Sch40 Mild Steel Pipe

Sch40 mild steel pipe is a widely used type of steel pipe, combining the characteristics of standard wall thickness grade (Schedule 40) and low carbon steel materials, suitable for a variety of industrial scenarios.

What is Sch40 mild steel pipe

Sch40 mild steel pipe is the product of the combination of wall thickness standard (Schedule 40) and low carbon steel materials.

1. Schedule 40

The wall thickness grade defined by the American ASME standard represents the standard wall thickness under a specific pipe diameter. The larger the Sch value, the thicker the wall thickness and the higher the pressure bearing capacity; Sch 40 belongs to the medium wall thickness grade and is the most widely used. The wall thickness of Sch40 increases with the increase of nominal pipe diameter (NPS), but the ratio of wall thickness to pipe diameter gradually decreases. Its core feature is “dynamic adjustment of wall thickness according to pipe diameter”. For example:

1-inch (DN25) pipe outer diameter 33.4mm, wall thickness 3.38mm;

6-inch (DN150) pipe outer diameter 168.3mm, wall thickness 7.11mm.

This design not only ensures the pressure-bearing requirements, but also avoids material waste.

2. Mild steel pipe

Mild steel pipe is a carbon steel pipe made of low-carbon steel (carbon content ≤0.25%), which has both weldability and processability. Typical materials such as ASTM A53 Gr.B have a tensile strength of ≥415MPa and a yield strength of ≥240Mpa, which are sufficient to cope with conventional industrial loads.

Sch40 mild steel pipe specifications

Typical materials

1. ASTM A53 Gr.B: Seamless/welded pipe, commonly used for low pressure fluid transportation.

2. ASTM A106 Gr.B: Seamless pipe, high temperature resistant (≤450℃), suitable for steam system.

3. API 5L Gr.B: Steel for oil and gas pipelines.

Performance parameters

1. Mechanical properties (taking ASTM A53 Gr.B as an example)

Tensile strength ≥415 MPa

Yield strength ≥240 MPa

Elongation ≥23% (gauge length 50mm)

2. Pressure resistance

Hydraulic pressure test pressure formula: P=2St/DP=2St/D

(S=allowable stress, t=wall thickness, D=outer diameter)

Example: The maximum working pressure of NPS 2" Sch40 pipe at 20℃ is about 150 psi (1.03 MPa).

3. Temperature limit

ASTM A106 Gr.B recommends a temperature of -29℃~450℃.

Manufacturing process

The performance difference of Sch40 mild steel pipe mainly comes from the manufacturing process

1. Seamless steel pipe

Process: Formed by hot rolling or cold drawing, without weld defects.

Advantages: High pressure bearing capacity, suitable for steam, high pressure gas and other scenarios.

Typical material: ASTM A106 Gr.B (temperature resistance up to 450℃).

2. Welded steel pipe

Process: ERW (resistance welding) or SAW (submerged arc welding) technology is used.

Advantages: Cost reduction of 30%~50%, suitable for low-pressure water and gas transportation.

Limitations: The weld is prone to corrosion starting point, and it needs to be used with galvanizing or coating.

Application scenarios

The application of Sch40 mild steel pipe spans multiple fields:

1. Fluid transportation system

Municipal water supply: Galvanized pipes are corrosion-resistant and have a service life of more than 20 years.

Low-pressure steam: ASTM A106 seamless pipes can withstand ≤2MPa steam pressure.

Natural gas transportation: API 5L Gr.B pipes meet the needs of medium and low pressure pipelines.

2. Structural engineering

Building scaffolding: The strength-to-weight ratio of Sch40 pipes is better than that of ordinary structural steel.

Machinery equipment frame: Modular structures can be quickly built by bolts or welding.

3. Special fields

Fire protection system: In compliance with NFPA standards, must pass 1.5 times the working pressure test.

Chemical pipeline: Surface coating of epoxy resin can withstand weak acid and alkaline media.

Summary

Sch40 mild steel pipe occupies an important position in low pressure fluid transportation and general structure with balanced strength, economy and easy processing. When selecting, it is necessary to comprehensively consider pressure, medium, temperature and corrosion conditions, and upgrade to Sch80 or alloy material if necessary. Special attention should be paid to welding quality and anti-corrosion measures during installation and maintenance to extend service life.

Read more: Difference between mild steel pipe and carbon steel pipe