Carbon steel and stainless steel two extremely popular grades of pipe and useful materials for industrial pipe fabrications. Each type of material comes with its own particular sets of pros and cons and likewise each materials has different fabrication considerations. Let’s take a look at some of the main considerations.
Carbon Steel vs. Stainless Steel
Since the invention of steel, metalworkers have produced different grades of steel depending on the application. This is done by varying the amount of carbon. Generally, steel recipes have a weight proportion of carbon in the 0.2% to 2.1% range. To enhance other properties of the base iron, mixtures may also include chromium, manganese, or Tungsten. Varying proportions of these elements produce steel with targeted values of ductility (the ability of a metal to be drawn into a wire), tensile strength (the ability to be stretched without breaking), and hardness. They can affect and control the thermal and electrical properties of the steel as well. The addition of these materials to the iron forms an alloy. The materials themselves serve to maintain the crystal lattice structure of the base iron atoms.
Carbon steel depends mainly on carbon to form the durable alloy. Carbon steel may contain other agents such as manganese, cobalt, or tungsten, but the proportion of these materials is not specified. The following shows the four types of carbon steel:
- Mild / low – contain very low percentages of carbon
- Medium – 0.3 to 0.59% carbon by weight
- High – 0.6 to 0.99% carbon
- Ultra high – 1.0 to 2.0% carbon
These alloys can withstand heat treatment successfully. Comparatively, these recipes produce very strong and hard grades of steel. However, carbon steel has relatively inferior ductility specs. It also suffers from a common drawback of most steel recipes in that it corrodes easily. Corrosion is an oxidation of the metal to a more stable molecular state that results in a weakening of the base steel. Bridges can display significant visible corrosion damage after only a few years of service. Bridge structures that would have otherwise lasted a hundred years must be repaired or replaced due to corrosion.
Stainless steel is a unique form of steel which does not corrode. It gets this property by employing chromium as a special hardening agent. Most forms of stainless steel have a mass proportion of 10.5% to 11.0% chromium. With the use of chromium, stainless steel has the basic properties of steel with the addition of its inability to rust.
The process of corrosion resistance for stainless steel is unique and interesting. Like carbon steel, stainless steel also reacts to the oxygen in the air to form an oxide layer. However, rather than form an iron oxide layer it forms a chromium oxide layer. Iron oxide is a volatile molecule which continues to aid in the oxidation process. In contrast, chromium oxide is inert. It forms a protective layer that prevents further oxidation.
Pipe Fabrication Factors
Both carbon steel and stainless steel are used to produce components and structural parts for a wide range of purposes. When making a choice for a particular application, engineers must consider several factors:
- Tensile Strength and Weight – both carbon and stainless steel have a tensile strength and weight that are comparable. Their use in pipe fabrication depends partly on the method of the fabrication. When a pipe extruded, the ability to maintain specs depends on the ductility of the material, which is similar for both alloys. Pipe fittings are generally milled, and metalworkers can again expect similar results between the two materials. Often, designers who desire the ductility of steel with a lower weight consider aluminum. Like stainless steel, aluminum does not corrode.
- Reactivity – for applications requiring no reactivity, stainless steel is the clear choice. A noteworthy application is kitchen pots and pans. Carbon steel (and aluminum) reacts with food, producing flavor changes and potential health hazards. Stainless steel does not cause these interactions.
- Workability – both materials are easy to work in an array of fabrication methods, including hardening to create long-lasting components, machining without chipping or cracking, and welding to create durable joints.
In summary, fabrication factors between carbon and stainless steel are similar. The resistance to corrosion is the main difference between the two alloys. STI Group is pleased to offer both stainless steel and carbon steel pipe fabrication.
