Introduction and selection of commonly used pipes

In recent years, the biggest hot spot in building water supply and drainage is the wide application of new pipes. Traditional galvanized steel pipes and ordinary cast iron pipes for drainage have been replaced due to easy corrosion, heavy weight, and inconvenient transportation and construction. At present, the commonly used pipes for building water supply and drainage mainly include plastic pipes, metal pipes and composite pipes. Now let's briefly discuss some characteristics, advantages and disadvantages, and scope of use of commonly used pipes.

1. Plastic tube

Plastic pipe is a product made of synthetic resin and additives by melt molding.

Additives include plasticizers, stabilizers, fillers, lubricants, colorants, UV absorbers, modifiers, etc.

It has the characteristics of light weight, corrosion resistance, beautiful appearance, no bad smell, easy processing and convenient construction. There are two types of plastic pipes: thermoplastic pipes and thermosetting plastic pipes.

The main resins used in thermoplastic pipes are polyvinyl chloride resin (PVC), polyethylene resin (PE), polypropylene resin (PP), polystyrene resin (PS), acrylonitrile-butadiene-styrene resin (ABS). ), polybutene resin (PB), etc.

The main resins used in thermosetting plastics are unsaturated polyester resins, epoxy resins, phenolic resins, etc.

1.1 Performance of plastic pipes

1.1.1 Physical Properties:

The physical properties of plastic pipes affect the installation method, use, compensation measures and pipe insulation of pipes.

1). The mechanical properties of PVC-U, PP, and ABS are relatively high, and they are regarded as "rigid pipes", which are better for surface installation. On the contrary, PE, PE-X and PB are suitable for concealed application as "flexible pipes".

2). The use temperature and heat resistance of plastic pipes determine that PVC-U, PE and ABS can only be used for cold water pipes, while PE-X, PP and PB can be used as hot water pipes. When the building has a hot water supply system and the hot and cold water uses a unified pipe, the heat resistance becomes the main indicator.

3). The plastic pipe has a high thermal expansion coefficient. When used as a hot water pipe, there are many thermal compensation measures such as flexible interfaces, expansion joints or various bending positions. Among them, polyolefins such as PE and PP are the most popular. If there is no sufficient

If enough attention is paid and corresponding technical measures are taken, the problem of pulling off of the expansion joint at the interface is very likely to occur.

4). Due to the low thermal conductivity, the thermal insulation performance of the plastic pipe is excellent, which can reduce the thickness of the thermal insulation layer or even eliminate the need for thermal insulation.

In addition to thermal conductivity, the comparison of thermal insulation between different plastic pipes is also related to their respective pipe wall thicknesses.

1.1.2 Pressure bearing performance:

The content involved in the pressure bearing performance is the internal pressure that the plastic pipe can withstand under certain conditions and the failure time under constant pressure. In order to determine the design parameters related to it, and to evaluate and monitor the quality of the pipe. Two tests are generally performed: hydraulic test and long-term high temperature hydraulic test.

1.1.3 Sanitary performance:

Physical and chemical health indicators. Among them, PE, PE-X, PP, PB and ABS are easy to meet the standard.

Non-toxic PVC resin and stabilizer should be used in the production of PVC-U pipes to meet the requirements of hygienic performance.

1.2 Advantages and disadvantages of plastic pipes:

The raw material composition of the plastic pipe determines the characteristics of the plastic pipe.

1.2.1 Advantages:

1). It has good chemical stability, is not affected by environmental factors and the composition of the medium in the pipeline, and has good corrosion resistance.

2). Small thermal conductivity, low thermal conductivity, thermal insulation, good energy saving effect.

3). The hydraulic performance is good, the inner wall of the pipe is smooth, the resistance coefficient is small, it is not easy to scale, and the flow area in the pipe does not occur with time

Change, the probability of pipeline blockage is small.

4). Compared with metal pipes, it has low density, light material, convenient transportation and installation, flexibility, simplicity and easy maintenance.

5). With natural bending or cold bending performance, the coil supply method can be used to reduce the number of pipe joints.

1.2.2 Disadvantages:

1). The mechanical properties are poor, the impact resistance is poor, the rigidity is poor, and the straightness is also poor, so the density of pipe clamps and hangers is high.

2). Poor flame retardancy, most plastic products are flammable and thermally decomposed when burning, releasing toxic gases and fumes.

3). The thermal expansion coefficient is large, and the expansion and contraction compensation must be emphasized.

1.3 Commonly used plastic pipes are:

●Rigid polyvinyl chloride pipe (PVC-U);

●High-density polyethylene pipe (PE-HD);

●Cross-linked polyethylene pipe (PE-X);

●Random copolymer polypropylene pipe (PP-R);

●Polybutene tube (PB);

• Acrylonitrile-butadiene-styrene copolymer (ABS).

1.4 Water supply plastic pipe:

Rigid polyvinyl chloride plastic pipes and fittings for water supply are made of food hygiene-grade polyvinyl chloride resin as the main raw material, adding non-toxic special additives, and then mixing, plasticizing, extruding or injecting. The products meet the national drinking water hygiene standards.

