Some standard content:
National Standard of the People's Republic of China
Buried polyethylene (PE) fittings for the supply of gaseous fuels
1 Content and scope of application
GB 15558.2-
This standard specifies the technical requirements, specifications, test methods, inspection rules, marking, packaging, transportation, storage and types of buried polyethylene fittings for gas (hereinafter referred to as fittings) made of polyethylene resin as the main raw material and injected by injection molding. In addition, the main performance requirements of the raw materials are also specified.
This standard is applicable to buried fittings for gas transmission with an operating temperature of -20 to 40°C and a maximum working pressure of no more than 0.4MPa. When the fittings are used to transport artificial coal gas and liquefied petroleum gas, the adverse effects of other components in the gas (such as aromatic hydrocarbons, condensate, etc.) on the performance of the fittings at a certain concentration should be considered. The pipe fittings produced according to this standard are suitable for use with polyethylene pipes produced according to the requirements of GB15558.1 "Buried polyethylene pipes for gas".
2 Reference standards
GB1033
GB 1842
GB2828
GB 2918
GB 6111
GB6283
GB 8806
GB 13021
Test methods for density and relative density of plastics
Test methods for environmental stress cracking of polyethylene
Count sampling procedures and sampling tables for batch inspection (applicable to inspection of continuous batches)Standard environment for conditioning and testing of plastic specimensMethod for determination of the damage resistance time of thermoplastic plastic pipes under long-term constant internal pressureDetermination of moisture content in chemical productsKarl Fischer method (general method)Method for measuring dimensions of plastic pipes
Determination of carbon black content of polyethylene pipes and fittings (thermal gravimetric method)GB 15558. 1
3 Raw materials
Buried polyethylene pipes for gas
3.1 Basic raw materials and additives
The basic raw material is polyethylene resin. Necessary additives such as antioxidants, UV stabilizers and colorants may be added. The added additives should be evenly dispersed.
3.2 Basic properties
The basic properties of the raw materials should meet the requirements of Table 1.
Approved by the State Administration of Technical Supervision on May 2, 1995, and implemented on December 1, 1995
Density, kg/m2
Thermal stability (200C), min
Moisture content, mg/kg
Volatile content, mg/kg
Carbon black content\, %
Resistance to gas components, h
(80C, 2. 0 MPa)
Long-term static hydraulic strength, MPa
(20℃, 50 years, 95%)
Resistance to environmental stress cracking, h
(100℃, 100% concentration)
Note: 1) Carbon black content is only applicable to black pipes. 4 Product classification
GB 15558.2-1995
Performance requirements
F. ≥1 000
According to the hot-melt connection method, it is divided into three categories: electric heating wire fusion connection, hot-melt butt connection, and hot-melt socket connection. Technical requirements
5.1 Color
The color of the pipe fittings is yellow or black.
5.2 Appearance
Test method
The inner and outer surfaces of the pipe fittings should be smooth and flat. No bubbles, cracks, obvious depressions, marks, uneven colors and other defects are allowed. The pipe fittings should be complete and free of defects, and the gates and overflows should be repaired and flat. 5.3 Specifications and Deviations
The specifications and deviations of the connection parts should comply with the provisions of Chapter 6. 5.4 Performance requirements
The performance requirements of pipe fittings shall comply with the requirements of Table 2:
Thermal stability (200℃)
No damage
Short-term static hydraulic strength
No leakage
Heating expansion
Performance requirements
>20 min
Ductile failure time>100 h
Brittle failure time165 h
Failure time>1000h
The change in the outer diameter and length of the pipe fitting shall not exceed ±5%. The shape of the pipe fitting is not allowed to change significantly
Test method
Note: 1) Only suitable for brittle failure. If ductile failure occurs within the required time (165h) above, select a lower failure stress and corresponding minimum failure time according to the table below.
Failure stress, MP:
Specifications and deviations of pipe fittings
GB15558.2—1995
Minimum failure time, h
Failure stress, MPa
Minimum failure time, h
6.1 Measured in accordance with the provisions of 7.3.1 and 7.3.2, the specifications and deviations of pipe fittings shall comply with the provisions of Figure 1, Figure 2, Figure 3, Figure 4, Table 3, Table 4, Table 5 and Table 6.
