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4.1.1 Materials used in the construction of the tanks shall satisfy the requirements of this Chapter.When using the material other than those listed in this Chapter，their Standards shall not be lower than all the requirements of the materials listed in this Standard.
4.1.2 When selecting the materials for tanks，service conditions（such as design temperature，fluid characteristics and position on which material is used），chemical composition，mechanical properties，weldability and processability of the material，and economic rationality shall be considered.
4.1.3 When determining the materials，the minimum design metal temperature of tanks（see 5.1.1 c）shall be considered.
4.1.4 I When special requirements（such as special smelting process，raising of impact energy value，more requirements for non-destructive examination and more percentage of mechanical property tests etc.）are necessary to be set forth for steels，the Designer shall prescribe them on the drawings or in corresponding technical documents.
4.2.1 Modulus of elasticity of the materials at various temperatures shall meet the requirements in Table 4.2.1.
Table 4.2.1 Modulus of elasticity
Note:Interpolation may be made for intermediate temperatures.
4.2.2 Standards，service limitations and allowable stresses of steel plates shall meet the requirements in Table 4.2.2.
4.2.3 Q245R and Q345R steel plates used for the walls of tanks with thickness greater than 30mm but not exceeding 36mm shall be ultrasonic tested on each piece using the methods specified in JB/T 4730，and their quality class shall not be lower than ClassⅢ.
4.2.4 For Q345R plates with thickness greater than 20mm，when operating temperature is less than-10℃but not less than-20℃，the charpy（V-notch）impact test（at low temperature）shall be conducted on one piece per lot.The test temperature shall be identical with the application temperature of steel plate，i.e.the minimum design temperature of corresponding pressure parts or with that as prescribed on drawing.
Sampled position and the direction taken for of Charpy（V-notch）impact test specimens shall meet the appropriate requirements of GB 713.Three standard specimens per group are used in the impact test，and average impact energy of three specimens， KV 2 ，shall not be less than 41 J.It is allowed that impact energy of one specimen is less than 41 J but not less than 29 J.
Table4.2.2 Service limitations and allowable stress values for simple tension of plates
Note:a Allowable stresses in this row are applicable only to those parts，of which a slight permanent deformation is permitted.For or other parts where a slight permanent deformation will result in leakage or trouble，these values of allowable stresses shall not be applied.
4.3.1 It is preferred that seamless steel pipes should be used for nozzles and tracing pipes for the tanks.Service limitations of seamless steel pipes shall meet the requirements in Table 4.3.1-1 and Table 4.3.1-2.
Table 4.3.1-1 Service limitations of seamless steel pipes
Table 4.3.1-2 Allowable stress values of seamless steel pipes
Note:The allowable stress of all high alloy steel pipes only applies to those parts，of which a slight permanent deformation is permitted.
4.3.2 For structural pipes used in stairways，ladders and platforms，welded pipes may be used.
4.4.1 Forgings for the tanks shall satisfy the requirements of NB/T 47008 or NB/T 47010.
4.4.2 The allowable stress values of the forgings shall meet the requirements in Table 4.4.2.
Table 4.4.2 Allowable stress values of forgings
Notes:1 Interpolation may be made for intermediate temperatures.
2 The allowable stress of all high alloy steel forgings only applies to those parts，of which a slight permanent deformation is permitted.
4.5.1 Steel standards and allowable stress values of bolting materials shall meet the requirements in Table 4.5.1.
Table 4.5.1 Allowable stress values of bolting materials
Note:Interpolation may be made for intermediate temperatures.
4.5.2 Hardness of bolts shall be slightly higher than that of nuts.This may be obtained by selecting the materials with different strength or selecting different heat treatment specification.
4.6.1 Structural shapes shall satisfy the requirements of the applicable structure shape codes and standards.
4.6.2 Strength design values of carbon steel structural shapes shall meet the requirements in Table 4.6.2.Strength design values of austenitic stainless steel shapes may be determined based on the applicable codes and standards.
Table 4.6.2 Strength design values of carbon steel structural shapes
4.7.1 Suitable welding consumables shall be selected based on chemical composition，mechanical properties and weldability of base metal，considering construction features and welding processes of the tanks.
4.7.2 Welding consumables shall be provided with certificates of quality，and satisfy the requirements of the applicable codes and standards.
4.7.3 The welding consumables recommended for commonly-used steel grades shall satisfy the requirements of NB/T 47015.
4.7.4 Generally，the welding consumables，which have good cracking resistance and match with the materials of lower strength，should be used for the welds between carbon steels，low alloy steels with different strength classes.
4.8.1 When selecting foreign materials，the proven materials allowed by the latest foreign codes for the tanks shall be used.Their service limitations shall satisfy the requirements of the applicable codes and standards of the country in which the materials are produced，and certificates of quality for the materials shall be provided.
4.8.2 Chemical composition and mechanical properties of foreign materials，if used，shall not be lower than the requirements of similar materials in this Standard.
4.8.3 The allowable stress of steel plates shall be the lesser of R m /2.7 and R eL /1.5（ R p 0.2 /1.5 for high alloy steel）.