SMLS Pipe Types & Material

What is SMLS in Piping?

SMLS pipe ((short for Seamless Steel Pipe) is a hollow steel section with no weld seam along its length. Unlike welded pipes, which are formed from steel strips or plates and joined by welding, seamless pipes are produced from solid round steel billets through a process of heating, piercing, and rolling, resulting in a uniform, continuous structure with no potential weak points. 

▶ For a complete overview, see our full guide: [What is SMLS Pipe?].

SMLS Pipe Classification

1) By Production Method

● Hot-rolled tube: Produced by heating billets and rolling them into shape at high temperatures. Suitable for large diameters and general structural applications.
● Cold-rolled tube: Rolled at room temperature for improved dimensional accuracy and surface finish. Offers tighter tolerances than hot-rolled products.
● Cold-drawn tube: Drawn through a die at room temperature to achieve precise dimensions and a smooth surface. Ideal for hydraulic cylinders and precision mechanical components.
● Extrusion pipe: Formed by forcing heated billet through a die. Suitable for specialty alloys and complex cross-sections.

2) By Cross-Sectional Shape

● Round tube: The most common shape, used in the majority of fluid transmission and structural applications.
● Shaped tube: Includes square, rectangular, elliptical, semi-circular, triangular, hexagonal, convex-shaped, and plum-shaped tubes. Used in specialized mechanical and structural applications where round tubes are not suitable.

3) By Material (ASTM/API Standards)

Seamless pipes are manufactured to various international standards. The most commonly specified standards for carbon and alloy steel seamless pipes include:

4) By Material Type

Based on material composition, SMLS pipes are divided into:

● Ordinary carbon structural steel – For general structural and low-pressure applications.
● High-quality carbon structural steel – Such as 20#, 45#, offering improved mechanical properties.
● Low-alloy structural steel – Higher strength than carbon steel, suitable for heavier loads.
● Alloy structural steel – With added elements like chromium and molybdenum for enhanced performance.
● Stainless steel – For corrosive environments and high-temperature service.

5) By Special Purpose

● Boiler tube: Used for water walls, superheaters, economizers, and other boiler heat exchange surfaces.
● Oil pipe & tubing: Used for casing and tubing in oil and gas well construction.

● Geological tube: Used in drilling and exploration applications.

SMLS Pipe Manufacturing Process Flow

Tubing - Inspection - Peeling - Inspection - Heating - Perforation - Pickling - Grinding - Lubrication drying - Welding head - Cold drawing - Solution treatment - Pickling - Pickling passivation - Inspection - Cold rolling - Oil removal - cutting head - Air drying - Internal polishing - External polishing - Inspection - Logo - Finished packaging

Application

Smls pipe is used in fluid transportation, boiler plant, engineering, machinery processing plant.

Read more:

● Types of Seamless Carbon Steel Pipes

● What is Seamless Black Steel Pipe?

● SMLS Pipe Manufacturing Standards in Different Countries

● Seamless Steel Pipe Manufacturing Process Guide