6.2 Measured in accordance with the provisions of 7.3.3, the minimum wall thickness of pipe fittings shall not be less than the wall thickness of pipes of the same specifications specified in GB15558.1. 6.3 Electric heating wire fusion socket pipe fittings
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L+ L,/2
Di-average inner diameter of fusion zone;Dz—minimum inner diameter of socket;D-minimum inner diameter of fitting;L—insertion depth,L2—heating lengthL3-non-heating lengthD, ≥ 1. 002D,mm;
D. ≥ D. - 2e,
L≥5 mm;
L, ≥el+5mm, minimum is 10 mm;
For D,≤90,0.2D.+10mm≤L≤0.6D.+25mm, minimum is 20mm; for D,≥110,0.2D,+10mm≤L,≤D./3+45mm. Note: 1) In the formula, e is expressed in mm and refers to the wall thickness of the pipe connected to the pipe fitting (socket). 6.3.1 Dimensions and deviations of socket fittings for electric heating wire fusion Table 3 Dimensions and deviations of socket parts for electric heating wire fusion Nominal diameter
Average inner diameter of fusion zone
Heating length L2
Insertion depth L1
Nominal true diameter
Note: SDR
GB 15558.2-1995
Continued Table 3
Average inner diameter of fusion zone
Heating length L2
Standard size ratio, that is, the ratio of nominal outer diameter to wall thickness. 6.4 Hot-melt butt-melt and plug-in fittings
Insertion depth L
D average outer diameter of the end; Dz average outer diameter of the fitting, Ds minimum inner diameter; L,--length before internal cutting; L--external cutting length For D,≤90,1z≥0.6D,+25mm; for -fD.≥110.L2≥D/3+45mm.
6.4.1 Dimensions and deviations of hot-melt butt-jointed and spigot fittings 326
Nominal diameter
GB15558.2-1995
Dimensions and deviations of hot-melt butt-jointed and spigot fittings Table 4
Average outer diameter D,
6.5 Hot-melt saddle fittings
Absolutely not round
Minimum inner diameter
W--~Width of fusion surface, should not be less than 12mm; d--Saddle projection diameter; R--6.5.1 Dimensions of hot-melt saddle fittings
Inner cutting length L,||tt ||Radius of saddle welding surface
External cutting length L2
Nominal diameter
6.6 Hot-melt socket fittings
GB15558.2-1995
Table 5 Dimensions and deviations of hot-melt saddle fittings
Radius of saddle welding surface R
Saddle projection diameter
D,…Average inner diameter of socket mouth: I), average inner diameter of socket root D-minimum inner diameter, L-minimum length of socket; l, actual length of socket; L-heating length of fittings, L-insertion depth of pipe; L-heating length of pipe for 20 ≤D≤ 63
L = 0. 3D, + 8. 5mm;
L2. 5mmLz≤L
L-3.5mm≤L, ≤L-1mm
L2 L, + imm;
for 75≤D,≤125
L = 0.2D, + 15mm;
L≥ L;
L 4mm ≤L,≤L;
L- 5mm≤L≤L-1mm;
Lz≥ L+ 1mm;
L4 ≥ Ls.
6.6.1 Dimensions and deviations of hot-melt socket fittings
Average inner diameter of socket
Nominal diameter
Mouth D,
Minimum" maximum
Root D,
109.4110.0107.7108.5
124.4125.0122.6123.2
Test method
7.1 Sample pretreatment
|GB15558.2—1995
Table 6 Dimensions and deviations of hot-melt socket
Absolute non-roundness
Minimum inner diameter
Minimum length of socket
Heating length of pipe fittings
Insertion depth of pipe
The test environment shall be in accordance with the provisions of GB2918, with a temperature of 23±2℃. The sample shall be conditioned for more than 24 hours according to the test environment conditions before the test.
