Is Appendix F of GB/T150.3, which deals with the verification against low-temperature brittle fracture, used to verify that “MDMT≥VTrs”?”
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Dear teachers, is there an error in what is written here in Figure 1? It should be checked that “MDMT ≥ the lowest operating temperature of the container”, right? It shouldn’t be the design temperature Also, in Figure 2, what is the relationship between this \"minimum allowable operating temperature\" and the material’s ductile-brittle transition temperature VTrs? What is the logical connection between the two? ”Was the concept of \"minimum allowable operating temperature\" proposed to avoid reaching the material’s ductile-brittle transition temperature? Is this verification essentially checking whether “MDMT ≥ VTrs”? – Is the basic principle behind crack resistance verification that, when MDMT is specified, it should be set above the lower temperature limit for material use given in 150.2, but MDMT must not reach the material’s ductile-to-brittle transition threshold; in other words, even under conditions such as low temperatures at the location where the equipment is installed or local temperature drops caused by valve discharge, the temperature should not cause the material to shift from ductile fracture to brittle fracture at low temperatures?
Your understanding of the verification for preventing low-temperature brittle fracture in Appendix F of GB/T150.3 is generally correct, but some detailed concepts need to be clarified: 1. There are indeed imprecise expressions or misunderstandings in Figure 1. The correct approach should be: - MDMT: refers to the minimum allowable metal usage temperature specified in the container design (the lowest temperature that the equipment can actually reach). - Verification principle: It is required that MDMT must be greater than or equal to the lower limit temperature for the safe use of the material (i.e., the “minimum allowable operating temperature”). Therefore, you are correct in your understanding; it is inappropriate to use the term “design temperature” here in the standards – it should be “Minimum Allowable Operating Temperature (MDMT)”. 2. The relationship between the \"minimum allowable operating temperature\" and the material’s ductile-brittle transition temperature (VTrs): VTrs, or the ductile-brittle transition temperature, is typically a physical property determined through material testing; it represents the critical temperature value or range at which there is a significant shift in the material’s fracture behavior from ductile to brittle ； - The minimum allowable operating temperature is a more conservative value obtained by taking into account VTrs and applying a safety margin specified by standards (usually several degrees lower than VTrs, such as 10°C, 20°C, or more); it represents the minimum safe operating temperature directly provided in standards or specifications. Logical relationship: Minimum allowable operating temperature = VTrs – safety margin (or an empirical value specified by standards). In other words, the \"minimum allowable operating temperature\" must be below the material’s ductile-to-brittle transition temperature (lower than VTrs), in order to ensure a certain safety margin and prevent entry into the region where the material becomes significantly brittle. 3. Essence of the crack resistance verification: – It is not simply a matter of “MDMT≥VTrs”; rather, it is necessary to ensure that “MDMT≥the minimum allowable safe operating temperature specified in the standards”. - In practical engineering, this minimum allowable operating temperature takes into account factors such as the VTrs of the material, thickness effects, and stress conditions, while also providing an appropriate margin. Therefore, you can consider the minimum allowable operating temperature specified by the standards as a corrected, safety-guaranteed lower limit temperature for the ductile-brittle transition. 4. Principles for selecting “MDMT” (as you mentioned): It is indeed as you understand it—firstly, MDMT is determined based on the actual environmental conditions (including the lowest temperature at the installation site, the lowest temperature required for the operation of the process, and local low temperatures caused by discharge or abnormal operating conditions) ； - Then, the determined MDMT is compared with the minimum allowable service temperature for materials specified in the standard (GB/T150.2), to ensure that the selected material will not suffer from brittle fracture under MDMT conditions. In summary, your overall understanding is correct; there are indeed some imprecisions in certain parts of the standards (such as the terminology used in Figure 1), but these do not affect the overall understanding and application. The core logic for checking against low-temperature brittleness failure is: MDMT ≥ the minimum allowable operating temperature specified in the standards (taking into account VTrs and safety margins), ensuring that the container will not enter the brittle region of the material under the actual lowest operating temperatures, and will not reach or approach the material’s ductile-brittle transition temperature, thereby avoiding failure. .
Hello, two questions: 1) The sentence \"The minimum allowable operating temperature is determined based on VTrs, taking into account the safety margin specified by standards (usually a few degrees higher than VTrs, such as 10°C, 20°C, or more)\\" should read that it is \"a few degrees higher than VTrs, such as 10°C, 20°C, or more\", right? It shouldn’t be \"lower\" 2) “Compare the determined MDMT with the minimum safe operating temperature for materials specified in the standard (GB/T150.2)” – is the minimum safe operating temperature for materials determined according to GB/T150.3Appendix F? Isn’t it Table 3 in GB/T150.2?