# Introduction to JIS G3458 Alloy Steel Boiler Tube Standard Specifications
The JIS G3458 standard is designed specifically for heat-resistant alloy steel pipes that serve as high-temperature fluid conduits in heaters and boiler systems. These pipes play a crucial role in ensuring the safe and efficient operation of various industrial applications.
## Production Method:
| **Grade** | **Heat Treatment** |
|-----------|-----------------------------------------------------------------------------------|
| STPA 12 | Low-temperature annealing, isothermal annealing, full annealing, normalizing, or normalizing followed by tempering. |
| STPA 20 | Same as STPA 12. |
| STPA 22 | Same as STPA 12. |
| STPA 23 | Low-temperature annealing, isothermal annealing, full annealing, or normalizing followed by tempering. |
| STPA 24 | Same as STPA 23. |
| STPA 25 | Same as STPA 23. |
| STPA 26 | Same as STPA 23. |
## Chemical Composition:
| **Grade** | **Chemical Composition %** |
|-----------|---------------------------------------------------------------------------------------------|
| | **C** | **Si** | **Mn** | **P** | **S** | **Cr** | **Mo** |
| STPA 12 | 0.10~0.20 | 0.10~0.50 | 0.30~0.80 | 0.035 max. | 0.035 max. | - | 0.45~0.65 |
| STPA 20 | 0.10~0.20 | 0.10~0.50 | 0.30~0.60 | 0.035 max. | 0.035 max. | 0.50~0.80 | 0.45~0.65 |
| STPA 22 | 0.15 max. | 0.50 max. | 0.30~0.60 | 0.035 max. | 0.035 max. | 0.80~1.25 | 0.45~0.65 |
| STPA 23 | 0.15 max. | 0.50~1.00 | 0.30~0.60 | 0.030 max. | 0.030 max. | 1.00~1.50 | 0.45~0.65 |
| STPA 24 | 0.15 max. | 0.50 max. | 0.30~0.60 | 0.030 max. | 0.030 max. | 1.90~2.60 | 0.87~1.13 |
| STPA 25 | 0.15 max. | 0.50 max. | 0.30~0.60 | 0.030 max. | 0.030 max. | 4.00~6.00 | 0.45~0.65 |
| STPA 26 | 0.15 max. | 0.25~1.00 | 0.30~0.60 | 0.030 max. | 0.030 max. | 8.00~10.00 | 0.90~1.10 |
## Mechanical Properties:
| **Grade** | **Tensile Strength (kgf/mm² {N/mm²})** | **Yield Point or Proof Stress (kgf/mm² {N/mm²})** | **Elongation (%)** |
|-----------|-----------------------------------------|--------------------------------------------------|-----------------------------------------------------------------------------------|
| | | | **No. 11 or No. 12 Test Piece** | **No. 5 Test Piece** | **No. 4 Test Piece** |
| | | | **Longitudinal** | **Transverse** | **Longitudinal** | **Transverse** |
| STPA 12 | 39 {382} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 20 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 22 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 23 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 24 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 25 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
| STPA 26 | 42 {412} min. | 21 {206} min. | 30 min. | 25 min. | 24 min. | 19 min. |
In summary, the JIS G3458 standard specifies a range of grades of alloy steel pipes designed for demanding industrial applications. Each grade has specific chemical compositions and mechanical properties, ensuring optimal performance under high temperatures and pressures. Understanding these specifications is essential for selecting the right material for your particular application. Whether you're working with STPA 12 or STPA 26, each grade offers unique advantages depending on the required strength, ductility, and resistance to heat.
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