Design specifications for fatigue-resistant containers with proven successful application experience

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For containers that have been successfully used under cyclic loading, with the approval of the technical responsible person of the design unit, they may be designed in accordance with this standard; additional fatigue analysis and evaluation shall be carried out in accordance with Appendix C of JB 4732, while also meeting the relevant manufacturing requirements. The general meaning of this statement is that for a certain type of fatigue-resistant container, if there is prior successful usage experience, the analysis and design steps can be omitted, based on the preparation of an additional analysis report. This sentence raises the following questions: Question 1, how can successful usage experience be determined? Can the design experience from other units be used? The answer to this question can be found in the answers to questions in GB/T150-2011. Regarding the successful application experience of this clause, in principle, the specific requirements should be the same as those of the empirical design method specified in Appendix D of this standard; design work can also take into account the experience of other organizations. The similarity ratio of the design conditions and structure between the newly designed container and the reference-designed container shall meet the corresponding requirements in Appendix D. In other words, the definition of successful usage experience should be based on the \"Appendix D: Comparative Experience Design Methods\". The successful usage experiences of other units are acceptable. The design conditions and structural requirements shall comply with Appendix D. Let’s take a look at how Appendix D stipulates this. Experience requirements: The reference containers should be those that are already in actual production use, with a safe operating life of no less than 5 years. The actual operating conditions of the vessel shall not be less than 80% of its design conditions. Requirements for design conditions: Same structure as the reference vessel; same medium. The design temperature shall not be higher than the design temperature of the reference vessel ； For vessels designed for temperatures below 0°C, the design temperature of the vessel shall not be lower than that of the reference vessel. The design pressure shall not be higher than that of the reference container. Structural requirements: The container designed based on comparative experience should have the same or similar structure as the reference container, with the structural similarity ratio of the main dimensions to be between 0.85 and 1.15. While ensuring the functional capabilities of the container designed through comparative methods, structural optimization should be considered to reduce the effects of secondary stresses and peak stresses caused by overall structural discontinuities and local structural discontinuities. The requirements outlined in these sentences of Appendix D are roughly as follows: 1. The reference container must have been running successfully for at least 5 years ； 2. The reference container should operate at full load; at least 80% load is recommended ； 3. The structural similarity ratio between the container to be designed and the reference container is 0.85~1.15 ； The first two points above are relatively easy to determine. However, the third point is rather abstract: how should the similarity ratio of coefficient structures be calculated and determined? Question 1 has been resolved; let’s move on to the next question. Question 2: According to Appendix C of JB 4732, supplementary fatigue analysis and evaluation are required. Do the organizations and designers need to obtain qualifications for analytical design? The answer is no, it’s not necessary. The answer can be found in the standard definitions. For vessels subjected to cyclic loading that have a proven track record of successful use, with the approval of the technical responsible person at the design unit, they may be designed in accordance with this standard. Additionally, fatigue analysis and evaluation shall be conducted in accordance with Appendix C of JB4732, while also meeting all relevant manufacturing requirements. In principle, the specific requirements should be the same as those specified in Appendix E of this standard for the analysis and assessment of local structural stresses: generally, no design qualifications are required of the design agencies and designers, but the designers should possess the ability to conduct such stress analysis, classify the results, and assess them. This issue has also been resolved; let’s move on to the next question: Question 3 – what does it mean to meet the relevant manufacturing requirements at the same time? What this sentence means is that for the containers designed, the manufacturing requirements must not only meet those specified in GB/T150.4, but also comply with the requirements of GB/T4732.6-2024. Question 4: Regarding the container, can it be of a conventional design? Personal opinion: No! Think about it: the reference container is supposed to be analyzed and designed in accordance with the specifications, yet you carried out a conventional design, which is already a non-compliant approach. Now you even use it as a reference for others. It is a false proposition in itself; if one cannot prove it even for themselves, how can it be used as evidence for others? Using a false proposition to prove the reliability of your design is simply absurd. If the reference container is of conventional design, then whom did you refer to when designing it in the first place? This question is now concluded. In my personal opinion, it is not recommended to waive the fatigue analysis using this method. If exemption is granted in this way, the effort and money spent will not be less than those required for analysis and design. There are two reasons: first, it is not easy to obtain information based on the actual operating conditions of the container. This requires the use of units provided by the supplier. Which organization would be willing to do something that entails taking such responsibility without any benefits? II. The design specifications for reference containers are not easily available. If it’s the design work from our own team, it’s easier to handle, but if it’s a product designed by another design firm, will they be willing to provide it to you? III. The design of the reference container should be for analyzing designed products.