The water supply plastic pipe has a single structure, many kinds of materials and different properties.

The characteristics of common water supply plastic pipes are as follows:

Model Connection method Advantages Disadvantages PVC-U bonding, thread Strong corrosion resistance, easy to bond, cheap, hard texture Yes

UPVC monomer and additives bleed and are not suitable for hot water delivery.

PP-R hot melt good temperature resistance under the same pressure and medium temperature

Under the conditions, the wall of the pipe is the thickest

PEX extrusion clamping Good temperature resistance and creep resistance Only metal can be used

Piece connection; cannot be recycled and reused

HDPE extrusion clamping/thermal fusion/electric fusion Good toughness, good fatigue strength, better temperature resistance

Good, light weight, good flexibility and impact resistance Welding requires electricity, mechanical connection, connection

large

PB extrusion clamping, thermal fusion, electric fusion Good temperature resistance, good tensile and compressive strength,

Impact resistance, low creep, high flexibility There is no PB resin raw material in China, relying on imported

mouth, high price

ABS bonding, threading, electro-fusion High strength, impact resistance Poor UV resistance, long bonding curing time

In general, because of its low price, PVC pipes are the first choice for cold water water supply systems without considering the impact of water quality. When the temperature is high, polyethylene pipes or cross-linked polyethylene pipes, polypropylene pipes, polybutene pipes can be used. Tube.

1.5 Drainage plastic pipe:

The material is relatively simple: hard polyvinyl chloride.

Various structural forms: core layer foam tube, hollow wall tube, spiral tube, core layer foam spiral tube, hollow wall spiral tube.

1.5.1 Disadvantages:

1). The thermal expansion coefficient is large, which needs to be solved by setting up a telescopic compensation device.

2). The rigidity is small and the straightness is poor, so it is necessary to encrypt the pipe clamps, brackets and hangers.

3). Poor heat resistance and low softening temperature, it is necessary to limit the drainage temperature, limit the use site and control the distance from the heat source.

4). The flame retardancy is poor, and fire-stop rings and fire-proof casings should be set at the roof panels that pass through the floor, the roof, the firewall, and the wall of the pipeline well.

5). Poor mechanical shock resistance.

6.) The sound insulation is poor, the noise of the plastic pipe is greater than that of the cast iron pipe, the problem is particularly prominent when the pipe is exposed and the pipe is located close to the bedroom.

The core layer foam pipe and the hollow wall pipe are taken to improve the sound insulation effect of the pipe material to achieve noise reduction; another way to reduce noise is to change the water flow conditions, and the spiral pipe is developed based on this idea. The idea of combining the two methods resulted in a core foamed helical tube and an empty walled helical tube. Under the same conditions, the noise measurement results of drainage plastic pipes with different structures are: ordinary pipe>core layer foam pipe>empty wall pipe>spiral pipe

1.6 Commonly used plastic pipes

1.6.1 Rigid Polyvinyl Chloride Pipe (UPVC)

In the world, UPVC pipe is the most consumed variety of various plastic pipes, and it is also a new type of chemical building material that is being vigorously developed at home and abroad. The use of this kind of pipe can play a positive role in alleviating the situation of steel shortage and energy shortage in our country, and the economic benefits are remarkable. UPVC pipe has the following characteristics:

1). Good chemical corrosion, no rust;

2). It is self-extinguishing and flame retardant;

3). Good aging resistance, can be used between -15℃-60℃ for 20-50 years;

4). The inner wall is smooth and the surface tension of the inner wall makes it difficult to form scale, and the fluid transport capacity is 43.7% higher than that of cast iron pipes;

5). Light weight, easy flaring, bonding, bending, welding, installation workload is only 1/2 of the steel pipe,

Low labor intensity and short construction period;

6). Good resistance performance, volume resistance 1-3 × 105Ω. cm, breakdown voltage 23-2kv/mm;

7). Low price;

8). Save metal energy;

9). The toughness of UPVC pipe is low, the coefficient of linear expansion is large, and the operating temperature range is narrow.

Main application fields of rigid polyvinyl chloride pipe (UPVC):

1) Building water supply and drainage pipeline system;

2) Building rainwater system;

3) Pipes for building electrical wiring;

4) Air conditioning condensate water system

1.6.2 Core layer foamed pipe (PSP)

The core layer foamed pipe is a new type of pipe with a low foaming layer with a relative density of 0.7-0.9 in the middle, which is produced by a three-layer co-extrusion process. Due to the use of the I-type structure principle in material mechanics in structure, and the foam core layer with energy absorption and sound insulation effect, it has gradually become a

A plastic pipe that replaces cast iron pipes, rigid PVC solid wall pipes, etc.

Core layer foam pipe (PSP) has the following characteristics:

1). The impact strength is significantly improved: its hoop rigidity is 8 times that of ordinary UPVC pipes.

2). Wide range of use: it can be used at -30℃-100℃, and the size is stable when the temperature changes

good sex.

3). The foamed core layer can effectively block the noise transmission, which is more conducive to the drainage system of high-rise buildings.

