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GB/T 25996-2019 English PDF (GBT25996-2019)

GB/T 25996-2019 English PDF (GBT25996-2019)

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GB/T 25996-2019: Test method for thermal insulations on external stress corrosion cracking of austenitic stainless steel
This Standard specifies the terms and definitions, instruments and equipment, reagents and materials, preparation of stainless steel specimens, preparation of thermal insulation specimens, test methods, qualification verification of sensitized stainless steel specimens for test, inspection of stainless steel specimens after test, test results, test report of test method for thermal insulations on external stress corrosion cracking of austenitic stainless steel.
GB/T 25996-2019
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 91.120.10
Q 25
Replacing GB/T 25996-2010
Test method for thermal insulations on external stress
corrosion cracking of austenitic stainless steel
ISSUED ON: OCTOBER 18, 2019
IMPLEMENTED ON: SEPTEMBER 01, 2020
Issued by: State Administration of Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
Introduction ... 5
1 Scope ... 6
2 Normative references ... 6
3 terms and definitions ... 7
4 Instruments and equipment ... 7
5 Reagents and materials ... 9
6 Preparation of stainless steel specimens ... 9
7 Preparation of thermal insulation samples ... 12
8 Test methods ... 14
9 Qualification verification of sensitized stainless steel test specimens for test ... 16
10 Inspection of stainless steel specimens after test ... 17
11 Test results ... 18
12 Test report... 18
Test method for thermal insulations on external
stress corrosion cracking of austenitic stainless steel
1 Scope
1.1 This Standard specifies the terms and definitions, instruments and
equipment, reagents and materials, preparation of stainless steel specimens, preparation of thermal insulation specimens, test methods, qualification verification of sensitized stainless steel specimens for test, inspection of stainless steel specimens after test, test results, test report of test method for thermal insulations on external stress corrosion cracking of austenitic stainless steel.
1.2 This Standard applies to thermal insulations and products for covering austenitic stainless steel, which mainly include mineral wool, calcium silicate, composite silicate, expanded perlite, foamed asbestos, foam glass, aerogel, and thermal insulation fireproof coatings. It also applies to cement and adhesives.
1.3 This Standard provides two test methods, i.e. Dana method and drip
method. The applicability is as follows:
- Dana method applies only to wicking-type insulations; drip method applies to all insulations that can be cut or shaped into test specimens;
- When the insulation can be heat treated into a wicking-type insulation, it can be tested by either Dana method or drip method;
- When the insulation cannot be treated into a wicking-type insulation or the heat treatment temperature is higher than the manufacturer's
recommended temperature, use drip method for test.
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 of the referenced document (including any amendments) applies.
GB/T 228 Metallic materials - Tensile testing at ambient temperature
4.1.6 Thermocouple type thermometer.
4.1.7 Precision bending machine.
4.1.8 Wet belt sander: The belt specification is P80.
4.1.9 Stainless steel bolt: 65 mm long, 5 mm in diameter, with insulating washer and stainless steel nut.
4.1.10 Microscope: X10 ~ X30.
4.1.11 Drill bit: ϕ 7 mm.
4.1.12 Magnifier: X10 ~ X20.
4.1.13 Electric saw.
4.1.14 Box-type resistance furnace: The maximum temperature is not lower than 1200 °C.
4.2 Instruments and equipment for drip method
4.2.1 Heating device: The outer diameter of the heating tube is 38 mm, and the temperature of the outer wall is the water boiling point temperature ± 6 °C. 4.2.2 Multi-channel peristaltic pump or other water supply device: It is used to supply 250 mL/d sodium chloride solution, distilled water or deionized water to each sample.
4.2.3 Glass bottle: 1 L.
4.2.4 Specimen holder.
4.2.5 Thermocouple type thermometer.
4.2.6 Cylindrical sampler: The outer diameter is 25.5 mm.
4.2.7 Precision bending machine.
4.2.8 Box-type resistance furnace: The maximum temperature is not lower than 1200 °C.
4.2.9 Wet belt sander: The belt specification is P80.
4.2.10 Stainless steel bolt: 65 mm long, 5 mm in diameter, with insulating washer and stainless steel nut.
4.2.11 Microscope: X10 ~ X30.
where:
δ - the deflection of the stainless steel specimen after applying a certain stress, in millimeters (mm);
S - the elastic stress, in megapascals (MPa);
R - the bending radius, in millimeters (mm);
h - the thickness of the stainless steel plate, in millimeters (mm);
L - the length of the straight part of the stainless steel specimen, in millimeters (mm);
E - the elastic modulus, in megapascals (MPa);
L0 - the distance between the two inner planes of the U-shaped stainless steel specimen after applying stress, in millimeters (mm).
7 Preparation of thermal insulation samples
7.1 General requirements
7.1.1 During the entire preparation process, clean polyethylene gloves shall be worn to avoid direct contact with the thermal insulation with bare hands and to prevent chloride ion pollution.
7.1.2 If the surface and the interior of the thermal insulation are different, the thermal insulation shall be tested at the location determined to be the most likely to cause corrosion.
