Characteristics and applications of mild steel pipes

What is mild steel pipe?

As the name suggests, mild steel pipes (MS pipe full form) are steel pipes with mild content. Generally speaking, mild steel pipes are different from seamless carbon steel pipes. Mild steel pipes refer to steel pipes with a carbon content of less than 0.3%. Seamless mild steel tube belong to one of them. In addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, and other steel pipes, mild steel pipes also include carbon thin-walled steel pipes, alloy thin-walled steel pipes, and stainless steel thin-walled steel pipes, Shaped steel pipe.

 

Low carbon steel is also called mild steel because of its low strength, low hardness and softness. It includes most ordinary carbon structural steels and some high-quality carbon structural steels, most of which are used for engineering structural parts without heat treatment, and some are used for mechanical parts requiring wear resistance after carburizing and other heat treatments. Mild steel with carbon content from 0.10% to 0.30% is easy to accept various such as forging, welding and cutting, and is often used in chains, rivets, bolts, shafts, etc.

1. Production process

The production of mild steel pipes mainly includes the following steps: raw material preparation → forming → heat treatment → surface treatment.

Raw material preparation: The main raw materials for producing mild steel pipes are iron ore, scrap steel, and alloying elements. These raw materials are converted into molten steel through smelting and steelmaking processes.

Forming: Molten steel is cast or rolled into steel billets, which are then processed into tubular shapes through hot rolling or cold rolling.

Heat treatment: To improve the performance of mild steel pipes, heat treatment is usually required. Heat treatment can improve the microstructure of the steel pipe and enhance its mechanical properties.

Surface treatment: Before leaving the factory, mild steel pipes usually undergo surface treatment to improve their corrosion resistance and aesthetics. Common surface treatment methods include spraying and galvanizing.

2. Common standards

The parameters of mild steel pipes vary significantly across different national standards. The following is a comparison of the mainstream standards:

Standard	Maximum Carbon Content	Tensile Strength (MPa)	Main Applications
ASTM A53	0.25%	330-500	Pressure piping, structural use
GB/T 3091	0.20%	315-490	Water and gas pipes, scaffolding
JIS G3444	0.23%	300-470	Mechanical structural components

Note: ASTM A53 Grade B has a higher yield strength requirement (≥240MPa) and is suitable for high-pressure applications.

3. Dimensions

Mild steel pipes typically range in inner diameter from 1/8 inch to 6 inches. Outer diameters range from a minimum of 0.406 inches to a maximum of 6.5 inches. Always refer to the mild steel pipe size chart to determine the appropriate pipe size for your application.

4. Chemical composition

The chemical composition of mild steel pipes typically includes:

Carbon: 0.05–0.25%

Silicon: 0.10–0.35%

Manganese: 0.30–1.60%

Phosphorus: ≤ 0.045%

Sulfur: ≤ 0.050%

Copper: 0.20–0.55%

Chromium: ≤ 0.30%

Nickel: ≤ 0.30%

5. Mechanical properties

Phase transition temperature (approximate value) Ac1=735°C, Ac3=855°C, Ar3=835°C, Ar1=680°C

Normalizing specification temperature 920 ~ 950 ℃, air cooling out of the furnace. Hardness 131~156HBS.

Specifications for softening treatment of cold-pressed blanks: Temperature is 700~720°C, holding time is 8~15h, and then at a cooling rate of 50~100°C/h, the temperature is lowered with the furnace to ≤550~600°C, and the furnace is air-cooled. The hardness before treatment is ≤143HBS, and the hardness after softening is ≤131HBS.

Quenching specification temperature 910℃±10℃, 10%NaCl brine cooling.

Measured yield strength fy=245Mpa, elastic modulus E=206Gpa, Poisson's ratio ν=0.3.

The shear strength is 275~392MPa, the tensile strength is 253~500MPa, the yield strength is 275MPa, and the elongation is 25%.

The annealing temperature is only 600-650 degrees, and the holding time is 1-2h.

