ASTM A193 Grade B16 Bolting Specification
ASTM A193 / ASME SA-193 Grade B16
is the chromium-molybdenum-vanadium alloy steel bolting designation
(UNS K14072) under the ASTM A193/A193M specification for
pressure-vessel, valve, flange, and fitting bolting in high-temperature
service. B16 carries 0.25 to 0.35 % vanadium as a required alloying
element on top of the AISI 4140 / 4142 Cr-Mo base, and is tempered
at a minimum of 1200 °F (650 °C). That combination extends
the continuous-service envelope to 840 °F (450 °C) and
qualifies the alloy for stress-rupture testing at 1100 °F
(595 °C) per Supplement S12 (B16R suffix), which is the canonical
high-temperature A193 grade above the Grade B7 service limit.
TorqBolt supplies B16 bolts, stud bolts, hex bolts, socket-head cap
screws, and threaded rods to ASTM A193/A193M-22 from 1/4 inch
through 4 inch and M6 through M100, with EN 10204 3.1 or 3.2
inspection certification, NORSOK M-650 manufacturer qualification,
and PED 2014/68/EU compliance.
The 0.25 to 0.35 % vanadium addition is the defining chemistry
difference between B16 and the sister Grade B7. Vanadium combines
with carbon during the elevated tempering to form fine V4C3
carbides that pin austenite grain boundaries and impede dislocation
motion, delivering the creep and stress-relaxation resistance that
B7 lacks above 750 °F. B16 is the ASTM A193 bolting designation
for the Cr-Mo-V composition that EN 10269 specifies as 21CrMoV5-7
(Werkstoff 1.7709), DIN 17240 / 17243 carries as the same grade,
JIS designates as SNB16, AFNOR lists as 40CDV04-05, and the UNS
system numbers as K14072.
Both Grade B7 and Grade B16 are alloy-steel bolting grades meeting the same nominal
125 ksi (860 MPa) minimum tensile strength and 105 ksi (725 MPa) minimum yield strength in the standard ≤2½" / ≤M64 size class.
Three structural differences justify the B16 premium for high-temperature service.
- Vanadium microalloy (0.25 to 0.35 %) in B16.
Vanadium forms fine V₄C₃ carbides during tempering that pin grain boundaries and resist coarsening in long-term high-temperature service. Grade B7 contains no vanadium and suffers tempered-martensite embrittlement above roughly 750 °F (399 °C) over service life.
- Higher minimum tempering temperature of 1200 °F (650 °C) in B16 versus 1100 °F (593 °C) in B7. The 1200 °F floor produces a more thermodynamically stable tempered structure and matches the 1100 °F S12 stress-rupture test temperature, which guarantees no further tempering occurs in service.
- Stress-rupture qualification path (Supplement S12, suffix B16R). Grade B16 is the only A193 alloy-steel grade with a defined creep-rupture acceptance criterion (25 h minimum rupture life at 1100 °F / 595 °C and 20 ksi / 140 MPa) baked into the specification itself. B7 has no equivalent rupture-test path within ASTM A193.
For pressure-vessel flanges and steam-piping joints operating in the 700 °F to 1000 °F (370 °C to 540 °C) band,
Grade B16 retains bolt preload through repeated thermal cycles whereas B7 relaxes and requires retightening campaigns.
On refinery FCC unit bolting, steam turbine flange bolting, and fired-heater header bolting,
B16 is the default A193 alloy grade specified by ASME B31.1 and B31.3 piping codes. Refer to the in-depth
A193 B16 vs A193 B7 comparison for side-by-side chemistry, mechanical, and service-window tables.
ASTM A193 Grade B16 is supplied in the quenched-and-tempered (Q&T) condition. The standard mandates the following heat-treatment route:
- Austenitize at 1650 °F to 1700 °F (900 °C to 925 °C) for time sufficient to achieve full austenite transformation throughout the bar cross-section.
