1 Historical background China's copper water pipe was first used in overseas investment in high-grade hotels, all imported products, 90% of which used the American standard or British standard (later replaced by the European standard). After the application of practice shows the excellent performance of copper water pipe system, in the last one or two decades of domestic investment in high-grade hotels, high-grade residential and public **** building, the use of copper pipe is becoming more and more common. Domestic copper processing enterprises see this business opportunity, and actively involved in the development of this series of products, initially mainly for individual projects to do the matching fittings, the standard of implementation of the American Standard or British Standard. Later, the more powerful enterprises began to create their own brands and reference to the American Standard and British Standard formulated the enterprise standards for copper water pipes and fittings, the earliest domestic copper water pipe standard GB/T1527-87 began to be implemented in 1987, and the corresponding pipe fittings standards also began to be implemented in 1989. The latest revised version of GB/T11618-1999 (fittings), GB/T18033-2000 (copper water pipe). This paper introduces the differences and similarities between the three standards and their practical applications. 2 standard overview 2.1 U.S. standards 2.1.1 Copper: ASTMB88-1996 standard specifies the material, size and tolerance of copper pipe, mechanical properties of the three technical requirements and test methods. Size range: 1/4′-12′ (DN10-DN300mm) Wall thickness: K, L, M three types, M type for thin-walled economic L and K for higher pressure systems, such as steam or medical gases and other systems. State: soft coil or hard state straight tube. 2.1.2 copper fittings: ANSI/ASMEB16.221995/1998 standard specifies the fittings material, dimensions and tolerances, mechanical properties of the technical requirements and test methods. Size range: 1/4′-12′ (DN10-DN300mm) Fittings Wall Thickness: only one series, for K, L, M three types of copper pipe. Condition: Hard state. 2.2 British (European) Standards 2.2.1 Copper Tubes: EN1057-1996 (replacing the original standard BS2871-1971) Size range: ∮6- ∮267 (DN5-DN250mm) Wall thickness: a variety of optional thickness, refer to the original standard for details. The market mostly follows the original BS2871 standard recommended two series: X series - thin-walled economic type; Y series - higher pressure occasions. Status: R220 soft (#6-#54), R250 semi-hard (#6-#159), R290 hard (#6-#267). 2.2.2 Fittings: EN1254-1998 Size range: ∮6- ∮108 Wall thickness: only one thickness is applicable to a wide range of wall thicknesses of copper tubes. 2.3 National standard 2.3.1 Copper pipe: GB/T18033-2000 Size range: ∮6- ∮219 (DN5-200mm) Wall thickness: there are a variety of optional thicknesses, but the standard recommends A, B and C series. Class C is basically equivalent to BS2871-X series, Class B is basically equivalent to BS2871-Y series or ASTMB88M series, Class A is basically equivalent to ASTMB88L series and K series. Condition: Soft state (M), semi-hard state (Y2), hard state (Y). Outside diameter tolerance: ordinary precision and high precision level of two, the latter according to nearly ASTMB88 or EN1 057 requirements. 2.3.2 Copper fittings: GB/T11618-1999 Size range: ∮6- ∮219 (DN5-DN200mm) Wall thickness: divided into PN1.0MPa and PN1.6MPa two kinds of 3 Differences and Similarities Comparison 3.1 Material, see Table 1 for details. 3.1.1 American Standard and European standards require copper pipe or fittings material for deoxidized phosphorus copper and the national standard does not specify. 3.1.2 American and European standards for copper alloy fittings in the zinc content of the limit while the national standard does not specify. 3.2 size and tolerance, see table 2. 3.2.1 wall thickness size of the three standards are different, can not be mixed in the same project, for example: the national standard DN80 copper pipe 85mm × 1.5mm (C level); and EN1057 for 76.1mm × 1.5mm (X series); the American Standard for 79.38mm × 1.83mm (M type). DN65 copper pipe national standard 67mm × 1.5mm (M type). DN65 copper pipe national standard 67mm × 1.5mm, the European standard 66.7mm1 × .2mm, the American standard 66.68mm × 1.65mm. 3.2.2 Size range: American standard maximum, copper pipe and fittings are up to DN300; national standard is second, copper pipe and fittings are up to DN200; the European standard is the smallest, the copper pipe up to DN250, the fittings up to DN100 . 3.2.3 Wall thickness design and working pressure (see Table 3) Copper: American Standard M type are above 2.3MPa, European standard X, national standard C level are above 1.3MPa. National standard B grade are above 2.2MPa. Pipe fittings: American Standard and European Standard are only a thickness, while the national standard has two thicknesses, the actual application of the two thicknesses of the pipe fittings inconvenience procurement and site management, should be unified for a thickness. From the above analysis, it can be seen that the American Standard M-type design is more reasonable, suitable for high-rise buildings, the price is lower than the European standard Y series or national standard B, A series, suitable for design selection. 3.2.3 Tolerance with the most stringent American Standard, followed by the European standard, the worst national standard (see Table 2). According to the U.S. National Bureau of Standards for 3/4′ tube and fittings test report "BMS58": when the weld gap of more than 0.25mm, capillary welding (domestically known as brazing) will be difficult to ensure the quality. Therefore, the American Standard 6′ within the specifications with the gap are controlled between 0.025-0.25mm. 3.3 Mechanical properties of the American Standard, the European standard and the national standard is basically the same. 4 the actual application of the three standards 4.1 The application of the national standard is narrower, most manufacturers are still in accordance with the European standard or American standard system of production, to facilitate the market supporting. 4.2 Because the American Standard system requires the highest tolerance with the highest production costs, so the market is not much available. 4.3 The so-called European standard pipe fittings actually did not 100% meet the requirements of the standard, mainly reflected in the material and tolerance with. 4.4 Because of the strict implementation of the same standard system, domestic copper pipe and fittings in the practical application of the quality of the hidden problems often exist, the problem is concentrated in the reliability and stability of the quality of the welded joints. These products often leak after many years of use, which has a negative impact on the market image of copper pipes. The reasons are analyzed as follows: 4.4.1 Material: American Standard and European Standard require deoxidized phosphorus copper, which has the advantages of high production cost but good welding performance, more corrosion resistance and higher strength. However, due to technical and cost issues, most of the domestic T2 or T3 copper, while the loss of zinc in the copper alloy is also no manufacturer has the ability to solve the problem. 4.4.2 Matching tolerance: the domestic standard itself is too loose, with a minimum or even negative fit gap, meaning that the copper pipe can not be inserted into the pipe fittings; the maximum of more than 2.5mm, more than 10 times the U.S. standard, 5 times the European standard. Ordinary precision-grade copper tubes and fittings are far from meeting the technical requirements for brazing (≤0.25mm). The integrity and stability of the welded joints are very poor, and it is not difficult to understand the hidden danger of water leakage. 4.4.3 Welding process: the excessive fit gap leads to workers not being able to correctly adopt brazing process, but using poor liquidity of poor-quality electrodes, and sealing the welded joints with overlay welding, which is prone to leakage in water pressure fluctuation and thermal expansion and contraction. 5 Conclusion From the above comparison, we can see that the American Standard system is more perfect and strict, the size range is also the widest, wall thickness design is more economical and reasonable. It is recommended to choose the American Standard system as much as possible in the project. The national standard system should be amended urgently, with the international advanced standards.