With the continuous improvement of people’s living standards, the decoration of bedrooms is becoming more and more beautified. It is the minimum requirement for decoration to bury various indoor pipelines. The “Code for Design of Urban Gas” (GB50028-937.2.17) allows pipelines to be installed concealed, but the requirements are strict. They can only be installed in suspended flat ceilings or in pipe trenches and pipe troughs. Pipe trenches and pipe troughs should be equipped with movable doors and ventilation holes. Hidden design under such conditions is difficult to accept in interior decoration. After the user understands these conditions. Some have no choice but to take risks and hide the gas pipes privately. In 1997 alone, during a safety inspection, our company found 55 households who secretly hid gas pipes. Among them, 15 households would rather have their gas supply stopped than make corrections. It is understood that this situation also exists in many cities with pipeline gas. If this problem is not solved, the development of pipeline gas will face obstacles and lose a lot of market share in the competition with bottled gas.
In today’s market economy. Can’t develop customers. is facing a crisis.
In order to meet the aesthetic requirements of users, our company has formulated some solutions for outdoor pipe layout as early as the beginning of its development: such as outdoor centralized metering, and the pipes behind the meter should be wrapped around the outer wall as much as possible. These methods meet the requirements of some users, but there are still some problems:
(1) The installation cost is high and users may not be able to afford it.
(2) The increase in exterior wall pipes makes maintenance and repair work more difficult. This problem is particularly prominent in high-rise buildings.
(3) If the user’s furnace or water heater is placed far away from the exterior wall, the indoor pipes will still be more exposed.
(4) In order to ensure the beautiful appearance of the building, some construction units or property management companies do not allow the installation of horizontal pipes on the exterior walls.
Under this circumstance, the company began to consider trial installation of hidden indoor pipes starting in 1997.
2Selection and determination of concealed pipe materials
In order to select pipe materials, our company’s technical staff repeatedly studied the “Urban Gas Design Code”, conducted in-depth research and discussion on Article 17 of Chapter 7, Section 2, and came to the following understandings:
(1) For pipelines, corrosion of the inner and outer walls and quality problems at the joints may cause gas leakage in the pipes. Installing movable doors and vents on hidden pipes can detect problems in time and facilitate maintenance.
(2) The pipe has strong corrosion resistance and has no interfaces, so there is no need to inspect the pipe frequently and no maintenance is required. This means that facilities such as movable doors and ventilation holes can be omitted, and the pipe can be buried directly. According to this idea, we have set several requirements for selecting pipe materials:
①Corrosion resistance, anti-aging, long life;
② There must be no interfaces in the directly buried part, that is, the pipe can be of any length and can be bent freely;
③ Its strength meets the requirements for conveying pressurized gas;
④The price is moderate and the installation is easy.
Seamless steel pipes and galvanized steel pipes are our most commonly used pipes. However, if these two pipes are buried concealed, the connection method must be welded. It is not practical to weld and perform weld flaw detection in every household. In addition, Anti-corrosion, as well as more expensive seamless elbows and other pipe fittings, the comprehensive cost is also unacceptable and obviously cannot be considered.
After repeated screening and comparison of various pipe materials, we found that copper pipes for air conditioning and aluminum-plastic composite pipes, which have only been launched in China in recent years, can basically meet the above requirements.
According to the information provided by the manufacturer, the composite pipe is made of a middle layer of longitudinally welded aluminum pipe, an inner and outer layer of PE (polyethylene), and a hot melt adhesive between the aluminum pipe and the inner and outer PE layers. Polyethylene has stable chemical properties and is insoluble in any organic solvent at room temperature. Its ignition point is also very high, reaching 340°C. The aluminum layer sandwiched in the middle strengthens the polyethylene, greatly improving the compressive strength of the pipe, and absorbs the rebound energy of the pipe wall when bending, so that the pipe can be shaped at will. The length of the pipe can be cut arbitrarily according to the user’s requirements (generally each roll is 100m-200m long), and the supporting pipe joints can easily connect it to other pipes and fittings, especially galvanized pipes. The Standards and Quotas Department of the Ministry of Construction clearly pointed out in its product standard evaluation report on a certain enterprise that aluminum-plastic composite pipes can be used as gas pipelines. The physical and chemical properties of the composite pipe are shown in Table 1 [excerpted from the test report of the National Chemical Building Materials Testing Center No. (91) Quantitative (Guo) Zi (80585)]:
Copper pipe is a more familiar material. According to information provided by the International Copper Association (China), gas systems in the United States, the United Kingdom and Australia have widely adopted the hidden copper pipe technology. It is easy to form, easy to install, has good plasticity, and has high strength, with a melting point as high as 1356K (1083℃). It will not burn in pure oxygen, but will only be flame retardant. It will not melt or release harmful or toxic gases in a general fire. The corrosion resistance of copper is also very good. Its corrosion resistance in some media is shown in the table. 2[Excerpted from “Corrosion and Protection Handbook”] It can be seen from Table 2 that copper is almost corrosion-resistant to various media that may be encountered in ordinary homes. Among the substances that are not resistant to corrosion, moisture has attracted our attention. Will the liquefied natural gas we currently use and the natural gas we will use in the future contain it? After our investigation and analysis, we found that this worry is unnecessary, because first, the current Imported liquefied products are commonly used in Guangdong, which have better temperament and fewer impurities. Our company has entrusted authoritative organizations to conduct component analysis on the purchased liquefied products several times, and no sulfide components were found. Second, the natural gas that will be used in Guangdong in the future is imported liquefied natural gas. Its liquid temperature is -161.5°C and it becomes solid at -82.90°C. Theoretically, it is a piece of cake to remove it in terms of technology. China National Offshore Oil Corporation The gas composition provided (see Table 3) also proves this.
