Forge or Cast for Duplex Stainless Steel? Forge or Cast for Duplex Stainless Steel? mmbguide (Mechanical) (OP) 2 Oct 16 05:55 hello everybody By which method the trunnion mounted ball valve (Class 1500, 3PCS) should be produced? Forge or Cast? is there any mandatory by one method? thank you RE: Forge or Cast for Duplex Stainless Steel? MickMc (Mechanical) 3 Oct 16 05:04 They can be forged or cast, normally smaller sizes are generally forged in most valve types and larger cast. The only mandatory method I know of would be clients specifications which would typically say where specified forged substitution of casting is not permitted without prior company approval. Additional testing is usually required with casting to detect any flaws.