Must the welding joint coefficient for the shell of a fixed-tube-sheet heat exchanger always be set at 1.0?
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This post was last edited by Douwan on 2018-6-13 08:14. Must the welding joint coefficient for the shell of a fixed-tube-sheet heat exchanger always be set at 1.0? Today, I happened to hear from a friend that he discussed this issue while having dinner with a colleague, who said that the welding joint factor for the shell of fixed-tube plate heat exchangers must always be set at 1.0. The reason for this is that internal inspections cannot be carried out after welding, as it’s not possible to get inside. Looking again at the definitions in the fixed-volume code and GB/T150.4, as shown in the screenshot below: However, after examining many drawings and past practices, it seems that this approach was not used. Further research into the Q&A sections and examples provided in GB150 yielded such an explanation (although the document states that these answers are not part of the official standard specifications and therefore lack legal validity, they are still responses given by the Standardization Committee for Pressure Vessels and are useful for reference), as shown in the figure. Colleagues, when designing fixed-plate heat exchangers, do you all use a welding joint factor of 1.0 for the shell side?
I believe that the shell of a fixed-tube-sheet heat exchanger should not fall under the scope of clause 10.3.1 d) of GB/T 150.4. Clause 10.3.1 d) stipulates: containers that are required to undergo internal inspection after use but cannot be inspected accordingly ； For fixed-tube-sheet heat exchangers, what’s the purpose of going inside? Which area should be tested? Can the shell-side cylinder be inspected externally?
A pressure vessel that cannot be internally inspected after use refers to a pressure vessel that cannot have its inner surface inspected after use? Is that how it’s defined?
Further research was conducted; according to the fixed-volume specification and clause 10.3.1 d) of GB/T 150.4, a pressure vessel that \"cannot be internally inspected after use\" refers to a pressure vessel for which it is not possible to inspect its internal surface after use. Therefore, the conclusion should be: if the shell side cylinder with a fixed tube sheet requires surface inspection, then this cylinder must undergo 100% ultrasonic or radiographic testing. Examples of fixed tube sheets in such situations include Cr-Mo steel, stainless steel with a thickness of over 20 mm, high-strength steels with Rm≥540 MPa, and composite steel plates, among others. I’m not sure if I understand correctly? Welcome forum members to point out any errors
This post was last edited by wanlirn on 2018-3-5 at 17:57. It’s not necessary to use the value 1; our company follows the guidelines set out in the relevant regulations. I’ve forgotten which year it was – it must have been many years ago. For ordinary heat exchangers, the value 0.85 is used, and 100% testing is required with a grade of III as the standard for acceptance. The drawings also specify the regular inspection intervals for the shell thickness as well as the acceptable values. Have you ever attended any of these training sessions, OP? It’s said in the classes that these are unofficial explanations, but following what they say will definitely not cause any problems; that’s just how things are in this country
When I was in Beijing in 2011, there was a presentation on the GB150-2011 standard; I attended it, but I don’t remember whether that specific clause was covered in the lecture – maybe it wasn’t discussed, or maybe it was discussed but I’ve forgotten. However, as for different shifts, the content covered by the experts does vary
I think it’s not possible to conduct inspections inside; it must be done using devices placed at the back, as it’s not feasible to check the interior through access holes or manholes. Since internal inspection isn’t possible, quality control must be ensured from the very beginning of the manufacturing process!
Some of the drawings I’ve seen do not require 100% non-destructive testing for the shell side. I think a container that cannot be inspected from the inside doesn’t necessarily mean it’s 100% damage-free; it depends on the medium.
Early version of the standards provided exemptions for heat exchanger shells, but these were later removed. Theoretically, 100% non-destructive testing is required; this was brought up by the review team during the design renewal process. But in reality, the standards are not strict, especially for carbon steel heat exchange tubes. Before the casing developed problems, the heat exchange tubes had already been completely corroded.
This post was last edited by cxd11888 on 2018-3-7 09:43. Shouldn’t it be carried out in accordance with the provisions of 4.6.3 in GB/T151-2016?