- Quench in oil to develop a fully martensitic structure. Section size below 2½" (65 mm) routinely achieves through-hardening to centre; sections above 2½" may show a tempered-bainite core acceptable under the standard.
- Temper at 1200 °F (650 °C) minimum, held long enough at temperature to achieve the tensile, yield, elongation, reduction-of-area, and hardness limits in ASTM A193 Table 2. Producers typically temper at 1200-1275 °F to balance strength retention against ductility and creep resistance.
- Air cool after tempering. Slow cool is preferred for the largest sections to minimise residual stress.
Each heat-treat lot is tested per ASTM A193 §6 and §7 for chemistry (heat analysis plus product analysis per Table 1) and mechanical properties (Table 2). When Supplement S12 is invoked, one stress-rupture test is performed per heat-treat lot. When Supplement S4 is invoked, hardness is verified on each bolt or stud rather than on a sample basis.
Grade B16 service temperature is best understood as three nested windows:
- Continuous service up to 840 °F (450 °C) - the upper bound for routine bolting in pressure vessels, valve bonnets, and flanges per the ASME B31.1, B31.3, and B16.5 piping and flange codes. Creep is negligible in this window and bolt-preload relaxation is dominated by gasket creep, not bolt creep.
- Stress-rupture-qualified service up to 1100 °F (595 °C) with Supplement S12 (B16R). At 1100 °F, the 20 ksi (140 MPa) stress level is below the creep strain limit for ≥25 h rupture life. For flange bolting at 1000 °F service with bolt prestress of 50-70 ksi, B16R provides a documented creep-rupture margin.
- Peak excursion service to roughly 1100 °F (595 °C) for short-duration upsets and start-up transients. Above this temperature, creep degradation accelerates and the alloy is displaced by Grade B5 (A193 5Cr-Mo) at lower stress, or by precipitation-hardened austenitic grades such as A453 Grade 660 above 1000 °F continuous.
Minimum service temperature is approximately -20 °F (-29 °C) for routine field service. Below -20 °F, Charpy V-notch testing should be specified (typically supplement S6 or equivalent purchase-order requirement) since Grade B16's tempered-martensite microstructure does not have an inherent low-temperature ductile-to-brittle transition guarantee like the low-temperature
ASTM A320 Grade L7 low-alloy steels which are quenched-and-tempered with mandatory Charpy testing to -150 °F (-101 °C).
The canonical companion nut for ASTM A193 Grade B16 studs is ASTM A194 Grade 7. The pairing is mandated by ASME B16.5 §5 flange-bolting tables and is the default specified by major engineering houses for refinery, power-gen, and petrochemical procurement.
Pairing Grade B16 studs with Grade 2H nuts is incorrect for any sustained service above 750 °F: the Grade 2H carbon-steel nut creeps and relaxes while the B16 stud retains tension, producing thread-jacking and loss of clamp force. Pairing with Grade 8 stainless nuts is also unsafe at high temperature due to the coefficient-of-thermal-expansion mismatch (austenitic stainless expands roughly 60 % more than B16 alloy steel over the same Δt), which over-stresses the bolt during heat-up. Refer to the dedicated A193 B16 + A194 Grade 7 nut compatibility page for torque values, thread-lubricant recommendations, and proof-load tables.
TorqBolt manufactures the full ASTM A193 Grade B16 product family in both imperial and metric thread series. Ready-stock diameters and indent windows are summarised below.
Engineering specifications outside the ASTM/ASME world reach the same Cr-Mo-V alloy-steel composition through several parallel grade systems. Use this table when reviewing inquiry documents that name a non-ASTM grade equivalent to A193 B16.
Equivalence is approximate. For NORSOK M-650-qualified, EN 10269-traceable, or ASME Section II Part A material certification, the bolting must be melted, forged, heat-treated, and tested to the named standard's exact route. TorqBolt holds qualified procedures for A193 Grade B16, EN 10269 21CrMoV5-7 (1.7709), and JIS SNB16. Refer to the in-depth A193 B16 equivalent materials reference for chemistry overlap tolerances and certificate cross-reference language.