7.2 Appearance inspection
Observe directly with the naked eye, and the inner wall can be illuminated by a light source. 7.3 Measurement of pipe fitting dimensions
7.3.1 Inner and outer diameters of the socket of pipe fittings
Use an inner diameter gauge with an accuracy of 0.01mm to measure two inner diameters perpendicular to each other and calculate their arithmetic mean. The outer diameter is measured according to GB8806
7.3.2 The depth of the socket part of the pipe
is measured with a vernier caliper with an accuracy of 0.02mm. 7.3.3 The wall thickness of the pipe
is measured according to the provisions of GB8806. If necessary, the pipe can be cut open for measurement. 7.4 Density determination
Tested according to the method specified in GB1033.
7.5 Thermal stability (200℃)
7.5.1 Test instrument
GB15558.2—1995
7.5.1.1 A differential scanning calorimeter (DSC) or thermal analyzer that can continuously record the temperature of the sample with an accuracy of 0.1C. 7.5.1.2 A temperature measuring instrument with an accuracy of 0.1℃. 7.5.1.3 An analytical balance with a sensitivity of 0.1mg. 7.5.1.4 Oxygen and high-purity nitrogen gas supply with a switch. 7.5.1.5 Gas flow meter.
7.5.2 Samples
7.5.2.1 Preparation of pipe sample:
Saw a 2-3 cm wide ring from the pipe, cut a cylinder with a diameter slightly smaller than the inner diameter of the thermal analyzer sample tray radially on the surface of the ring, and use a sharp blade to cut a disc weighing 15±0.5 mg from the cylinder as a sample. 7.5.2.2 Preparation of raw material sample:
Put the raw material in a cylindrical compression mold tray, heat it at 150±3℃ for 2 minutes, cut a cylinder with a diameter slightly smaller than the inner diameter of the thermal analyzer sample tray, and use a sharp blade to cut a disc weighing 15±0.5 mg from the cylinder as a sample. 7.5.3 Test steps
7.5.3.1 Calibrate the thermal analyzer.
7.5.3.2 Adjust the nitrogen flow rate to allow 50±5cm*/min of nitrogen to flow through the thermal analyzer, then switch the switch to oxygen, adjust the oxygen flow rate to allow 50±5cm/min of oxygen to flow through the thermal analyzer, and then switch to nitrogen. 7.5.3.3 Place the open aluminum pan containing 15±0.5mg of the sample into the thermal analyzer, heat it at a rate of 20℃/min, keep the temperature constant at 200±0.1℃, and start recording the temperature change over time. 7.5.4 Test results
On the temperature change over time curve, as shown in Figure 5, mark the point (A1) at which the nitrogen is switched to oxygen for 1 minute, draw the tangent line with the largest slope when the temperature rises, and mark the intersection of this tangent line and the baseline (A2). (A1-A2) is the oxidation induction period (min) representing the thermal stability of the sample. The test is carried out at least five times, and the test results are taken as the arithmetic mean of the five tests. True induction period
7.6 Determination of moisture content
Determine according to the method specified in GB6283, and the sample is not conditioned. 7.7 Determination of volatile matter content
Determine according to Article 5.7 of GB15558.1. 7.8 Determination of carbon black content
Test according to the method specified in GB13021.
7.9 Resistance to gas components
GB 15558.21995
Test medium: 50% (weight ratio) n-decane (99% concentration) and 50% (weight ratio) trimethylbenzene mixed liquid. Test medium temperature: 80℃.
Test hoop stress: 2.0MPa.
Before the test, the mixed liquid should be injected into a 32×3.0mm tubular specimen with a free length of not less than 250mm. After being placed in an environment of 23±2℃ for 1500h, the test should be carried out in accordance with the provisions of GB6111. 7.10 Short-term static hydraulic strength
The test should be carried out in accordance with the provisions of GB6111. The test is carried out on the assembly. The performance of the pipe fittings is expressed by the performance of the assembly. The assembly is recommended to be composed of 63mm or 32mm pipes of the SDRn series and one or more pipe fittings connected by hot-melt socket, hot-melt butt, electric heating wire socket and hot-melt saddle, see Appendix A (supplement). 7.11 Environmental stress cracking resistance
The test should be carried out in accordance with the method specified in GB1842. The test results are expressed as the time (F.) when the probability of specimen damage is 0. 7.12 Heating expansion
On the surface of the pipe to be tested, mark the position for measuring the outer diameter and length at random; after measuring the outer diameter and length at the marked point, place the pipe in glycerin at 110±2℃ for 1h; or place the pipe in an oven at 110±2℃ for 260min for wall thickness ≤8mm; 2120min for 8mm< wall thickness ≤16mm; 240min for wall thickness>16mm.
