Malleable Iron Fittings

• Are class 150 & 300 malleable iron pipe fittings steam rated?
• What are the pressure ratings for Class 150 and Class 300 malleable fittings?
• What is the weight holding capacity for malleable iron couplings and other configurations?
• Can I weld on a malleable iron fitting?
• Why are there no Class 300 Malleable Iron Plugs or Bushings?