SS 347 FastenersASTM A193 B8C · Manufacturer, stockist & exporter, India
Also sold as AISI 347 · UNS S34700 · W.Nr 1.4550 · Niobium-stabilised stainless
SS 347 fasteners — stud bolts, hex bolts, nuts and washers — are made from ASTM A193 B8C bar stock to ASME B18 dimensions. It is a niobium-stabilised austenitic stainless steel, chosen for welded high-temperature piping in refineries and power plants. Kanak Steel & Engineering Co. supplies it with EN 10204 3.1 mill certificates from Mumbai to buyers across India, the Gulf, South-East Asia, South America, Europe, the UK and the USA.
- Stock & mill supply
- EN 10204 3.1 / 3.2
- PMI on every heat
- Export packing
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is SS 347 Fasteners?
SS 347 fasteners is a niobium-stabilised austenitic stainless steel supplied as fasteners to ASTM A193 B8C (UNS S34700). Buyers specify it for welded high-temperature piping in refineries and power plants. It is also sold as AISI 347, UNS S34700, W.Nr 1.4550.
- What it is
- Niobium-stabilised austenitic stainless steel
- Bar stock
- ASTM A193 B8C
- Dimensions
- ASME B18.2.1 · B18.2.2 · B18.31.2
- Threads
- UNC · UN-8 · metric
- Sizes
- M10 – M64 · ½" – 4"
- Best at
- Welded high-temperature piping in refineries and power plants
SS 347 Fasteners Specification & Sizes
| Material | ASTM A193 B8C |
|---|---|
| Dimensional standards | ASME B18.2.1 (bolts) · B18.2.2 (nuts) · B18.31.2 (studs) · DIN 931 / 933 / 934 |
| Types | Stud bolt · Hex bolt · Heavy hex nut · Hex nut · Washer · Threaded rod · U-bolt · Eye bolt · Anchor bolt · Foundation bolt · Socket head cap screw · Machine screw |
| Threads | UNC, UN-8 and metric coarse |
| Coating | Plain · PTFE on request |
| Documents | EN 10204 3.1 |
SS 347 Stud Bolts: Grade & Nut Pairing
Pressure bolting in this material is ASTM A193 B8C studs with ASTM A194 8C heavy hex nuts. A193 B8-series bolting comes in Class 1 (carbide solution treated) and Class 2 (strain hardened, higher strength) — state the class.
Torque (T = K × F × d), stud length and coatings are covered in the fasteners guide.
| Galling | Stainless and nickel-alloy threads gall — always use anti-seize, and avoid high-speed tightening |
|---|---|
| Coatings | Usually supplied plain; PTFE coating on request to ease tightening |
| Marking | Grade symbol and maker's mark on each stud end and nut, as the standard requires |
| Certificates | EN 10204 3.1 for the bar heat; mechanical test reports on the finished bolts on request |
SS 347 Fasteners Chemical Composition
| Element | Weight % |
|---|---|
| Chromium | 17.0 – 19.0 |
| Nickel | 9.0 – 13.0 |
| Niobium | 10 × C min, 1.00 max |
| Carbon | 0.08 max |
| Manganese | 2.00 max |
| Silicon | 0.75 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.030 max |
| Iron | Balance |
SS 347 Fasteners Mechanical Properties
| Annealed plate & sheet | Value |
|---|---|
| Tensile strength | 515 MPa · 75 ksi |
| Yield strength 0.2% | 205 MPa · 30 ksi |
| Elongation | 40% |
| Hardness | 201 HB max |
Density & Physical Properties
| Property | Value |
|---|---|
| Density | 7.96 g/cm³ |
| Melting range | 1400 – 1425 °C |
| Magnetic | Non-magnetic annealed |
| PREN (approx.) | ≈ 18 |
SS 347 Equivalent Grades
Values follow ASTM A240 for UNS S34700. Always check against the edition named on your purchase order.
Six-digit Harmonized System heading (iron and steel, chapter 72–73). Your country adds its own digits — confirm with your customs broker. All HS codes.
How to Verify SS 347 Fasteners with PMI
Positive material identification with a handheld XRF gun confirms the alloy on the piece itself, in seconds, before it is cut or welded. SS 347 is most often mixed up with SS 321 — the table shows which elements tell them apart.