The length of annealed copper coil can reach more than 50m, which can fully meet the requirements of hidden pipes without interfaces.
Among these two types of pipes, copper pipes should have more advantages than composite pipes in terms of strength, fire resistance, environmental protection and ease of installation (small pipe diameter, small bending radius), but the anti-corrosion performance of composite pipes is slightly better than that of copper pipes. One chip. When it comes to choosing which pipe material is better, practice is the only criterion for testing the truth. When it is difficult to judge the quality of the two pipe materials for a while, our company decided to conduct a pilot concealed installation of composite pipes and copper pipes at the same time. According to the installation and usage conditions Then decide the choice.
3. Formulation of installation technical standards
After initially selecting the materials for hidden pipes, the company formulated the installation regulations for hidden pipes based on relevant specifications, the performance characteristics of composite pipes and copper pipes, and the indoor pipe installation situation of residents in Foshan urban area. The main contents are as follows:
(1)Pipe diameter selection
When the length is ≤1Om, choose φ16×2 (1612) composite pipe or 1O×1 pure copper pipe.
When the length is >10m, choose φ18×2 (1814) composite pipe or 12×1.5 pure copper pipe.
(2) Burial requirements
① Composite pipes or copper pipes are installed in kitchens, bathrooms and living rooms, but installation in bedrooms is strictly prohibited.
② It should be buried in the leveling layer of the floor. If it is buried in the wall, it should be buried above the indoor elevation of 2m or below 1m to prevent nails from puncturing the pipe in the future (because most of the hanging objects are nailed at this location).
③If the composite pipe passes through the ceiling, a flexible armored casing (metal snakeskin pipe) or metal wire trough must be added for protection to prevent rat bites.
④The concealed pipe part must not have any interfaces.
⑤ Composite pipes can be installed in the open, but they cannot be laid on exterior walls to prevent ultraviolet rays from affecting the life of the pipes.
⑥When the exposed composite pipe is installed vertically from top to bottom, the horizontal clear distance from the edge of the stove should be greater than 0.4m to prevent fire.
⑦ Regardless of whether it is exposed or concealed, when the pipe crosses over the stove, the clear distance should not be less than 1.4m.
(3) Acceptance regulations
① A pressure test should be carried out immediately after the pipeline is installed. The test pressure is 10KPa. If there is no pressure drop within 10 minutes, it is qualified. Before ventilating and igniting, test the pressure again according to this standard. Only after it passes the test can ignition be carried out.
② The direction and relative elevation of the pipeline must be clearly marked on the as-built drawing, and a copy of the as-built drawing must be given to the user for reference.
4 Trial installation situation and summary
After the company launched the concealed pipe installation solution, it was widely welcomed by users. They came to the company one after another to inquire about the situation and put forward installation requirements. In the first half of 1998, 185 households had concealed composite pipes installed in their homes, and 40 households had concealed copper pipes installed in their homes. Many real estate companies were also very interested in this, and proposed installation intentions as part of their sales promotions. selling point. The comprehensive cost of copper pipes (material fees and installation fees) is about 20 yuan/m, which is lower than 30 yuan/m of composite pipes. However, more users use composite pipes than copper pipes, mainly because of the advertising of the composite pipe manufacturers themselves. And the sales network is doing better.
In order to understand the installation and use of hidden pipes, we continue to collect and study the opinions of installers and users, paying special attention to negative situations. So far, no users have been found to have problems with hidden pipes, but they were discovered during the inspection before ventilation and ignition. There are many problems that need to be corrected before ventilating. See Table 4 for details of this situation in 1998. The main problems focus on composite pipes.
We analyzed and compared the reasons for unsuccessful ignition and found that the reason why composite pipes fail to ignite more is that there are problems with the properties of the pipes and fittings themselves:
(1) The composite pipe itself is not strong enough and can be easily penetrated by nails. It may be damaged if the decoration workers do not pay attention to the hidden project completion drawings provided by us. Moreover, the diameter of composite pipes is larger than that of copper pipes, so the probability of being nailed is relatively higher.
(2) The connection between the composite pipe and the hose in front of the furnace must be in the form of a pipe fitting – Cock – hose. In order to avoid twisting the Cock without causing the composite pipe to move, a pipe code must be added to the exposed wall surface. , but since the addition of control codes is usually done after the magnetic sheets are pasted on the wall, a second visit is required. It often happens that residents forget to inform and code. The copper tube can be directly connected to the rubber tube (the copper tube is inserted into the rubber tube for more than 2cm and a tube clamp is added), without coding.
(3) The allowable bending radius of composite pipes is 5 times D, if it is less than this value. Or if the auxiliary spring is not inserted when bending, the pipe will easily be dented. If the decoration workers do not pay attention when attaching the magnetic sheets, this situation will occur. The bending radius of copper pipes can be as small as 3 times D, and the surface hardness is high, making this problem less likely to occur.
(4) The quality of existing pipe fittings is not high and they are prone to bursting under stress.
These problems with composite pipes seem to be avoidable with a little attention, but because they involve installers, residents, and decoration workers
Link to this article：Research and practice on indoor gas pipe installation
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