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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by and is under the jurisdiction of Committee of City Gas of China Association for Engineering Construction Standardization.
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Introduction
This standard is formulated according to the requirements of the Notice on Issuing the Pilot Project Plan of the First Batch of Product Standards of China Association for Engineering Construction Standardization in 2017 (JIANBIAOXIEZI [2017] No.015) issued by China Association for Engineering Construction Standardization.
Closed expansion vessels with built in diaphragm
1 Scope
This standard specifies the classification and model, material and construction, performance requirements, test methods, inspection rules, marking, instructions for use, packaging, transportation and storage of closed expansion vessels with built in diaphragm (hereinafter referred to as "expansion vessels").
This standard is applicable to closed expansion vessels with normal working temperature not greater than 70°C, maximum working temperature not greater than 90°C, maximum working pressure not greater than 3 MPa and effective volume not greater than 12 L, which are used for heating or water supply systems.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 191 Packaging — Pictorial marking for handling of goods
GB/T 528 Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
GB/T 531.1 Rubber, vulcanized or thermoplastic — Determination of indentation hardness — Part 1: Durometer method (Shore hardness)
GB/T 1690 Rubber, vulcanized or thermoplastic — Determination of the effect of liquids
GB/T 2941 Rubber — General procedures for preparing and conditioning test pieces for physical test methods
GB/T 2828.1 Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection
GB/T 3098.1-2010 Mechanical properties of fasteners — Bolts, screws and studs
GB/T 3098.2-2015 Mechanical properties of fasteners — Nuts
GB/T 3512 Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
GB/T 5781 Hexagon head bolts — Full thread — Product grade C
GB/T 7306.1 Pipe threads with 55 degree thread angle where pressure-tight joints are made on the threads — Part 1: Parallel internal and taper external threads
GB/T 7306.2 Pipe threads with 55 degree thread angle where pressure-tight joints are made on the threads — Part 2: Taper internal and external threads
GB/T 7307 Pipe threads with 55 degree thread angle where pressure-tight joints are not made on the threads
GB/T 7759.1 Rubber, vulcanized or thermoplastic — Determination of compression set — Part 1: At ambient or elevated temperatures
GB/T 9286-1998 Paints and varnishes — Cross cut test for films
GB/T 10125 Corrosion tests in artificial atmospheres — Salt spray tests
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
clench joints
joint that permanently holds two parts of an expansion vessel together with a separate metal ring
3.2
no rivets riveting
process method in which two metal plates and diaphragms are sealed together in a stamping process by using a special connecting mould and utilizing the plasticity of the material itself
3.3
expansion vessel
expansion tank
tank that absorbs or compensates for changes in water volume due to changes in factors such as temperature by expansion and contraction of a built-in diaphragm separating water and air/nitrogen of pre-flush pressure on both sides, in which the water contained does not contact any other gaseous or liquid medium
3.4
deep drawing
machining method enabling the metal parts of the expansion vessel to form from a flat state into a three-dimensional shape without reducing or increasing raw materials by means of pressure and mould
3.5
diaphragm
flexible or elastic membrane, which is fixed in the expansion vessel in an air-tight way and divides the expansion vessel into water side and air side. The diaphragm includes (closed) air bag diaphragm and (open) cup diaphragm
3.6
experimental test
any form of test used within the framework of a design of experiments method in place of the calculation of an expansion vessel component or the entire expansion vessel
Note: Refer to Annex A for the experimental test.
3.7
nozzle
short pipe mounted on the shell of an expansion vessel
3.8
maximum working pressure
pmax
maximum allowable working pressure of an expansion vessel
3.9
effective volume
Ve
water volume after the water side is injected to reach the maximum working pressure when the gas side reaches pre-charging pressure
4 Classification and model
4.1 Classification
4.1.1 Classification by applicable system
See Table 1 for classification by applicable system.
Table 1 Classification by applicable systems for expansion vessels
Category Applicable appliances and systems Code
Heating system Heating appliances and heating water system N
Domestic hot water system Hot water supply appliances and hot water supply systems R
Tap water system Tap water piping system Z
4.1.2 Classification by expansion vessel shape
See Table 2 for classification by expansion vessel shape.
Table 2 Classification by expansion vessel shape
Category Shape of expansion vessel Code
Round Oblate Y
Square Flat square F
Tank Tank G
Others Shapes other than the above three shapes Q
4.2 Model
4.2.1 Model preparation
4.2.2 Example
Example: The model of an expansion vessel for the tank heating system with serial number of the manufacturer of ×××× and effective volume of 2.5 L is expressed as XNG2.5-××××.
5 Materials and construction
5.1 Material
5.1.1 Expansion vessel shell
The shell material of an expansion vessel should be selected according to Table 3. Materials other than Table 3 may also be used after being proved to meet the requirements of this standard.
