ASTM A178 ERW Pipe
Basic Overview
ASTM A178 (identical to ASME SA-178) is the standard specification for electric-resistance-welded (ERW) carbon steel and carbon-manganese steel tubes intended for use as boiler tubes, boiler flues, superheater flues, and safe ends [citation:2, citation:4]. These tubes are specifically designed to withstand high temperatures and pressures in steam-generating systems .
Name Explanation
| Part | Meaning |
|---|---|
| ASTM | ASTM International (American Society for Testing and Materials) |
| A178 | Standard specification for electric-resistance-welded carbon steel and carbon-manganese steel boiler and superheater tubes |
| ERW | Electric Resistance Welded – pipe formed from steel coil and welded longitudinally without filler metal |
Key Features
| Feature | Description |
|---|---|
| Manufacturing | Electric Resistance Welded (ERW) – high-frequency welding process |
| Grades | Grade A (low carbon steel), Grade C (medium carbon steel), Grade D (carbon-manganese steel) [citation:3, citation:4] |
| Size Range | 1/2 to 5 inches (12.7 to 127 mm) outside diameter |
| Wall Thickness | 0.035 to 0.360 inches (0.9 to 9.1 mm) minimum wall |
| Primary Application | Boiler tubes, superheaters, heat exchangers, condensers [citation:1, citation:4] |
Chemical Composition
| Element | Grade A | Grade C | Grade D |
|---|---|---|---|
| Carbon (C) | 0.06 – 0.18% [citation:1, citation:7] | 0.35% max [citation:4, citation:7] | 0.27% max [citation:4, citation:7] |
| Manganese (Mn) | 0.27 – 0.63% [citation:1, citation:7] | 0.80 – 1.15% max [citation:4, citation:7] | 1.00 – 1.50% |
| Phosphorus (P) | 0.035% max [citation:1, citation:4] | 0.035% max [citation:4, citation:7] | 0.030 – 0.035% max |
| Sulfur (S) | 0.035% max [citation:1, citation:4] | 0.035% max [citation:4, citation:7] | 0.015 – 0.035% max |
| Silicon (Si) | 0.10 – 0.35% | - | 0.10% min |
Mechanical Properties
| Property | Grade A | Grade C | Grade D |
|---|---|---|---|
| Tensile Strength (min) | 325 MPa (47,100 psi) [citation:1, citation:4] | 415 MPa (60,000 psi) [citation:4, citation:7] | 485 MPa (70,000 psi) [citation:4, citation:7] |
| Yield Strength (min) | 180 MPa (26,100 psi) [citation:1, citation:4] | 255 MPa (37,000 psi) [citation:4, citation:7] | 275 MPa (40,000 psi) [citation:4, citation:7] |
| Elongation (min) | 35% [citation:1, citation:4] | 30% [citation:4, citation:7] | 30% [citation:4, citation:7] |
| Hardness (max) | 72 HRB | - | - |
Dimensional Specifications
| Parameter | Range/Tolerance |
|---|---|
| Outside Diameter | 1/2" to 5" (12.7 to 127 mm) |
| Wall Thickness | 0.035" to 0.360" (0.9 to 9.1 mm) |
| Length | 3 m, 6 m, 9 m, 18 m |
| OD Tolerance (< 50 mm) | ±0.05 mm |
| OD Tolerance (≥ 50 mm) | ±1% |
| Wall Thickness Tolerance | ±10% to ±12.5% [citation:4, citation:7] |
Heat Treatment Requirements
After welding, all tubes shall be heat treated at a temperature of 1650°F (900°C) or higher and followed by cooling in air or in the cooling chamber of a controlled-atmosphere furnace .
