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How do you specify SS 304H or SS 347H superheater tubes?
Short answer
Order to ASTM A213 with the exact grade (TP304H, TP321H, TP347H or TP347HFG), carbon 0.04–0.10%, the required grain size, the solution-treatment temperature, OD and minimum wall, length or bends, hydro or eddy-current testing, and IBR documents where the boiler is in India.
Key takeaways
In brief
- Checklist: ASTM A213 grade: TP304H, TP321H, TP347H or TP347HFG Grain size requirement (No.
- Related grades: See SS 304H, SS 321H and SS 347H for full data.
Checklist
- ASTM A213 grade: TP304H, TP321H, TP347H or TP347HFG
- Grain size requirement (No. 7 or coarser, or fine-grain for HFG)
- Carbon within 0.04–0.10%
- Solution treatment temperature and quench
- OD × minimum wall and length, plus bends if needed
- Hydro or eddy-current testing
- IBR documentation if applicable
Related grades
Choosing between SS 304H, SS 321H and SS 347H
SS 304H is the economical creep-range grade. SS 321H and SS 347H add titanium or niobium stabilisation, which improves resistance to intergranular attack and, for SS 347H, gives higher creep strength. Fine-grained TP347HFG is specified in modern superheaters for better steam-side oxidation resistance. Compare the stabilised grades in SS 321 vs SS 347 and SS 347 vs SS 347H.
Bending and handling
Tight-radius bends in H-grade tubes can need solution annealing after bending, depending on the strain and the code. State bend radii and post-bend treatment on the order, and keep tubes capped and protected from chloride contamination in transit.
Related guides, comparisons and articles
Frequently asked questions
Why is grain size specified for H grades?
A coarser grain improves creep-rupture strength, so ASTM requires a grain size of No. 7 or coarser for most H grades. Fine-grain 347HFG is the deliberate exception, chosen for oxidation resistance.
Can SS 304 be used instead of SS 304H?
Not in the creep range. Standard SS 304 has no minimum carbon or grain-size requirement, so its creep strength is not assured.
Do you supply superheater tubes with IBR certification?
Yes, A213 H-grade tubes can be supplied with IBR documentation on request.
Does Bright Tubes supply the materials discussed in this article?
Yes. SS 304H Stainless Steel, SS 347H Stainless Steel and related products are supplied from stock or mill-sourced, with EN 10204 certificates.
Can I get technical advice for my application?
Yes. Share your service conditions and specification, and our team can help shortlist suitable grades for your engineer to confirm.