Table 3 Steel categories used for expansion vessel shell
Category Mechanical properties/MPa Chemical composition (mass fraction)/%
A Lower yield strength ReLd ≤ 460 C ≤ 0.25; Si ≤ 0.60; Mn ≤ 1.70; P ≤ 0.045; S ≤ 0.045; Cu ≤ 0.40; Ni ≤ 0.50; Cr ≤ 0.30 (0.40 casting)
B Yield strength ReH ≤ 275 C ≤ 0.25; Si ≤ 0.60; Mn ≤ 1.70; P ≤ 0.045; S ≤ 0.045; Cu ≤ 0.40; Ni ≤ 0.50; Cr ≤ 0.30 (0.40 casting)
C — Austenitic stainless steel with Cr ≤ 19
5.1.2 Diaphragm
Diaphragm materials should be selected according to Table 4. Materials other than Table 4 may also be used after being proved to meet the requirements of this standard.
Table 4 Commonly-used materials of diaphragm
Name of diaphragm material Abbreviation
Isobutylene isoprene rubber IIR
Acrylonitrile-butadiene rubber NBR
Natural rubber NR
Styrene butadiene rubber SBR
Ethylene propylene diene monomer EPDM
Note: Refer to Annex B for tests related to diaphragm in production.
5.1.3 Fastener
5.1.3.1 Bolts and screws that have a performance level of 5.6 or 8.8 specified in GB/T 3098.1-2010 should be used. Nuts to be used shall conform to performance level of 5 or 8 specified in GB/T 3098.2-2015.
5.1.3.2 Hexagon head bolts specified in GB/T 5781 should be used for flange connection.
5.1.3.3 Nozzle threads shall comply with requirements of GB/T 7306.1, GB/T 7306.2 or GB/T 7307.
5.1.4 Welding materials
Welding materials shall be suitable for base metal.
5.1.5 Expansion vessels for domestic hot water and tap water systems
Metal parts in contact with water shall be stainless steel, corrosion resistant steel or have anti-corrosion measures, and the materials used shall not pollute the water quality.
5.2 Construction
5.2.1 Inner surface
5.2.1.1 The inner surface of the expansion vessel which may come into contact with the diaphragm shall not have sharp edges and corners.
5.2.1.2 The opening in the wall of the expansion vessel shall not damage the diaphragm during riveting.
5.2.1.3 The gap of lap joints shall not be greater than 2 times the thickness of diaphragm at any position.
5.2.2 Outer surface
5.2.2.1 The expansion vessels shall show no burrs and sharp edges on their outer surfaces.
5.2.2.2 The blank holder of the upper and lower shells of the products shall be flat and smooth; the surface shall be free of variegated color and be bright after treatment, without obvious scratches, indentations, pits, bumps and other defects.
5.2.2.3 The spraying surface appearance shall be flat, uniform and free of bubbles, accumulation, sagging and missing coating.
5.2.3 Diaphragm
5.2.3.1 The surface of the diaphragm shall show no crack and bubble.
5.2.3.2 The diaphragm shall be sized to match the expansion vessel and shall not be damaged under inflation pressure.
5.2.4 Inspection opening
The expansion vessel with replaceable diaphragms shall be provided with an opening for inspecting and replacing diaphragms.
6 Performance requirements
6.1 Wall thickness of shell
The wall thickness at any position of the stamped shell shall not be less than 0.8 mm.
6.2 Pre-charge pressure
The absolute deviation between the pre-charge pressure on gas side and the manufacturer's claimed value shall not be greater than 0.02 MPa.
6.3 Shell strength
It shall be free of leakage and deformation.
6.4 Volume change rate
It shall be free of leakage, and the volume change rate shall not be greater than 4%.
6.5 Tightness
The leakage shall not be greater than 10 mL/h, or the expansion vessel shall be free of bubbles.
6.6 Effective volume
It shall be greater than 95% of the manufacturer's claimed value.
6.7 Diaphragm performance
6.7.1 Diaphragm thickness
The thickness at any position of the diaphragm shall not be less than 1 mm.
6.7.2 Tensile strength at break
The tensile strength at break of the diaphragm shall not be less than 10 MPa.
6.7.3 Elongation at break
The elongation at break of the diaphragm shall not be less than 450%.
6.7.4 Shore hardness
The Shore hardness of cup diaphragm shall be within 50 Shore A ~ 65 Shore A; the Shore hardness of airbag diaphragm shall be within 43 Shore A ~ 65 Shore A.
6.7.5 Compression set in air
The compression set of cup diaphragm in air shall not be greater than 40%; the compression set of airbag diaphragm in air shall not be greater than 60%.
