Determination of forging grade

(HY-industry technical centre)

The forgings are divided into four levels: Ⅰ, Ⅱ, Ⅲ, and Ⅳ. The inspection items for each level are specified in the following table:

Forging level

Inspection item

  Inspection quantity

Hardness (HB):

check piece by piece;

Tensile and impact:

Same smelting furnace number, same batch, one sample for each batch;

Tensile and impact:

Same as smelting furnace number, same batch, one sample for each batch. Ultrasonic testing: check piece by piece;

Tensile and impact:

piece by piece inspection, ultrasonic detection: piece by piece inspection;

So how are the forging grades specified in various pressure vessel standards?
GB 150.4-2011
6.1.3 The following steel forgings should use grade III or grade IV:
It is used as the cylindrical, ring and bowl-shaped forgings of container cylinder and head.
Low alloy steel forgings with nominal thickness greater than 300mm.
Low-alloy steel forgings with a standard tensile strength lower limit equal to or greater than 540 MPa and a nominal thickness greater than 200 mm.
Use low-temperature steel forgings with a temperature lower than -20℃ and a nominal thickness greater than 200mm.

6.1.4 For 20MnMoNb, 20MnNiMo, 12Cr2Mo1V and 12Cr3Mo1V grade III or IV steel forgings with a design temperature higher than 300℃, the design documents shall specify that the steel forgings shall be designed at batch (level III) or piece by piece (level IV) For the tensile strength test under high temperature, please refer to Appendix B for its yield strength value.
HG/T 20581-2011

6.4.2 Forgings whose size and quality meet one of the following conditions are small and medium-sized forgings, and those exceeding the following conditions are large forgings.
The flange size is not greater than PN2.5, DN600 manhole flange or other ring forgings of the same size.
Pie-shaped, cylindrical and shaped forgings with a mass of forgings not greater than 800 kg (such as tees, valve bodies, etc.).
Bar or shaft forgings with a diameter not greater than 200mm and a mass not greater than 1500kg.

HG/T 20592-2009
6.4.3 Forgings for pressure vessels should be selected according to their conditions of use, size and quality.
Flanges with a design pressure of less than 10.0 MPa and forgings with similar geometric dimensions shall meet the requirements of Class II or above.
Forgings with a design pressure greater than or equal to 1.6Mpa shall meet the requirements of Class II or above.
Small and medium-sized forgings with a design pressure greater than or equal to 10.0 MPa should meet the requirements of Class III, and large forgings should meet the requirements of Class III or Class IV.
Forgings with extremely toxic or highly hazardous media and forgings with a nominal thickness greater than 300 mm shall meet the requirements of Class III or Class IV.
HG/T 20592-2009

4.0.2 The grade and technical requirements of forgings (including forged and rolled) for pipe flanges shall comply with the following two provisions:
If it meets one of the following conditions, it shall meet the requirements of forgings of Grade III or above:
Those whose nominal pressure is greater than or equal to PN100;
Chrome-molybdenum steel forgings with a nominal pressure greater than PN40;
Ferrite steel forgings with nominal pressure greater than PN16 and operating temperature less than or equal to -20°C.
In addition to the above provisions, forgings with a nominal pressure not greater than PN63 shall meet the requirements of forgings of Class II or above.
HG/T 20585-2011
6.0.8 Forgings for low-temperature pressure vessels shall be in accordance with the requirements of “Low-alloy Steel Forgings for Low-temperature Pressure Equipment” NB/T 47009 and “Stainless Steel and Heat-Resistant Steel Forgings for Pressure Equipment” NB/T 47010, and shall not be less than the requirements of Grade II. When the design pressure is greater than or equal to 1.60Mpa, it shall not be lower than Grade III.

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