Common Issues in Pressure Vessel Design – Drawing Section 1

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Preface: What I would like to share with you today are some common issues that arise during the drawing of pressure vessel diagrams, for your reference. 1. Part sequence in the details column: (1) The component along with its corresponding part drawings should, whenever possible, be drawn on the same sheet or on adjacent sheets numbered consecutively, with the component diagram placed at the right side or lower right corner of the sheet. (2) When several different components need to be arranged across multiple drawings, it is advisable to arrange the important or structurally complex components along with their related parts first, or to organize them in order of part numbers. (3) Relevant components that are closely related in terms of processing, installation, and structure should be arranged on the same drawing as much as possible. 2. Interrelationships between drawings: When a device is highly complex and a single assembly drawing cannot contain all the projections, views, tables, and technical specifications, it is permissible to create two or more assembly drawings. However, the following principles must be followed: (1) The front view, technical specifications, table of technical characteristics, list of pipe connections, detail columns, and annotations should be included in the first drawing. (2) Top views, side views, front views, enlarged views, cross-sections, etc. should be placed on the 2nd or 3rd drawing. (3) On each drawing, the relationship between this drawing and other drawings should be indicated. For example, on the front view drawing, it should be noted that the top view and the view from direction A are on drawing xxx-2 (i.e., the second drawing). Indicate on the top-view drawing that the front view and technical requirements are on drawing xxx-1 (i.e., the first drawing). 3. Draw part drawings on the assembly drawing. Part drawings should generally not be included within the area of the assembly drawing. Since the parts need to go through several processing steps, placing them on the assembly drawing sheet makes it impossible to separate them, which is very inconvenient. Section 4.5.1 of HG/T 20668-2000 \"Regulations on the Preparation of Design Documents for Chemical Equipment\" stipulates that \"...for simple equipment that consists of only a few components, it is permissible to place the components and the assembly diagram on the same sheet; in such cases, the sheet size should not exceed size No. 1, with the assembly diagram placed on the right side of the sheet.\" That is, the part drawings can be separated from the assembly drawing and used independently. 4. Inconsistent names: For example, a certain angle steel ring is referred to as angle steel in the details column, as a support ring in the technical requirements or specifications, and as a reinforcement ring in the component title column. Another example: a certain type of reinforcement plate may have various names in different detail lists or technical specifications and descriptions, such as steel plate, reinforcement plate, support plate, strengthening plate, connection plate, etc. The correct designation is such that any given part or component has only one identical and uniform name in all the details or textual descriptions within a set of drawings. 5. Repeated symbols: It is incorrect to use the same symbol (or code) to represent different meanings or different shapes multiple times on the same drawing. For example: A-A expansion, A-A section, A-A view, A-A rotation, A baseline, A elevation view. To avoid confusion and misunderstandings, the above examples should be represented in the following correct manner: A-A section, B-B view, C-C rotation, D-D expansion, A baseline, B elevation view. If the cutting symbols for different parts of a single component represent the same sectional view (such as multiple identical keyways on the same diameter shaft), then the same cutting symbol can be used repeatedly on the same drawing. 6. No specific scale indicated: All views in the drawing, as well as the dimensions of the parts and components within each view, shall be drawn at the same scale. This is especially true for the assembly areas of the main components as well as other critical parts. If not drawn in proportion, it can easily lead to illusions or distortions in the pattern, and may even result in structural errors that go unnoticed. When not in proportion, the words “not in proportion” should be indicated. When individual dimensions are not to scale, it is recommended to draw a thin solid line below the dimension numbers.