Questions regarding the “lower limit of operating temperature for steel plates”
Thread Content
This post was last edited by Douwan on 2018-6-5 09:45. Hello, fellow forum members. I’ve always had this doubt, and it’s resurfaced in my mind today, so I decided to seek everyone’s opinions. The content is as follows: Table 4 of GB/T 150.2 specifies the minimum operating temperature for steel plates made of carbon steel and low-alloy steel, as well as the corresponding impact test requirements; see the screenshot. Well, here’s the question: For a Q345R steel plate with a thickness of 12 mm, according to Table 4, it can be understood that \"the manufacturer conducts impact tests at 0°C in accordance with GB713 standards, so the plate can be used at -20°C\". This interpretation is also addressed in the FAQs for GB150; see the screenshot. But I clearly remember that at a continuing education training course in Xi’an last year, expert Zhang Yong answered this question. When someone asked whether a steel plate tested at 0°C could be used at -20°C, he said: Definitely not. (I promise I heard it right.) ； Another question: if the steel plant conducts impact tests at 0°C upon shipment, and then additional impact tests at -20°C are carried out after the material returns to the plant and those tests pass, can it be used at -20°C? Expert Zhang added: The impact test at -20°C is carried out during procurement; that is, it is required to be done by the steel mill, rather than after the product is purchased. Be careful about this. In other words, it still doesn’t work. In other words, according to Expert Zhang, the temperature used for impact testing must include the design temperature (the low temperature). For example, if the design temperature is -20°C, then the steel plate must be subjected to impact testing at -20°C. I went to the **General Administration for Quality Supervision, Inspection and Quarantine to look into it again, and found different answers, as shown in the image. Regarding this issue, neither the GB150 FAQs nor the responses from expert Zhang Yong nor those from the **General Administration for Quality Supervision, Inspection and Quarantine can be considered official replies; moreover, it’s not certain that the supervision departments will acknowledge them. If one really encounters this problem, it is indeed difficult to resolve. 1. For Q345R steel plates with a thickness of 12 mm, impact testing is standardly conducted at 0°C; can it be used at -20°C? 2. For Q345R steel plates with a thickness of 12 mm, the impact test is standardly conducted at 0°C; an additional impact test at -20°C was carried out upon return to the factory and it passed. Can they be used at -20°C? 3. For Q345R steel plates with a thickness of 36 mm, the impact test is standardly conducted at 0°C; an additional impact test at -20°C was carried out upon return to the factory and it passed. Can they be used at -20°C?
It’s really hard to deal with situations like this.
For 12mm Q345R steel plates, it is advisable to conduct an impact test at 20°C as well if they are to be used at -20°C; other plates can be used as long as they pass the impact test at -20°C. Originally, -20°C is a temperature that has been artificially set. Q345R materials of different thicknesses have different transition-to-ductility temperatures, but all of them are below -20°C; however, these test results have not yet been officially published.
This is due to different interpretations of the standards; according to the literal provisions of GB150, the minimum allowable temperature is -20°C. If the local supervision agency does not approve it, it will depend on your company’s public relations skills.
This post was last edited by zjq1962 on 2018-6-5 at 12:37. According to the GB150 standard, Expert Zhang’s first conclusion is definitely incorrect; it’s also possible that the expert overlooked the factor of thickness, as it’s after all just an immediate impression without careful consideration. The second conclusion is in line with the standards, while the reply from the General Administration for Quality Supervision, Inspection and Quarantine clearly does not conform to the standard requirements – otherwise why would the standard use the term “agreement” rather than “re-inspection”? Steel mills normally produce steel plates with a 0-degree impact resistance; it is very difficult to find plates with -20-degree impact resistance on the market. Ordering such plates from steel mills in small quantities also seems impractical, which reflects a disconnect between standard specifications and actual market conditions. Of course, with this reply, there is a basis for using it again.
1. Refer to Table 4 in GB150.2; for Q345R, a shock test at -20 degrees is required when the thickness is 36 mm in order to be usable at -20 degrees. The website also states that it meets the requirements for -20-degree shock tests, so it can certainly be used at -20 degrees. 2. In your question, it is 6–12 mm; according to Table 4, an impact at 0 degrees can be applied at -20 degrees as well. 3. The expert’s answer cannot be determined without specific prerequisites; generally, they won’t give an answer without conditions.
For steel plates under 12 mm, it is no problem to use them in impact tests at 0°C down to -20°C; this is also what various design institutes do； As for retesting thick plates after impact testing at -20°C for use at -20°C, there is no problem with that either; just as specified in the solid material specifications, when there are doubts regarding the authenticity of the material certificate or its properties and chemical composition, retesting and passing such tests allows the material to be put into use. Experts’ explanations cannot serve as an official basis.
Recently, there happened to be a batch of equipment with a designed temperature of -15°C, and plate thicknesses of 16mm, 20mm, and 32mm—all made of Q345R. What a coincidence, right?:lol After consulting the local inspection authorities as well as my own understanding of the standards, the final solution was as follows: for 16mm thick plates, impact testing at 0°C in the factory; for 20mm thick plates, impact testing at -20°C in the factory (since this value falls right at the boundary specified by the standards, the inspection authorities required impact testing at -20°C). PS: That’s just how our inspection officer is—for Q32mm thick plates, impact testing at -20°C in the factory plus normalization. As for doing the impact tests ourselves after purchasing the materials, I’m not sure what would happen there:victory:
That’s how it’s understood, but in practice, not everyone necessarily thinks that way.
1. Your thinking is a bit messy. 2. The first issue is that it won’t work; a 0-degree impact cannot handle -20 degrees. The second option is acceptable; -20 degrees is sufficient, so -20 degrees can be used. The key question is whether you can ensure that it meets the requirements. If it fails, the materials are wasted and have to be purchased again. If I were the boss, wouldn’t I fire the designer? The third question is the same as the second one. Qualified and usable. 3. In general engineering practice, when designing equipment, the designer first determines the minimum design temperature for that equipment (as specified by the customer). If it is -20 degrees, then the material requirements outlined in the drawings specify that the materials must be supplied after passing an impact test at -20 degrees. GB713 allows customers to request -20-degree impact testing, so that steel mills can take technical measures.