SMLS pipe vs. ERW pipe

Seamless steel pipe (SMLS) and straight seam electric resistance welded pipe (ERW) are two main types of steel pipes in the industry. They have significant differences in manufacturing process, performance, appearance, cost, and application scenarios. The following is a detailed comparison:

1. Manufacturing process

SMLS pipe: The raw material is round billet, the process is complicated, and the production speed is slow.
Production process: billet perforation → hot rolling/cold drawing (no weld)

Features: SMLS has no weld, better overall uniformity, and is suitable for high pressure/high stress environment.

ERW pipe: The raw material is hot-rolled or cold-rolled steel plate, the process is simple, and the production efficiency is high.
Production process: steel plate curling → high-frequency resistance welding (with a longitudinal weld)
Features: ERW depends on welding quality, and the weld may become a weak point (need to be inspected).

2. Performance comparison

Performance	SMLS steel pipe	ERW steel pipe
Strength	High (no weld weak zone)	Medium (slightly lower strength in weld zone)
Pressure resistance	Excellent (suitable for high pressure)	Good (medium and low pressure occasions)
Corrosion resistance	Uniform (no weld corrosion risk)	Welds are prone to rust (anti-corrosion treatment required)
Dimensional accuracy	High (cold drawn tube accuracy ±0.1mm)	General (hot rolled coil limit)
Low temperature toughness	Good (no welding heat affected zone)	Weld zone may be brittle (process control required)

3. Appearance and inspection difference

SMLS pipe: There is no weld on the surface of the steel pipe, and the surface is smooth. The wall thickness uniformity needs to be checked (hot rolled pipe has large deviation).
ERW pipe: A longitudinal weld can be seen on the surface of the steel pipe (needs to be polished), and the quality of the weld needs to be ensured by hydrostatic test and non-destructive testing.

4. Cost and economy

SMLS pipe: high raw material cost (high price of round billet), can only be produced in single piece during production, low production efficiency, suitable for small diameter production. Suitable for high pressure/high precision requirements.
ERW pipe: low raw material cost (easy to obtain steel coil), continuous forming during production, high production efficiency, can produce large diameter. Suitable for low pressure scenes, relatively economical.

5. Typical application areas

SMLS pipe: oil drilling, high pressure transmission pipe, boiler pipe (high temperature medium transmission), hydraulic cylinder, special load-bearing structure.
ERW pipe: water pipe, gas pipe, building scaffolding, structural support, ordinary low pressure fluid pipe.

FAQ:

1: Can ERW steel pipe replace SMLS steel pipe?

Low pressure/static load: Yes (such as building structure).
High pressure/dynamic load: No (such as oil cracking pipe).

2: Will ERW welds rust?
Possibly! Need to do galvanizing, plastic coating or choose stainless steel ERW pipe (such as 304 ERW).

3: What is the maximum diameter of SMLS steel pipe?

Hot-rolled seamless pipe: usually ≤Φ660mm (larger requires extrusion molding, which is extremely expensive).

ERW welded pipe: up to Φ1420mm (such as spiral welded pipe).

Read more: Seamless Pipe vs Welded Pipe Price or API 5L PSL1/PSL2 Pipe Specification