ASTM A193 B7M STUD BOLT NACE MR 1075 Comliance
Stud Bolt grade B7M, being under the A193 standards, the Specification for Alloy Steel and Stainless Steel Bolting for High Temperature or High Pressure Service.It can be used in specific applications within the oil and gas industries where the bolting could be exposed to the environments containing H2S. NACE MR 0175 compliance
Grade B7M is a heat-treated chromium-molybdenum alloy steel with minimum tensile requirement of 100 ksi, yield of 75 ksi and maximum hardness of 99 HRB.It is made from AISI 4140 alloy steel.
Bolting that can be exposed directly to a sour environment, or that is buried, insulated, equipped with flange
protectors or otherwise denied direct atmospheric exposure, shall conform to the general requirements of Designers and users should be aware that it can be necessary to lower equipment pressure ratings when using SSC-resistant bolting and fasteners. The use of SSC-resistant bolting and fasteners with API flanges shall be in accordance with ISO 10423.
Acceptable bolting materials
Bolts Nuts
ASTM A193 grade B7M ASTM A194 grades 2HM,
Chemical Composition of B7M fasteners
ASTM A193 B7M is made from AISI 4140 / 4142 alloy steel, which provides high strength and moderate corrosion resistance.
| Element | Composition (%) |
|---|---|
| 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 |
Note:B7M has the same composition as B7, but with reduced hardness and strength for sour service applications.
Mechanical Property of B7M fasteners
| Mechanical Property | Min | Max |
|---|---|---|
| Ultimate Tensile Strength (UTS) | 690 MPa | |
| 0.2% Proof Stress | 550 MPa | |
| Elongation | 18% | |
| Gauge Length | A4D | |
| Hardness (Brinell) | 235 HB | |
| Hardness (Rockwell B) | 99 HRB |
Heat treament of B7M fasteners
B7M shall be heat treated by quenching in a liquid medium and tempering. For B7M fasteners, the final heat treatment, which may be the tempering operation if conducted at 1150 °F [620 °C] minimum, shall be done after all machining and forming operations, including thread rolling and any type of cutting.
Size Range of B7M stud bolt
- Standard Diameters: ¼” to 4” (M6 to M100)
- Standard Lengths: 1” to 24” (25mm to 6000mm)
- Thread Types: UNC, UNF, and Metric
- Custom sizes available upon request.
Thread Type:
Unified National Coarse (UNC) – Most common in U.S. applications.
Unified National Fine (UNF) – Used in specific engineering applications.
Metric Coarse & Fine – DIN 13
Coatings & Surface Treatments
B7M bolts are used in corrosive and H₂S-rich environments, often requiring protective coatings:
Zinc Plating
Hot-Dip Galvanizing (HDG)
Xylan/PTFE Coating :Xylan 1070 /xylan 1424 – Low friction, high chemical resistance.
Cadmium Plating – High corrosion resistance (restricted in some industries).
How to Order ASTM A193 B7M Stud Bolts
When ordering ASTM A193 B7M stud bolts, you need to provide detailed specifications to ensure you receive the correct product for your application.
ASTM A193 Grade B7M (Indicates material and heat treatment requirements)
Specify the bolt size,length and Hex nuts numbers
Specify the Thread Type
- UNC (Unified National Coarse) – Standard for ASME applications
- UNF (Unified National Fine) – Used in specific engineering applications
- Metric Coarse or Fine – International standards (ISO 261, DIN 13, etc.)
Typical Example:
- Stud Bolt: ASTM A193 B7M, ¾”-10 UNC x 6”
- Nuts: ASTM A194 2HM
- Washer: ASTM F436
- Surface:HDG or PTFE Xylan 1070 coated
What is the difference between A193 B7 and B7M stud bolt?
Both A193 B7 and B7M stud bolts are widedly used in flange connection.basicly,they are the same material grade of AISI 4140.
However,There are some significant differences in both the mechanical properties and the testing requirements of A193B7M and A193 B7. The most notable difference from a manufacturing perspective is that when providing A193B7M bolts, every individual bolt or stud in the lot must be hardness tested according to ASTM A193,as B7M is used for Sour Service,NACE MR 0175 compliance is required.
