Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A193 Grade B16 Hex Bolts
Cr-Mo-V Alloy Steel Hex Bolts for High-Temperature Pressure-Vessel and Flange Service
ASTM A193 Grade B16 hex bolts (also written A193 B16 hex cap screws, ASTM A193 Gr B16 hex bolts, SA-193 B16 hex bolts, UNS K14072 hex bolts) are chromium-molybdenum-vanadium quenched-and-tempered alloy-steel fasteners manufactured to ASTM A193 / A193M Table 2 mechanical limits and ASME B18.2.1 / B18.2.3.5M dimensional standards for high-temperature pressure-vessel and flange service above the B7 envelope. TorqBolt produces the full B16 hex-bolt family from its Rajkot plant with imperial diameters from 1/4 in to 3 in and metric diameters from M6 to M76, both fine and coarse threads, in stock and on indent.
Hex bolt configurations
B16 hex bolts are supplied in three standard configurations per ASME B18.2.1 (inch) and B18.2.3.5M (metric):
- Hex cap screws (ASME B18.2.1 / B18.2.3.1M) - finished-head precision bolt with chamfered head and tight tolerances on width-across-flats and thickness. Default selection for flange and machinery service.
- Heavy hex bolts (ASME B18.2.1 / B18.2.3.6M) - thicker head and longer wrench-engagement surface, used in heavy-section pressure vessels and refinery hot-bolted joints.
- Hex bolts (regular) (ASME B18.2.1) - looser tolerances than hex cap screws; available on request for retrofit and shop-bolt applications.
Diameter and length range
| Series | Stock diameter range | Indent diameter range | Length range (stock) | Length range (indent) |
|---|---|---|---|---|
| Inch hex cap screw (B18.2.1) | 1/2 in to 2 in | 1/4 in to 3 in | up to 12 in | up to 36 in |
| Metric hex (B18.2.3.5M) | M12 to M48 | M6 to M76 | up to 300 mm | up to 900 mm |
| Heavy hex bolt (B18.2.1) | 1/2 in to 2-1/2 in | 1/4 in to 3 in | up to 16 in | up to 40 in |
B16 hex bolt material
B16 hex bolts are forged from AISI 4140 / 4142 chromium-molybdenum-vanadium alloy steel, conforming to the ASTM A193 Table 1 chemistry envelope. Vanadium addition of 0.25 to 0.35 % is the key differentiator from the B7 grade and is responsible for the creep and stress-relaxation resistance that justifies the B16 premium at elevated service temperatures.
| Element | Cr-Mo-V (% by mass) | Product analysis variation |
|---|---|---|
| C | 0.36 - 0.47 | 0.02 |
| Mn | 0.45 - 0.70 | 0.03 |
| P (max) | 0.035 | 0.005 |
| S (max) | 0.040 | 0.005 |
| Si | 0.15 - 0.35 | 0.02 |
| Cr | 0.80 - 1.15 | 0.05 |
| Mo | 0.50 - 0.65 | 0.03 |
| V | 0.25 - 0.35 | 0.03 |
B16 hex bolt mechanical properties
| Diameter, in. | 2-1/2 and under | over 2-1/2 to 4 | over 4 to 8 |
|---|---|---|---|
| Min. tempering temperature, °F | 1200 | 1200 | 1200 |
| Tensile strength, min, ksi | 125 | 110 | 100 |
| Yield strength, min, 0.2 % offset, ksi | 105 | 95 | 85 |
| Elongation in 4D, min, % | 18 | 17 | 16 |
| Reduction of area, min, % | 50 | 45 | 45 |
| Hardness, max | 321 HBW / 35 HRC | 321 HBW / 35 HRC | 321 HBW / 35 HRC |
Heat treatment
B16 hex bolts are supplied in the quenched-and-tempered (Q&T) condition. The standard heat-treatment route is: austenitise at 1650 to 1700 °F (900 to 925 °C), oil quench to develop a fully martensitic structure, then temper at 1200 °F (650 °C) minimum for time sufficient to meet the ASTM A193 Table 2 mechanical limits. Each heat-treat lot is tested per A193 sect 7. When Supplement S12 is invoked, stress-rupture testing at 1100 °F / 20 ksi is performed (suffix B16R). When Supplement S4 is invoked, hardness is verified on each hex bolt.
Companion nut grade for B16 hex bolts
The canonical companion nut for B16 hex bolts is ASTM A194 Grade 7. Do not pair B16 hex bolts with A194 Grade 2H nuts for sustained service above 750 °F - the Grade 2H carbon-steel nut creeps while the B16 hex bolt retains tension, producing thread-jacking and loss of clamp force. Do not pair B16 hex bolts with A194 Grade 8 or 8M austenitic stainless nuts at elevated temperature due to coefficient-of-thermal-expansion mismatch.