Take out the pipe and cool it naturally in air at 23±2℃, then measure it separately, calculate the change rate and change amount by the following formula, and take the average value of 3 tests.
L= [(L - L)/L.]100
I. Change rate of outer diameter or length, %;
L——outer diameter or length before test, mm; L——outer diameter or length after test, mm. 7.13 Long-term hydrostatic strength
The test shall be conducted in accordance with the provisions of Appendix A (Supplement) of GB15558.1. 8 Inspection rules
8.1 Products shall be inspected and qualified by the quality inspection department of the manufacturer and accompanied by a certificate of conformity before they can leave the factory. 8.2 Batch
The pipe fittings of the same specification produced under the same raw materials, formula and process are a batch, and the quantity of each batch shall not exceed 2000 pieces. If the production quantity is small and the production period is less than 2000 pieces in 10 days, the production in 10 days shall be a batch. 8.3 Factory inspection
8.3.1 The factory inspection items are 5.1, 5.2, 5.3, 5.4 (excluding the short-term hydrostatic strength test with a failure time of more than 1000h at 80℃).
8.3.25.1,5.2,5.3 inspection shall be carried out according to GB2828 with a normal inspection and one-time sampling plan, taking the general inspection level I and the qualified quality level 6.5, see Table 8.
8.4 Type inspection
Inspect 5.1,5.2,5.3 according to the technical requirements of this standard and the provisions of 8.3.2, and randomly select sufficient samples from the qualified samples to carry out the tests in 5.4. If any of the following situations occurs, type inspection shall be carried out: a. Preliminary evaluation of new products or old products for transfer to factory production; b. After formal production, if there are major changes in equipment, raw materials, and processes, which may affect product performance; c. When the product is resumed after a long period of suspension; when the factory inspection results are significantly different from the previous type inspection results; d.
GB15558.2-1995
When the national quality supervision agency proposes the requirement for type inspection. Table 7
Batch range
151~～280
281~500
501~1200
1201～3200
8.5 Judgment rules
Sample size
Number of qualified judgments
Unit: piece
Number of unqualified judgments
5.1, 5.2, 5.3 Judge according to the provisions of Table 7. If one of the items in Article 5.4 fails to meet the specified indicators, double samples can be randomly selected for re-inspection of the item. If it still fails, the batch is judged to be unqualified. 9 Marking, packaging, transportation, storage
9.1 Marking
The pipe fittings should have the following obvious permanent marks, and the marks should not weaken the performance of the pipe fittings, but should be located away from the welding position. a.
Specification size;
b. This standard number;
Manufacturer name (or trademark).
9.2 Packaging
The pipe fittings should be placed in sealed plastic bags, in batches or individually, and placed in thick cardboard boxes to prevent damage. The cardboard boxes should be marked with the manufacturer's name and address, the size and type of the pipe fittings, the production date, the number of pipe fittings in the box and the specified storage conditions and storage time limit, and be accompanied by a product quality certificate. 9.3 Transportation
Pipe fittings must not be subjected to severe impact, scratches, falls, exposure to the sun, rain and pollution during transportation. 9.4 Storage
Pipe fittings should be stored in a warehouse away from heat sources, with a storage temperature not exceeding 40°C, a flat floor and good ventilation. The storage period of pipe fittings is generally not more than one year.
Note: 1) The minimum free length of the pipe is D. . GB 15558.2—1995
Appendix A
Schematic diagram of assembly test system
(supplement)
Pipe 1
Saddle-type pipe fittings
Reducing pipe
Butt joint
90° elbow
Steel-plastic joint (to air compressor)
63×32
B1 Heating wire sleeve
Nominal diameter
Heating wire 90° elbow||t t||GB15558.2—1995
Appendix Bbzxz.net
Shapes and dimensions of buried polyethylene pipe fittings for gas (reference parts)
20.2±0.2
25.3±0.2
32.2±0.2
40.8±0.2
63.3±0.3
90.5±0.5
110.5±0.5
Dimensions of heating wire sleeves
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