I. Overview of ERW Stainless Steel Pipes
ERW stainless steel pipes are manufactured by longitudinally welding stainless steel coils using high-frequency resistance welding, followed by straightening, polishing, or coating.
Common materials include 304 and 316, which possess characteristics such as strong corrosion resistance, high dimensional accuracy, and good processing performance.
Main Features:
- Excellent corrosion resistance: 304 is suitable for general industrial environments, while 316 is suitable for chemical, marine, and highly corrosive environments.
- High dimensional accuracy: The ERW welding process ensures uniform outer diameter and wall thickness, facilitating pipe connection and secondary processing.
- Good processing performance: Can be cut, bent, welded, and threaded, adapting to various industrial applications.
- Economical and efficient: Compared to seamless pipes, ERW pipes have lower costs and higher production efficiency.
- Wide range of applications: Industrial pipelines, chemical liquid transportation, water supply systems, structural support, food and pharmaceutical equipment, etc.
II. Chemical Composition and Mechanical Properties of ERW Stainless Steel Pipes
i. Chemical Composition Table (%)
| Steel grade | C | Cr | Ni | Mo | Ti | Mn | Si | P | S |
| 304 | ≤0.08 | 18–20 | 8–10.5 | – | – | ≤2 | ≤1 | ≤0.045 | ≤0.03 |
| 304L | ≤0.03 | 18–20 | 8–12 | – | – | ≤2 | ≤1 | ≤0.045 | ≤0.03 |
| 316 | ≤0.08 | 16–18 | 10–14 | 2–3 | – | ≤2 | ≤1 | ≤0.045 | ≤0.03 |
| 316L | ≤0.03 | 16–18 | 10–14 | 2–3 | – | ≤2 | ≤1 | ≤0.045 | ≤0.03 |
| 321 | ≤0.08 | 17–19 | 9–12 | – | ≥5×C | ≤2 | ≤1 | ≤0.045 | ≤0.03 |
ii. Mechanical Properties Table
| Grade | Yield Strength Rp0.2 (MPa) | Tensile Strength Rm (MPa) | Elongation A (%) | Impact Toughness (J) | Remarks |
|---|---|---|---|---|---|
| 304 | ≥205 | 515–735 | ≥40 | ≥70 | General industrial use, good resistance to moderate corrosion |
| 304L | ≥170 | 485–700 | ≥45 | ≥70 | Low-carbon grade, reduced risk of weld hot cracking |
| 316 | ≥205 | 515–700 | ≥40 | ≥70 | Superior corrosion resistance, suitable for marine and chemical piping |
| 316L | ≥170 | 485–700 | ≥45 | ≥70 | Low-carbon 316, excellent weldability for highly corrosive environments |
| 321 | ≥205 | 515–700 | ≥40 | ≥70 | Stabilized stainless steel for high-temperature steam and industrial piping |
III. Practical Guide for Selecting ERW Stainless Steel Pipes
When selecting ERW stainless steel pipes, follow these six steps in order: Industry Application → Operating Conditions → Material Selection → Wall Thickness and Diameter → Processing and Installation → Standards and Certifications. This ensures the selected pipes are safe, durable, and cost-effective.
1. Clarify Industry Application
- Chemical/Petrochemical Industry: For transporting corrosive liquids such as acids and alkalis, 316/316L ERW pipes are recommended. The low-carbon L grade steel has good welding performance and strong corrosion resistance.
- Food/Pharmaceutical Industry: For transporting clean water, food raw materials, or liquid medicines, 304/304L ERW pipes are recommended. Their smooth surface is easy to clean and meets hygiene standards.
- Municipal Water Supply or Drainage Pipelines: For ordinary water quality, 304 ERW pipes are sufficient and cost-effective.
- Marine/Shipbuilding Environment: For saltwater or high-humidity environments, 316/316L ERW pipes are recommended. High corrosion resistance ensures long-term use.
- Building Structures or Mechanical Supports: For indoor or outdoor structural piping, 304 or 321 ERW pipes can be selected, balancing strength and corrosion resistance.
- High-Temperature Steam or Hot Water Pipelines: For high-temperature working environments, 321 ERW pipes are recommended. The addition of Ti element provides stabilization and prevents intergranular corrosion.
2. Determining Operating Conditions
Working Pressure:
- Low pressure/gravity flow → SCH10~SCH40
- Medium pressure → SCH40~SCH80
- High pressure or critical pipelines → Select thick-walled or special steel grades based on design calculations
Temperature:
- Ambient temperature → 304/316
- High-temperature steam → 321
Medium Corrosiveness:
- General water or non-corrosive liquids → 304 is sufficient
- Saltwater or highly corrosive media → 316/316L
3. Material and Steel Grade Selection
- 304: General industrial and building support, resistant to moderate corrosion
- 304L: Low-carbon welding pipes, low risk of hot cracking during welding
- 316: Chemical industry, marine, high-corrosion environments
- 316L: Low-carbon version of 316, welding pipes for high-corrosion/high-temperature environments
- 321: High-temperature steam or hot water pipelines, Ti stabilized to prevent intergranular corrosion
- Selection principle: The stronger the environmental corrosiveness, the higher the corrosion-resistant steel grade should be prioritized; for pipes requiring welding, low-carbon L steel grades should be prioritized.
4. Determining Wall Thickness and Pipe Diameter
- Determine based on pressure rating, flow requirements, and available space at the construction site.
- Avoid excessively thin walls that could lead to bursting or excessively thick walls that would waste costs.
- SCH series wall thickness is the most commonly used reference standard.
5. Considering Processing and Installation
- Welding: Low-carbon L-grade steel (304L/316L) is safer.
- Bending/Cutting/Threading: Ensure uniform pipe diameter and wall thickness, and good outer diameter roundness.
- Outdoor or humid environments: Galvanized or polished surface treatment can extend service life.
6. Standard Certification Confirmation
- Domestic: GB/T 12771-2008
- International Export: ASTM A312, A269, A249 or EN 10216-5, 10217-7
- Confirming the standard ensures dimensional accuracy, mechanical properties, weld quality, and corrosion resistance.