7.1.3 When the thermal insulation can be heat treated into a wicking-type insulation, the heat treatment shall be carried out at the temperature
recommended by the manufacturer. If necessary, the treatment temperature can be the maximum use temperature of the thermal insulation.
7.2 Preparation of samples of thermal insulation with consistent surface and interior
7.2.1 CUT the thermal insulation into sample blocks of 102 mm × 178 mm × 38 mm. USE the sampler to drill a hole in the center of each sample block, and then CUT it into two parts to make samples of 102 mm × 89 mm × 38 mm, of which the quantity if not less than four. INSTALL each sample on the
corresponding bolted stainless steel specimen. If they do not match each other, USE a clean chlorine-free water-resistant abrasive paper to grind the sample to fit the stainless steel specimen, and BLOW the polished sample with air to electronic transformer are connected by copper wires.
8.1.3 PLACE the temperature measurement end of the thermocouple in the
middle of the bottom of the stainless steel specimen concave, COVER the thermocouple with aluminum powder, and then DROP a few drops of epoxy
adhesive on the aluminum powder to make the contact tip of the thermocouple reliably adhere to the stainless steel specimen.
8.1.4 FILL the crystallizing dish with distilled or deionized water until the level is about 13 mm below the bottom of the stainless steel specimen groove. TURN ON the power and heat up. When the temperature reaches the water boiling point temperature, start timing. The test duration is 28 d ± 6 h. In the event of a power outage during the 28-day test, the time taken for the power outage shall be compensated.
8.1.5 ADJUST the water level of each specimen in time according to the
temperature. The increase of the water level will decrease the temperature. The amount of water required to control each specimen is 200 mL/d ~ 600 mL/d. 8.1.6 After the test, TURN OFF the power to cool the stainless steel specimens, DISCONNECT the electrical wires, and REMOVE the stainless steel
specimens from the thermal insulation sample.
8.1.7 At the same time, carry out the qualification verification of sensitized stainless steel test specimens for test in accordance with 9.2.
8.2 Drip method (arbitration method)
8.2.1 PLACE each stainless steel specimen on the heating tube, with the opening downward; APPLY the thermal grease between the stainless steel
specimen and the heating tube to bring them into close contact with each other; INSTALL the bolts and nuts in accordance with 6.10.
8.2.2 WET the thermal insulation sample to be tested with distilled water or deionized water. If it cannot be made wet, immerse it for 10 min. Take it out and place it on the stainless steel specimen and fix it, and make them fully contact. 8.2.3 INSERT the drip tube that is connected to each glass bottle through the peristaltic pump IN the center of the thermal insulation sample, START the peristaltic pump, ADJUST the dripping speed, and ENSURE that each thermal insulation sample is evenly dripped with (250 ± 25) mL of water every day. During the test, (250 ± 25) mL of water is added to the glass bottle
corresponding to each thermal insulation sample every day.
8.2.4 TURN ON the heating device. The temperature of the outer wall of the tube shall be controlled at the water boiling point temperature ± 6 °C. After the temperature is reached, start the timer. The test duration is 28 d ± 6 h. In the event of a power outage during the 28-day test, the time taken for the power outage shall be compensated.
8.2.5 After the test, TURN OFF the power to cool the stainless steel specimens, and then carefully REMOVE the stainless steel specimens.
8.2.6 At the same time, carry out the qualification verification of sensitized stainless steel test specimens for test in accordance with 9.2.
9 Qualification verification of sensitized stainless steel
test specimens for test
9.1 Dana method
9.1.1 REPLACE the thermal insulation sample with borosilicate glass wool (5.7). The stainless steel specimen shall contact the top of the glass wool block. 9.1.2 INJECT sodium chloride solution into the crystallizing dish until the liquid level is in the range of 6.4 mm to 19 mm from the bottom of the stainless steel specimen. KEEP the temperature within the range of the water boiling point temperature ± 6 °C, and the amount of evaporated water is 250 mL/d ~ 1000 mL/d. When the temperature is reached, start the timer. The test duration is 72 h ± 30 min.
9.1.3 CARRY OUT a 28-day blank test on the 4 U-shaped stainless steel
specimens with distilled or deionized water in the same way.
9.1.4 When all the 4 stainless steel specimens corroded by sodium chloride solution show cracks, and none of the 4 stainless steel specimens in the blank test show cracks, it proves that this batch of stainless steel is qualified and can be used for test in this Standard.
9.2 Drip method
9.2.1 REPLACE the thermal insulation sample with low-dust wiping paper of neutral wicking type, and PLACE it on the stainless steel specimen. INSTILL evenly (250 ± 25) mL of sodium chloride solution into the center of the low-dust wiping paper through a peristaltic pump daily. Add (250 ± 25) mL of sodium chloride solution to the glass bottle corresponding to each stainless steel specimen every day.
9.2.2 TURN ON the heating device. The temperature of the outer wall of the tube shall be controlled at the water boiling point temperature ± 6 °C. The timer shall be started after reaching the temperature. The test duration is 72 h ± 30
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