What Is ASTM A1082? Duplex Stud Bolts
ASTM A1082/A1082M is the standard specification for high-strength precipitation-hardened and duplex stainless steel bolting for use in pressure vessel and piping applications. The standard covers stud bolts, bolts, screws, and studs manufactured from duplex (UNS S31803/S32205) and super duplex (UNS S32750, S32760) stainless steels, providing a combination of high mechanical strength and excellent corrosion resistance that neither A193 B7 (strong but corrosion-prone) nor A193 B8 (corrosion-resistant but low strength) can match individually.
| Feature | Specification |
|---|---|
| Standard | ASTM A1082/A1082M |
| Scope | Duplex and super duplex SS bolting for pressure service |
| Grades | Grade S31803, S32205, S32750, S32760, others |
| Heat treatment | Solution annealed |
| Matching nuts | ASTM A1082 (same standard, self-matching) |
| Thread standard | ASME B1.1 (Unified coarse) |
Mechanical Properties
| Property | S31803/S32205 (Duplex) | S32750 (Super Duplex) | A193 B7 | A193 B8 Cl.1 |
|---|---|---|---|---|
| Tensile strength (min) | 90 ksi (620 MPa) | 116 ksi (800 MPa) | 125 ksi (862 MPa) | 75 ksi (517 MPa) |
| Yield strength (min) | 65 ksi (450 MPa) | 80 ksi (550 MPa) | 105 ksi (724 MPa) | 30 ksi (207 MPa) |
| Elongation (min) | 25% | 15% | 16% | 30% |
| Hardness (max) | 290 HB | 310 HB | 331 HB | 223 HB |
Super duplex grade S32750 achieves yield strength (80 ksi) more than double that of A193 B8 Class 1 (30 ksi), approaching B7 territory while maintaining superior corrosion resistance. Standard duplex S31803 falls between B8 and B7 in strength.
Composition
| Element | S31803 (Duplex) | S32750 (Super Duplex) |
|---|---|---|
| Chromium (Cr) | 21-23% | 24-26% |
| Nickel (Ni) | 4.5-6.5% | 6-8% |
| Molybdenum (Mo) | 2.5-3.5% | 3-5% |
| Nitrogen (N) | 0.08-0.20% | 0.24-0.32% |
| Carbon (C) | 0.030% max | 0.030% max |
| PREN | 34-38 | 40-46 |
The PREN (Pitting Resistance Equivalent Number) indicates corrosion resistance. Super duplex PREN >40 provides seawater resistance comparable to nickel alloys at a fraction of the cost.
When to Specify A1082
| Application | Why A1082 |
|---|---|
| Subsea piping | Seawater corrosion + high strength needed |
| Offshore platforms | Marine atmosphere, splash zone |
| Desalination plants | Chloride resistance |
| Chemical plants (HCl, H2SO4) | Acid corrosion + bolt load requirement |
| Duplex piping systems | Material compatibility with duplex flanges (A182 F51, F53) |
| FPSOs and marine vessels | Combined strength and corrosion resistance |
A1082 duplex bolting is the natural match for duplex stainless steel pipe and duplex flanges (ASTM A182 F51/F53). Using A193 B7 bolts on duplex flanges in corrosive environments creates a galvanic cell where the carbon steel bolt corrodes preferentially.
A1082 vs A193 B7 vs A193 B8
| Feature | A1082 S32750 | A193 B7 | A193 B8 Cl.1 |
|---|---|---|---|
| Strength | High (80 ksi yield) | Very high (105 ksi yield) | Low (30 ksi yield) |
| Corrosion resistance | Excellent | Poor | Good |
| Chloride SCC resistance | Excellent | N/A | Poor (B8 is susceptible) |
| Max service temp | 300 degC (572 degF) | 450 degC (840 degF) | 540 degC (1,000 degF) |
| Min service temp | -46 degC (-50 degF) | -29 degC (-20 degF) | -254 degC (-425 degF) |
| Cost | 8-15x B7 | Baseline | 3-5x B7 |
| NACE MR0175 | Compliant (solution annealed) | B7M required | Not typical |
| Magnetic | Partially (ferrite phase) | Yes | No |
Temperature Limits
Duplex stainless steels lose toughness below approximately -46 degC due to the ferritic phase, and suffer from 475 degC embrittlement at prolonged exposure above 300 degC. A1082 bolting should not be used for cryogenic service (use A320 B8 instead) or continuous service above 300 degC (use A453 Grade 660 instead).
A1082 stud bolts require anti-seize compound (nickel-based preferred) to prevent galling, and controlled torque per the ASME bolt chart.
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