Grade B16's combination of creep resistance, stress-rupture qualification, and ASME pressure-vessel pedigree places it on three classes of high-temperature service:
- Power generation. Steam turbine inner and outer casing bolts, high-pressure (HP) and intermediate-pressure (IP) cylinder splits, boiler feedwater pump flange bolting, superheater header bolting, main steam-line flanges at 540 °C reheat temperature. Refer to A193 B16 in power generation.
- Refinery and petrochemical. Fluid catalytic cracker (FCC) reactor and regenerator flange bolting, catalytic reformer feed-effluent exchanger bolting, delayed coker drum bolting, hydrocracker high-temperature isolation valve bolting, sulfur recovery unit reheater bolting. Refer to A193 B16 in refineries.
- Oil and gas - high-temperature wellhead and surface. Steam-flood injector wellhead bolting on heavy-oil projects, high-pressure-high-temperature (HPHT) Christmas tree bolting where dynamic-temperature service exceeds B7's window.
Below 750 °F continuous, Grade B7 is the economic default. Above roughly 1000 °F continuous, B16 is displaced by Grade B5 (5Cr-½Mo) at lower stress allowable or by precipitation-hardened austenitic grades such as ASTM A453 Grade 660 (UNS S66286 / A286). For low-temperature service below -20 °F (cryogenic, sub-Arctic, LNG), ASTM A320 Grade L7 is the correct A193-family low-temperature counterpart.
TorqBolt supplies ASTM A193 Grade B16 bolting with the following certification levels:
- EN 10204 Type 3.1 mill test certificate - standard offering covering heat analysis, product analysis, mechanical-properties test (per A193 §7), and traceability to heat number. Default for non-critical-service B16.
- EN 10204 Type 3.2 third-party-witnessed certificate - DNV, Lloyd's Register, TÜV, or Bureau Veritas witnesses sampling and testing. Default for offshore NORSOK M-650 / North Sea / API 17D bolting.
- NORSOK M-650 qualified test record (QTR) - five-year validity, alerts at 180 / 90 / 60 / 30 days before expiry per TorqBolt internal QMS, essential-variable changes trigger re-qualification.
- NACE MR0175 / ISO 15156-2 sour-service certificate - B16 is not a default sour-service grade; B7M is. For combined high-temperature and sour service, B16 requires a project-specific NACE waiver supported by stress-rupture and SSC testing.
- PED 2014/68/EC certificate - European Pressure Equipment Directive compliance for vessel-attached bolting.
- API 6A / API 17D Product Specification Level (PSL) - for wellhead and subsea applications; PSL-3 traceable testing supported for B16.
ASTM A193 Grade B16 is referenced by, or invoked under, the following bolting and pressure-vessel codes:
- ASTM A193 / A193M-22 - base specification, current edition
- ASME SA-193 / SA-193M - ASME Section II Part A reproduction of A193 with identical chemistry and mechanical limits
- ASME B16.5 - pipe flange dimensions; specifies A193 bolting by reference for Class 150 through Class 2500 flanges
- ASME B31.1 / B31.3 - power piping and process piping codes; specify A193 B16 for high-temperature flange joints
- ASME BPVC Section VIII Div. 1 / Div. 2 - pressure vessel code; specifies A193 bolting under Table UCS-23
- API 6A / API 17D - wellhead and subsea wellhead equipment; B16 invoked for high-temperature service classes
- API 20E - alloy and carbon steel bolting for use in the petroleum and natural gas industries; specifies quality and certification regime for B16
- NORSOK M-650 / M-630 - Norwegian offshore qualification of materials manufacturers; B16 listed as a qualified Cr-Mo-V grade
- EN 10269 - steels and nickel alloys for fasteners with specified elevated and / or low temperature properties; lists 21CrMoV5-7 (1.7709) as B16 equivalent
- ISO 15156-2 / NACE MR0175 - sour service materials selection; B16 not natively listed (B7M is the natural NACE grade) but allowed with project waiver
- 10 CFR 50 Appendix B - US nuclear quality assurance; B16 allowed for non-safety-related bolting in commercial nuclear plants
S4.1 For bolts or studs 2½ in. [65 mm] or smaller, the hardness for Grade B16 shall be measured on or near the end of each bolt or stud using one of the methods prescribed in §9.2.1 for the Brinell or Rockwell C test. The hardness shall be in the range 253–319 HBW or 25–34 HRC.
