What Is ASTM A453?
ASTM A453 is the standard specification for high-temperature bolting made from iron-base superalloys with expansion coefficients comparable to austenitic stainless steels. The most widely used grade is A453 Grade 660 (based on A-286 alloy, UNS S66286), a precipitation-hardened iron-nickel-chromium alloy that maintains high strength at temperatures up to 650 degC (1,200 degF) while having a thermal expansion rate close to that of austenitic stainless steel flanges.
When to Use ASTM A453
A453 Grade 660 bolting is specified when standard A193 B7 loses strength at elevated temperatures and when thermal expansion mismatch between the bolt and flange must be minimized:
- Austenitic stainless steel flanges (A182 F304, F316, F321) at high temperature
- Power generation: steam turbine bolting, HRSG connections
- Refinery service above 450 degC (840 degF) where B7 loses yield strength
- Ammonia and hydrogen service at elevated temperatures
- Expansion-matched joints where differential thermal expansion between bolt and flange would reduce gasket stress
| Feature | Specification |
|---|---|
| Standard | ASTM A453/A453M |
| Primary grade | Grade 660 (A-286 alloy, UNS S66286) |
| Composition | 25% Ni, 15% Cr, 1.25% Mo, 2% Ti, bal. Fe |
| Heat treatment | Solution treated + precipitation hardened (aged) |
| Max service temp | 650 degC (1,200 degF) |
| Matching nut | ASTM A453 Grade 660 (self-matching) |
| Thread standard | ASME B1.1 (Unified coarse) |
Mechanical Properties
| Property | A453 Gr.660 (Class A) | A453 Gr.660 (Class B) | A193 B7 (for comparison) |
|---|---|---|---|
| Tensile strength (min) | 130 ksi (896 MPa) | 115 ksi (793 MPa) | 125 ksi (862 MPa) |
| Yield strength (min) | 85 ksi (586 MPa) | 75 ksi (517 MPa) | 105 ksi (724 MPa) |
| Elongation (min) | 15% | 15% | 16% |
| Reduction of area (min) | 18% | 18% | 50% |
| Hardness | 248-341 HB | 248-321 HB | 235-331 HB |
| Max service temp | 650 degC | 650 degC | 450 degC |
Class A (higher strength) is the default for most applications. Class B is specified for larger diameters or when reduced aging response limits achievable strength.
Thermal Expansion Advantage
The primary reason for specifying A453 Grade 660 on stainless steel flanges is thermal expansion matching. Alloy steel bolts (A193 B7) expand at approximately 12 x 10^-6 per degC, while austenitic stainless flanges expand at approximately 17 x 10^-6 per degC. At high temperatures, the flange expands faster than the bolt, reducing gasket stress and potentially causing leaks.
| Material | Thermal Expansion Coefficient (x 10^-6/degC) |
|---|---|
| A193 B7 (Cr-Mo alloy steel) | 12.0 |
| A193 B16 (Cr-Mo-V alloy steel) | 12.0 |
| A453 Grade 660 (A-286) | 16.0 |
| Austenitic SS (304, 316) | 17.0 |
A453 Grade 660 expansion (16.0) closely matches austenitic stainless (17.0), maintaining bolt load and gasket stress as temperature increases.
A453 Grade 660 vs A193 B7 and B16
| Property | A453 Gr.660 | A193 B7 | A193 B16 |
|---|---|---|---|
| Max service temp | 650 degC | 450 degC | 540 degC |
| Thermal expansion | 16.0 x 10^-6/degC | 12.0 | 12.0 |
| Yield strength | 85 ksi | 105 ksi | 105 ksi |
| Corrosion resistance | Good (25% Ni, 15% Cr) | Poor | Poor |
| Flange match | Austenitic SS | Carbon steel | Carbon/alloy steel |
| Cost | 5-10x B7 | Baseline | 1.5-2x B7 |
| Availability | Specialty order | Stock | Limited stock |
A453 Grade 660 stud bolts require controlled bolt torque with appropriate anti-seize compound (nickel-based recommended for the alloy surface). Pair with the correct gasket type for the service conditions.
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