Summary Table of Common Delivery Conditions
| Delivery Condition | Key Characteristics | Primary Advantages | Common Applications |
|---|---|---|---|
| Hot-Rolled Seamless | Pipe is formed from a solid billet at high temperatures. | Superior strength, uniformity, no seam. | High-pressure systems, critical structural columns, heavy-duty applications. |
| Welded (SAW/ERW) | Formed from rolled plate/skelp and welded. | Cost-effective, larger diameters, readily available. | Structural frameworks, architectural elements, non-critical pressure applications. |
| Cold-Drawn (CDS) | Cold-worked after hot-rolling or welding. | Excellent dimensional accuracy, smooth surface, high strength. | Precision machinery, hydraulic cylinders, bearing sleeves. |
| Normalized | Heat-treated to refine grain structure. | Enhanced toughness, improved weldability, stress relief. | Critical applications in low-temperature environments or for heavy welding. |
Detailed Explanation of Each Condition
1. Hot-Rolled Seamless (HRS)
Process: A solid steel billet is heated and pierced through the center to form a hollow shell (mandrel), which is then elongated and rolled to the final size and wall thickness at high temperatures.
Advantages:
No weld seam, making it structurally uniform in all directions and ideal for high-pressure applications.
Generally superior mechanical properties, especially in thicker walls.
Disadvantages: More expensive, limited to smaller diameters compared to welded pipes.
Standards: ASTM A106, ASTM A53 (Type S), API 5L.
2. Welded (The Most Common Type)
This category includes two main subtypes:
a. Electric Resistance Welded (ERW):
Process: A strip of steel (skelp) is cold-formed into a cylindrical shape and the longitudinal seam is fused together using electrical current.
Characteristics: A narrow, clean weld seam. Modern ERW processes produce very high-quality pipes.
b. Submerged Arc Welded (SAW):
Process: Formed from steel plate, and the seam is welded automatically under a blanket of flux. Can be single (SAW) or double (DSAW) seam.
Characteristics: Can produce pipes with very large diameters and thick walls. The weld seam is prominent.
Advantages: Most cost-effective, can produce a wide range of sizes, especially large diameters.
Disadvantages: The weld seam can be a potential point of weakness if not properly executed and inspected.
Standards: ASTM A587 (ERW), ASTM A847 (Structural), ASTM A671 (SAW).
3. Cold-Drawn Seamless (CDS)
Process: A hot-rolled seamless pipe is drawn through a die at room temperature to achieve the final dimensions.
Advantages:
Exceptional dimensional accuracy and tight tolerances.
Very smooth internal and external surface finish.
Increased strength and hardness due to strain hardening.
Disadvantages: Significantly more expensive, less ductile, and available in smaller sizes.
Applications: Less common for weathering steel in structural roles, but used where precision is key.
4. Heat-Treated Conditions
Pipes can be supplied in heat-treated states to enhance certain properties:
Normalized (N): Heated to approximately 900°C and air-cooled. This refines the grain structure, improving toughness and impact strength, especially important for welded structures in cold climates.
Normalized-Rolled (NR): The final deformation pass in the rolling mill is done within the normalization temperature range, offering a similar benefit to full normalization.