6.7.6 Ageing resistance
The change of diaphragm performance shall meet those specified in Table 5 after the ageing test is conducted.
Table 5 Ageing resistance
Physical performance Qualified value
Absolute value of change rate of tensile strength at break /% ≤ 25
Absolute value of change rate of elongation at break /% ≤ 25
Shore hardness change value /Shore A ≤ 5
6.7.7 Durability
After the test, the pressure on the gas side shall not be less than 50% of the pre-charge pressure, and the pressure drop shall not be greater than 0.015 MPa.
6.7.8 Permeability resistance
The percentage of pressure drop shall not be greater than 2%.
6.8 Salt spray resistance
After salt spray test, the sprayed surface shall not rust and blister.
6.9 Cross-cut resistance
The cross-cut resistance of the sprayed surface shall at least be Grade 2 specified in GB/T 9286-1998.
7 Test methods
7.1 Test conditions and instruments and apparatuses
7.1.1 Test conditions
7.1.1.1 Laboratory conditions
The laboratory shall meet the following conditions:
b) Laboratory temperature: 20°C±5°C;
b) Laboratory inlet-water temperature: 20°C±5°C.
7.1.1.2 Power supply condition
The voltage fluctuation of AC supply used in the laboratory shall be within ±2%.
7.1.2 Instruments and apparatus
The instruments and apparatuses for test shall meet those specified in Table 6, or those with equivalent precision may also be adopted.
Table 6 Instruments and apparatuses
Test item Instrument and apparatus example Specification or range Precision/minimum scale
Temperature Ambient temperature/°C Thermometer 0°C ~ 50°C 0.5°C
Water temperature Thermistor thermometer 0°C ~ 150°C 0.1°C
Humidity Ambient relative humidity Hygrothermograph 0% ~ 100% 1%
Pressure Water pressure Pressure gauge 0 MPa ~ 0.6 MPa Grade 1.0
Pressure gauge 0 MPa ~ 6 MPa Grade 1.6
Gas pressure Digital pressure gauge 0 MPa~0.6 MPa ±0.4% FS
Pressure gauge 0 MPa ~ 6 MPa Grade 1.6
Time Within 1 h Stopwatch — 0.1 s
Greater than 1 h Clock — —
Mass Electronic scale 0 kg ~ 100 kg 20 g
Tightness Gas leakage detector — 0.01 mL/min
Materials and construction Vernier caliper 0 mm ~ 150 mm 0.02 mm
Groove vernier caliper 0 mm ~ 150 mm 0.02 mm
Thread gauge — —
Diaphragm thickness Thickness gauge 0 mm ~ 10 mm 0.01 mm
Tensile strength at break and elongation at break Tensile testing machine 0 kg ~ 200 kg Grade I
Hardness Shore A durometer 0 Shore A ~ 100 Shore A ±1 Shore A
Cross-cut test Cutting tool Meet the requirements specified in GB/T 9286
7.2 Measurement of shell wall thickness
Measure the deformation position of each part in the stamped vessel parts for three times at the same position, and take the mean value.
7.3 Pre-charge pressure test
Connect the pressure gauge to the valve of the expansion vessel, tighten the pressure gauge to press the core into the valve cavity, and read the reading on the pressure gauge.
7.4 Shell strength test
Confirm that the shell is not inflated at the gas side and the test pressure is 1.5 times the maximum working pressure claimed by the manufacturer, inject water from the water inlet to raise the pressure slowly, and hold the pressure for 5 min. If the maximum working pressure claimed by the manufacturer is not greater than 0.6 MPa, air pressure may be used instead of water pressure.
7.5 Test for volume change rate
Make several holes on the diaphragm of the expansion vessel or fill the water side and the gas side with water by other means, inject water to the maximum working pressure claimed by the manufacturer, measure the mass of injected water, continue to inject water to 2 times the maximum working pressure, hold the pressure for 5 min, then release the pressure, re-inject water to the claimed maximum working pressure, measure the mass of injected water, and calculate the change value of injected water before and after testing.
7.6 Tightness test
The tightness test may only be carried out after the shell strength test is accepted. Confirm that the shell is not inflated at the gas side and the test pressure is 1.1 times the maximum working pressure claimed by the manufacturer, and inject water from the valve and water inlet respectively to raise the pressure to the test pressure while venting to the atmosphere at the other side. The test time by bubble method shall not be less than 8 min.
Foreword i
Introduction ii
1 Scope
2 Normative references
3 Terms and definitions
4 Classification and model
5 Materials and construction
6 Performance requirements
7 Test methods
8 Inspection rules
9 Marking and instructions
10 Packaging, transportation and storage
Annex A (Informative) Experimental test
Annex B (Informative) Tests related to diaphragm in production process
