A193 B7M Stud Bolts

In wet H₂S service, hard steels can crack under load without warning. NACE MR0175 / ISO 15156 limits carbon and low-alloy steel bolting hardness for that reason, and B7M is built to meet that limit.

• Controlled hardness. 235 HBW maximum keeps the stud under the 22 HRC limit for sour service.
• Every piece tested. A193 requires 100 percent hardness testing of B7M, not a sample.
• Useful strength. 100 ksi minimum tensile and 80 ksi minimum yield. That is lower than B7, so check preload and torque with your engineer.
• Matched joint. Pair with A194 2HM nuts, which are also hardness limited.

B7M has a single set of minimum properties up to 4 in diameter.

Torque values for B7 studs do not apply to B7M. Use values based on the lower yield strength.

B7M uses the B7 chemistry; the difference is the heat treatment and hardness limit. The mill test report for your heat is the controlling document.

• Fully threaded studs, threaded end to end, for flange bolting where grip length varies.
• Double-end studs, threaded on both ends with an unthreaded center.
• Tap-end studs, with one end made to thread into a tapped hole.

• Sour oil and gas: Wellheads, Christmas trees, manifolds and gathering lines in H₂S service. See Oil & Gas.
• Gas processing and refining: Amine, sulfur recovery and sour water units. See Petrochemical & Refining.
• Offshore production: Process and pipeline flanges handling sour fluids.

Patriot Bolt is ISO 9001:2015 certified. Each B7M order includes mill test reports traceable to the heat, along with a certificate of conformance to the specification on your purchase order.

Studs are marked with the grade symbol and our identification, as the specification requires.

B7M certifications include the hardness results required by the specification.

Compare B7M with other bolting grades in our Fastener Materials Matrix.

Is B7M required for sour service?

Carbon and low-alloy steel bolting exposed to sour fluids must meet the hardness limits in NACE MR0175 / ISO 15156. B7M is the A193 grade made for that limit; standard B7 is not acceptable.

Why is B7M weaker than B7?

To get hardness down to 235 HBW, the steel is tempered further. That lowers minimum tensile strength to 100 ksi and yield to 80 ksi.

Which nut goes with B7M?

ASTM A194 Grade 2HM, which is hardness limited to 235 HBW and 100 percent tested. Grade 7M is the alloy steel alternative.

Can B7M be used in low-temperature sour service?

For cold service the equivalent grade is A320 L7M, which adds impact testing. Tell us the minimum design temperature and we will confirm the grade.