Handheld XRF does not measure carbon or nitrogen; those come from the mill certificate or optical emission (OES) testing. We PMI-test nickel alloys as standard and any grade on request.
| Element | SS 347 | SS 321 |
|---|---|---|
| Nickel | 9.0 – 13.0 | 9.0 – 12.0 |
| Chromium | 17.0 – 19.0 | 17.0 – 19.0 |
| Titanium | residual | 5 × (C + N) min, 0.70 max |
| Niobium | 10 × C min, 1.00 max | residual |
| Iron | Balance | Balance |
| Manganese | 2.00 max | 2.00 max |
SS 347 fasteners by type
SS 347 Fasteners Applications
SS 347 is specified when the cheaper grade will not survive the service but a higher alloy would be more than the job needs. These are the jobs our buyers use it for.
SS 347 Fasteners vs 321, 304 and 310S
| Grade | Fasteners standard | PREN (approx.) | Pick it when |
|---|---|---|---|
| SS 321 | ASTM A193 B8T | ≈ 18 | High-temperature service between 425 and 815 °C |
| SS 304 | ASTM A193 B8 · A194 8 | ≈ 18 | General corrosion resistance, food, water and architectural work |
| SS 347 | ASTM A193 B8C | ≈ 18 | Welded high-temperature piping in refineries and power plants |
| SS 310 / 310S | ASTM A276 / A479 | ≈ 25 | Furnaces, burners and heat treatment at high temperature |
PREN = Cr + 3.3 Mo + 16 N, from mid-range chemistry. A screening guide, not a substitute for corrosion data on your medium.
SS 347 Corrosion Resistance — Element by Element
Each alloying addition has a job. Knowing which one protects against your medium is the quickest way to judge whether 347 fits.
About 18% chromium forms the passive film that makes the steel stainless.
Nickel keeps the structure austenitic — tough at low temperature and easy to form and weld.
Niobium binds carbon more stably than titanium, so 347 holds up in welded high-temperature service.
347H is the choice for hot hydrogen and high-temperature refinery piping.
How your 347 fasteners order runs
- 01Enquiry review — we confirm size, standard edition and documents against your MR or drawing.
- 02Heat selection & PMI — the mill certificate is checked and material is PMI-tested before processing.
- 03Processing — cutting, machining or bevelling to your specification, with heat numbers marked.
- 04Inspection — your third-party inspector witnesses, or we share photos and test reports.
- 05Packing & dispatch — seaworthy packing from Nhava Sheva (JNPT), Mumbai, FOB or CIF, documents sent before the vessel sails.
Welding & Fabricating SS 347 Fasteners
SS 347 welds by all common arc processes. A few points our buyers ask about:
| Matching filler | ER347 (AWS A5.9) |
|---|---|
| Over-alloyed filler | ERNiCr-3 for dissimilar joints |
| Preheat | Not required; keep interpass temperature low |
| Cutting | Thermal or abrasive cutting; grind off heat-tinted edges before welding |
Follow your approved WPS; this is general guidance. See also 347 fittings and 347 flanges for the matching pipe-system parts.
How to Order SS 347 Fasteners: RFQ Checklist
Get an accurate quote the first time. Copy this list into your enquiry:
- Fastener type, size and length
- Thread form
- Material and marking
- Quantity in sets
- Certificate type
- Delivery port and date
SS 347 fasteners for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiSS 347 fasteners — questions buyers ask
Is SS 347 the same as AISI 347?
Yes. AISI 347, UNS S34700, W.Nr 1.4550 all refer to the same material, and fasteners is ordered to ASTM A193 B8C whichever name is on the enquiry.
Why use SS 347 bolts instead of B7 carbon steel?
On SS 347 flanges in corrosive service, carbon-steel bolts corrode first. Matching-alloy bolting avoids galvanic corrosion and bolt failure.
What nut goes with SS 347 stud bolts?
ASTM A194 8C heavy hex nuts.
How do I stop SS 347 bolts galling?
Use an anti-seize compound on threads and nut faces, tighten at moderate speed, and do not reuse galled nuts.
SS 347 or SS 310 / 310S — which should I choose?
SS 347 is chosen for welded high-temperature piping in refineries and power plants. SS 310 / 310S is the step up when you need more pitting resistance or strength. See the comparison table on this page, or ask us with your process conditions.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026