4). Good thermal insulation, 35% lower heat transfer efficiency than non-foamed solid wall pipes.

5). The foamed core layer greatly improves the compression resistance of the inner wall.

6). Compared with solid wall pipes, it can save more than 25% of raw materials, and the larger the diameter, the more raw materials can be saved.

7). The pipe is light, easy to transport and install.

8). The service life in the bent state is more than ten years longer than that of the solid wall pipe.

The main application fields of the core layer foamed pipe (PSP);

1). Drainage system of civil buildings;

2). Industrial protection and conveying liquids;

3). Agricultural microporous irrigation, drainage and irrigation;

4). Electricity, communication cable conduit.

1.6.3 Rigid PVC muffler pipe

Rigid polyvinyl chloride muffler pipe is a new type of building drainage pipe developed by South Korea in the early 1970s. It has obtained patents in Japan, Germany, France, Switzerland and other countries.

The inner wall of the UPVC muffler pipe is provided with six triangular convex helix lines, so that the sewage flows freely and continuously in a spiral shape along the inner wall of the pipe, and the drainage is rotated to form the best drainage conditions, so as to play a good role in energy dissipation at the bottom of the riser and reduce noise. . At the same time, the unique structure of the muffler pipe can make the air form an air column in the center of the pipe to be discharged directly, there is no need to set up a special ventilation pipe as in the past, so that the drainage and ventilation capacity of high-rise buildings can be increased by 10 times, the drainage volume is increased by 6 times, and the noise is higher than that of ordinary UPVC drainage. Pipes and cast iron pipes are 30-40Db lower. UPVC silencer with

When used together with the muffler pipe fittings, the drainage effect is good.

In addition to the characteristics of UPV, the rigid PVC muffler pipe also has the following characteristics:

1) High water-passing ability and fluid conveying ability;

2) High ventilation capacity;

3) Noise reduction and sound insulation;

4) Economical and energy saving;

5) Easy to construct and maintain;

6) Can withstand temperature and settlement deformation of buildings. No expansion joints are required.

Rigid PVC muffler pipe is mainly used in drainage pipe system, especially in high-rise building drainage pipe system.

1.6.4 Plastic bellows

The plastic corrugated pipe adopts a special "annular groove" special-shaped section in the structural design. This kind of pipe has a novel design and a reasonable structure, breaking through the "plate" traditional structure of ordinary pipes, so that the pipe has sufficient compressive and impact resistance strength. , and has good flexibility. According to the different forming methods, it can be divided into single split corrugated pipe and double wall corrugated pipe.

Features of plastic bellows:

1). It has both rigidity and flexibility, which not only has sufficient mechanical properties, but also has excellent flexibility;

2). Compared with the plate pipe, the corrugated pipe per unit length has the advantages of light weight, material saving, energy consumption reduction and price reduction.

Cheap;

3). The bellows with smooth inner wall can reduce the flow resistance of liquid in the pipe and further improve the conveying capacity;

4). Strong chemical corrosion resistance, can withstand the influence of acid and alkali in the soil;

5). The corrugated shape can strengthen the load resistance of the pipeline to the soil without increasing its flexibility, so that it can be continuously laid on uneven ground;

6). The interface is convenient, the sealing performance is good, the handling is easy, the installation is convenient, the labor intensity is reduced, and the construction period is shortened;

7). Wide temperature range, flame retardant, self-extinguishing, safe to use;

8). It has good electrical insulation performance and is an ideal material for wire sleeves.

The main application areas of plastic bellows:

1) Municipal water supply and drainage pipeline system;

2) Building electrical wiring and piping;

3) Agricultural irrigation;

4) Piping of automobile oil pipeline;

1.6.5 Chlorinated Polyvinyl Chloride Pipe (CPVC)

Chlorinated polyvinyl chloride pipe is a kind of plastic pipe with good heat resistance obtained by processing the so-called perchlorinated vinyl resin with a chlorine content of up to 66%. Chlorinated polyvinyl chloride resin is obtained by chlorination of PVC resin. With the increase of chlorine content in the resin, its density increases, its softening point, heat resistance and flame retardancy increase, its tensile strength increases, and its melt viscosity increases. Large, excellent chemical resistance, no deformation in boiling water. Features of CPVC pipe:

1). Wide temperature range: -40℃-95℃;

2). Has good strength and toughness;

3). Has good chemical corrosion resistance;

4). The flame retardant performance is self-extinguishing;

5). Low thermal conductivity, about 1/200 of steel;

6). The content of heavy ions in the medium reaches the standard of ultrapure water;

7). The hygienic performance meets the requirements of national sanitation standards;

7). The wall of the pipe is clean and smooth: it has less frictional resistance and adhesion when transporting fluid;

8). Light weight: equivalent to 1/5 of the steel pipe, 1/6 of the steel pipe;

9). Easy installation: can be connected by bonding, threading, welding, etc.;

10). Excellent anti-aging and anti-ultraviolet performance, long normal service life.