When the purchase order invokes S6, Grade B16 shall be impact tested in the longitudinal direction using a Charpy V-notch specimen per Test Methods A370. The minimum average absorbed energy for three specimens shall be specified by the purchaser (typical: 27 J at -20 °F per ASME B31.3 process piping requirements for impact-tested bolting).
When the purchase order invokes S7, surface examination by magnetic particle per Test Methods E709 shall be performed. Linear indications longer than 1.5 mm (0.06 in.) are rejectable. S7 is commonly invoked for refinery and offshore wellhead bolting in B16.
Supplement S11 establishes a stress-relaxation test at elevated temperature with a defined maximum stress drop over a defined hold time. Less commonly invoked for B16 than S12; used for steam-turbine inner-casing studs where stress relaxation governs bolt-up procedures.
S12.1 One test shall be made for each heat-treat lot. Testing shall be conducted using a combination test bar in accordance with Test Methods E292. Rupture shall occur in the smooth section of each test specimen. The test shall be conducted at 1100 °F [595 °C] and 20 ksi [140 MPa]. The test shall be continued until the sample ruptures. Rupture life shall be 25 h minimum. Testing is not required on material less than ½ in. [12 mm] thick.
S12.2 When a purchase order for bolting components invokes S12, the grade symbol applied shall be "B16R."
Grade B16 is a chromium-molybdenum-vanadium alloy steel (UNS K14072), based on the AISI 4140 / 4142 family with vanadium added at 0.25 to 0.35 % to form fine V₄C₃ carbides that resist coarsening at elevated temperature. The base composition is roughly 0.36-0.47 % C, 0.80-1.15 % Cr, 0.50-0.65 % Mo, 0.25-0.35 % V, balanced with manganese and silicon. The steel is supplied quenched and tempered at 1200 °F (650 °C) minimum.
Both grades meet the same 125 ksi tensile and 105 ksi yield strength in the ≤2½" size class. B16 adds vanadium (0.25-0.35 %) for creep resistance and is tempered 100 °F (55 °C) higher than B7 (1200 °F floor versus 1100 °F). Grade B16 also has a stress-rupture qualification path (Supplement S12, suffix B16R). The practical difference is service window: B7 below 750 °F continuous, B16 up to 840 °F continuous and 1100 °F with S12 qualification.
Grade B8 (and B8M) is austenitic stainless steel (Type 304 / 316), solution-treated, with much lower yield strength (~30 ksi annealed, ~65-100 ksi strain-hardened) but excellent corrosion resistance. Grade B16 is alloy steel (Cr-Mo-V), heat-treated to 125 ksi tensile, with no corrosion resistance unless coated. Select B8 when corrosion governs, select B16 when high-temperature creep resistance governs. For combined high-temperature and corrosive service above 1000 °F, neither grade is sufficient - use ASTM A453 Grade 660 or a nickel-alloy bolting grade.
UNS K14072 (USA UNS designation), DIN / EN material 21CrMoV5-7 (Werkstoff 1.7709 per EN 10269), JIS SNB16 (Japan), GOST 25Cr2MoV (Russia), AFNOR 40CDV04-05 (France), AISI 4140 + V (base steel reference). See the equivalent grades cross-reference for full chemistry-overlap tolerances.
35 HRC maximum (321 HBW maximum) in the standard supply condition. Under Supplement S4 (per-piece hardness verification), the acceptable range is 253-319 HBW or 25-34 HRC. In the annealed condition, hardness is typically 187 HBW; the quenched-and-tempered service condition is 25-34 HRC.
