Inconel 625 Tube Sheet
A solid-solution-strengthened nickel alloy that holds its strength and oxidation resistance up to roughly 980°C — the grade reached for once stainless and duplex have both run out of temperature margin, without moving all the way to a specialist alloy like Hastelloy.
Chemical Composition
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | 58.0 | — |
| Chromium (Cr) | 20.0 | 23.0 |
| Molybdenum (Mo) | 8.0 | 10.0 |
| Niobium + Tantalum (Nb+Ta) | 3.15 | 4.15 |
| Iron (Fe) | — | 5.0 |
Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength | 827 MPa min (annealed) |
| Yield Strength (0.2% offset) | 414 MPa min (annealed) |
| Elongation | 30% min |
| Max. Practical Service Temp. | ~980°C (oxidation-limited) |
Equivalent Grades
| Standard | Designation |
|---|---|
| ASTM / UNS | N06625 |
| EN / DIN | 2.4856 |
| JIS | NCF625 |
| Trade Name | Inconel® 625 (Special Metals) |
Use the international grade and specification reference to keep the N06625 designation separate from product-form specifications: ASTM B443 covers plate/sheet/strip, ASTM B564 covers forgings, and ASTM B446 covers rod/bar only — not plate for tube-sheet blanks.
Temperature Capability in Context
*316L's high number reflects oxidation resistance alone; its practical strength-limited service temperature for pressure parts is considerably lower. Always confirm allowable stress at temperature against the governing code, not oxidation limits alone.
Purchasing Specifications by Form
When a drawing or purchase order names Inconel 625 / UNS N06625, the ordered product form determines which ASTM B-series specification applies. Naming a B-series number alone does not define finished tube-sheet geometry, hole pattern or inspection scope — the drawing remains the owner of those requirements.
| Element | Reference |
|---|---|
| Common name | Inconel 625 |
| UNS | N06625 |
| Plate / sheet / strip | ASTM B443 (SB-443 where applicable) |
| Forging | ASTM B564 (SB-564 where applicable) |
| Bar / rod | ASTM B446 — not a plate path |
Do not treat B443, B564 and B446 as interchangeable. B443 and B564 cover different product forms; B446 is bar/rod only.
ASME SB-* designations may apply by product form and Code edition — confirm context on the purchase order. NPRO does not claim ASTM or ASME certification by listing these references.
| Specification | Product form / role | How to read it for tube sheets |
|---|---|---|
| ASTM B443 / SB-443 | Plate, sheet and strip | Lead plate path when the tube-sheet blank is machined from flat product |
| ASTM B564 / SB-564 | Nickel-alloy forgings (N06625 where listed) | Use when the purchaser requires a forged blank — not interchangeable with B443 |
| ASTM B446 | Rod and bar | Not plate. Do not treat B446 as a tube-sheet plate purchasing specification |
Useful information to include in an RFQ (not mandatory for every enquiry):
- Alloy / grade (Inconel 625) and UNS (N06625)
- ASTM / ASME callout if purchaser-specified (B443 plate vs B564 forging)
- Plate vs forged blank (and clad face if applicable)
- Tube-sheet OD / dimensions / thickness
- Tube OD, pitch, hole diameter and pattern
- Drawing + revision, quantity, machining tolerance, inspection / testing
Continue from grade identity into product form and machining:
Available Product Forms
Inconel 625 is most commonly ordered as U-Tube Tube Sheets for high-temperature boiler and refinery service, and as Forged Tube Sheets for large, high-pressure applications.
Applications
Refinery high-temperature process streams, sour gas service resistant to sulfide stress cracking, and power generation components exposed to cyclic high-temperature operation where stainless would show creep or oxidation degradation.
Advantages & Limitations
Advantages
- Excellent strength retention at high temperature
- Good resistance to sour (H₂S-bearing) service
- No age-hardening heat treatment required
Limitations
- Significant cost premium over stainless and duplex
- Slower machining, higher tool wear than stainless
- Overkill for services that don't need the temperature margin
FAQ
Usually yes — if the service temperature is within stainless or duplex's practical range, 625 adds significant cost without a corresponding benefit. It earns its cost premium specifically in high-temperature, sour, or highly oxidizing services where those grades fall short.
Both resist sulfide stress cracking, but 625 generally offers a higher strength and broader temperature range at a higher cost, while 825 is often selected as a more cost-effective option when its lower temperature capability is still sufficient for the service.
Longer than stainless or duplex due to lower stock availability and more demanding machining — send your specification and quantity for a confirmed lead time rather than assuming standard turnaround.