Stainless Steel 347 (UNS S34700)
SS 347 is stabilized by additions of niobium (columbium) and tantalum. Niobium forms stable niobium carbides, preventing chromium depletion in severe elevated-temperature environments where cyclic heating occurs between 425°C and 850°C.
Material Quick Reference
| Material Classification | Niobium / Columbium-Stabilized Austenitic Stainless Steel |
|---|---|
| Pitting Resistance (PREN) | 18 - 20 |
| Temperature Limits | -196°C to +870°C |
| Governing Specifications | ASTM A312 TP347, ASTM A403 WP347, ASTM A182 F347, ASME Section II |
Typical Engineering Applications
- Refinery hydrocracker and catalytic reformer lines
- High-pressure steam headers
- Aviation and gas turbine exhaust piping
- Radioactive and nuclear waste processing
Chemical Environment & Corrosion Resistance
High resistance to intergranular corrosion and polythionic acid stress cracking in sulfur-rich refinery atmospheres.
Performance in Qatar's Coastal & Industrial Climate
Specified in Ras Laffan and Mesaieed refineries for heavy hydrocarbon hydroprocessing units.
Welding & Fabrication Guidelines
Welded using ER347 / E347 filler wire. Excellent arc stability compared to titanium-bearing grades.
Positive Material Identification (PMI) Requirements
XRF verification of Nb content (Nb >= 10x C, max 1.0%).
Key Advantages
- Superior weld metal transfer vs 321
- Higher creep rupture strength at 550°C+
Engineering Limitations
- Susceptible to knife-line attack in extremely narrow zones adjacent to weld fusion lines under specific corrosive media
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