Research On Minimum Design Metal Temperature Of Typical Chinese Steels For Pressure Vessels

In recent years,several Chinese steels for pressure vessel was gradually concluded in ASME Code.Q345R steel and other steels in Chinese national standard GB/T 713-2008"Boiler and pressure vessel steel plate" such as Q370R,15CrMoR were concluded in SA/GB713.However,Q345R,earliest concluded in "ASME BPVC II Code Case 2642",is the only Chinese steel permitted using at low temperature with very conservative specific requirements as the exemption curve A for the Minimum Design Metal Temperature.That means,the design temperature of Q345R in ASME codes is even higher than the conservative stipulation of-20 ? in the Chinese national standard GB/T 150.Such background has greatly limited the application of Chinese steel for pressure vessels with excellent mechanical properties at low temperature and severely lowered the international competitiveness of Chinese steel for pressure vessels products and caused a very negative impact on the commodity export of Chinese pressure vessels.China is eager to break such deadlock,but lacks reliable support of experimental data.In addition,in Chinese standards,the procedure for the material selection for pressure vessel at low temperature remains keeping the early concept for brittle fracture prevention in early version of standards or codes in United States and Europe and the selection method based on the experience of "one size fits all".If applying an advanced material selection method at low temperature which synthesizes the factors of materials of construction,wall thickness,stress state and heat treatment,will be greatly helpful to the development of the whole industry,the use of the materials at low temperature will be greatly expanded,the production cost can be reduced,and will further reveal and verify the excellent mechanical properties of Chinese steel for pressure vessels at low temperature,significantly improve the international competitiveness of the products.With the financial support from the R&D Special Fund for Public Welfare industry of AQSIQ of China "Research on the Method for Determination of Minimum Design Metal Temperatures for Pressure Vessel Steels"(Project No.201010027),based on the background above,studies were conducted in view of some questions concerning the minimum design metal temperature for typical Chinese steels for pressure vessel of Q345R,Q245R,Q370R,16MnDR,12Cr2Mo1R and S30408.The main content and conclusions are shown as follows:(1)Based on massive experimental investigation,the regularities of distribution for mechanical properties of typical Chinese steels for pressure vessel at low temperature was obtained,and the toughness of Q345R is severely underestimated in ASME codes.Such experimental data set provides a strong and relieable support for establishing standards related to brittle fracture prevention,improving international competitiveness of Chinese steels,and gaining more objective and impartial recognition internationally.(2)Based on massive experimental data on mechanical properties at low temperature,The method of derivation exemption curve of the ASME codes was optimized and improved,and the impact test exemption curve and Minimum Design Metal Temperature of typical Chinese steel for pressure vessels were determined.The feasibility of the minimum design metal temperature determined by using the Master Curve method instead of the Charpy impact tests was discussed.And it was revealed that the exemption curve based on the Master Curve method can further expand the using temperature range of the material.(3)The applicability of the existing expression fitting to the relationship between the CVN energies and lateral expansion(LE)of Q345R,Q245R,Q370R,16MnDR and 12Cr2Mo1R was discussed.And a new piecewise correlation method was established and discussed based on the experimental data.In addition,the relationship of the CVN energies and LE for impact tests of the standard and Sub-sized specimens for the S30408 austenitic stainless steel welded joint was studied,and the most appropriate requirement was determined.The cold stretching exerted less influence on the CVN and LE relationship.