ASTM B444 Nickel Alloy Tube
ASTM B444 nickel alloy tube is a cold-worked seamless pipe and tube product family covering nickel-chromium-molybdenum-niobium alloys UNS N06625 and UNS N06852, plus nickel-chromium-molybdenum-silicon alloy UNS N06219. In current ASTM editions, the product scope is tied to ASTM B444 for the alloy-specific requirements and ASTM B829 for the general seamless nickel alloy pipe and tube requirements. For procurement, this means the most important buying points are the exact UNS designation, heat-treatment condition, dimensional tolerance, surface finish, and whether hydrostatic and nondestructive electric testing are specified in the purchase order.
Specifications
| Item |
Description |
| Material |
Nickel-chromium-molybdenum-niobium alloy / nickel-chromium-molybdenum-silicon alloy |
| Standard |
ASTM B444; general requirements per ASTM B829 |
| Grade |
UNS N06625 Grade 1, UNS N06625 Grade 2, UNS N06852, UNS N06219 |
| Manufacturing route |
Cold-worked seamless pipe and tube |
| Outside diameter |
Common ASTM B444 supply range starts from 1/2 in. (12.7 mm); practical OD range depends on finish route and mill capability |
| Wall thickness |
According to specified tube size and schedule / minimum wall requirement |
| Length |
1-12 m, customizable |
| Tolerance range |
According to ASTM B444 + ASTM B829 purchase requirements |
| Straightness |
Commercially straight or as agreed in PO |
| Surface condition |
Bright annealed, annealed and pickled, or ground OD depending on finish route and order requirement |
| Heat treatment |
N06625 Grade 1: annealed at 1600°F (871°C) minimum; N06625 Grade 2: solution annealed at 2000°F (1093°C) minimum, with or without a subsequent stabilization anneal at 1800°F (982°C) minimum; N06219 and N06852: solution annealed condition |
| Testing |
One tensile test per lot; each tube subjected to hydrostatic test or nondestructive electric test unless otherwise specified |
Main Features
- Defined high-strength minimums, not generic “high performance” wording. ASTM B444 sets the minimum room-temperature tensile properties at 120 ksi / 60 ksi / 30% for UNS N06625 Grade 1, 100 ksi / 40 ksi / 30% for UNS N06625 Grade 2, 96 ksi / 39 ksi / 30% for UNS N06219, and 85 ksi / 35 ksi / 30% for UNS N06852.
- Heat-treatment condition is directly linked to service intent. ASTM B444 assigns N06625 Grade 1 as annealed and Grade 2 as solution annealed, and producer data for Alloy 625 shows that the solution-treated condition is preferred where optimum creep or rupture resistance is needed, while annealed material can be advantageous for fatigue strength and tensile/yield strength in lower-temperature service.
- Corrosion-resistant chemistry with tight niobium-molybdenum control. For UNS N06625, ASTM B444 requires Cr 20.0-23.0%, Mo 8.0-10.0%, Nb+Ta 3.15-4.15%, Fe max 5.0%, and Ni min 58.0%, which is the chemistry basis behind Alloy 625’s broad resistance to oxidizing and reducing media.
- Testing is written into the product standard. Each tube is subject to either hydrostatic or nondestructive electric test, and tension testing is required per lot. This is important for EPC, pressure equipment, and MRO buyers who need verifiable inspection language on the PO.
- ASTM B444 is a seamless specification. That matters where buyers want to reduce weld-related risk in aggressive chloride, mixed-acid, or high-purity service. The scope itself is for cold-worked seamless pipe and tube rather than welded tubing.
Our Advantages
1. Clear condition control instead of ambiguous “625 tube” quotations.
Professional buyers usually ask whether the offered tube is N06625 Grade 1 or Grade 2, because ASTM B444 treats them differently and even defaults to Grade 1 if no grade is specified. We solve that by quoting UNS number, ASTM edition, temper, and heat-treatment route directly on the MTC and order acknowledgment.
2. Inspection language that matches the standard, not a vague QC promise.
Buyers commonly care about whether the tube will be hydrotested, eddy-current tested, or both. ASTM B444 requires each tube to undergo hydrostatic testing or nondestructive electric testing, with the test type selectable by manufacturer unless the purchase order says otherwise. We therefore recommend stating the exact inspection route on the PO, so supply matches project QA documents from the start.
3. Stronger material traceability for PMI and corrosion-critical service.
For nickel alloy procurement, PMI and heat traceability are a serious risk-control issue because similar-looking alloys differ in Nb, Mo, Fe, and C limits. Industry PMI guidance specifically highlights niobium content as a key differentiator for Alloy 625-family materials and recommends structured documentation tied to heat number and test records. We build that into supply with heat-level traceability, MTC review, and PMI support when requested.