The main application areas of chlorinated polyvinyl chloride pipes:

1). Building air-conditioning system, drinking water pipeline system, underground water discharge pipeline, swimming pool and hot spring

pipeline;

2). Industrial piping system;

3). Food processing pipeline system;

4). Water supply and sewage plant piping system;

5). Agricultural irrigation.

1.6.5 High Density Polyethylene Pipe (HDPE)

High-density polyethylene pipe is valued by the pipeline industry due to its excellent chemical properties, toughness, wear resistance, low price and installation cost

, it is the second most used plastic pipe material after polyvinyl chloride. High-density polyethylene pipe (HDPE) double-wall corrugated pipe is a kind of pipe with low material consumption, high rigidity, excellent flexibility, corrugated outer wall and smooth inner wall. Compared with ordinary pipes of the same specification and strength, the double-wall pipe can save 40% of material, and has the characteristics of high impact resistance and high compression resistance. Widely used as drainage pipes, sewage pipes, underground cable pipes, agricultural irrigation and drainage pipes.

1.6.7 Random copolymer polypropylene pipe (PP-R)

Polypropylene can be divided into homopolypropylene and copolymerized polypropylene, and copolymerized polypropylene is further divided into block copolymerized polypropylene (PPC) and random copolymerized polypropylene (PP-R).

Random copolymer polypropylene, also known as tri-type polypropylene, is a copolymer in which propylene and other comonomer segments are randomly distributed on the main chain. The raw material of PP-R is polyolefin, and its molecule only has carbon and hydrogen elements, which is non-toxic and has reliable hygienic performance.

PP-R will not adversely affect the human body and the environment in the whole process of raw material production, product processing, use and disposal, and it has become a green building material with the same generation of cross-linked polyethylene pipes.

In addition to the advantages of general plastic pipes, such as light weight, good strength, corrosion resistance and long service life, PP-R pipes have the following characteristics:

1). Non-toxic hygiene: meet the requirements of national hygiene standards:

2). Heat-resistance and heat preservation: the Vicat softening point of PP-R tube is 131.3℃, and the maximum service temperature is 95℃.

The operating temperature is 70℃; the thermal conductivity is 0.21W/m, ℃, which is only 1/200 of the steel pipe, and has good thermal insulation performance;

3). Simple and reliable connection and installation: PP-R pipe has good hot melt welding performance, and the pipe is connected with the pipe fittings.

The strength of the part is greater than the strength of the pipe itself, and there is no need to consider whether the connection will leak during long-term use;

4). Good elasticity and anti-freeze cracking: The excellent elasticity of PP-R material makes pipes and fittings resistant to frost heave liquids

Expand together so that they are not burst by frost heaving liquids;

5). Good environmental performance;

6). The linear expansion coefficient is larger, 0.14-0.16mm/m. k;

7). Poor anti-ultraviolet performance: easy to age under long-term direct sunlight.

The main application areas of pipes:

1) Public and civil buildings are used to transport cold and hot water and heating systems;

2) In industrial buildings and facilities, it is used to transport daily water, oil or corrosive liquids;

3) Due to its corrosion resistance to salt water, it is used for water supply pipelines in seaside facilities;

4) Air conditioning piping system;

5) Agricultural irrigation system;

1.6.7 Polybutene Pipe (PB)

PB resin is a high molecular polymer obtained by synthesizing 1-butene, and is an isotactic polymer with a slightly lower isotacticity than polypropylene. It not only has the impact toughness of polyethylene, but also the stress cracking resistance and excellent creep resistance higher than that of polypropylene, and has the characteristics of rubber, and can withstand the stress of 90% of the gas yield strength for a long time.

In addition to the advantages of general plastic pipes, such as good hygienic performance, light weight, easy installation and long life, polybutene pipe (PB) also has the following characteristics:

1). Heat resistance: high heat distortion temperature, easy to use heat resistance, 90 ℃ hot water can be used for a long time;

2). Antifreeze: low embrittlement temperature (-30°C), freezing will not crack within -20°C;

3). Good flexibility; bending radius is only R12;

4). Good thermal insulation;

5). Good insulation performance;

6). Corrosion resistance (easy to be attacked by hot and concentrated oxidizing acid);

7). Environmental protection and economy: waste can be reused, and no harmful gas is produced when burned.

The main application areas of polybutene pipe (PB);

1). Used for various hot water pipes: residential hot water, hot spring water diversion, greenhouse hot water, road and airport snow melting

Waiting for hot water pipes;

2). Industrial pipes

3). Gas pipeline;

4. ) Used to transport abrasive and corrosive hot materials in industrial sectors such as mining, chemical and power generation.

1.6.8 ABS pipe

ABS resin is a terpolymer developed on the basis of polystyrene resin modification. ABS resin is composed of three elements of acrylonitrile-butadiene-styrene. where A represents acrylonitrile, B represents diene, and S represents styrene.

ABS pipe is a new type of corrosion-resistant pipe, it has good impact strength and surface hardness within a certain temperature range, good comprehensive performance, easy to form and machine, and the surface can also be chrome-plated. It has both the corrosion resistance of PVC pipes and the mechanical properties of metal pipes.