Coatings and surface finish
B16 hex bolts are supplied in the following finish options:
- Plain (uncoated, as-machined) - default; protective oiling prevents shipping corrosion
- Black oxide - light protective finish for low-corrosion environments
- Hot-dip galvanised (HDG) per ASTM A153 - thick zinc coating for atmospheric service; baking required to prevent hydrogen embrittlement
- Zinc plating per ASTM B633 - thinner electroplated coating
- Cadmium plating per ASTM B766 / AMS-QQ-P-416 - aerospace and chemical-service applications
- Xylan 1424 / 1070 fluoropolymer - subsea and offshore high-temperature service
- PTFE coating (Teflon-based) - chemical-process flange bolting
- Geomet 500B / 720 - chromium-free corrosion protection for offshore
- Magni 565 / 575 - zinc-aluminium flake coating
- Phosphate and oil - shipping protection
Quality certification regime
TorqBolt supplies B16 hex bolts with the following certification options:
- EN 10204 Type 3.1 - default mill test certificate covering heat analysis, product analysis, mechanical-properties test, and heat traceability
- EN 10204 Type 3.2 - third-party-witnessed certificate (DNV, Lloyd’s Register, TÜV, Bureau Veritas) for offshore and pressure-vessel projects
- NORSOK M-650 qualified test record (QTR) - five-year validity, essential-variable changes trigger re-qualification
- NACE MR0175 / ISO 15156-2 sour-service certificate - project waiver required (B16 is not a default sour-service grade; B7M is)
- PED 2014/68/EC certificate - European Pressure Equipment Directive compliance for vessel-attached bolting
- API 6A / 17D PSL-3 - subsea and surface wellhead high-temperature applications
- Charpy V-notch impact test (Supplement S6) - on request, for piping below -20 °F
- Magnetic-particle examination (Supplement S7) - for refinery and offshore wellhead service
- ISO 17782 manufacturer-of-standard-fasteners certification - subsea SUBSEA+ pressure-traceability tier (offshore project requirement)
Lead time and procurement
Stock diameters (1/2 in to 2 in / M12 to M48) ship within 3 to 5 business days of order confirmation. Indent diameters (1/4 to 1/2 in / M6 to M10 with custom length, or 2 to 3 in / M48 to M76) carry a 4 to 8 week lead time depending on heat-treatment lot consolidation and certification level (3.1 vs 3.2 vs NORSOK QTR). For NORSOK M-650 QTR-required hex bolts, expect 8 to 12 weeks for first-time grade qualification or 4 to 6 weeks for repeat orders under valid QTR. MOQ on stock is 5 pieces; on indent is 25 pieces per diameter / length combination.
Why engineers specify B16 hex bolts
B16 hex bolts replace B16 stud bolts wherever the joint geometry rules out double-side wrench access. Four service contexts dominate the order book: steam-turbine casing covers (parted gland-rings and inner casings where the wrench reaches one face only), valve bonnets and yoke caps on B16.34 / API 600 gate and globe valves, blind-pocket connections on B16.5 raised-face flanges that pair into a tapped boss rather than a through-drilled flange pair, and compressor-casing studs replaced with cap screws during turnaround inspections where casing-stud removal would damage the threaded boss. In these joints the bolt must carry both the proof load and the assembly torque through a head feature, so head-flat tolerance and head-thickness compliance per ASME B18.2.1 sect 3.4 are first-line acceptance criteria, not nice-to-haves. Hot-service applications above 750 °F require the under-head fillet radius per B18.2.1 Table 5 to prevent stress-concentration cracks during repeated thermal cycling. TorqBolt’s B16 hex-bolt production uses cold-headed AISI 4140 bar followed by controlled-atmosphere Q+T to 35 HRC max, with head dimensional inspection on every lot per the manufacturing-quality-plan attached to the order, and a sample magnetic-particle examination per Supplement S7 on diameters 1-1/2 in and larger.
Frequently asked questions
What is the maximum service temperature for A193 B16 hex bolts?
840 °F (450 °C) for continuous service per ASME B31.1 / B31.3 / B16.5 flange-bolting tables. 1100 °F (595 °C) for stress-rupture-qualified service with Supplement S12 (suffix B16R, 25 h rupture life at 20 ksi). Some industry sources cite 1000 °F as a conservative peak.
Are B16 hex bolts NACE-compliant for sour service?
B16 is not a default NACE MR0175 / ISO 15156-2 sour-service grade. For combined high-temperature and sour service, B16 requires a project-specific NACE waiver supported by stress-rupture and sulphide-stress-cracking testing. The default NACE sour-service A193 grade is B7M (impact-tested, hardness-controlled). For high-temperature sour service, an A193 B7M / B16 split assessment is often required.
Can B16 hex bolts be used at cryogenic temperature?
No. B16 has no Charpy V-notch requirement below -20 °F (-29 °C). For cryogenic service, use ASTM A320 Grade L7 (UNS G41400) which is the low-temperature counterpart of B16 with mandatory Charpy testing to -150 °F (-101 °C).
When should I specify a tap-end hex bolt instead of a through-bolt?
Tap-end (or "stud-form") hex bolts are used when one face of the joint is a tapped boss rather than a clearance through-hole — typical for valve bonnets, compressor casing covers, and small-flange-to-vessel-shell pads. The tap-end is threaded into the boss as a permanent installation and the head sits above the second mating face for normal wrench access. Through-bolts (clearance both ends) work only when both faces are flanged with through-drilled bolt holes. For B16 service at sustained temperature, prefer tap-end on the tapped-boss side and torque to ASME B16.5 / API 6A target preload with a graphite-or-PTFE thread lubricant to keep the friction coefficient predictable.
Related TorqBolt resources
- ASTM A193 Grade B16 bolting specification overview
- A193 B16 vs A193 B7 - full side-by-side comparison
- B16 stud bolts
- B16 heavy hex bolts
- B16 threaded rods
- B16 round bar (mill source)
- ASME SA-193 Grade B16 bolting specification
- B16 anchor bolts (high-temp foundation anchoring)
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