SCH American Standard Seamless Steel Pipe

When purchasing American standard seamless steel pipes, you may often see specifications like: ASTM A106 Gr.B 6" SCH40. Here, SCH40 refers to the "wall thickness grade." "SCH" is an abbreviation for Schedule, used by the American Standard to specify the wall thickness series of steel pipes. It is one of the core parameters for identifying American standard steel pipe specifications.

Meaning of SCH:
SCH does not simply represent a simple thickness dimension; it reflects a complete design logic. Its calculation formula is:

Sch = P / [σ]t × 1000

Where P represents the design pressure, and [σ]t represents the allowable stress of the material at the design temperature. Therefore, the SCH number directly relates to the pipe's pressure-bearing capacity and temperature resistance. The higher the value, the greater the design pressure it can withstand, and correspondingly, the thicker the pipe wall.

Wall Thickness Grade System:

The wall thickness grades of American standard seamless steel pipes mainly follow the following two standards:

● ANSI/ASME B36.10: Applicable to seamless tubes of carbon steel and alloy steel.
● ANSI/ASME B36.19: Applicable to seamless tubes of stainless steel (usually with an "S" suffix after the grade).

1. "SCH" Grades for Carbon Steel and Alloy Steel

According to ANSI B36.10, commonly used wall thickness grades include: Sch10, Sch20, Sch30, Sch40, Sch60, Sch80, Sch100, Sch120, Sch140, and Sch160.

In practical applications, Sch40 and Sch80 are the two most commonly used grades.
● Sch40 (STD): Known as Standard weight tube, suitable for most conventional applications. For example, for tubes smaller than 6 inches, Sch40 is approximately equivalent to Standard tube (STD).
● Sch80 (XS): Known as Extra weight tube. Sch80 (Strong) has higher pressure resistance and is often used in high-pressure or corrosion-tolerant applications. For pipes smaller than 8 inches, Sch80 is approximately equivalent to thickened pipe (XS).
● Sch160 and XXS: These belong to the extra-thick wall series and are used in extremely high-pressure environments.

2. Stainless Steel "SCH" Grades

Stainless steel pipes follow the ANSI B36.19 standard. Common grades include: Sch5s, Sch10s, Sch40s, and Sch80s. The suffix "s" is specifically used to identify the stainless steel material. Although the naming is similar, the actual wall thickness corresponding to the SCH grade of stainless steel may differ from that of carbon steel pipes for the same nominal diameter. Therefore, they should not be directly applied.

Engineering Significance of SCH:

For purchasing and design personnel, understanding SCH allows for quick comprehension of three key points:

a. Directly determining wall thickness: For example, when purchasing 6-inch steel pipes, the wall thickness of SCH40 is typically 7.11mm, while the wall thickness of SCH80 is 10.97mm.
b. Back-calculated pressure resistance: A higher SCH grade means the pipe can withstand a greater design pressure.
c. Material identification: Seeing an "s" suffix after the number (e.g., Sch10s) indicates it refers to stainless steel.

Conclusion: 

SCH American standard seamless steel pipes are steel pipe products that conform to American standards (e.g., ASTM A106). Their core characteristic is that pressure resistance is defined by the SCH wall thickness grade. When purchasing, in addition to confirming the outer diameter and material (e.g., ASTM A106 Gr.B), the SCH grade (e.g., SCH40 or SCH80) is a parameter that must be confirmed.

Read more: Schedule 40 Pipe Pressure Rating