Features of ABS pipe;

1). Has good impact strength, which is 5-6 times that of PVC pipe; and can withstand higher working pressure

force, about 4 times that of PVC pipe;

2). Stable chemical properties: non-toxic and tasteless, resistant to acid and alkali, and also non-toxic and non-toxic when used in the food industry

taste;

3). Wide operating temperature range: the operating temperature range is -40℃-80℃;

4). Light weight and low resistance; ABS pipe is light, 0.8 times that of PVC, and the inner and outer walls of the product are smooth.

small resistance;

5). The pipeline connection is convenient and the sealing performance is good;

The main application areas of ABS pipe:

1). Purified water system;

2). Petrochemical industry piping system;

3.) Environmental protection industry.

Types and applications of plastic pipes

Types of pipes/municipal water supply/municipal drainage/building cold water/building hot water/building drainage/threading pipes/floor radiant heating/pipeline maximum diameter (mm/stiffness

rigid polyethylene pipe

（PUC-U ） ● ● ● ● ● ≤1000 straight pipe rigid PVC noise reduction ● ● 75, 110 straight pipe chlorinated polyvinyl chloride pipe (PVU-C ● ● ≤200 straight pipe core layer foam composite pipe (PSP ) ● ● ● 50-160 straight pipe plastic corrugated pipe ● ● ● 300 straight pipe random copolymer polypropylene pipe (PP-R) ● ● ● 110 coil/straight pipe cross-linked polyethylene pipe (PEX) ● ● ● ● 63 Coiled/Straight High Density Polyethylene Pipe (HDPE) ● ● ● 315 Coiled/Straight Polybutylene Pipe (PB) ● ● 32 Coiled/Straight ABS Pipe ● 200 Straight

2. Metal tube

2.1 Galvanized steel pipe

The replacement of galvanized steel pipe does not mean that metal pipes are replaced, nor does it mean that galvanized steel pipes are replaced in the entire building water supply field.

Steel pipes are divided into seamless steel pipes and welded steel pipes according to their manufacturing methods.

Seamless steel pipes are made of high-quality carbon steel or alloy steel, and are divided into hot-rolled and cold-rolled (drawn).

Welded steel pipes are made of rolled steel plates and welded with butt or spiral seams.

In terms of manufacturing methods, it is further divided into welded steel pipes for low-pressure fluid transportation, spiral seam electric welded steel pipes, direct coil welded steel pipes, and electric welded pipes.

Seamless steel pipes can be used for various liquid and gas pipelines, etc. Welded pipes can be used for water pipes, gas pipes, heating pipes, etc.

2.2 Cast iron pipe

Compared with steel pipes, cast iron pipes for water supply have the advantages of not easy corrosion, low cost and good durability, and are suitable for buried laying. The disadvantage is that it is brittle, heavy, and small in length. The connection method generally adopts socket connection and flexible connection. The traditional gray cast iron pipe destroys the iron base due to the "splintering" effect of the flake graphite on the iron base. In addition, the pipe wall is rough and easy to block; the cement interface needs maintenance, causing construction trouble and other reasons, which have been gradually eliminated from the market.

Ductile cast iron, also known as spheroidal graphite cast iron, has strength and toughness comparable to that of steel, good ductility, and the same internal corrosion as gray cast iron. Ductile iron pipes produced with spheroidal graphite cast iron have good adaptability to more complex use environments

2.3 Copper and copper alloy pipes:

The most advantageous metal pipes are copper pipes. Copper pipes have been used for a long time and have many advantages. The pipes and fittings are complete, and the interface methods are various. They are mostly used in hot water pipelines. The main problem at present is the folding of copper. The output is easy to exceed the standard.

Copper pipes are mainly made of pure copper and phosphorus deoxidized copper, which are called copper pipes or red copper pipes.

Brass pipes are made of ordinary brass, lead brass and other brass.

2.4 Stainless steel tube

2.4.1 Advantages

1). Excellent corrosion resistance.

The thin and strong oxide film on the surface of stainless steel makes stainless steel have excellent corrosion resistance in all water quality and is suitable for various water quality. There is no corrosion and excessive exudate, which can keep the water pure and hygienic and prevent secondary pollution.

2). Excellent mechanical and physical properties.

Stainless steel water pipes have very high strength, can withstand vibration and shock well, and have the characteristics of no leakage, no bursting, fire resistance, shock resistance, etc., so they are very safe and reliable; at the same time, they have good thermal insulation performance, especially suitable for hot water transportation. Field corrosion test data show that the service life of stainless steel water pipes can reach 100 years, and stainless steel water pipes hardly need maintenance. Therefore, its performance-price ratio is very good, the operating life cost is low, and the economic benefits are significant. Due to the advantages of stainless steel pipes, they are widely used in food, medical, chemical, and petroleum industries. However, in the past, industrial stainless steel pipes had thick walls and were expensive to manufacture. The field of water supply has been greatly restricted, and the emergence of thin-walled stainless steel pipes has solved this problem.

