Relationship between the maximum permissible creep strain and defectiveness of steam pipe materials

Conclusions

• 1. A correlation was found between the plastic deformation during creep and the defectiveness of the material.

• 2. As the strain characteristic from which one can determine the defectiveness of the material in steam pipes we propose using the ratio$\dot \varepsilon _i /\dot \varepsilon _y$, which defines the acceleration of creep in the third stage.

• 3. During prolonged operation of steam pipes it is necessary to measure the creep strain periodically. With the transition to the third stage of creep it is necessary to determine the creep rate; the steam pipe should be replaced when deformation in the third stage accelerates to$\dot \varepsilon _i /\dot \varepsilon _y = 3$.

• 4. The maximum permissible creep strain after 200,000 h of operation is 2% for steam pipes of steels 12Kh1MF and 15Kh1M1F with structures meeting TU requirements and 1% for pipe of steel 12Kh1MF with a structure of temper bainite.