GB/T 35974.5-2018Plastics and plastic lining pressure vessels—Part 5: Fabrication, inspection and testing for pressure vessels with plastic lining (English PDF)

3.3.2.1.3 Cooling

Cool down the shell that is already heated. During the cooling process, the shell shall maintain the rotatory state. One of the following cooling modes, or a combination of several cooling modes may be adopted for cooling: natural cooling, water mist cooling or water spray cooling. During the cooling process, the difference between the air temperature in the shell and the external surface temperature of the shell shall not exceed 40 °C. When the external surface temperature of the shell decreases to 50 °C ~ 80 °C, stop the rotation of the shell.

3.3.2.1.4 Post-processing

After the shell cools down to room temperature, adopt vibration method to eliminate the internal stress of the lining-layer plastics.

3.3.2.2 Procedure evaluation

Procedure evaluation shall at least include the items listed in Table 1. The various item indexes shall comply with the designed value and the stipulations in GB/T 35974.2.

3.3.3 Winding sintering

3.3.3.1 Methods

3.3.3.1.1 Bar stock preparation

Use 20-mesh sieve to sieve powdered resin, so that it would be in a loose state. Evenly add it into steel mold. Use a scraping cutter to make it flat. On a pressing machine, compact it, then, slowly add pressure, so that air would be exhausted. After demolding, place it on a sintering furnace to start heating, plasticization and sintering. Sintering temperature shall be controlled at 380 °C ± 5 °C. Moreover, maintain the temperature, till it reaches a translucent state. Cool it down in the furnace, till it reaches the room temperature, then, take out the bar stock.

3.3.3.1.2 Thin strip processing

Use a lathe to cut the bar stock into thin strips at the width of 20 mm ~ 30 mm; wind and organize it into coils.

3.3.3.1.3 Winding

Wind the thin strips on an appropriate mold. After reaching the stipulated thickness, wind 3 layers ~ 4 layers of alkali-free glass ribbon. During the wrapping, properly tighten it; the various parts shall receive uniform stress.

4.7 Negative Pressure Resistance Test

Lining negative pressure test shall be conducted in accordance with HG/T 4093. Lining shall not manifest phenomena like distortion, flattening, deformation or cracks. At normal temperature, negative pressure resistance value shall take 80% of the failure value as the safe service value.

5.1 Inspection Methods

5.1.1 Appearance

Under the condition that illuminance is not less than 750 lx, adopt the mode of visual inspection to inspect the appearance.

5.1.2 Minimum wall thickness of lining

Use a thickness gauge, whose accuracy is not less than 0.02 mm, to measure the minimum wall thickness of lining.

5.1.3 Pressure resistance test

5.1.3.1 External shell safety test of lining vessels

External shell safety test of lining vessels shall be conducted in accordance with the methods stipulated in GB/T 150.4. Test temperature shall be normal temperature.

Pressure resistance test may select one of the following methods: hydraulic test, gas pressure test and gas-liquid combined pressure test.

Generally speaking, in hydraulic test and gas-liquid combined pressure test, liquid is water. In gas pressure test and gas-liquid combined pressure test, gas shall be dry and clean air, nitrogen or other inert gas.

When hydraulic test is adopted, test pressure shall be determined in accordance with Formula (1). Maintain the pressure for 30 min.

When gas pressure test and gas-liquid combined pressure test are adopted, test pressure shall be determined in accordance with Formula (2). Maintain the pressure for 10 min. The test shall have safety protection measures.

When it is stipulated in design documents, comply with the methods and requirements stipulated in design documents. There shall be safety protection measures in the test.

After lining vessels are qualified in the shell safety test, and the lining is completed, leakage test of lining vessels may be conducted. Lining vessels which are qualified in gas pressure test may not need air tightness test in the leakage test.

5.1.4.2 Air tightness test

Air tightness test shall be conducted in accordance with the methods stipulated in GB/T 150.4. Test temperature shall be normal temperature. Test pressure shall be determined in accordance with Formula (3). Maintain the pressure for 10 min.

5.1.4.3 Helium leak detection

In accordance with the methods stipulated in NB/T 47013.8, conduct helium leak detection. Test temperature shall be normal temperature. The maximum test pressure shall not exceed 1.15 times of the design pressure. Maintain the pressure for 30 min.

During the helium leak detection process, negative pressure is not allowed to emerge.

5.1.5 Electric spark test

Electric spark test parts are the whole internal surface of lining vessels. Particularly pay attention to parts which have dramatic changes in the shape, such as the circular bead and branch pipe of lining vessels. The same part shall not be repeatedly scanned for a long time. If there are any defects, mark the locations where defects are detected.

Electric spark test shall be conducted in accordance with the methods stipulated in HG/T 4090.

5.1.6 Thermal expansion and cold contraction test

Thermal expansion and cold contract test shall be conducted in accordance with the methods stipulated in HG/T 4092.

5.1.7 Negative pressure test

Negative pressure test shall be conducted in accordance with the methods stipulated in HG/T 4093.

5.2 Inspection Rules

5.2.1 Inspection classification

Inspection shall be divided into exit-factory inspection and type inspection. Unless it is otherwise stipulated in design documents, inspection items shall comply with the stipulations in Table 3.

5.2.4 Determination

5.2.4.1 Determination of exit-factory inspection

When the result of exit-factory inspection complies with the requirements, products shall be determined as qualified. If products fail to comply with one or more requirements, they shall be determined as disqualified. Disqualified products may be returned for re-fabrication. One re-fabrication is allowed on welded joints. Two re-fabrications are allowed on other parts. After the re-fabrication, products shall be re-inspected. If products are still disqualified in the re-inspection, they shall be determined as disqualified. If there is re-fabrication, the time, the parts and the situation of the re-fabrication shall be recorded in the quality certificate.

5.2.4.2 Determination of type inspection

When the result of type inspection complies with the requirements stipulated in Table 3, products shall be determined as qualified in type inspection. If products fail to comply with one or more requirements, they shall be determined as disqualified in type inspection.

6.1 Exit-factory information

6.1.1 Fabrication organizations shall provide exit-factory information to lining vessels' purchaser. When there are special requirements towards the usage of lining vessels, they shall also provide an instruction manual.

6.1.2 Exit-factory information of lining vessels shall at least include the following content:

a) Lining vessels' general completion drawings;

b) Lining vessels' documentary quality certificates (including product certificate, product data sheet and quality certificate);

c) Lining vessels' characteristics (including design pressure, operating pressure, design temperature, operating temperature and applicable medium);

6.2 Vessel Nameplate

6.2.1 Lining vessels shall have a permanent nameplate, which shall be fixated on an obvious location. The nameplate of cryogenic vessel shall not be directly riveted on the shell.

6.2.2 Nameplate shall at least include the following content: […]