6. Allowable stress

The allowable stress of mild steel at 225°C: (16-36mm) between 111-124MPa; (6-16mm) between 117-131MPa

Allowable stress of mild steel at 100°C: 108MPa

Mild Steel Pipes Properties

Mild steel pipe has the characteristics of strong hardness, good toughness, high temperature resistance, and superior impact resistance. The surface of mild steel pipe is compact and has many advantages. It can even be galvanized when additional corrosion protection is required.When additional corrosion protection is required, it can even be galvanized, and it has fast forming speed, high output, and does not damage the coating. It can be made into a variety of cross-sectional forms to meet the needs of the use conditions.

1. Good Plasticity and Toughness

MS pipes can withstand greater deformation under stress, reducing the risk of fracture.

2. Easy to Process

MS pipes have good weldability, are suitable for various processing and forming methods, and can meet different design requirements.

3. Lower Cost

Compared to high-alloy steel pipes, MS pipes have lower production costs, making them suitable for large-scale applications.

4. Lower Strength

MS pipes are not as strong as high-carbon steel pipes and may not be suitable for heavy-load applications.

5. Moderate Corrosion Resistance

Although MS pipes have a certain degree of corrosion resistance, surface treatment is still required in some harsh environments.

Application of mild steel pipe

Mild steel pipe is an essential tool in many areas of construction including industrial applications, transport projects and even architectural jobs.

According to the amount of carbon element, iron is usually divided into high carbon steel, medium carbon steel and mild steel. The higher the carbon content, the harder the iron, the poorer the toughness, and the easier it is to break.Mild steel is generally rolled into angle steel, channel steel, I-beam, steel pipe, steel strip or steel plate, and is used to make various building components, containers, boxes, furnaces and agricultural machinery.

At the same time, mild steel pipe, also an important tool in many fields.

 

1. Construction Industry

Mild steel pipes are commonly used in the supporting components of building structures, providing excellent strength and stability. In modern high-rise buildings, they are widely used in frame structures, staircases, and railings.

 

2. Machinery Manufacturing

In the machinery manufacturing industry, mild steel pipes are used to manufacture various mechanical parts, such as shafts, rods, and supports. These parts require a certain level of strength and toughness, which mild steel pipes perfectly meet.

 

3. Petrochemical Industry

Mild steel pipes also have important applications in the petroleum and chemical industry, primarily for transporting liquids and gases. Due to their good corrosion resistance and weldability, mild steel pipes maintain good stability under high temperature and high pressure environments.

 

4. Transportation

Mild steel pipes are also widely used in the transportation sector, such as in the manufacture of frames and structural components for automobiles, trains, and ships. These applications require materials with good strength and toughness to withstand constantly changing external environments.

What is the difference between high carbon steel and mild steel pipe?

1. The difference in toughness

The annealed structure of mild steel is ferrite and a small amount of pearlite, its strength and hardness are low, and its plasticity and toughness are good. Therefore, its cold formability is good, and it can be cold formed by curling, bending, stamping and other methods. 

After proper heat treatment or cold drawing hardening, high carbon steel has high strength and hardness, high elastic limit and fatigue limit, and the cutting performance is acceptable, but the welding performance and cold plastic deformation ability are poor.

2. Application difference

Mild steel has good weldability. Mild steel with carbon content from 0.10% to 0.30% is easy to accept various processing such as forging, welding and cutting, and is often used to manufacture chains, rivets, bolts, shafts, etc. High carbon steel is mainly used to make springs and wear-resistant parts. Carbon tool steel is a high-carbon steel that basically does not add alloying elements. It is also a tool steel with low cost, good cold and hot workability, and a wide range of applications.

3. Different carbon content

Mild steel is carbon steel with a carbon content of less than 0.25%, which has low strength and hardness, and good plasticity and toughness; high-carbon steel is often called tool steel, and its carbon content ranges from 0.60% to 1.70%, with high strength and hardness, high elastic limit and fatigue limit, acceptable cutting performance, but poor welding performance and cold plastic deformation ability.

Read more: Difference between mild steel pipe and carbon steel pipe or Mild steel pipe standards