SMLS Carbon Steel Pipe Sizes

What Does SMLS Stand For?

"SMLS" stands for Seamless, often written as "SMLS pipe" or "seamless steel pipe." SMLS pipe means that the product has no weld seams during the manufacturing process, making it stronger and more reliable, suitable for high-pressure or critical applications. In the steel pipe industry and engineering terminology, it is often used as a prefix or suffix to clearly identify the manufacturing process as seamless steel pipe, distinguishing it from welded steel pipe.

Seamless pipe/tube refers to a hollow steel pipe formed by heating, piercing, rolling, or extruding a solid steel billet (such as carbon steel or stainless steel) to achieve uniform deformation, with no weld seams on the pipe body.

Common Combinations: 

In technical documents, product catalogs, or purchasing contracts, it often appears in combination with other terms:

SMLS Pipe
SMLS Carbon Steel Pipe
ASTM A106 Gr.B SMLS
Seamless (SMLS) Tube

Why is SMLS emphasized?

In the industrial sector, SMLS (High Pressure resistant) and Welded (Medium and Low Pressure resistant) are two completely opposite pipe types. Explicitly specifying SMLS in the specifications ensures that the supplier provides seamless, monolithic steel pipes to meet the requirements of high pressure, high temperature, or stringent safety regulations.

SMLS Carbon Steel Pipe Sizes:

The size of an SMLS carbon steel pipe is determined by three parameters: outer diameter, wall thickness, and length.

1. Outer Diameter Standards and Series
The outer diameter of seamless steel pipes is not arbitrarily customized but follows a standardized series. According to the ASME B36.10M standard dimensional chart, the internationally accepted outer diameter series are as follows:

●Small diameter: 10.3mm (1/8"), 13.7mm (1/4"), 17.1mm (3/8"), 21.3mm (1/2"), 26.7mm (3/4"), 33.4mm (1"), 42.2mm (1-1/4"), 48.3mm (1-1/2"), 60.3mm (2")
●Medium diameter: 88.9mm (3"), 114.3mm (4"), 141.3mm (5"), 168.3mm (6"), 219.1mm (8"), 273.0mm (10"), 323.8mm (12")
●Large diameter: 355.6mm (14"), 406.4mm (16"), 457.2mm (18"), 508mm (20"), 610mm (24"), etc., up to larger.

2. Wall Thickness Standards and Representation Methods
Common Series: SCH 10, SCH 20, SCH 30, SCH 40 (STD), SCH 60, SCH 80 (XS), SCH 100, SCH 120, SCH 140, SCH 160, XXS.

STD: Standard wall thickness, usually consistent with SCH 40.
XS: Reinforced wall thickness, usually consistent with SCH 80.
XXS: Double-reinforced wall thickness.

Important Rule: 

The specific wall thickness value of SCH 40 or SCH 80 is not fixed; it increases with the increase of the outer diameter. For example, the wall thickness of SCH 40 for NPS 2" (60.3mm) is 3.91mm, while that for NPS 8" (219.1mm) is... The wall thickness of SCH 40 is 8.18mm.

3. Size Inquiry and Comparison
To obtain specific SMLS carbon steel pipe size data, the most authoritative method is to consult the following standard:
ASME B36.10M: "Welded and Seamless Rolled Steel Pipes". This is the most widely used steel pipe size standard globally, providing complete data on outer diameter, wall thickness, weight, etc., from NPS 1/8" to NPS 48".

4. Length
The length of seamless steel pipes is generally divided into:

Unspecified length: Delivered according to the length range specified in the standard (e.g., typical length is 3-12 meters).
Fixed length: Delivered according to the precise length required by the contract (e.g., 6 meters, 12 meters, etc.).

Multiple length: Delivered in integer multiples of the length required by the contract, with machining allowance.

Read more: Customizing Your SMLS Carbon Steel Pipe or SMLS Pipe Sizes and Weights