ASTM A193 Grade B5
5 Cr-½ Mo bolting for hot, sulfur-bearing refinery service — the grade that matches P5 piping and furnace hardware.
What A193 B5 is.
ASTM A193 Grade B5 is a 5 percent chromium, half percent molybdenum steel (AISI 501) supplied quenched and tempered. The chromium gives it noticeably better resistance to oxidation and to sulfur-bearing hydrocarbons at temperature than B7, which is why it is specified for bolting on 5 Cr piping, refinery furnaces and hydroprocessing equipment.
Strength is a step below B7, at 100 ksi minimum tensile, but B5 keeps that strength further up the temperature scale. We machine it from certified bar and pair it with ASTM A194 Grade 3 nuts made from the same 5 Cr-Mo steel.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.10 | — |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 4.0 | 6.0 |
| Molybdenum | Mo | 0.40 | 0.65 |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 4D, min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| 4 and under | 100 | 80 | 16 | 50 | Not specified |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A193 B5 ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A193 B5 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B5, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B5?
B5 is the 5 percent chromium grade in A193, made from AISI 501 bar and heat treated by quenching and tempering. Chromium at this level forms a protective oxide that slows scaling and resists attack by hydrogen sulfide and other sulfur compounds at the temperatures found in crude and vacuum units, cokers and hydroprocessing trains. The alloy is the bolting counterpart of the 5 Cr-½ Mo pipe and fittings (P5 / F5) used in those services, so the joint expands and corrodes at the same rate as the flanges it clamps.
B5 versus B7 and B16
B7 is stronger at room temperature and is the default below roughly 800 °F. B16 holds strength to about 1100 °F but has only around 1 percent chromium, so it offers little extra corrosion resistance. B5 gives up some strength, 100 ksi rather than 125 ksi, in exchange for oxidation and sulfidation resistance, and is the right choice when the piping specification itself is 5 Cr. Many refinery bolting standards call it out by line class.
Nuts for B5 studs
Use ASTM A194 Grade 3 heavy hex nuts, the 5 Cr-Mo nut grade, so the whole joint shares one corrosion behaviour. Grade 7 nuts are sometimes substituted where Grade 3 is unavailable, but check the line class before doing so.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol B5 and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
ASTM A194 Grade 3
The 5 Cr-Mo heavy hex nut for A193 B5 studs — matched corrosion behaviour on hot, sulfur-bearing refinery lines.
ASTM A193 / ASME SA-193ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.
ASTM A193 / ASME SA-193ASTM A193 Grade B16
Vanadium-strengthened Cr-Mo bolting that holds its strength where B7 starts to relax — steam turbines, HP steam flanges and hot valve bonnets.