**1. What is the difference between ERW and LSAW pipes?**
* **ERW (Electric Resistance Welded):** Pipes are formed by rolling steel strip/skirt into a cylindrical shape and welding the seam using electrical resistance heat (no filler metal). The weld seam is longitudinal (straight).
* **LSAW (Longitudinal Submerged Arc Welded):** Pipes are formed from steel plates (skelps). The edges are beveled, formed into a "J" or "U" shape, then pressed open into an "O" shape. The longitudinal seam is welded using the submerged arc welding (SAW) process, which uses a consumable electrode and granular flux, creating a thick, high-integrity weld.
**Key Difference:** ERW uses electrical resistance for welding without filler, while LSAW uses submerged arc welding *with* filler and flux. LSAW pipes are typically thicker-walled and used for larger diameters and higher-pressure applications than ERW.
**2. What is SSAW pipe?**
* **SSAW (Spiral Submerged Arc Welded):** Pipes are formed by helically winding (spiraling) a continuous steel strip/skirt onto a forming mandrel at an angle. The continuous spiral seam is welded on the outside (and often inside) using the submerged arc welding (SAW) process, which involves a consumable electrode and granular flux. Also commonly called HSAW (Helical SAW).
**3. What is the difference between ERW and DSAW?**
* **ERW (Electric Resistance Welded):** Pipes are formed by rolling steel strip/skirt into a cylinder and welding the straight longitudinal seam using electrical resistance heat. No filler metal is used.
* **DSAW (Double Submerged Arc Welded):** This refers to LSAW pipes where the longitudinal seam is welded using the SAW process *both* from the outside and the inside. This creates a weld with exceptionally high integrity. DSAW is a specific *type* of LSAW pipe manufacturing.
**Key Difference:** ERW uses resistance heating without filler metal for a straight seam. DSAW (a subset of LSAW) uses the submerged arc process *with* filler and flux to weld the straight seam from both inside and outside.
**4. What is ERW and EFW pipe?
* **ERW (Electric Resistance Welded):** A specific type of welding where pipes are formed and their longitudinal seam is welded using heat generated by electrical resistance as the edges pass through electrodes. No filler metal is added.
* **EFW (Electric Fusion Welded):** This is a **broader category** encompassing *any* pipe manufacturing process where the seam is welded using an electric arc as the primary heat source to melt and fuse the base metal, often with added filler metal. **ERW is one specific method within the EFW category.** Other EFW processes include:
* **SAW (Submerged Arc Welding):** Used in LSAW/DSAW/SSAW pipes.
* **HFW (High Frequency Welding):** Often considered a modern subtype of ERW, using high-frequency current for better weld quality.
* **TIG/GTAW (Tungsten Inert Gas)**
* **MIG/GMAW (Metal Inert Gas)**
**In essence:** **ERW** is a specific *resistance* welding technique within the larger **EFW** category, which covers *all* arc welding processes used for pipe seams. The terms are sometimes confused or used interchangeably (incorrectly), especially ERW vs. EFW. When someone says "EFW pipe," they are often referring to pipes made using arc welding processes *other than* traditional ERW, particularly SAW processes (LSAW, DSAW, SSAW).
5. What is an EFW pipe?
EFW (Electric Fusion Welded):** This is a **broader category** encompassing *any* pipe manufacturing process where the seam is welded using an electric arc as the primary heat source to melt and fuse the base metal, often with added filler metal. **ERW is one specific method within the EFW category.** Other EFW processes include:
* **SAW (Submerged Arc Welding):** Used in LSAW/DSAW/SSAW pipes.
* **HFW (High Frequency Welding):** Often considered a modern subtype of ERW, using high-frequency current for better weld quality.
* **TIG/GTAW (Tungsten Inert Gas)**
* **MIG/GMAW (Metal Inert Gas)**
