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/A193M Grade B7M Stud Bolts – UNS G41400
Controlled-hardness 4140 alloy steel stud bolts for sour gas and hydrogen sulfide service, meeting NACE MR0175 hardness requirements for SSC-resistant bolting.
ASTM A193/A193M Grade B7M Stud Bolts are manufactured from UNS G41400 chromium-molybdenum 4140 alloy steel and are quenched and tempered to achieve a controlled maximum hardness of Rockwell C 35 (equivalent to approximately 327 HBW Brinell hardness), as specified in ASTM A193 to prevent susceptibility to sulfide stress corrosion cracking (SSC) and hydrogen embrittlement in sour service environments containing hydrogen sulfide and free water in accordance with NACE MR0175/ISO 15156. While Grade B7M has reduced minimum mechanical property requirements compared to standard Grade B7 — owing to the higher tempering temperature required to achieve lower hardness — it retains sufficient strength for the majority of pressure equipment bolting applications and is the standard alloy steel grade specified in sour oil and gas production wellheads, production separators, gas sweetening amine units, sour water strippers, and any pressure boundary flanges exposed to wet H2S service where uncontrolled hardness in standard B7 would create an unacceptable risk of catastrophic stress corrosion cracking failure.
ASTM A193/A193M Grade B7M Chemical Composition - Ferritic Steels
| Grade | Description and
UNS Designation |
C | Mn | P | S | Si | Cr | Mo |
|---|---|---|---|---|---|---|---|---|
| ASTM A193 Grade B7M | Cr-MoC | 0.38-0.48D | 0.75-1.00 | 0.035 | 0.040 | 0.15-0.35 | 0.80-1.10 | 0.15-0.25 |
| Product Analysis VariationB | 0.02 | 0.04 | 0.005 | 0.005 | 0.02 | 0.05 | 0.02 |
ASTM A193/A193M Grade B7M Mechanical Requirements - Ferritic Steels (Metric)
| Class | Diameter,
[mm] |
Min.Tempering
Temp. °C |
Tensile Strength,
min, MPa |
Yield Strength,min,
.2% offset, MPa |
Elongation in 4D,
min, % |
Reduction of Area, min, % | Hardness,
max |
|---|---|---|---|---|---|---|---|
| ASTM A193 Grade B7M | M100 and under | 620 | 690 | 550 | 18 | 50 | 235 HBW or 99 HRB |
| over M100 to M180 | 690 | 515 | 18 | 50 | 235 HBW or 99 HRB |
ASTM A193/A193M Grade B7M Bolting Components Marking - Ferritic Steels
| Grade | Grade Symbol |
|---|---|
| ASTM A193 Grade B7M | TB B7M or B7M |
Related ASTM A193 Grades & ASME Companion Dimensions
Frequently Asked Questions
- What is ASTM A193 Grade B7M?
- ASTM A193 Grade B7M is a bolting material covering AISI 4140 Cr-Mo for NACE MR0175 sour service (UNS G41400). Used in high-temperature, high-pressure flange, pressure-vessel and heat-exchanger bolting service per ASTM A193/A193M.
- What is the UNS designation for ASTM A193 Grade B7M?
- The UNS designation for ASTM A193 Grade B7M is UNS G41400. This corresponds to AISI 4140 Cr-Mo for NACE MR0175 sour service. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications.
- Why is ASTM A193 B7M used instead of B7?
- B7M is the NACE MR0175 / ISO 15156-3 compliant version of B7 — same Cr-Mo chemistry but tempered to a maximum hardness of 235 HBW (22 HRC). This hardness ceiling prevents sulfide-stress-cracking in sour-service hydrocarbon environments.
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