Let’s talk about carbon steel pipe. Steel is an alloy. An alloy is a mixture of at least two elements, one of which must be metallic. In its simplest form, steel is two elements mixed together: iron and carbon. Though carbon is the main alloying material for iron, some other elements, like tungsten, chromium, manganese, can also be used for the purpose. This is called “carbon steel.”
The more carbon there is contained in the steel, the stronger it gets when heated. This makes the steel become less ductile. The difference between steel and carbon steel is the amount of carbon in the material. The amount of carbon in mild steel ranges from 0.16% to 0.3%. Carbon steel pipe is a steel alloy that contains carbon ranging from 0.12% all the way to 2%. The percentage of alloy in carbon steel affects weldability, the hardening process, and resistance to corrosion.
Carbon steel pipes are widely used in a number of industries because of these main reasons:
There are three broad categories of carbon steel: high carbon steel, medium carbon steel, and low carbon steel. The content of carbon contained in these varieties of steel determines the use in the manufacturing processes. High carbon steel has the most carbon content at 0.60%-0.99% and it is the hardest carbon steel. High carbon steel has much better tensile strength so it is commonly used to make cutting tools, blades, punches dies, springs, and high-strength wire. Medium carbon content is at 0.30%-0.59%. Medium carbon steel is easier to machine, adding silicon and manganese improves the overall quality of the carbon. It is commonly used structurally in buildings, bridges, axles, gears, rails, shafts, cars, refrigerators, washing machines, and pipelines. Low carbon steel has the least amount of carbon at 0.16%-0.29% and is the softest carbon steel. Low carbon steel is made into flat-rolled sheets and strips, which is then used for shipbuilding, wire, vehicle bodies, and domestic appliances. It is also used for fencing, gates, and railings because it is hard but not too brittle. There is also ultra carbon steel which tends to be less brittle and very hard. This is used to make extremely hard components like blades, cutting tools, large machine parts, hot water radiators, industrial castings, and metal lamp posts. Ultra carbon steel is also called “cast iron” which is also used to make cooking pots.
Carbon steel piping has one major drawback, iron oxide (aka rust). The iron in the steel chemically reacts with atmospheric oxygen and creates iron oxide. Iron oxide, or rust, is what causes corrosion. Iron oxide weakens the steel. If left untreated, the pipe will ultimately fail. Corrosion of carbon steel usually happens when the relative humidity of the air is 70% to 80% and the air temperature is above 32F. To prevent corrosion of the steel, the pipes are often coated with a type of rust inhibitor. That could be black mill lacquer, varnish, fusion bonded epoxy, water-based rust inhibitor, or other various treatments. Rarely will you see bare steel pipe.
Which Type of Carbon Steel Piping Is Best?
One is not better than the others. It just depends on your application and your budget for the steel. There are different specs and grades for carbon steel, compared to other steel that has different properties.
Carbon steel pipes have a wide range of uses. For instance, they are ideal for transporting water, sewage, oil and other fluids because they are resistant to vibrations caused by changing water pressures, as well as the shock pressure resulting from a water hammer. Carbon steel pipes, particularly internally galvanized carbon steel pipes, are used in sprinkler systems, irrigation systems, and water wells. They are also used for laying water pipelines under roadways. Carbon steel pipes are also prominent in the automotive industry, primarily for lancing pipes and conveyor belt idlers.