2.5 Introduction of commonly used metal pipes:

2.5.1 Welded steel pipe:

1). Welded steel pipe and galvanized welded steel pipe for low pressure fluid transportation

Welded steel pipes for low-pressure fluid transportation are made of mild carbon steel and are the most commonly used small-diameter pipes in pipeline engineering. They are suitable for transporting water, gas, steam and other media. Zinc pipe (commonly known as white iron pipe) and non-galvanized pipe (commonly known as black iron pipe). The inner and outer walls coated with a zinc protective layer are about 3%-6% heavier than the non-galvanized ones. According to the different wall thickness of the pipe, it is divided into three types: thin-walled pipe, ordinary pipe and thickened pipe. Thin-walled pipes are not suitable for conveying media and can be used as casings.

2). Straight seam coiled electric welded steel pipe

The straight seam coiled electric welded steel pipe can be divided into electric welded steel pipe and straight seam welded steel coiled and welded by steel plates on site.

Tube. Several wall thicknesses can be made.

3) Spiral seam welded steel pipe:

Spiral seam welded steel pipe is divided into two types: automatic submerged arc welded steel pipe and high frequency welded steel pipe.

a). Spiral seam automatic submerged arc welded steel pipe is divided into two categories: Class A pipe and Class B pipe according to the pressure of the conveying medium. Type A pipes are generally welded with ordinary carbon steel Q235, Q235F and ordinary low-alloy structural steel 16Mn, and Type B pipes are welded with steels such as Q235, Q235F and Q195, and are used as low-pressure fluid conveying pipes. b). Spiral seam high frequency welded steel pipe Spiral seam high frequency welded steel pipe, there is no unified product standard, generally made of ordinary carbon steel Q235, Q235F and other steel.

2.5.2 Seamless steel pipe:

Seamless steel pipes are divided into hot-rolled pipes and cold-drawn (rolled) pipes according to the manufacturing method.

The maximum nominal diameter of cold drawn (rolled) pipe is 200mm, and the maximum nominal diameter of hot rolled pipe is 600mm. In pipeline engineering, when the diameter of the pipe exceeds 57mm, the hot-rolled pipe is often used, and when the pipe diameter is less than 57mm, the cold-drawn (rolled) pipe is often used.

1). General seamless steel pipe:

Generally, seamless steel pipes are referred to as seamless steel pipes. They are made of ordinary carbon steel, high-quality carbon steel, ordinary low-alloy steel and alloy structural steel. They are used to make liquid pipelines or make structures and parts.

Seamless steel pipes are supplied according to the outer diameter and wall thickness. There are various wall thicknesses under the same outer diameter, and the pressure range is large. Usually the length of steel pipe is 3-12.5m for hot-rolled pipe and 1.5-9m for cold-drawn (rolled) pipe.

2). Seamless steel pipes for low and medium pressure boilers:

Seamless steel pipes for low and medium pressure boilers are made of No. 10 and No. 20 high-quality carbon steel.

2.5.3 Cast iron pipes:

Cast iron pipes are made of pig iron.

According to the different manufacturing methods, it can be divided into: sand type centrifugal socket straight pipe, continuous cast iron straight pipe and sand type iron pipe. According to the different materials used, it can be divided into: gray iron pipe, ductile iron pipe and high silicon iron pipe.

Cast iron pipes are mostly used in plumbing projects such as water supply, drainage and gas.

1) Feed water cast iron pipe:

a). Sand type centrifugal cast iron straight pipe:

The sand type centrifugal cast iron straight pipe is made of gray cast iron, which is suitable for the transportation of pressure fluids such as water and gas. b). Continuous cast iron straight pipe:

The continuous cast iron straight pipe is the continuously cast gray cast iron pipe, which is suitable for the transportation of pressure fluids such as water and gas. c). Drainage cast iron pipe:

Ordinary drainage cast iron socket pipe and pipe fittings.

Flexible anti-seismic interface drainage cast iron straight pipe, this type of cast iron pipe is sealed with rubber rings and fastened with bolts, and has good flexibility and elasticity under internal water pressure. Can adapt to large axial displacement and lateral deflection deformation, suitable for indoor drainage pipes of high-rise buildings, especially suitable for earthquake areas.

d). Ductile iron pipe:

The advantages are outstanding:

The pipe wall is uniform, the structure is dense, the surface is smooth, and there are no defects such as trachoma and slag inclusion;

●Excellent sound insulation effect;

●Flexible interface, easy to install and save construction cost; It can be slightly disturbed and has excellent shock resistance; ●High strength, impact resistance, corrosion resistance, long service life and good fire resistance;

Ductile iron pipes can also be lined with various protective layers according to the use environment and the nature of the conveying medium to meet different use requirements. It has been widely used in construction, municipal, petrochemical and other industries.

2.5.4 Aluminum and aluminum alloy pipes

Aluminum and aluminum alloys refer to industrial pure aluminum containing 98% aluminum and aluminum alloys with copper, magnesium, manganese, zinc, chromium and other alloying elements as the main body. Aluminum and aluminum alloy pipes are drawn or extruded from industrial pure aluminum or aluminum alloys.

