Some issues with design, materials, manufacturing, and inspection

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Design 1. The drawings of pressure vessels do not bear the design qualification stamp. 2. When large-diameter nozzles are rolled from steel plates, the weld coefficient remains 1.0 (the main weld coefficient for the cylinder body is 0.85). 3. For components with minimum formability thickness requirements, this minimum thickness is indicated only in the overall layout diagram; it is not specified in the component diagrams. 4. For titanium heat exchangers, only compliance with the Pressure Vessel Regulations and GB151 is required. How are all-titanium tube boxes designed, manufactured, and inspected? JB/T4745 should be included, and our engineering specifications also require the reference to JB/T4745. 5. The materials used in the calculation sheet do not match those specified in the drawings or those actually used. The calculation book specified normalized plates for 16MnR thin sheets, but hot-rolled plates were actually used. For the tube sheet calculations, normalized 16MnR steel is used, whereas the drawings and actual purchases specify 16MnIII forgings; the allowable stress of forgings is lower than that of normalized steel, which affects the calculation results. 6. The allowable stress for Inconel625 components is actually calculated based on the tensile strength and yield strength specified in the material certificate. 7. In the calculation book, for the S.S. plates made of ASME materials, the negative deviation is actually 0.8; this was calculated using the SW6 calculation software for ASME materials. 8. For non-standard saddles, the lifting lugs are not included in the calculation documents at all. For two devices with the same structure, the same lifting lugs were selected; one lug has a spacer plate, while the other does not. 9. After the SW6 calculation document was generated, no one even took a look at it – the layout was incorrect, the device names in the document did not match those on the drawings, and the unit for elastic modulus was mistakenly given as mm. Especially regarding the calculation of the reverse flange, due to a program bug and without referring to the calculation sheet, the default thickness specified in that sheet is 10 mm. 10. Selection of the corrosion margin for the tower skirt base. The standard requires that the corrosion allowance for the skirt be no less than 2 mm. However, in this case, both the tower skirt and the shell are made entirely of titanium. The corrosion allowance for the shell is set to 0, while that for the skirt is set to 1.6. Is the environmental corrosion more severe than the corrosion caused by the process materials? 11. The welding symbols in the drawings are incorrectly marked; even the most basic fillet weld symbols are not marked properly. The drawings for the external reinforcement ring specify full welding on one side and intermittent welding on the other; the symbol indicating intermittent welding is rather unclear, and it’s not obvious how the workers manage to understand it. Perhaps it’s a unique notation used by this manufacturer (there are **standards in place – one shouldn’t create such notations just to show individuality). To find out for sure, I went to the manufacturer’s site to see the actual product, and found that 50 units were welded together with 100 units left unwelded. However, this does not comply with the requirement that the total length of the welds on one side of an external reinforcement ring for a pressure vessel must be at least half of the vessel’s outer perimeter. It’s unclear whether this is a special requirement from the design or whether the workers made mistakes in interpreting those confusing welding symbols. 12. Special requirements not specified on the drawings for locations with such needs. The double-ended studs on the equipment’s manhole are to be tightened on site using a hydraulic bolt tensioner; therefore, they are much longer than ordinary studs. There are neither illustrations nor written descriptions of this in the drawings. As a result, during assembly, workers had no way of dealing with these excessively long studs. Fearing that they might interfere with transportation, they placed the excess length entirely on the flange side, while on the manhole cover side, the studs were left protruding by their normal amount. In that case, on-site it will be necessary for someone to use a hydraulic stretching device to pull it. Material: 1. For the procurement of 20# steel pipes with a wall thickness >10mm, GB8163-standard steel pipes were used. However, according to the allowable stress table in GB150, the maximum wall thickness for GB8163 steel pipes is 10mm. Moreover, the calculation document also uses GB9948 steel pipes as the basis for calculations. GB8163 is not the only steel pipe that can be used; the substitution sequence for steel pipes is basically GB5310→GB6479→GB9948→GB8163. Request for redoing~ For 2.GB/T3625 titanium heat exchange tubes, according to clause 4.2.6.3 of JB/T4745, σr0.2 is required to be a specified value; however, the material standard states that this value is provided only when required by the contract. Therefore, when purchasing heat exchange tubes made in accordance with GB/T3625, it is necessary to request that this value be provided. Currently, this value is not indicated in the quality certificate, nor is any retesting arranged. 3. The part drawings for Inconel 625, as well as the calculation documents, specify grade 1; yet the final quality certificate indicates grade 2. Although grade 2 is generally superior to grade 1 in most cases, this is not the case for this part, and there are no procedures permitting the use of an alternative grade. 4. Titanium shell plates larger than 20 mm are to be subjected to UT inspection on a per-sheet basis in accordance with clause 4.2.6.1 of JB/T4745; however, the quality certificate does not include an UT item, and no such inspection is carried out upon arrival of the materials. Ultimately, UT inspection is only performed on the formed cylinder. 5. For titanium shell plates that are also larger than 20 mm, if the tensile strength specified in the quality certificate does not meet the requirements, they should be treated in accordance with the requirements noted in Note 2 of Table 4-1 in JB/T4745. 6. The non-destructive testing standard specified in the quality certificate for the composite panel is still JB4730-94. 7. If the manufacturer has special requirements when purchasing materials, those special requirements must be specified; materials should not be purchased solely in accordance with the standard specifications. There is also the issue of qualified suppliers. As a customer of material suppliers, the manufacturer has more than just a simple payment-and-delivery relationship with them. A qualified supplier should understand the customer’s needs and meet them. Since the manufacturer is a pressure vessel producer, the material supplier should supply materials that meet the requirements for such vessels. 20# steel pipes and 16MnR plates are the most commonly used materials. If you order 20# steel pipes with a thickness of over 10 mm, the material supplier should not provide those that comply with GB8163 standards; whereas for 16MnR plates with a thickness of over 30 mm, the supplier should provide normalized plates. This should be common sense. Unqualified suppliers should be eliminated as early as possible, to avoid ending up being removed by the construction company themselves. Manufacturing, inspection, testing: 1. The signal hole is placed arbitrarily during the assembly of the reinforcement ring. 2. The ellipticity of the rolled tube sections is severe, as is the angle distortion. In an ordinary factory, it’s understandable if the quality isn’t up to standard due to limitations in equipment; but this factory has comprehensive and advanced equipment, yet it still manages to produce such substandard products. 3. The tube sheet is not cleaned before the heat exchange tubes are inserted. It is required that this process be carried out in a clean factory, but what’s the use of inserting tubes when the tube sheet is covered in oil even in the cleanest factory? 4. There is no clear guideline for the expansion bonding of tubes and tube sheets; workers are only told what the desired result should be. No testing is done on samples, and decisions are made based on experience and intuition. But do workers really have that much experience? For tubes that have just been expanded, only the expansion head was replaced; the expansion pressure wasn’t adjusted either, and the titanium tube was expanded directly. **The strength of the tube sheet is much higher than that of titanium tubes and 16MnIII tube sheets, so it is not prone to damage due to expansion. Is it true that only one crimping pressure is used regardless of what is being crimped? In the end, the expansion tube suffered as a result. 5. The workers here are versatile; they can do everything from riveting to electric welding and TIG welding, all by chance. 6. The titanium test plate passed the testing according to JB4744, but it should have been evaluated in accordance with JB/T4745. 7. The inspection in the workshop is inadequate; inspections are carried out purely based on experience, with no regard for the inspection requirements specified in the drawings, let alone compliance with engineering standards.