Product Name: ASTM A351 CF8 Dual Plate Check Valve
Type: Lug Type, Dual Plate
Standard: API 594
Size: 20 Inch, DN500, 500 mm
Pressure Rating: Class 150 LB, PN20
Body Material: ASTM A351 CF8 (SS 304)
Plate Material: ASTM A182 F304L with STL 6
Seat Material: Integral Seat with STL 6 Overlay
Spring Material: Inconel X-750

Source: https://www.landee.cn/astm-a351-cf8-dual-plate-check-valve-api-594-20-inch-lug.html