Several ASTM specifications are followed by an “M” that denotes it being an equivalent metric standard. While there is actually an A193M Grade B7 specification which is applicable to metric fasteners, this is not the case with ASTM A193 Grade B7M. This is a different grade of material than A193 Grade B7. So how exactly does A193 Grade B7M differ from A193 Grade B7?
There are some significant differences in both the mechanical properties and the testing requirements of A193B7M and A193B7. For instance, A193B7M has a minimum tensile strength of 100 ksi for diameters under 4”. The minimum tensile strength for A193B7 is 125 ksi for diameters under 2-1/2”, and 115 ksi for 2-1/2” – 4” diameter. Hardness is probably the most significant difference between A193B7M & A193B7. The maximum hardness of ASTM A193B7M is 235 HB or 99 HRB, while the maximum hardness of A193B7 is 321 HB or 35 HRC. 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. A193B7M fasteners will also require a different grade of heavy hex nut than A193B7, which would be ASTM A194 Grade 2HM.
While A193B7 is specified relatively often in the construction industry, A193B7M is a specification that is not seen as regularly. This makes it important to understand the differences between the two specifications so that the correct material is ultimately provided.
Dear Sir
I have two question for stud bolt & machine bolt.
1- What is the technical difference between stud bolt & machine bolt?
2- Can we use the washer for stud bolts ? why no / why yes
We know that usually the stud bolt will use for flanges, valves,… fastener and machine bolt for structure.
Best Regards,
M.R.Ashkiani
@Ashkiani- A stud bolt is a threaded stud with no head, whereas a machine bolt has a forged head on one end. Washers can, and are sometimes used with both stud bolts and machine bolts. It is up to the designer or engineer if they are required or not.
F436 is the recommended washer for A 193 B7 bolts, and can a mild steel washer be used for A 193 B7?
@Oktay- ASTM A193 does not make reference to any washers, but F436 is the normally provided washer. A mild steel washer is not hardened and will likely not perform as well with B7 bolts or studs.
what is equivalent grade for UNI5739 class 8.8, from following.
A193 B7, A193 B7M, A 193 B8 Class1 or a193 B8 Class2
@Vijay- Of those, A193 B7 is the closest to grade 8.8. It is not exact, but the closest of the four grades you listed.
We have a valve with Grade B7 bolts that need to be change out, we will need longer bolts when going back together. Will Grade 8 bolts work as a replacement? If Grade 8 will not work will Grade B7 threaded studs work as a replacement for the Grade B7 bolts?
@Joe- Grade 8 bolts might work, but you’d really need to get that approved by an engineer. There are some differences between the two. As for the studs, same answer, make sure an engineer is ok with the substitution as there may be pros and cons to making the switch.
We have B7M thread rod and we cut it to some required short length stud bolts did now it is again required heat treatment. While as per clause 6.1.5 it is written that after all type of cutting heat treatment required
@Waqas- You are correct, no further processing is permitted after final heat treatment. Even a simple cutting process will require an additional heat treat process.