During steel manufacturing, oxygen is forcibly injected into it to ledel. The oxygen combines with excess carbon and is released as a gas. Excess oxygen is, however, unavoidably left in the molten steel. This results in the formation of oxide inclusions in the steel, or porosity, which appear upon solidification. The process of removing the oxygen is known as deoxidizing. Deoxidation is achieved by adding silicon, aluminum, or other deoxidizing agents to the molten steel. The degree of deoxidation create three different type of steel.
Killed Carbon Steel is completely deoxidized steel, no free Oxygen is left in the steel. Resulting uniform composition and superior toughness as compared to other types.
Semi-Killed Carbon Steel is Partially deoxidized and some free Oxygen is still left in the steel. Properties of semi-killed steel in between fully killed and rimmed steel.
Steel produced without deoxidization is known as a rimmed steel. Which is brittle and have poor elongation.
Only fully killed steel is used in process piping.
Cast Iron Vs Cast Steel
There is difference between Cast iron and Cast Steel. Let’s talk about cast iron.
- Ferrous metal that contains more than or equal to 2% of Carbon by weight is cast iron
- It is hard and brittle material, so not useful for process piping
- However, Ductile iron pipes are widely used in water distribution network because its good corrosion resistant property
- Another example of the use of cast iron is Manhole covers for the drainage
- There are other types of cast iron, that also used for different industrial purposes other than piping. Such as Grey cast iron (ASTM A48), White cast iron, Malleable iron (ASTM A47), A74, A746.
- Cast Steel is a ferrous metal that contains less than < 2% Carbon by weight.
- Cast steel is used in various casting material used in process industries. It used in manufacturing of valve body and cast fittings
- ASTM A216 Gr WCB, A352 Gr LCB/C are example of cast steel grades.
Carbon Steel is also fit under the definition of cast steel, but the main difference is in manufacturing method. Carbon steel is manufactured by rolling, forging and drawing methods.
- Carbon steel is extensively used piping material in process industry
- Iron is the main element in carbon steel with other elements in non-significant amount.
- Please keep in mind that carbon steel is type of alloy steel.
The other elements that present in carbon steel are both metallic and non-metallic in nature
- Metallic alloying elements present in Carbon steel are
- Manganese, Nickel, Chromium, Molybdenum, Vanadium, Aluminum, Copper, Silicon etc.
- Non- Metallic alloying elements present in Carbon steel are
- Carbon, Phosphorus, Sulfur etc.
- These alloying elements have different effects on the metal Some of these elements, when added in calculated amount will greatly improve material property
Classification of carbon steel
- Based on carbon %, steel can further classify as
- Low carbon steel: in which Carbon is in range from- 0.05% to 0.25%
- Medium Carbon Steel: in which Carbon is in range from- 0.25% to 0.5%
- High Carbon Steel it is in range from- 0.5% to less than 2%
Here you can see the some of the commonly use carbon steel grade in Process piping.
- For Pipes: ASTM A53 Gr A/B, A106 Gr A/B/C, API 5L Gr B
- For Wrought products: ASTM A234 Gr.WPA/B, A420 Gr.WPL6
- For Forged product: ASTM A105, A350 Gr LF1/LF2, A181
- ASTM A53 Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded, and Seamless
- ASTM A106 Seamless Carbon Steel Pipe for High-Temperature Service
- ASTM A134 Pipe, Steel, Electric-Fusion (Arc)-Welded (Sizes NPS 16 and Over)
- ASTM A135 Electric-Resistance-Welded Steel Pipe
- ASTM A139 Electric-Fusion (Arc)-Welded Steel Pipe (NPS 4 and Over)
- ASTM A182 Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
- ASTM A252 Welded and Seamless Steel Pipe Piles
- ASTM A333 Seamless and Welded Steel Pipe for Low-Temperature Service
- ASTM A335 Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service
- ASTM A369 Carbon and Ferritic Alloy Steel Forged and Bored Pipe for High-Temperature Service
- ASTM A381 Standard Specification for Metal-Arc-Welded Steel Pipe for Use with High-Pressure Transmission Systems
- ASTM A426 Centrifugally Cast Ferritic Alloy Steel Pipe for High-Temperature Service
- ASTM A523 Plain End Seamless and Electric-Resistance-Welded Steel Pipe for High-Pressure Pipe-Type Cable Circuits
- ASTM A524 Seamless Carbon Steel Pipe for Atmospheric and Lower Temperatures
- ASTM A530 General Requirements for Specialized Carbon and Alloy Steel Pipe
- ASTM A691 Carbon and Alloy Steel Pipe, Electric-Fusion-Welded for High-Pressure Service at High Temperatures
- ASTM A694 Carbon and Alloy Steel Forgings for Pipe Flanges, Fittings, Valves, and Parts for High-Pressure Transmission Service
- ASTM A714 High-Strength Low-Alloy Welded and Seamless Steel Pipe
- ASTM A733 Welded and Seamless Carbon Steel and Austenitic Stainless Steel Pipe Nipples
- ASTM A865 Threaded Couplings, Steel, Black or Zinc-Coated (Galvanized) Welded or Seamless, for Use in Steel Pipe Joints
- ASTM A984 Steel Line Pipe, Black, Plain-End, Electric-Resistance-Welded
- ASTM A1005 Steel Line Pipe, Black, Plain End, Longitudinal and Helical Seam, Double Submerged-Arc Welded
- ASTM A1006 Steel Line Pipe, Black, Plain End, Laser Beam Welded