Cold-drawn tubes shall be heat treated after the final cold-draw pass at a temperature of 1200°F (650°C) or higher
Grade D steel shall be killed (fully deoxidized)
Testing Requirements
| Test Type | Requirement |
|---|---|
| Flattening Test | Evaluates ductility and strength [citation:4, citation:7] |
| Flare Test | Determines ability to withstand deformation [citation:4, citation:7] |
| Crush Test | For Grade A tubes |
| Tension Test | Verifies tensile and yield strength |
| Hydrostatic Test | Ensures welded seam and pipe body withstand specified pressure [citation:4, citation:7] |
| Nondestructive Electric Test | Detects imperfections along weld seam [citation:4, citation:7] |
| Reverse Flattening Test | Additional weld integrity verification |
Grade Comparison
| Characteristic | Grade A | Grade C | Grade D |
|---|---|---|---|
| Carbon Content | Lowest (0.06-0.18%) | Higher (0.35% max) | Medium (0.27% max) |
| Strength | Lowest | Higher than Grade A | Highest (70,000 psi tensile) |
| Manganese | 0.27-0.63% | 0.80-1.15% | 1.00-1.50% |
| Typical Use | General-purpose boiler tubes | Higher mechanical property requirements | Highest strength requirements |
| Forge Welding Suitability | Suitable | Not suitable for safe-ending | Not suitable for safe-ending |
Common Applications
| Application | Description |
|---|---|
| Boiler Tubes | Used in boiler systems for steam generation [citation:1, citation:4] |
| Superheaters | Withstand high temperatures and pressures [citation:4, citation:7] |
| Heat Exchangers | Facilitate heat transfer in industrial applications [citation:1, citation:4] |
| Condensers | Key components in cooling systems |
| Safe Ends | For high-temperature and high-pressure environments [citation:4, citation:7] |
International Equivalents
| ASTM Grade | Korean/Japanese (KS/JIS) | German (DIN) |
|---|---|---|
| Grade A | STBH 340 / STB 35 [citation:4, citation:7] | St 37.8 (1.0315) [citation:4, citation:7] |
| Grade C | STBH 410 / STB 42 [citation:4, citation:7] | St 42.8 (1.0498) [citation:4, citation:7] |
Key Advantages
| Advantage | Description |
|---|---|
| Cost-Effective | ERW process is economical, reducing material and manufacturing costs |
| High Efficiency | Welding process produces strong, uniform continuous weld |
| Versatility | Suitable for a range of high-temperature and high-pressure applications |
| Heat Transfer Efficiency | Optimized for boiler and heat exchanger performance |
| Multiple Grades | Grade selection allows matching properties to service conditions |
Important Considerations
1. Grade Selection
Grade A: For general-purpose applications where lower mechanical properties are acceptable
Grade C: For applications requiring higher mechanical properties
Grade D: For applications requiring highest strength and enhanced corrosion resistance
2. Size Limitations
Standard sizes: 1/2" to 5" OD
Other dimensions may be furnished if all requirements are met
Mechanical property requirements do not apply to tubing smaller than 1/8" ID or 0.015" thickness
3. Manufacturing Process
Tubes are manufactured by the electric-resistance welding process
Hot-rolled steel is used as the base material
After welding, all tubes receive mandatory heat treatment
4. Surface Condition
Finished tubes shall be free of scale
A slight amount of oxidation is not considered scale
5. Complementary Standards
ASTM A450/A450M covers general requirements for carbon and low alloy steel tubes
This standard is referenced for additional testing and inspection procedures
Summary
ASTM A178 ERW pipe is the standard specification for electric-resistance-welded carbon steel and carbon-manganese steel tubes used in boiler, superheater, and heat exchanger applications [citation:1, citation:4, citation:9].
Key features:
Three grades available – Grade A (low carbon, 180 MPa yield), Grade C (medium carbon, 255 MPa yield), Grade D (carbon-manganese, 275 MPa yield)
Size range – 1/2" to 5" OD with wall thicknesses from 0.035" to 0.360"
Mandatory heat treatment – All tubes heat treated at 1650°F (900°C) minimum after welding
Stringent testing – Flattening, flare, hydrostatic, and nondestructive electric tests [citation:4, citation:7]
Common applications:
Boiler tubes and superheater flues [citation:1, citation:4]
Heat exchangers and condensers [citation:1, citation:4]
Safe ends for high-temperature service
International equivalents:
KS/JIS: STBH 340/STB 35 (Grade A), STBH 410/STB 42 (Grade C) [citation:4, citation:7]
DIN: St 37.8 (Grade A), St 42.8 (Grade C) [citation:4, citation:7]
When ordering, specify: quantity, product name, wall thickness, standard specification, grade, size, unit length, and end finish. For example: ASTM A178 Grade A ERW boiler tube, 2″ OD × 0.120″ wall, 6 m length .
