Summary of Technical Requirements for Pressure Vessels (21)

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Low-alloy steel vessels with Rm≥540MPa have the following mandatory requirements: 01 Sphere storage tanks shall undergo an internal inspection one year after being put into use. 02 During regular inspections, the length for surface defect detection shall be no less than 20% of the length of the butted weld. 03 During regular inspections, if the material is unknown, its identity must be determined. 04 For welded joints that have a tendency to reheat cracking or delayed cracking (referring to Cr-Mo steels and low-alloy steels with Rm≥540 MPa), magnetic particle or penetrant testing should be performed on their surfaces. For materials prone to delayed cracking, surface testing should be carried out at least 24 hours after welding; for materials prone to reheat cracking, additional non-destructive testing should be conducted after heat treatment. 05 The comparative experience design method shall not be used. 06 For steel plates with a thickness greater than 36 mm and an Rm value of ≥540 MPa, a drop hammer test may be conducted; the test is carried out in accordance with GB/T6803 using P-2 type specimens. The acceptance criteria regarding the temperature at which no plastic transformation occurs are specified in the design documents. 07 Low-alloy steel forgings with a nominal thickness greater than 200 mm and an Rm of ≥540 MPa shall use grade III or grade IV. 08 Reinforcing ring structures shall not be used.