ASTM A193
Grade B7M Stud Bolts
Mumbai · India
What Is ASTM A193 Grade B7M Stud Bolts
Grade B7M starts from the same chromium-molybdenum alloy steel as standard Grade B7 — but where B7 is quenched and tempered to a relatively high hardness for maximum strength, B7M is heat treated to a deliberately lower, tightly controlled hardness ceiling of 235 HB (22 HRC). That difference exists because of a specific failure mechanism: in sour environments containing H2S, hardened low-alloy steel above a certain hardness threshold becomes susceptible to sulfide stress cracking (SSC) — a brittle, often sudden failure mode that standard B7’s hardness makes it vulnerable to.
B7M’s controlled hardness keeps the material below the threshold where SSC becomes a practical risk, at the cost of somewhat lower mechanical strength than full B7. That trade-off is exactly why NACE MR0175/ISO 15156 — the material selection standard for oil and gas equipment exposed to H2S — specifically references B7M rather than standard B7 for sour service stud bolting. Specifying the wrong one isn’t a paperwork issue; it changes whether the fastener is actually suitable for the well it’s going into.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our A193 Grade B7M stud bolt range is manufactured and hardness-tested to confirm compliance with the 235 HB ceiling, with full mill test documentation under our ISO 9001:2015 quality system.
Where Hardness Control Genuinely Matters
Sulfide Stress Cracking Resistance
Every batch hardness-tested to confirm compliance with the 235 HB (22 HRC) ceiling required for genuine sour service reliability.
NACE MR0175/ISO 15156 Familiarity
We understand where B7M is specifically required versus where standard B7 remains acceptable, and quote accordingly.
Full Batch Traceability
Heat number traceable mill test documentation confirming hardness, tensile, and chemical composition for every lot.
Matching L7M Available
Where lower-temperature sour service is also required, we can supply the closely related Grade L7M alongside B7M.
Grade B7 vs B7M vs L7M
The choice here isn’t about corrosion resistance in the usual sense — it’s about whether H2S is present and whether the fastener’s hardness puts it at risk of sulfide stress cracking. The comparison below is the one we walk through with buyers before quoting, so the grade actually matches the well or process condition.
| Property | Grade B7 | Grade B7M | Grade L7M |
|---|---|---|---|
| Base Alloy | Cr-Mo (4140/4142 type) | Cr-Mo (4140/4142 type) | Cr-Mo, low-temperature toughness |
| Max Hardness | Not specifically restricted for sour service | 235 HB / 22 HRC | 235 HB / 22 HRC |
| Min Tensile Strength | 125 ksi (860 MPa) | 100 ksi (690 MPa) | 100 ksi (690 MPa) |
| Sour Service Suitability | Not NACE-qualified as standard | NACE MR0175/ISO 15156 qualified | NACE MR0175/ISO 15156 qualified |
| Low-Temperature Toughness | Standard | Standard | Enhanced (Charpy tested) |
| Best Suited For | Standard high-temp piping, non-sour service | General sour service flanged joints | Sour service with low-temperature exposure |
ASTM A193 B7M Product Range
B7M Stud Bolts
Hardness-controlled Cr-Mo stud bolts for NACE-qualified sour service flanged joints.
Grade 2HM Heavy Hex Nuts
Matching hardness-controlled heavy hex nuts designed to pair correctly with B7M studs.
L7M Stud Bolts
Enhanced low-temperature toughness variant for sour service with cold climate exposure.
B7 Stud Bolts
Standard higher-hardness Cr-Mo stud bolts where sour service qualification isn’t required.
Grade B7M Technical Overview
Alloying Elements (4140/4142 Type)
- Chromium 0.80 – 1.10%
- Molybdenum 0.15 – 0.25%
- Carbon 0.38 – 0.48%
- Manganese 0.75 – 1.00%
- Iron Balance
Property Ranges (per ASTM A193)
- Tensile Strength 100 ksi min (690 MPa)
- Yield Strength 80 ksi min (550 MPa)
- Max Hardness 235 HB / 22 HRC
- Elongation 16% min
- Testing MTC / NABL on request
Available Dimensions
- Diameter Range 1/4″ – 4″
- Metric Equivalent M6 – M100
- Stud Length Custom to drawing
- Thread Type UNC / UNF / 8UN
- Finish As-machined / Coated on request
Application Areas
Wherever H2S-containing service makes standard B7 unsuitable.
Wellhead & Christmas Tree Equipment
flange and valve bolting
Sour Gas Pipelines
transmission flange bolting
Sour Crude Processing
equipment sour service bolting
Gas Sweetening Units
sulfur recovery unit bolting
Offshore Sour Service
process equipment bolting
Sour Water Stripping
equipment flange bolting
Underground Gas Storage
wellhead and piping bolting
General Sour Oil & Gas
bolting across sour applications
Standard Export Documentation
Prepared as standard practice for every Grade B7M shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition, hardness, and mechanical property verification for every lot.
Hardness Test Report
Batch-level hardness testing confirming compliance with the 235 HB / 22 HRC ceiling.
Certificate of Conformance
Confirms the shipment matches the purchase order specification and grade in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
Bill of Lading
Ocean or air freight shipping document confirming carrier, mode, and consignee details.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
ASTM A193 Grade B8 Stud Bolts
Austenitic stainless steel option where corrosion resistance matters more than raw strength.
View Grade B8 →Different Types of Nuts and Bolts
A guide to bolt head and nut designs across every standard fastening application.
View Nut & Bolt Types →High Tensile Bolts Specifications
Carbon and alloy steel property classes for structural and mechanical bolting.
View High Tensile Specs →Hastelloy B-3 Stud Bolts
Where sour service alone isn’t enough and severe reducing acid resistance is also required.
View Hastelloy B-3 →Is Your Project
Under NACE MR0175?
Tell us whether H2S is present and we’ll confirm whether B7M, L7M, or standard B7 is the correct grade for your flanged joint. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in