Applicable Standards
| System |
Brief reference |
| ASTM |
ASTM B444 is the alloy-specific seamless tube standard; ASTM B829 covers the general seamless nickel alloy tube requirements. |
| ASME |
ASME SB-444 is the boiler and pressure-vessel adoption route of ASTM B444 for pressure equipment procurement. ASTM B444 itself notes related ASME Code applications. |
| EN |
For Alloy 625 equivalency, the commonly cross-referenced EN material designation is W.Nr. 2.4856 / NiCr22Mo9Nb. |
| GOST |
In many export inquiries, GOST is handled as an equivalent-grade cross-reference rather than a direct one-to-one B444 tube standard; project buyers usually keep ASTM B444 as the governing product specification and map the alloy designation separately. This is a procurement practice inference based on how ASTM and EN references are commonly published. |
| JIS |
JIS buyers often cross-reference by alloy designation rather than by a direct B444-equivalent seamless tube standard, so ASTM B444 remains the controlling tube specification for export orders unless the customer specifies otherwise. This is also a procurement-side inference. |
| GB |
Chinese buyers commonly cross-reference N06625 to local designations such as NS336 / NiCr22Mo9Nb while keeping ASTM B444 as the governing export tube standard. |
Application Field
Wet flue gas desulfurization absorber spray header tube
For one concrete product application, ASTM B444 UNS N06625 tube is widely suited to absorber spray header tubing in wet FGD systems, where chloride-bearing condensate, acidic environments, and the need for reliable weldability and corrosion resistance make Alloy 625 a practical choice. Alloy 625 is also widely recognized for strong seawater and mixed-acid corrosion resistance.
Chemical Composition
ASTM B444 formally covers three UNS alloy designations and four orderable conditions. Because you requested a 5-grade comparison table, the fifth row below is a widely used EN-equivalent sourcing reference for UNS N06625, clearly marked as an equivalent rather than an additional ASTM B444 alloy.
| Grade |
Standard / Reference |
C % |
Mn % |
Si % |
P % |
S % |
Cr % |
Mo % |
Nb+Ta / Nb % |
Fe % |
Al % |
Ti % |
Co % |
Cu % |
Ni % |
| UNS N06625 Grade 1 |
ASTM B444 |
≤0.10 |
≤0.50 |
≤0.50 |
≤0.015 |
≤0.015 |
20.0-23.0 |
8.0-10.0 |
3.15-4.15 (Nb+Ta) |
≤5.0 |
≤0.40 |
≤0.40 |
≤1.0 |
— |
≥58.0 |
| UNS N06625 Grade 2 |
ASTM B444 |
≤0.10 |
≤0.50 |
≤0.50 |
≤0.015 |
≤0.015 |
20.0-23.0 |
8.0-10.0 |
3.15-4.15 (Nb+Ta) |
≤5.0 |
≤0.40 |
≤0.40 |
≤1.0 |
— |
≥58.0 |
| UNS N06219 |
ASTM B444 |
≤0.05 |
≤0.50 |
0.70-1.10 |
≤0.020 |
≤0.010 |
18.0-22.0 |
7.0-9.0 |
— |
2.0-4.0 |
≤0.50 |
≤0.50 |
≤1.0 |
≤0.50 |
Balance |
| UNS N06852 |
ASTM B444 |
≤0.05 |
≤0.50 |
≤0.50 |
≤0.015 |
≤0.015 |
20.0-23.0 |
8.0-10.0 |
0.51-1.00 (Nb) |
15.0-20.0 |
≤0.40 |
≤0.40 |
— |
— |
Balance |
| W.Nr. 2.4856 / NiCr22Mo9Nb |
EN-equivalent reference for Alloy 625 |
0.03-0.10* |
≤0.50 |
≤0.40 |
≤0.01 |
≤0.01 |
21.0-23.0 |
8.0-10.0 |
3.2-3.8 (Nb+Ta) |
≤5.0 |
≤0.40 |
≤0.40 |
≤1.0 |
up to 0.50 in some specs* |
58.0-71.0 |
Mechanical Properties
| Grade |
Condition |
Tensile Strength |
Yield Strength (0.2% offset) |
Elongation |
| UNS N06625 Grade 1 |
Annealed |
≥120 ksi / 827 MPa |
≥60 ksi / 414 MPa |
≥30% |
| UNS N06625 Grade 2 |
Solution annealed |
≥100 ksi / 690 MPa |
≥40 ksi / 276 MPa |
≥30% |
| UNS N06219 |
Solution annealed |
≥96 ksi / 660 MPa |
≥39 ksi / 270 MPa |
≥30% |
| UNS N06852 |
Solution annealed |
≥85 ksi / 586 MPa |
≥35 ksi / 241 MPa |
≥30% |
| W.Nr. 2.4856 / VDM Alloy 625 |
Room-temperature minimum short-time properties |
≥105.9 ksi / 730 MPa |
≥47.9 ksi / 330 MPa |
≥35% |
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