What Is ASTM A193?
The global standard for alloy and stainless steel bolting used in pressure vessels, valves, flanges, and fittings for high-temperature and high-pressure service.
ASTM A193 / A193M covers alloy steel and stainless steel bolting materials for high-temperature or high-pressure service, or other special-purpose applications. It is the most widely referenced bolting standard in the oil & gas, petrochemical, and power generation industries.
Service Conditions
- High Temperature: B7 and B8 grades rated for sustained elevated temperatures
- High Pressure: B7M and B8M-2 for critical pressure-boundary applications
- Corrosive Environments: B8 (SS 304) and B8M (SS 316) for chemical and marine exposure
- Sour Service (NACE): B7M specifically qualified for H?S-containing environments per NACE MR0175 / ISO 15156
ASTM A193 Grade Breakdown
Each grade is engineered for specific temperature, pressure, and corrosion conditions. Choose the right grade for your service environment.
B7
Material: AISI 4140 / 4142 / 4145 Cr-Mo steel, quenched & tempered
Temp Range: -29°C to +427°C
Typical Use: General high-pressure flanges, valves, pressure vessels, heat exchangers
Hardness: 321 HBW max | Size: 1/4" to 2-1/2" inclusive
B7M
Material: Same Cr-Mo base as B7, but with restricted hardness for sour service
Temp Range: -29°C to +427°C
Typical Use: NACE MR0175 sour gas service, subsea manifolds, critical pressure boundaries
Hardness: 235 HBW max (critical for H?S resistance) | Size: 1/4" to 2-1/2"
B8
Material: AISI Type 304 stainless steel, solution treated (carbide not solution treated)
Temp Range: -196°C to +816°C
Typical Use: Chemical processing, food & pharma, general corrosive service at moderate temperatures
Hardness: 223 HBW max | Size: 1/4" to 1-1/2" inclusive
B8M
Material: AISI Type 316 stainless steel, solution treated (carbide not solution treated)
Temp Range: -196°C to +816°C
Typical Use: Marine, coastal UAE projects, chloride-rich environments, chemical plants
Hardness: 223 HBW max | Size: 1/4" to 1-1/2" inclusive
B8M-2
Material: AISI Type 316 stainless steel, strain hardened for higher strength
Temp Range: -196°C to +427°C (strength drops above 427°C)
Typical Use: High-strength stainless bolting where both corrosion resistance and elevated strength are required
Hardness: 321 HBW max | Size: 1/4" to 1-1/2" inclusive
Tensile & Hardness Requirements
All values per ASTM A193 / A193M latest edition. Tested on full-size fasteners or machined specimens.
| Grade | Size Range | Min Tensile (MPa) | Min Yield (MPa) | Elongation % | RA % | Max Hardness (HBW) |
|---|---|---|---|---|---|---|
| B7 | 1/4" – 2-1/2" | ? 860 | ? 720 | ? 16 | ? 50 | 321 |
| B7M | 1/4" – 2-1/2" | ? 690 | ? 550 | ? 18 | ? 50 | 235 |
| B8 Class 1 | 1/4" – 1-1/2" | ? 515 | ? 205 | ? 30 | ? 50 | 223 |
| B8M Class 1 | 1/4" – 1-1/2" | ? 515 | ? 205 | ? 30 | ? 50 | 223 |
| B8M Class 2 | 1/4" – 1-1/2" | ? 860 | ? 690 | ? 12 | ? 35 | 321 |
Chemical Composition by Grade
Alloy Steel Grades (B7 / B7M)
| Element | B7 / B7M (AISI 4140/4142) |
|---|---|
| Carbon (C) | 0.38 – 0.48% |
| Manganese (Mn) | 0.75 – 1.00% |
| Phosphorus (P) | ? 0.035% |
| Sulfur (S) | ? 0.040% |
| Silicon (Si) | 0.15 – 0.35% |
| Chromium (Cr) | 0.80 – 1.10% |
| Molybdenum (Mo) | 0.15 – 0.25% |
Stainless Steel Grades (B8 / B8M / B8M-2)
| Element | B8 (SS 304) | B8M / B8M-2 (SS 316) |
|---|---|---|
| Carbon (C) | ? 0.08% | ? 0.08% |
| Manganese (Mn) | ? 2.00% | ? 2.00% |
| Phosphorus (P) | ? 0.045% | ? 0.045% |
| Sulfur (S) | ? 0.030% | ? 0.030% |
| Silicon (Si) | ? 1.00% | ? 1.00% |
| Chromium (Cr) | 18.0 – 20.0% | 16.0 – 18.0% |
| Nickel (Ni) | 8.0 – 11.0% | 10.0 – 14.0% |
| Molybdenum (Mo) | — | 2.0 – 3.0% |
The addition of 2–3% Molybdenum in B8M / B8M-2 (SS 316) provides superior resistance to chloride-induced pitting and crevice corrosion — critical for UAE coastal and offshore applications.
Where to Use Each Grade
Oil & Gas — B7 / B7M
B7 for general high-pressure flanges and process piping. B7M for sour service (H?S) wells, subsea manifolds, and NACE-compliant pressure boundaries. Both paired with ASTM A194 2H or 2HM nuts.
Marine & Coastal — B8M / B8M-2
SS 316 bolting for offshore platforms, desalination plants, and coastal infrastructure in the UAE. B8M-2 when higher strength is needed alongside corrosion resistance.
Power Generation — B7 / B8
B7 for steam turbine bolting and boiler feed pumps. B8 (SS 304) for exhaust stacks, heat recovery systems, and applications requiring oxidation resistance up to 816°C.
Chemical Processing — B8 / B8M
Stainless steel grades for reactors, distillation columns, and acid-handling equipment. B8M preferred for chloride-rich process streams.
Desalination — B8M
SS 316 stud bolts resist chloride attack in reverse osmosis plants and multi-stage flash distillation units — a major sector across the GCC.
Complete RFQ Format
"ASTM A193 B7M stud bolt, 3/4"–10 UNC × 4-1/2" L, fully threaded, with 2 ASTM A194 2HM heavy hex nuts, plain finish, with mill test certificate and NACE compliance."
Complementary ASTM & ASME Standards
| Standard | Description | Pairs With |
|---|---|---|
| ASTM A194 | Carbon & alloy steel nuts for high-pressure service | 2H (with B7), 2HM (with B7M), 8 (with B8), 8M (with B8M) |
| ASTM A320 | Alloy steel bolting for low-temperature service | L7, L7M for cryogenic applications |
| ASME B16.5 | Pipe flanges & flange fittings — bolting dimensions | Determines stud bolt lengths for flange classes 150–2500 |
| ASME B18.2.1 | Square & hex bolts & screws — dimensions | Hex head bolt geometry |
| ASME B18.31.2 | Continuous & double-end stud bolts — dimensions | Stud bolt thread lengths and overall dimensions |
| NACE MR0175 / ISO 15156 | Materials for use in H?S-containing environments | B7M qualification for sour service |
| API 6A | Wellhead & Christmas tree equipment | B7M for wellhead flanges |
| API 660 | Shell-and-tube heat exchangers | B7 / B8M for tube sheet & channel bolting |
Frequently Asked Questions
Need ASTM A193 Stud Bolts in UAE?
We stock B7, B7M, B8, B8M, and B8M-2 stud bolts with ASTM A194 companion nuts. Full material certification, NACE compliance, and same-day dispatch from RAK FREEZONE across UAE & GCC.
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