ASTM A193 B7M AND B7 Stud bolt difference
Both A193 B7 and B7M stud bolts are widedly used in flange connection.basicly,they are the same material grade of AISI 4140.
So they have the chemical compositions.
The “M” in B7M means “Modified”.
However,There are some significant differences in both the mechanical properties and the testing requirements of A193B7M and A193 B7.
you will find the difference between B7 and B7M grade stud bolts
1. Tensile Strength & Hardness
- B7: Higher tensile strength (minimum 125 ksi) and hardness (Rockwell C35 max).
- B7M: Lower tensile strength (minimum 100 ksi) and Lower hardness (Rockwell C23 max) to improve toughness and ductility.
2. Heat Treatment
- B7: Quenched and tempered
- B7M: Quenched and tempered
3. Application
- B7: Commonly used in standard high-pressure, high-temperature environments (e.g., refineries, chemical plants).
- B7M: Used in environments where hydrogen sulfide (H₂S) is present, Sour Service,NACE MR 0175 compliance
4. Marking
- B7: Typically marked with “B7” on the bolt head.
- B7M: Marked with “B7M” and often comes with additional testing requirements for harndess
The most notable difference from a manufacturing perspective is that when supplying A193 B7M bolts, each individual bolt or stud in the batch must be tested for hardness. 100% Hardness tested. A193 B7M fasteners also require a different type of heavy-duty hex nut ,which is ASTM A194 Grade 2HM.
