ASTM A193 supplementary S6, ASME B16.5 flange service, NACE MR0175 sour-service, full MTC EN 10204 type 3.2
Ferralium 255 stud bolts (UNS S32550, EN 1.4507) are super duplex fasteners used for bolted flange joints in seawater, sour hydrocarbon, and chloride-bearing chemical service where standard 22Cr duplex (S31803/S32205) does not meet the PREN requirement. The 25Cr-5Ni-3Mo-2Cu-0.2N composition delivers PREN ≥ 40 and CPT ≥ 35 °C per ASTM G48 Method A, with the 2% copper addition improving resistance to reducing acids that attack standard duplex grades. TorqBolt manufactures per ASTM A193 supplementary requirement S6 (super duplex stainless steel bolting), ASME B18.31.2 dimensional, with hardness ≤ 32 HRC documented per heat for NACE MR0175 / ISO 15156-3 sour-service compliance. NORSOK M-650 manufacturer qualification (MDS D55) available on request. RFQs to info@torqbolt.com, +91-22-66157017, or WhatsApp.
Standard inch and metric series, B7-equivalent length convention, full-thread or stud-and-nut configuration.
| Series | Diameter range | Length range | Thread form | Standard |
|---|---|---|---|---|
| UNC inch | 1/4" to 4" | 1" to 60" | Coarse, class 2A | ASME B1.1 |
| 8UN inch | 1-1/8" to 4" | 4" to 60" | 8 TPI constant pitch, class 2A | ASME B1.1 |
| UNF inch | 1/4" to 1-1/2" | 1" to 24" | Fine, class 2A | ASME B1.1 |
| Metric coarse | M6 to M100 | 25 mm to 1500 mm | Coarse, 6g | ISO 261, ISO 965-2 |
| Metric fine | M8 to M64 | 25 mm to 600 mm | Fine, 6g | ISO 261 |
Stud-and-nut sets ship with two heavy hex nuts per ASTM A194 S7 / 7M (Ferralium 255 nuts) plus optional flat washers per ASTM F436 in the same heat. Length is measured first thread to first thread, excluding chamfers, per ASTM A193 paragraph 14.
ASTM A193 / A193M is the umbrella specification for high-temperature and high-pressure bolting. Super duplex stainless steel grades are covered by supplementary requirement S6, which references the chemical composition limits of ASTM A479 for the qualifying UNS designations including UNS S32550 (Ferralium 255), UNS S32750 and UNS S32760 (Zeron 100). S6 mandates solution annealing at 1040 to 1120 °C with rapid quench, hardness in the as-supplied condition, and the MTC must report ferrite content per ASTM E562 within the qualifying band of 35 to 55 percent.
| Property | Requirement | Test method |
|---|---|---|
| Tensile strength, min | 760 MPa (110 ksi) | ASTM E8 / A370 |
| Yield strength 0.2%, min | 550 MPa (80 ksi) | ASTM E8 / A370 |
| Elongation 4D, min | 15% | ASTM E8 |
| Reduction of area, min | 40% | ASTM E8 |
| Hardness, max | 32 HRC (for NACE MR0175) | ASTM E18, E10 |
| Ferrite content | 35 to 55% | ASTM E562 (point count) |
| Impact toughness, transverse, min | 45 J at -46 °C (typical Aramco / Statoil) | ASTM E23 (Charpy V-notch) |
Ferralium 255 is listed in ISO 15156-3 Table A.10 (super duplex stainless steel bolting) with environmental limits: max H2S partial pressure 100 kPa (15 psi), max in-situ temperature 232 °C, max chloride at 100 °C of 167 g/L. The hardness cap is 32 HRC measured at the bolt mid-radius location per NACE TM0177 and the ferrite content must be within 35 to 55 percent. Each heat is documented on the MTC including hardness traverse (head, mid, threaded portion), ferrite-content point count per ASTM E562, and copy of the NACE MR0175 conformance statement.
For brine and CO2-rich sweet service Ferralium 255 stud bolts perform comparably to 2507 super duplex at lower stocked-cost. Where service contains free elemental sulphur or where the H2S partial pressure exceeds 100 kPa, specifying engineers should review with TorqBolt before substituting Ferralium 255 for nickel-base alloys such as Inconel 718 or Hastelloy C-276.
TorqBolt manufactures Ferralium 255 stud bolts from cold-drawn or hot-rolled bar to ASTM A479. Bar stock is verified for chemistry per heat, then cut to length, end-faced, point-chamfered and threaded by single-point lathe (for sizes above 1-1/2 inch) or thread-rolling (for sizes 1-1/4 inch and below where roll dies of compatible hardness are available). Roll-threading produces a higher fatigue limit by introducing compressive residual stresses at the thread root, and is preferred for offshore cyclic-load applications.
Solution-annealing at 1080 °C for 60 minutes per inch of cross-section, water quenched within 90 seconds, is the standard heat treatment. Cold work in excess of 5 percent strain triggers re-solution; otherwise the as-cold-drawn condition is acceptable provided hardness and ferrite content remain within band. Stress-relief heat treatment in the 300 to 1000 °C range is forbidden because it precipitates sigma, chi and Cr2N phases that destroy corrosion resistance and toughness (see sigma phase page).
| Grade | UNS | PREN | NACE limit | Use case |
|---|---|---|---|---|
| ASTM A193 B7 | K04007 | n/a (carbon) | n/a (sweet only) | Standard hydrocarbon, no H2S |
| ASTM A193 B8M (316) | S31600 | 26 | 22 HRC | Mild marine, no chloride pitting |
| ASTM A193 S1 (duplex 2205) | S31803/S32205 | 35 | 28 HRC | General sour service, mild chloride |
| ASTM A193 S6 (Ferralium 255) | S32550 | 40 | 32 HRC | Severe sour, brine, chemical, subsea |
| ASTM A193 S6 (2507) | S32750 | 43 | 32 HRC | Higher PREN, cost premium |
| ASTM A193 S6 (Zeron 100) | S32760 | 41 | 32 HRC | W-bearing variant, similar duty |
| ASTM A193 B8M Cl 2 (316 SH) | S31600 | 26 | 35 HRC* | Strain-hardened, low PREN, NACE-restricted |
See the dedicated Ferralium 255 vs duplex 2205 and Ferralium 255 vs 2507 pages for detailed substitution analysis and stocked-cost comparison.
Each consignment ships with EN 10204 type 3.2 MTC (third-party witnessed) covering: chemical composition with each element to two decimal places against ASTM A479 limits, tensile and yield with ASTM E8 specimen sketch, hardness traverse at three locations per stud, ferrite-content point count per ASTM E562 with grid sketch, Charpy V-notch energy at the qualifying temperature, NACE MR0175 / ISO 15156-3 conformance statement with Table A.10 reference, and traceability back to the melt heat number. PED 2014/68/EC AD 2000 W2 / W7 / W10 conformance documentation, NORSOK M-650 QTR (MDS D55) and customer-specific PSL test data are available on request.
