-resistant metal jacket and the inter vening space between jacket and insulation poured full of high melting-point asphalt or left as an air space. In these conduits, the pipes are supported by precast rings or guida to maintain alignment and to prevent pressure on insulation. Fittings are available for.joints, bends, etc. Some of these conduits are also available with cast-iron *a-ringa , j Tile conduit E, Fig. 1, is constructed of specially-shaped glazed vitrified beil-and-spigot tile. In the conduit shown, the base drain is made in separate units and is designed to support the main conduit and pipe lines, and to drain the conduit. Ail joints are cemented. There are several types of tile conduits. Monolithic conduits F and G, Fig. 1, are similar to the solid-pour type except that the insulation, referred to as in sulating concrete, serves also as a conduit and is poured di rectly around the steam min The insulation consists of expanded-mica, shredded-rubber or other cellular materials mixed with Portland cement or asphalt; or of a special foaming material mixed with Portland cement. The latter process creates a multitude of minute air cells in the con crete to obtain its insulating qualities. The poured structure is often protected by a water-proofing membrane and strengthened by a concrete duct. COVERED WITH HOTPITCH A B .IC*I.Lr CORRU GATED ZtNC COATED MOOT IRON COt<OUT C 0 District Heating Graaul&r-fused type conduits such as H, Fig. 1, consist , a specially si$ed and selected granular bitumen which is in the trench around the pipes. The manufacturers jyise that the conduit is formed when beat passing through the pipes forms three distinct concentric zones, all resistant to water penetration. A plastic area surrounds the pipe, outside of which is a sintered sane providing thermal insula- tjou, and finally, an outer layer of unconsolidated particles nitrviding further insulation value. This unconsolidated gone is also the load-bearing portion of the structure. Waterproof conduits are intended for use where perma- ppnffy and thoroughly tight joints are required. Some of the prefabricated conduits, C and D, Fig. 1, can be supplied with water-tight cast-iron p and fittings. The casing shown in I, Fig. 1, consists of cast-iron pipe with lead-caulked joints enclosing the insulated steam main. It is water tight and intended for special applications, where, for instance the duct may be submerged, subject to flooding, or laid in ex tremely wet soil. All of the preceding conduits have their application and the choice' depends upon local conditions. Any underground conduit is only as good as, among other things, its founda tions to prevent settlement, its external and internal drain age, its ability to stand up under the corrosive action of cer tain ground conditions (see Buried Pipe lanes, Chapter 15 of the 1961 Guide And Data Book), its strength to carry the load imposed on it, its field installation, and its insulating properties. Manholes When conduits are used for underground piping, manholes may be required to house valves and other accessory equip ment. They are built of a variety of materials such as rein forced concrete block. They should have adequate volume to permit men to work on equipment. They should be as nearly waterproof as possible and precaution should be taken to prevent entrance of surface water around the covers. Pro vision should be made for lifting necessary equipment from the pipe line, for drainage, for ventilation, and for auto matic water-removal equipment if a sewer is not accessible. -Details of typical manhole construction housing a single expansion joint are shown in the NDHA District Heating Handbook, Third Edition, p. 164. If more equipment is in stalled, the size should be increased accordingly. Where water removal equipment is required, sumps are installed under the manholes. Water can be removed periodi cally with portable pumps, or, where water conditions are bad or periodic inspection is not feasible, by installed sump pumps or water ejectors. .. The motors for electric pumps should be enclosed in a separate compartment which is ventilated to protect it from heat and vapors. Precautions should be taken against corro sion as mentioned in the Section Piping and Accessory Equipment. Piping Tunnels Because of their relatively high first cost as compared with conduits, walking tunnels are usually not provided for steam mains unless, as in some institutions, they are required to accommodate miscellaneous other utility services or to pro vide underground passage between buildings. Tunnels are usually built of reinforced concrete, brick, conc'tte blocks or other suitable structural materials, and are waterproofed on the outside. Provision for drainage and ventilation is essential. Since tunnels and conduits are apt to be hot and humid, apecial precautions should be taken to reduce temperatures 115 f*nd protect equipment. Heat loss from pipes and supports can be reduced by insulating return mains and using more than normal insulation on steam mains. A metal jacket over the pipe covering can permit insulation to carry the weight of the pipe.' The precautions on siting, design, installation, and pro tection against corrosion, for accessory equipment, as dis cussed in the sections Piping Accessory Equipment, and Conduits for Piping, should be taken for tunnels. Special precautions should be taken to prevent rapid deterioration of enclosed electrical conduit. All electrical boxes, junctions and outlets should be vapor proof. Ventilation of the tunnel can be obtained by installation of suitable fans or by natu ral means. Piping and Accessory Equipment A district heating distribution system is usually buried in the ground where it is not readily accessible for repairs or replacement. This makes it imperative that the system be carefully designed and installed. The American Standard Code for Pressure Piping ASA B-31.1--1955* has sections, covering district heating piping systems and fabrication de tails, from which general specifications and minimum re quirements for piping and accessory equipment can be ob tained. Suggestions for selection and installation of materials based on long operating experience of the district heating industry are given in following paragraphs. More detailed informa tion is available in the District Heating Handbook, Third Edition." Pipe, father steel or wrought-iron pipe is satisfactory. Welded construction is most desirable. Valves. Flanged cast-iron valves for pressures under 125 psig are satisfactory. For pressures from 125 to 300 psig flanged-steel and welded-end valves are used. .Outside screw and yoke valves are preferred. Fittings. Forged or rolled steel is used for pressures inexcess of 125 psig. Where pipe-line apparatus is to be re movable, Hanged fittings are preferred. Expansion Joints. Pipe bends to absorb expansion are preferable wherever feasible in order to eliminate the in spections, maintenance, and housing required by slip joints. Slip joints should be guided either externally or internally, or both. Corrugated-type joints should have stainless steel or copper corrugations depending upon operating conditions. Spare expansion capacity should be allowed for contingencies such as higher pressures, superheat, and installation toler^ ances. Anchors. Anchors can be of structural steel, special fittings, or U-shaped steel straps which partially encircle the pipes. Anchors should be firmly bolted or welded to a short length of cast or stainless steel set in concrete. Anchors are often fabricated by welding structural steel to pipe and embed ding the ends in manhole walls or concrete poured in connec tion with conduit. Anchors are subject to humid conditions in conduits and manholes, and can deteriorate rapidly. They should be designed for adequate strength, intended life, and the steam pressure to which they can be subjected, with liberal factors of safety and protection from corrosion. An chors should be attached to both rides of the pipe.Kigs should be welded to pipe on both sides of loop-type anchors to prevent slippage. The cantilever type of anchor should be avoided. Cast steel is preferred to cast iron for anchor material. Alignment Guides. To assure pipe alignment and proper operation of expansion joints, pipes should be adequately guided. Special precautions should be taken if the pipe de viates from a straight line.