ERW vs Seamless Stainless Steel Pipe

What is the difference between ERW and Seamless stainless steel pipes?

Simply put: stainless steel pipes are a general term, and steel pipes are made of stainless steel materials. Seamless pipes and ERW pipes refer to the categories or production processes of stainless steel materials into pipes.

The difference between seamless pipes and ERW pipes:
Simply put, one has a weld and the other does not; in addition, the raw materials processed are different. Seamless pipes are made of stainless steel round bars by heating and perforating, and ERW pipes are made of stainless steel strips by rolling and then welding.

Welded pipes are divided into straight seam welded pipes and spiral welded pipes according to the shape of the welds. ERW refers to straight seam welded pipes.

The main differences between ERW stainless steel pipes and Seamless stainless steel pipes are their raw materials, manufacturing processes, appearance, mechanical properties, cost-effectiveness, and application areas.

1. Raw materials
Seamless stainless steel pipes are made of solid round steel "billets", which are heated and pushed or pulled to form steel until the steel is formed into a hollow tube. Steel billets are purchased from well-known factories in China or abroad.

ERW stainless steel pipe is made of stainless steel strip or steel coil as raw material, through rolling and then welding.

‌2. Manufacturing process‌ 
ERW stainless steel pipe is made by resistance welding process, which involves rolling steel plate or steel strip continuously into a cylindrical shape, and then passing electric current to both ends to generate heat, so that the edges of the material melt and combine. In contrast, seamless stainless steel pipe is made by perforation and stretching method, without welds, so its production process is more complicated.

3. Appearance 
ERW (Electric resistance welding) pipe is made by rolling metal and then welding it longitudinally in its length. ERW stainless steel pipe has a weld seam, which is the key to its quality.

Seamless stainless steel pipe is made by perforating and extruding metal to the required length, without welds, which is due to their different production methods.
Therefore, in appearance, the cross section of ERW pipe has a welded joint, while the cross section of seamless pipe does not have any welded joints throughout its length.

4. Mechanical properties ‌
Since the weld of ERW stainless steel pipe is formed by melting the parent material of the steel strip body, its mechanical strength is generally better than that of general welded pipe. Seamless stainless steel pipe, due to its continuity and weld-free characteristics, shows better durability when handling fluid transmission at different temperatures and pressures. The pressure distribution on the wall of seamless steel pipe is more uniform, and it is not easy to break and leak.

5. ‌Cost-effectiveness ‌
The production cost of ERW stainless steel pipe is relatively low because it uses an efficient resistance welding process, while the production process of seamless stainless steel pipe is more complicated and the cost is relatively high.

6. Application 
ERW stainless steel pipe is widely used in building structures, machinery manufacturing, bridge engineering and other fields. Due to its high production efficiency, low cost, stable quality and easy automation, it is also widely used in various industrial sectors such as aviation, aerospace, energy, electronics, automobiles, light industry, etc., suitable for large-scale production and application. ERW (electric resistance welding) pipes are welded longitudinally and manufactured from strip steel/coils, with a maximum outer diameter of 24 inches. It is mainly used in low and medium pressure applications.

Since seamless stainless steel pipes are made of solid round billets, there are no welds or joints. Therefore, it has better corrosion resistance, higher mechanical strength and durability, excellent pressure resistance, and is very suitable for high-pressure applications and machinery manufacturing, such as hydrocarbon industry and refineries, oil and gas exploration and drilling, oil and gas transportation, and air and hydraulic cylinders, bearings, boilers, automotive industry, etc., and is often used in occasions with higher material performance requirements.

Common sizes of ERW pipe range from 1/2 inches OD to 24 inches OD, and various lengths to more than 100 feet. Surface treatment is available in both bare and coated forms, and processing can be processed on site according to customer requirements. The size and wall thickness specifications of seamless pipes are 1/8 inches to 26 inches OD. HSCO is one of the leading manufacturers and exporters of ERW welded pipes and seamless stainless steel pipes in China.

FAQs:

Q1: What are the fundamental differences in the manufacturing processes of stainless steel ERW pipes and seamless pipes?
A: The fundamental differences lie in the raw materials and the presence or absence of weld seams. Seamless steel pipe production requires high-temperature heating, piercing, and multi-pass rolling, resulting in high energy consumption, long processes, and significant material loss. ERW welded pipes, on the other hand, use rolled plates as raw material and employ a continuous production method of cold bending and welding, which is more efficient.

Q2: Is the weld quality of stainless steel ERW welded pipes reliable?
A: Yes. Modern ERW production technology is very mature. Qualified ERW welded pipes that have undergone rigorous non-destructive testing (such as ultrasonic testing and eddy current testing) have weld strength comparable to the base material. Reputable manufacturers will perform solution annealing to eliminate sensitization in the heat-affected zone of the weld and restore the material's corrosion resistance.

Q3: Which type of pipe has better mechanical properties?
A: Seamless steel pipes theoretically have superior mechanical properties, but ERW welded pipes are perfectly adequate for most conventional operating conditions.

Q4: Is there a difference in corrosion resistance between the two?
A: Under the premise of proper material selection and standardized production, the corrosion resistance of the two is basically the same. In highly corrosive environments, it is recommended to use ERW welded pipes that have undergone complete heat treatment (post-weld solution annealing + pickling and passivation), or directly use seamless steel pipes.

Read more: 7 Things to consider when purchasing stainless steel ERW pipes