Classification of multi-chamber pressure vessels
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This post was last edited by njtv on 2019-3-8 at 10:17. The construction is based on external design drawings (see the attached drawings for schematic diagrams and technical parameters). Upon reviewing these drawings, we found that several pieces of equipment fall under the category of Class I pressure vessels, in accordance with Articles 1.3, 1.7, and Appendix A of the TSG21 standards. We understand that the working pressure of the inner container does not meet the requirements specified in Article 1.3 of TSG21; therefore it does not fall under the category of containers covered by TSG21. The inner container shall not be classified based on its own characteristics, but rather should be classified according to those of its jacket. After communicating with the design party, they insisted on classifying it as two types of equipment: the inner vessel, due to the highly hazardous medium it contains, is classified as a Type 1 vessel, while the jacket is also a Type 1 vessel. The entire equipment constitutes a pressure vessel, and it should be classified according to the highest category among its various pressure chambers, as per the classification for multi-chamber pressure vessels. I’m posting this to discuss the classification of multi-chamber containers; I hope experts will kindly share their insights. Thank you!
It should be classified as a Category I container; although the inner cylinder contains a highly hazardous medium, the pressure is not high enough to place it in another category.
According to the classification rules in the Solid and Liquid Waste Regulations, the inner container is not classified as such; however, based on the design criteria it is classified as Category 2, which meets the design requirements.
The jacket is under vacuum conditions; therefore, 0.124 MPa should be used for the inner cylinder in the calculations. In other words, the design pressure of the inner cylinder should be increased by 0.124 MPa, making it a Class II vessel.
A vacuum condition in the jacket only occurs when the equipment malfunctions; under normal conditions, there is no vacuum. This was clearly communicated during discussions with the design team.
According to the classification regulations for multi-chamber vessels specified in the pressure vessel standards, it should be classified as a Class I vessel; however, the manufacturing requirements for the inner cylinder shall comply with those specified in GB/T150. According to the data table, the medium in the jacket is saturated water vapor, with a design pressure of 0.53 MPa; but why is the design temperature 190 degrees? ! (Temperature and pressure should correspond to each other.)
The design is based on the most dangerous conditions; being classified as Category 2 is better than being classified as Category 1.
The standards for classifying multi-chamber pressure vessels are quite clear; ensuring safety requires measures to be taken at the stages of design, manufacturing, and inspection.
I discussed this issue with the designers; there are two other units with exactly the same parameters, one of which indicates low-pressure steam while the other indicates medium-pressure steam. The designer’s reply was that such were the conditions specified in the process requirements.
For classification, it is first necessary to comply with the provisions of Article 1.3 of TSG21, and then, in accordance with Article 1.7, the classification shall be determined using Appendix A. If the inner container contains highly hazardous media, separate manufacturing requirements can be specified.
Containers are classified based on operating pressure; if the operating pressure is less than 0.1 MPa, they should not be classified.