Low temperature and low stress

It seems that the stresses acting on the film in all directions should be added together, right?

I don’t have 20585 on me. But there are clear regulations in Appendix 150; you might as well take a look. However, this stress should refer to the hoop stress.

This post was last edited by lne on 2010-4-17 at 12:51. The original poster is incorrect; please take a close look at clause 2.0.4 of HG20585. Additionally, I would like to ask experts why the definition of low temperature and low stress given here differs from that specified in Appendix C1.5 of GB150

The overall film stress here, for the cylinder, refers to the calculated stress of the cylinder at the design temperature. HG20585-1998 and GB150 have different calculations for low temperature and low stress. Using HG20585-1998, it is relatively easy for the equipment to be in a low-temperature geostress condition. But after all, GB150 is something we must comply with. We need to perform the calculations using the GB150 formula.

The original poster didn’t read carefully; in HG20585, for low-temperature and low-stress conditions, the overall film stress is less than or equal to 75% of the material’s allowable stress multiplied by the weld factor. The overall film stress at that location depends on the specific conditions of the compressed element; for example, in the case of a cylinder, it is circumferential stress ； A spherical head has circumferential stress equal to radial stress ； The elliptical head is the sum of film stress and bending stress.

The compilation notes state that the definition in GB150 is stricter than the requirements of American, European, and Japanese standards; in the design of chemical containers, there are cases where the stress level is low, but still not below 1/6 of the yield strength specified by GB150. Personally, I feel that HG is indeed more reasonable and detailed. Let’s wait and see how the new GB150 will be revised

Low temperature and low stress: It refers to a cryogenic vessel operating under specified temperature conditions, in which the overall film tensile stress within the vessel is less than or equal to the specified \"low stress\" level. There are several key terms in this definition: specified temperature, tensile stress, and specified low stress. Specified temperature: This varies **for each country – in China it is -20 degrees, in the United States it is -29 degrees; in Japan and Germany it is below -10 degrees, and in the UK it is below 0 degrees. This includes data related to **the lowest temperature in the area, among other things. Tensile stress: The concept of low stress at low temperatures applies only to vessels under internal pressure; the stress inside a shell under external pressure is not tensile stress, so there is no such thing as low stress at low temperatures. Specified low stress: GB150 stipulates that the circumferential stress on the shell should be less than or equal to one-sixth of the yield strength of the steel material at normal temperature, and not more than 50 MPa ； HG20585 is related to ASME and temperature. But for now, designing in accordance with national standards means following GB150, unless you choose not to design based on GB150. Steel under low stress has a reduced tendency to suffer from brittle fracture at low temperatures compared to when it is under full stress; therefore, if the stress is also relatively low at low temperatures, the risk of brittle fracture of the material is not high. In low-temperature and low-stress conditions, low-temperature containers allow for a lower allowable operating temperature for the materials used; in other words, the material selection for such containers is based on the adjusted temperature. No special requirements need to be added for the testing requirements of manufacturing and materials. Note: The temperature limit of -20 degrees for low-temperature vessels applies to carbon steel, low-alloy steel, and ferritic stainless steel. The low-temperature limit of austenite is -196 degrees. (The statement in the GB150 standard that austenitic stainless steels can only be used at temperatures down to -196 degrees is incorrect; 304 and 304L grades can be used at temperatures as low as -253 degrees.) For calculations related to low temperatures and low stresses, it is necessary to verify the values point by point below -20 degrees, and the working pressures at several different temperatures should be considered. When the temperature is below -20 degrees, the design pressure at normal temperatures cannot be used to calculate the circumferential stress of the casing. (In pressure vessel design, temperature and pressure are a pair; it is not possible to use a pressure-temperature combination that does not exist.)

This post was last edited by misket706 on 2010-4-19 at 11:14. Low-temperature and low-stress conditions represent a simplified approach; caution is required in practical applications.

GB150: Low-temperature and low-stress operating conditions – situations in which the design temperature of the shell or its stressed components is less than or equal to -20°C, with the circumferential stress being less than or equal to one-sixth of the yield strength of the steel at normal temperature, and not exceeding 50 MPa