Aluminum has good acid corrosion resistance.

3. Composite pipe

Most of the composite pipes are composed of working layer (requires water corrosion resistance), support layer, and protective layer (requires corrosion resistance). The composite pipe is generally made of metal as the supporting material, and the lining is mainly epoxy resin and cement. It is characterized by light weight, smooth inner wall, low resistance and good corrosion resistance;

There are also high-strength soft metals as support, instead of metal pipes on both sides, such as aluminum-plastic composite pipes, which feature that the inner wall of the pipe will not corrode and scale to ensure water quality;

There are also metal pipes on the inside and non-metal pipes on the outside, such as plastic-clad copper pipes, which use the poor thermal conductivity of plastics for thermal insulation and protection.

According to the metal material can be divided into:

(1).Steel-plastic composite pipe

(2).Stainless steel-plastic composite pipe, plastic coated stainless steel pipe

(3).Plastic clad copper tube

(4). Aluminum-plastic composite pipe, cross-linked aluminum-plastic composite pipe

(5) Plastic-lined aluminum alloy pipe

The connection of the composite pipe should adopt the cold working method, and the hot working method is easy to cause the expansion, deformation and even melting of the lining plastic. Generally, there are thread, ferrule, clamp and other connection methods.

3.1 Brief introduction of several commonly used composite pipes:

3.1.1 Steel-plastic composite pipe

Steel-plastic composite pipe is a kind of metal and plastic composite pipe, which is rolled into a steel pipe with galvanized steel strip and welded by argon arc, and has a plastic layer inside and outside.

The steel-plastic composite pipe overcomes the defects of easy rust, pollution, bulky, short service life, low strength, large expansion and easy deformation of the steel pipe, and has the common advantages of the steel pipe and the plastic pipe, such as oxygen barrier. good sex, high rigidity

High strength and high strength, buried pipes are easy to detect, etc.

advantage:

1). Excellent physical properties:

Compared with plastic pipes, it has higher strength, rigidity and impact resistance; it has low expansion coefficient and creep resistance similar to steel pipes. The buried pipe can withstand the external pressure much higher than that of the all-plastic pipe; excellent corrosion resistance, can be installed without any anti-corrosion treatment, saving engineering costs; small expansion coefficient, linear expansion coefficient is only 12 × 10-5/℃ .

2). Small damping coefficient

The pipe wall is smooth, the fluid resistance is small, and there is no scaling, and the head loss is 30% lower than that of the metal pipe under the same pipe diameter and pressure conditions.

3). Stable pressure bearing performance

The complete steel pipe layer is the main pressure-bearing layer of the pipe body, and the pressure-bearing capacity of the pipe is not affected by the performance change of the plastic layer.

4). Self-traceability

Magnetic metal detectors can be used for tracking, and there is no need to bury tracking or protection marks, which can avoid excavation damage and provide great convenience for emergency repair and maintenance.

5). Windability

Can be bent, underground installation can effectively withstand sudden shock loads caused by settlement, slip, vehicles, etc. Improved operational reliability. The fixed-length (12m) single steel-plastic composite pipe can be bent 25° in one direction, saving the consumption of small-angle steering elbows.

6). Wide temperature range

7). Low thermal conductivity

8). Light weight, easy to transport and install; long service life and low comprehensive cost.

3.1.2 Aluminum-plastic composite pipe

Generally, the middle layer is aluminum tube, and the inner and outer layers are polyethylene, which are compounded by hot-melt co-extrusion. The general working pressure is 1.0MPa, and the burst pressure is 7.0MPa.

advantage:

(1). Non-toxic and tasteless, fully comply with hygienic standards,

(2). It has the characteristics of high temperature resistance and low temperature resistance.

(3). Oxygen barrier, completely eliminate penetration.

(4). Absorb the rebound energy of the tube when bending, so that the tube can be arbitrarily formed; it can be bent without rebound, and a single tube can be

Up to several hundred meters in length, providing convenient conditions for construction and installation.

(5). With antistatic properties, it can be used to transport gas and oil.

(6). At room temperature, the inner and outer polyethylene layers are insoluble in any known solvent, and can resist the corrosion of various acids, alkalis and salt solutions.

(7) The buried position of the pipe can be detected with a metal detector,

(8). The thermal conductivity is 0.45W/m*k, which is far less than the thermal conductivity of metal pipes.

(9) The inner surface is smooth and the head loss is small.

(10). The cutting is convenient and the construction period is shortened.

Four, pipe fittings

Pipe fittings are also called pipe fittings, connectors, joint parts, etc. The pipes in various piping systems are connected with different joints and fittings to form a pipeline.

4.1 Malleable cast iron (Mal Steel) pipe fittings:

Made of malleable iron, threaded to the pipe. The working pressure is within 0.1Mpa. Its appearance is characterized by thick edges at the ends. to increase the connection strength.

