4.4　Application Requirement of Metallic Materials

4.4.1　The materials shall be selected according to their usability，process properties and economy.

4.4.2　The usability of materials shall be determined according to the design operating temperature，stress condition，characteristics of the medium，and endurance and safety performance of components.

4.4.3　The process properties of materials shall be determined according to the geometric shape，dimensions and manufacturing process of components，and the repair measures in case of failure of such component.

4.4.4　The selection of materials shall comply with the relevant national standards in force.The manufacturer shall provide quality materials accompanied with the certificate of conformity and the quality certificate which show the material designation，chemical composition，mechanical property，heat treatment process and necessary performance test results.

4.4.5　High temperature steam piping materials shall comply with the following requirements:

1　Have satisfactory creep limit，creep rupture strength，long-term plasticity，and oxidation resistance.For steam piping，the design strength of piping materials shall be determined based on l×105 h or 2×105 h creep rupture at high temperature，and checked using the creep limit.For low alloy heat resistant steel，the cumulative deformation due to relative creep throughout the operating period shall not exceed 1.5%.The deviation range of creep rupture strength and creep limit shall not exceed±20%.The elongation in terms of long-term plasticity shall not exceed 3%-5%.

2　Have stable metallurgical structure and properties during long-term operation under high temperature conditions.

3　Have satisfactory process properties，especially the welding property.

4　Have satisfactory thermal conductivity property and low thermal expansion coefficient.

4.4.6　The materials of piping used for conveying medium other than high-temperature steam shall comply with the following requirements:

1　Have satisfactory room-temperature strength and high-temperature strength.Generally，the design strength is based on the yield strength and tensile strength of the steel.

2　Be resistant to corrosion from the conveyed fluid.

3　Have satisfactory toughness.

4　Have lower strain rate sensitivity.

5　Have satisfactory process properties，especially the welding property.