Determination of the design temperature for the skirt base
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This post was last edited by jizhanwei22 on 2016-9-7 17:04. Discussion: How do the companies where everyone works determine the value for the design temperature of the skirt? 1. Clause 5.1.2.d of JB/T4710-2005 \"Steel Tower Vessels\": The design temperature for the skirt shell and foundation bolts shall be taken as the lowest value of the monthly average minimum temperatures in the area of use, plus 20°C. 2.HG20580-1998 stipulates that for outdoor steel structures such as skirt bases, the ambient temperature shall be used as the design temperature. Note: The ambient temperature here is taken as the \"outdoor design temperature for air conditioning in winter,\" with specific values provided in HG20652-1998 \"Technical Specifications for Tower Design.\" 3. Clause 4.2.2.d of NB/T47041-2014 \"Tower-Type Containers\": The design temperature for the skirt shell (excluding the transition section) and the anchor bolts shall be taken as the minimum value of the monthly average lowest temperatures in the area of use, plus 20°C. 4. Clause 4.2.3 of SH/T3098-2011 \"Code for Design of Petrochemical Columns\": The design temperature of the skirt shell can be determined according to Table 3. To summarize: the design temperature for the skirt shell (excluding the transition section) and the foundation bolts should take into account the influence of the environmental temperature in the area where the tower is to be built, with the environmental temperature to be taken as the lowest value among the monthly average minimum temperatures in that area. 5. Article 5.0.2 of HG/T20580-2011 \"Basic Provisions for the Design of Steel Pressure Vessels\": (1) For skirt bases with transition sections, the design temperature of the transition section shall be equal to the design temperature of the tower (or the bottom of the tower) ； The design temperature of the skirt shell below the transition section should take into account the influence of ambient temperature. (2) For skirt bases without a transition zone: when the design temperature of the tower (or tower bottom) is ≤ 200°C and > -20°C, the design temperature of the skirt base should take into account the influence of the ambient temperature. Among the standards listed for the 5 items, all specify a design temperature for the skirt base; the main difference lies in whether an additional 20°C is added to the ambient temperature (the lowest average monthly temperature in the area of use). NB/T 47041-2014 \"Tower-Type Vessels\" adopts the provisions of JB/T 4710-2005 \"Steel Tower-Type Vessels\" without any changes, namely the ambient temperature (the minimum value of the monthly average lowest temperatures in the area of use) + 20°C. All other standards use the ambient temperature (the lowest value of the monthly average minimum temperatures in the area of use). Discussion: How do the companies where you work determine the selected design temperature for skirt bases? Is it in accordance with the latest standard NB/T47041-2014, or with other more stringent standards? The significance of discussing this issue: 1. It determines whether Q235B steel plates can be used for the skirt shell. 2. When Q245R steel plates are used for the skirt shell, is it necessary to conduct low-temperature impact tests (in areas where the ambient temperature is low during tower construction)? 3. To be continued..
In fact, the main principle is safety, with the principle of cost-effectiveness also taken into account. If the project is in the Northeast, it’s advisable to use Q345 structural steel plates at the very least; Q235 is not recommended
Since the material for the skirt housing is selected based on its role as a compressive element, it should also be chosen according to temperature considerations. Of course, the temperature used here should be based on the actual temperature; the addition of 20 is intended to take into account the fact that the skirt housing is not subjected to internal pressure. It should be selected according to NB/T47041!
Paragraph P36 of the explanatory notes for HG20580-2011 states that the designer shall determine the design temperature using one of two methods: either +20, or without any specific value
For a tower, regarding the material used for the skirt cylinder, changing Q235B to Q345R results in little difference in cost; it is still better to opt for a material that is safe and reliable.
This post was last edited by ywqhfsj on 2017-5-27 at 11:52. Good question; those who design towers cannot avoid it.
This post was last edited by ywqhfsj on 2017-5-27 at 11:54. There are many standards for tower equipment, but problems still exist.
This post was last edited by ywqhfsj on 2017-5-27 at 12:00. The following describes the practices of our unit; all discussions herein do not include the skirt transition section. 1. The design temperature for the skirt shell and foundation bolts is taken as the lowest value of the monthly average minimum temperatures in the area of use, plus 20°C (this is the minimum requirement among several standards). 2. The material selection for the skirt shell and anchor bolts is determined based on the design temperature. The skirt shell is selected based on the material requirements of its structural components, and does not need to be considered as a compression member. Depending on the regional temperature, steel plates such as Q235-A, B, C, and D from the Q235 series can also be used (Q235-AF is not applicable). Currently, some clients require that materials be selected based on their use in compressive applications, and they do not allow the use of materials from the Q235 series; instead, only specialized materials for containers such as Q245R and Q345R are permitted. 3. Low-temperature impact tests on skirt material: 3.1 These tower design standards do not specify explicitly whether non-compressed components need to undergo impact tests at the design temperature (referring to the skirt, the same below). 3.2 Impact testing is also required when considering structural components (the standards for these materials stipulate that impact testing must be carried out at the time of leaving the steel plant), but the question is whether it is necessary to lower the test temperature to the design temperature. 3.3 The standards do not provide detailed specifications for impact tests on non-compressed components. Although the stress conditions on the skirt shell are simpler compared to those on compressed components, their importance is still significant. As a precaution, it is generally considered necessary to conduct impact tests at the design temperature. The actual conditions of non-compressed members are complex and diverse; it is difficult for standards to cover all possible scenarios of such members and establish uniform requirements for impact testing. However, as a very important non-compressive component, it is still hoped that the standards can establish specific requirements for skirt seats (it’s a bit disappointing in reality)! 3.4 But it is relatively easy to consider for a specific device. For example: the lowest average monthly minimum temperature is -23°C; the design temperature for the skirt is taken as -23 + 20 = -3°C, assuming that the thickness of the skirt shell is 14 mm. Consider several cases: If Q235D is selected (according to GB/T700, and the steel plant has already conducted impact tests at -20°C), no additional impact tests are required ； If Q245R is selected (according to GB/T713, with impact testing at 0°C already conducted by the steel manufacturer), then per Table 4 of GB/T150.2, the allowable operating temperature is -10°C for pressure-bearing components; therefore, no additional impact testing is required for the skirt parts that serve as structural elements. 4. The situation with anchor bolts is similar to that of pedestals, so no further explanation is needed.
20652 specifies clear requirements for impact tests and impact energy under design temperatures below 0°C.