Malleable iron pipe fittings are mainly used for extension, branching and turning of pipes. Malleable iron pipe fittings mainly have the following varieties:

4.1.1 Direct:

Used to connect pipes with the same diameter on the same line, there are two kinds of through wire and non-through wire;

The reducer is directly called the size head, which is used to connect two pipes with different diameters on the same line;

Different diameter eccentric head, the center lines of the big and small ends do not overlap, and it is used to connect two horizontal pipes with different diameters located on the upper and lower sides of the same horizontal line;

4.1.2 Elbow:

It is used at right-angle bends of pipes to connect two equal-diameter pipes that are perpendicular to each other;

Reducing elbow, connecting two pipes of unequal diameter that are perpendicular to each other;

4.1.3 45° bend;

4.1.4 Tee:

The two ends in the straight line have the same diameter and the end that is perpendicular to it is a small pipe diameter, which is used for the connection of small diameter branch pipes; the 45° inclined tee is also called a Y-shaped branch pipe. less resistance;

4.1.5 Four-way:

It is used for the vertical cross-connection of the pipe; the reducing cross is used when connecting two branch pipes with smaller pipe diameters vertically on the pipeline;

4.1.6 Tonic for heart:

Also known as inner and outer wire, inner and outer wire, the inner wire is small, the outer wire is large, the outer wire is connected with other pipe fittings, and the inner wire is directly connected to the pipe, which is used for the reducing connection of the pipe;

4.1.7 External screw short connector:

Used to connect two abutting pipe fittings; often replaced by short pipe joints spun by lathes, very short joints are called butt wires.

4.1.8 Thread plug:

Also known as a plug, the plug is an external thread used to block the orifice of the pipe fitting.

4.1.9 Union:

It consists of two male and female joints that can be buckled with each other, and a female set connecting the male and female mouths.

Use rubber pads or asbestos paper pads to prevent water leakage. The union is used in the pipeline where the same diameter pipeline needs to be connected, so as to facilitate disassembly and maintenance.

4.1.10 Lock nut:

Also known as root mother affix, root hoop, a short pipe section with a short thread at one end and a long thread at the other end (with no tip at the root) and a root mother, plus another inner wall with a straight wire directly forms a long thread. Silk, which acts as a live joint, is used as a detachable live connection.

4.1.11 Flange:

The left and right two pieces form a pair, and the function is the same as the live joint. The specification is more than d50mm in diameter. Since the two ends of the large-sized valve are mostly flanged interfaces, the flanges are also mostly used for the connection between the pipeline and the valve.

4.2 Steel and malleable iron pipe fittings:

When the steel pipe is connected by thread, if the working pressure is high (but within 1.6Mpa), steel pipe fittings can be used. Steel pipe fittings are made of carbon steel, commonly known as wrought iron pipe fittings. It has good weldability and can be used where welding is required.

There are mainly the following varieties:

4.2.1 Press the reducer

4.2.2 Welding elbows

4.2.3 Welded reducers (concentric, eccentric)

4.2.3 Welding three-energy, four-way

4.3 Cast iron pipe fittings for water supply:

Cast from grey cast iron.

There are two types of cast iron pipe fittings for water supply: socket type and flange type. Their uses are similar to malleable cast pipes. They mainly have the following types:

Cross tube, T-tube (including three-column cross tube, three-coil cross tube, four-column cross tube, four-coil cross tube, double-column T-tube, double-coil T-tube, three-column T-tube, three-coil T-tube, double-column single tube 90° elbow, 45° elbow; fork pipe; B-shaped pipe; fire hydrant pipe; casing, etc.

4.4 Drainage cast iron pipe fittings:

Mainly include socket and socket bending pipe, 90° elbow, 45°Y-shaped tee, 90°T-shaped tee, 90°TY-shaped tee, inclined tee, positive tee, TY-shaped reducing tee, reducing four Tee, pipe clamp, T-shaped bottle mouth tee, 45° elbow, Y-shaped reducing tee, socket and socket sweeping mouth, S-shaped water trap, P-shaped storage trap, floor drain and other varieties.

4.5 Plastic pipe fittings:

The specifications and functions are similar to the above-mentioned fittings, but the materials of manufacture are different.

4.6 Standard of pipe fittings:

4.6.1 Elbow:

The current international standard for elbows is the American national standard ANSIB16.9 and 16.28.

The standard outer diameter range is 1/2"~ 80". Generally, those within 24" are made of seamless steel pipes, and those from 26" to 80" are stamped with steel plates and then welded. The elbow is based on the radius of curvature. It can be divided into long-radius elbow and short-radius elbow. Long-radius elbow refers to its radius of curvature equal to 1.5 times the outer diameter of the pipe, that is, R = 1.5D. Short-radius elbow refers to its radius of curvature equal to the pipe Outer diameter, that is, R = D. The elbow is divided into 45 ° elbow, 90 ° elbow and 180 ° elbow. The maximum wall thickness can reach 60mm, and the minimum is

1.24mm.

4.6.2 Tee:

The outer diameter is in the range of 2.5"-60", from 26"-60" is welded tee, and the wall thickness is 28-60mm.

4.6.3 Size header:

Conventionally, we first talk about the big head specifications, and then talk about the small head specifications.

DN100-80;DN80-50