Piping Materials for Flanges, Fittings, Valves and Pipes 02

Mostly used cast irons for flanges, fittings and valves

According to the carbon contained or their mechanical properties, cast irons are classified as ductile iron, white iron, gray cast iron and malleable cast iron.

Gray cast iron(sometimes also written as "grey cast iron") is a cast iron produced by slow quenching of melt iron. The carbon exists in graphite flakes in a matrix of ferrite and pearlite structure which give the metal grey color and grey fracture appearance. The silicon contained makes gray cast iron easy to machine. In piping component application, it is widely used as a common material for valve bodies or closure members. The gray cast iron flanges and fittings are often used in water supply or sewage treatment systems. There are several Codes related to those applications:

1) ASTM A126: standard specification for gray iron castings for valves, flanges and pipe fittings.

2) ASTM A48: standard specification for gray iron castings.

3) ASME B16.1: cast iron pipe flanges and flanged fittings

4) ASTM A278/278M: gray iron castings for pressure containing parts for temperatures up to 650F
5) ASTM A319: standard specification for gray iron castings for elevated temperatures for non-pressure
containing parts
6) ASTM A436: standard specification for austenitic gray cast ion castings.

Ductile iron is a cast iron defined according to the shape of graphite contained. Unlike flake structure of graphite in gray cast iron, the graphite of ductile iron is in the form of spherical nodules which provides much more resistance to brittleness, impact and fatigue. The ductile iron also has high yield and tensile strength, good elasticity and ductility. Ductile cast iron are also widely utilized in pipes, fittings and valves for water supply, heat distribution, and sewage treatment service.
1) Ductile cast iron pipes and fittings: ISO 2531, ISO 7186, BS EN 545, BS EN 598, ISO 4179, ISO 8179,
BS 4027, BS 3416, ISO 4633, BS 2494, ISO 8180, ISO 7005-2,
ISO 4014, ISO 4032
2) Ductile iron grooved/threaded fittings: coupling, tee, elbow, cross, mechanical tee, reducer, cap, flange
3) Ductile iron valves: butterfly valve, gate valve, check valve, globe valve, double air release valve, etc.
4) Related American standards: ASTM A 395, ASTM A 439, ASTM A 536, ASTM A 571.

Malleable iron is a white cast iron that has been annealed, with a large proportion of its graphite evolved from cementite to elongated clusters that are ductile but still maintain a good hardness. A most famous application is malleable cast iron fittings: material in accordance to ASTM A 197, threads as per ASME B1.20.1. The surface of fittings can be either black or galvanized(hot-dipped). They're widely used in heat supply & distribution services.

Views: Author：hbmetals Date:15/02/07