1. Functional requirements of water supply network
The fundamental task of water supply enterprises is to provide users with clean drinking water, continuous water supply under pressure and reduce the cost of water supply. To this end, as an important part of the water supply system, the water supply network has the following five requirements for its hardware:
(1) A water supply pipe network with high sealing performance is a pressure-bearing pipe network, and only a good sealing of pipes is the basic guarantee for continuous water supply.
(2) It often takes several hours or even days to transport tap water with good water quality from waterworks to users through long pipelines. In fact, the pipe network is a large reactor, and the unfinished chemical reaction of the factory water will continue in the pipe network. The chlorine-containing water will come into new contact with the pipe wall, which may produce new reactions, including biological, sensory and physical and chemical reactions. Therefore, the inner wall of the pipeline is required to be corrosion-resistant and will not precipitate harmful substances into water.
(3) Good hydraulic conditions? Only when the inner wall of the water supply pipeline is free from scaling and smooth can the head loss be reduced and the service head be ensured.
(4) The spirit of equipment control In the water supply network of big cities, the total length of the pipeline ranges from several hundred kilometers to several thousand kilometers. There are thousands of special equipment in such a huge water supply network, which maintains the good operation of the network.
Special equipment on the pipeline network includes: valves, fire hydrants, ventilation valves, vent valves, flushing and drainage valves, pressure reducing valves, flow regulating valves, water hammer eliminators, manholes, expansion joints, slag hoppers, flow measurement and pressure measurement devices, etc. The integrity of these devices is the premise to ensure the smooth operation of the pipeline network and avoid pollution.
(5) The construction cost of water supply pipe network in investment provinces usually accounts for 50% ~ 70% of the construction cost of water supply system. Therefore, how to determine the construction scale of water supply pipe network through technical and economic analysis and reasonably select pipes and equipment is the guarantee for the reasonable operation of the pipe network.
2. Pipe type
2. 1 metal tube
(1) steel pipe (SP)
Steel pipes include: steel plate straight welded pipe and steel plate spiral welded pipe (suitable for large-diameter pipelines), seamless steel pipe (suitable for medium and small-diameter pipelines), stainless steel pipe (suitable for medium and small-diameter pipelines), galvanized steel pipe and steel-plastic composite pipe (suitable for small-diameter pipelines). In recent years, galvanized steel pipes have been abandoned in most cities.
(2) Cast iron pipe
(2. 1) gray cast iron pipe (GCIP)
Including centrifugal gray cast iron pipes and semi-continuous gray cast iron pipes (suitable for small and medium-sized pipelines). In recent years, most urban water supply enterprises have stopped using gray cast iron pipes.
(2.2) Ductile Iron Pipe (DCIP)
Including annealed ductile iron pipes and as-cast ductile iron pipes (suitable for all kinds of pipelines, mainly small and medium-sized pipelines), as-cast ductile iron pipes have gradually withdrawn from the market.
(3) Non-ferrous metal pipes include copper pipes and aluminum pipes (suitable for small-diameter pipes).
2.2 nonmetallic pipes
(1) cement pressure pipe
(1. 1) Asbestos cement pipe (ACP) is not widely used now;
(1.2) Self-stressing pipe (SSCP) is used for small and medium-sized pipelines in small towns and rural areas;
(1.3) Prestressed pipeline (PCP)
Including core-wound prestressed pipe (also known as tertiary pipe) (CTPCP), vibration extrusion prestressed pipe (also known as primary pipe) (PVCP) and prestressed steel cylinder concrete pipe (PCCP), which is suitable for large and medium-sized pipelines. Among them, prestressed concrete filled steel tube is a new generation product of the former.
(2) Plastic pipe
(2. 1) Thermoplastic pipes include rigid polyvinyl chloride pipes (UPVC) and high-density polyethylene pipes (HDPE) (suitable for small and medium-sized pipes); Polyethylene-aluminum clad composite pipe (PAP), perforated steel plastic composite pipe (PSSCP), crosslinked polyethylene pipe (PEX), modified polypropylene pipe (PP-R), polybutylene pipe (PB) and nylon pipe (suitable for small-diameter pipes); Engineering plastic pipe (ABS) based on acrylonitrile-butadiene-styrene terpolymer (mainly suitable for chlorine and water purifying agent pipelines in water plants, and there are also medium-caliber pipeline products at present).
(2.2) Thermosetting Plastic Pipe (GRP)? GRP pipe is also called glass fiber reinforced resin plastic pipe or glass steel pipe. There are two forming methods for glass steel pipe or sand-filled glass steel pipe, namely centrifugal casting method (Hobas method) and glass fiber winding method (Veroc method). FRP pipes have great application prospects in large-diameter industrial water pipelines, sewage pipelines and source water pipelines.