Continuous service up to 840 °F (450 °C) for routine bolting per ASME B31.1, B31.3, and B16.5 flange-bolting tables. Stress-rupture-qualified up to 1100 °F (595 °C) with Supplement S12 (suffix B16R, 25 h rupture life at 20 ksi). Some industry literature cites 1000 °F as a peak occasional temperature; this is a conservative shorthand. Below -20 °F, invoke Supplement S6 for Charpy V-notch impact testing.
ASTM A194 Grade 7 is the canonical companion. Grade 4 is legacy and phasing out. Do not pair B16 with A194 Grade 2H (that nut is for B7) for sustained service above 750 °F - the Grade 2H carbon-steel nut creeps while the B16 stud holds tension, producing thread-jacking and clamp-force loss. Do not pair B16 with Grade 8 / 8M stainless nuts in service above 750 °F due to coefficient-of-thermal-expansion mismatch.
Yes - chemistry, mechanical properties, and supplementary requirements are identical. ASME SA-193 is the ASME Boiler & Pressure Vessel Code Section II Part A reproduction of ASTM A193, used for pressure-vessel-attached bolting under the ASME stamp. The bolt material itself is interchangeable; the certificate language differs (ASME stamp markings, ASME data-package requirements) when the bolting is supplied under SA-193 to a pressure-vessel project.
- ASTM A193 Grade B16 stud bolts - primary product page with diameter / length tables and lead times
- A193 B16 vs A193 B7 - full side-by-side comparison
- A193 B16 vs A193 B8 - alloy steel vs austenitic stainless trade-offs
- A193 B16 chemical composition (full ASTM Table 1)
- A193 B16 mechanical properties (full ASTM Table 2)
- A193 B16 equivalent materials (UNS / EN / DIN / JIS / GOST)
- A193 B16 temperature range and service limits
- A193 B16 compatible nuts - A194 Grade 7
- ASME SA-193 Grade B16 bolting specification
- ASTM A193M Grade B16 metric edition
- UNS K14072 properties and equivalents
- A193 B16 in power generation (turbines, boilers, steam piping)
- A193 B16 in refineries (FCC, reformer, coker, hydrocracker)
- A193 B16 specification download (PDF)
Sister TorqBolt micro-sites covering adjacent A193 / A194 / A320 grades:
A320 (low-temperature counterpart),
A193 B7 (Cr-Mo, general service),
A193 B8 (austenitic, Type 304),
A193 B8M (austenitic, Type 316),
A194 (nuts for A193 bolting),
A453 Grade 660 (precipitation-hardened, >1000 °F service).
All six standard product forms in ASTM A193 Grade B16 are manufactured and stocked by TorqBolt for high-temperature pressure-vessel, flange, and equipment-anchor service. Click through to the form-specific page for diameter range, ASME dimensional standard, configurations, and FAQ. The canonical reference page for B16 raw material is the UNS K14072 material data sheet; the ASME-edition spec hub is at ASME SA-193 Grade B16 Bolting Specification.
- B16 stud bolts — canonical flange-bolting form per ASME B18.31.2 (inch) / B18.31.1M (metric), 1/4 in to 4 in / M6 to M100
- B16 hex bolts — single-side wrench-access service per ASME B18.2.1 / B18.2.3.5M, 1/4 in to 3 in / M6 to M76
- B16 heavy hex bolts — refinery and pressure-vessel application per ASME B18.2.1 / B18.2.3.6M
- B16 threaded rods — cut-to-length flange bolting per ASME B18.31.2 / B18.31.1M, 1 m and 3 m stock lengths
- B16 anchor bolts — high-temperature equipment foundation anchoring per ASTM F1554 + ASME B18.31.5
- B16 round bar — upstream mill source per ASTM A29 / A108, hot-rolled / cold-drawn / peeled / turned / ground finishes
