General Provisions On Pattern Design Technology For Pressure Vessels

General Provisions on Pattern Design Technology for Pressure Vessels

Construction drawings are legal documents, and even a tiny mistake in the drawing may very well result in the company paying out hundreds of thousands of dollars in compensation. A certain set of high-pressure heat exchangers undertaken by the Technology Department this year was returned by the Special Inspection Institute simply because the spacing between the section lines was not uniform, resulting in a 12-day delay in delivery.

Drawing size and format determine first impression

The format of the drawing cannot be cut as you wish. In March this year, the quality assurance department randomly inspected 47 sets of as-built drawings and found that the width of the frame lines in 8 sets did not comply with GB regulations. The binding margin of A0 drawings must be 25 mm. A new colleague felt that leaving too much paper wasted and reduced it to 15 mm without authorization. This set of drawings was sent to the archives and was directly returned.

The signature area of ​​the title bar is often used as a scratch pad. During the trial production phase of a project last year, the designer handwritten the words "Pay attention to chamfering" in the blank space. The processing master took it as a drawing and required strict implementation. As a result, three tube sheets were scrapped, each worth 4,800 yuan. Any markings other than those specified in the standards are not allowed to appear on the drawings.

Proportion selection is not based on feeling

Many people think that the larger the local enlargement, the clearer it is. In fact, it violates the principles of cartography. Last year, for a tower with a total height of 32 meters, the designer forcibly drew a section of the cylinder using a ratio of 1:5 on the A1 format. As a result, the drawing labels were squeezed outside the frame. According to GB regulations, priority is given to 1:2, 1:5, and 1:10 series. You can’t bid as much as you want.

Do the proportions of different views have to be consistent? It is not necessarily how to select a riveting and welding unit with pressure vessel design qualifications , but it must be clearly stated in the title bar and below the view. At the vessel review meeting last month, a reviewer discovered that the front view was 1:10 and the top view was 1:20. The general technical requirements for pressure vessel drawing design, but there was no text explanation on the drawings. Such drawings would cause confusion in dimensional understanding and were seriously wrong when delivered for construction.

Fonts and line types are basic literacy

The era of hand-drawing has long passed, but there are still people messing around with CAD font settings. According to statistics at the beginning of this year, there were three fonts in the same set of drawings: imitation Song Dynasty, black body, and regular script. According to regulations, Chinese characters must be in long imitation Song font , numbers must be in Arabic numerals, and the character height must be selected from 2.5, 3.5, 5, 7, and 10 mm. Those with 0.8 mm letter height cannot be seen clearly after posting the picture.

It is an old problem that the line thickness of the graph is not differentiated. The width of thick lines ranges from 0.5 to 1.4 mm according to the picture frame, and the thickness of thin lines is one third of that of thick lines. In some drawings, it can be seen that the outline line uses a 0.15 mm thin line, but the dimension line uses a 0.5 mm thick line. The workshop workers said that their eyes hurt after looking at it for a long time. Line style is not an artistic creation, each line has its own grammar.

Dimensions must not be ambiguous

Benchmark selection errors are the most fatal. In September last year, for a fermentation tank, the designer set the axial dimension benchmark as the tangent line of the head, but the process calculation benchmark was the center line of the lower nozzle. As a result, the positions of the support openings were all wrong, and it cost 38,000 yuan to cut off and re-weld on site. When marking, you must ask yourself: If the workers get this size, can they work without guessing?

Duplicate marking and closed dimension chains are committed every day. Last month I reviewed a set of storage tank drawings, and the total length, segment length, and cumulative dimensions were all marked. How to choose a riveting and welding unit with pressure vessel design qualifications ? The drawings were revised four times. According to regulations, the dimension chain must have open rings. If you jam all the dimensions, where should the processing errors be placed?

Symbol codes must be used nationwide

Don’t make up the weld symbols yourself. There was a small circle drawn on a certain heat exchanger drawing, and the annotation said "full welding." The inspector couldn't understand it. He called to ask about the design and found out that it meant the saddle fillet weld. According to GB regulations, fillet welds should be drawn with thin solid lines to form an isosceles right triangle, not a personal hieroglyph.

Roughness symbols are also often wrong. An old employee always drew the symbol for material removal with the opening facing to the right, and the standard has long since been updated to an equilateral triangle with the opening facing the left. Last year, the external audit opened an item of non-compliance because eight drawings still used old symbols from the 1990s. For pressure vessels, if the symbol is one generation off, it may cause seal failure.

Tolerances must be calculated clearly

Tolerances are not as tight as possible. At the beginning of the year, there was a batch of flanges designed with H7 precision. They were processed with a grinder in the workshop. The cost of a single piece increased from 80 yuan to 240 yuan. In fact, H11 is completely sufficient for this working condition. Before marking tolerances, ask yourself three questions: what parts will it fit with, how high will the speed be, and what will be the temperature? This will determine whether you save money for the company or burn money.

Geometric tolerance marking is most easily ignored. There is a vertical mixing vessel. The designer only marked the dimensional tolerance but not the verticality. During installation, the mixing shaft scraped the inner wall of the barrel, causing two consecutive shafts to be scrapped. The purchase price of each was 17,000. There is a ready-made tolerance class table in GB/T1184, and it only takes 10 seconds to check it.

Do you have any construction drawings on your computer hard drive that you dare not sign?