3. Overview of pipeline applicability
3. 1 steel pipe
(1) large diameter steel pipe? Q235B(A3) killed steel plate is usually used for steel pipes, which has high strength, easy pipe fitting processing and short construction period, especially in areas with complex terrain. However, the steel pipe is rigid, easy to deform, and has strict requirements for lining and external corrosion protection, so it needs cathodic protection. In the process of construction, the workload of combined welding is large. When the groundwater level is high, rubber ring flexible interface can be used to overcome this difficulty, which is more expensive than cement pressure pipe.
(1. 1) There are two forming processes for large diameter steel pipes, namely straight welded pipe and spiral welded pipe. Technological process of straight welded pipe;
Shear-groove-steel plate turning-pressing two circular arcs-pipe rolling (including spot welding)-welding internal and external straight seams (automatic welding)-pipe section butt joint (including spot welding)-welding ring mouth (automatic welding). ?
SY/T5037-92 Spiral Submerged Arc Welded Pipe for General Fluid Transportation is selected as the manufacturing standard of spiral welded pipe. The manufacturing process is divided into three stages, namely, strip steel manufacturing, spiral forming and internal welding, external welding of spiral pipe and fixed-length cutting of pipe section.
(1.2) The main requirement of steel pipe production quality is that steel pipe welding conforms to the current Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering (GB50268-97) and Code for Construction and Acceptance of Industrial Metal Pipeline Engineering (GB50235-97).
X-ray flaw detection and ultrasonic flaw detection of steel pipe welds shall conform to the current national standard Code for Construction and Acceptance of Welding Engineering of Field Equipment and Industrial Pipes. The number of steel pipe weld flaw detection is 5% in the factory and 10% in the field.
In actual inspection, one method can be selected, but when ultrasonic inspection is selected, X-ray inspection should be carried out on the ultrasonic inspection part, and the reinspection length should be 20% of the specified inspection quantity. Before leaving the factory, steel pipes still need to be subjected to water pressure test one by one, and the pressure test value is 1.25 times the pipeline test pressure. ? The weld appearance of straight welded pipe should meet the corresponding requirements, and the allowable deviation of pipe joint geometry size should meet the provisions in Table 1.
When assembling pipe joints, the longitudinal welds shall be staggered by 300mm, and when the pipe diameter is less than 600mm, the spacing shall be greater than 100 mm?
(1.3) The main requirement for the quality of steel pipe lining is cement mortar or epoxy resin.
A. Quality requirements of cement mortar lining
A. Before lining, check that the ellipticity of the pipeline is not more than 2% of the inner diameter of the pipeline, the inner wall of the pipeline is free of rust, sundries and grease, and the height of the weld in the pipeline is not more than 1/3 of the lining thickness.
B. Portland cement No.525 is used as cement, clean medium sand (particle size 0. 15 ~ 1.2 mm) is used as sand, the weight ratio of cement mortar is within 1: 1 ~ 2, the slump is 60 ~ 80 mm, and the compressive strength is ≥30MPa.
C. Lining thickness and allowable tolerance
D the roughness coefficient n of the inner wall of the cement mortar lining is less than or equal to n≤0.0 12.
E. When the width is ≤0.8mm and the axial length is not more than the circumferential length and not more than 2m, the cracks caused by the shrinkage of the lining shall not be repaired, otherwise they shall be repaired.
F surface defects (pits, sand holes, cavities) with an area greater than 5cm2 and a depth greater than the allowable tolerance value of the internal repair thickness, as well as recessed areas greater than 400cm2 shall be repaired.
B. What are the quality requirements for the inner spraying lining of epoxy resin? Because there is no corresponding national standard for the material and operation requirements of epoxy resin for internal injection lining, the following requirements are put forward with reference to the oil and gas industry standard SY/T4057-93:
A. the inner wall of the steel pipe is derusted by sandblasting, reaching the requirements of Sa2.5 standard of GB/T8923, so that the pipe wall has a metallic texture; ?
B the liquid epoxy resin used as the inner spraying lining shall have the hygiene license of the Ministry of Health, which is harmless to human body during construction; ?
C. The total thickness of the lining shall be ≥400μm (generally, five layers shall be sprayed, the first primer shall be finished within one hour after sandblasting and derusting, and the next layer shall be sprayed after the surface is dried);
D. The coating adhesion reaches 1 ~ 2 (test method GB1720); );
E. surface hardness, 2H with pencil, without scratches (test method GB 6739);
F flexibility 1.0mm (test method GB1731); +0); ?
G. impact resistance ≥4.9 (test method GB1732); );
H. viscosity ≥ 0.2 pa s (test method GB1723); ); I fineness ≤80μm (test method GB1724); );
J surface drying time ≤4h, actual time ≤24h (test method GB1728); );
The solid content of component K.A is ≥70%, and the solid content of component B is ≥80% (test method GB1725); ); In 100% NaOH, 30%H2SO4 and 100% NaCl, the chemical resistance was 180d (test method GB1763). );
Salt spray resistance reaches the first level after 500h (test method GB1771); +0);
Sewage resistance100 o; C 90d is qualified (test method GB 1733 B).
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