Regarding the question of when to use grade III forgings
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Dear sea friends: Under what circumstances should Grade I forgings be used, and under what circumstances should Grade II forgings be used, and under what circumstances should Grade III forgings be used? Are there any principles for selection based on standards? Thank you!
It is recommended to consult the relevant information on forgings in GB150 and HG20581
Generally, grade 2 forgings are selected. For extremely high toxicity or at low temperatures, grade 3 forgings are generally chosen!
PN100 and above require grade III forgings
1. Small and medium-sized forgings with a design pressure of 10.0 MPa or higher shall meet Class III requirements, while large forgings shall meet requirements of Class III or higher, or Class IV.2 Forgings with extremely hazardous toxicity due to the medium used, as well as those with a cross-sectional dimension greater than 300, shall meet the requirements of Grade III or Grade IV. 3. Cylindrical and bowl-shaped forgings used for cylinders and heads, as well as low-alloy steel forgings with an actual thickness greater than 300, should be selected from grade III or grade IV.
As a supplementary note, HG/T20592-2009 also specifies: 1. Cr-Mo steel forgings with a nominal pressure of greater than or equal to PN40; 2. Ferritic steel forgings with a nominal pressure of greater than or equal to PN16 and an operating temperature of less than or equal to -20 degrees Celsius. These require forgings of grade III or above
Sections 5.4.2, 5.4.3, and 5.4.4 of chapter 5.4 on forgings in HG20581-98 specify requirements for the use of short sections