ASTM B676 / ASME SB676 is the standard specification by ASTM International covering UNS N08367 (commercial grade AL-6XN, 1.4547) welded tube for general corrosion applications. The specification defines two NDT grades — Grade 1 (100% NDT) and Grade 2 (batch NDT) — and covers outside diameters from 1/8 to 5 inches (3.2–127 mm). The latest edition is ASTM B676-19 (reapproved 2024).
Zhengzhou Huitong (HT Pipe) supplies ASTM B676 UNS N08367 welded tube in solution-annealed condition with full Mill Test Certificates (MTC) per EN 10204 3.1.
1. Standard Scope & Designation
ASTM B676 covers UNS N08367 and UNS N08366 welded tube for general corrosion applications. The alloy is a super austenitic stainless steel characterized by high molybdenum (6%) and nitrogen (0.18–0.25%) content, providing exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-rich environments.
| Designation |
Issuing Body |
Common Trade Name |
Latest Edition |
| ASTM B676 |
ASTM International |
AL-6XN (N08367), 1.4547 |
B676-19 (2024) |
| ASME SB676 |
ASME (Section II Part B) |
Identical to ASTM B676 |
ASME SB676-2023 |
Scope Statement (ASTM B676-19): "This specification covers UNS N08367 welded tube for general corrosion applications. This specification covers outside diameter and nominal wall tube." The 2024 reapproval confirms the standard remains current for procurement.
| Parameter |
Imperial |
Metric |
| Outside Diameter Range |
1/8 – 5 in |
3.2 – 127 mm |
| Wall Thickness Range |
0.015 – 0.320 in |
0.38 – 8.13 mm |
| Manufacturing Process |
ERW or HFW Welded |
Electric Resistance / HFW |
| Heat Treatment |
Solution Annealed |
Solution Annealed |
| PREN (Pitting Resistance) |
45 – 48 |
45 – 48 |
| Density |
0.298 lb/in³ |
8.24 g/cm³ |
2. Grades Covered by ASTM B676
| Grade |
UNS No. |
NDE Requirement |
Typical Application |
| Grade 1 |
N08367 |
100% NDT (hydrostatic + eddy current) |
Nuclear, subsea, critical process, pharmaceutical |
| Grade 2 |
N08367 |
Batch sampling NDT |
General seawater, chemical processing, desalination |
UNS N08367 vs N08366: Both grades are covered by ASTM B676-19 (2024). N08367 (AL-6XN) has higher nitrogen (0.18–0.25%) resulting in yield strength of 295 MPa vs. lower for N08366. N08367 is the commercially dominant grade. PREN of N08367: Cr (20–22%) + 3.3 × Mo (6–7%) + 16 × N (0.18–0.25%) ≈ 45–48.
3. Chemical Composition — UNS N08367 (AL-6XN) per ASTM B676 Table 1
Values are maximum unless shown as a range. Heat and product analysis per ASTM B676-19.
| Element |
UNS N08367 (%) |
Key Role |
| Carbon (C) |
0.030 max |
Intergranular corrosion resistance (low carbon) |
| Manganese (Mn) |
2.00 max |
Deoxidizer, Austenite stabilizer |
| Silicon (Si) |
1.00 max |
Deoxidizer |
| Phosphorus (P) |
0.040 max |
Impurity (keep low) |
| Sulfur (S) |
0.030 max |
Impurity (keep low) |
| Chromium (Cr) |
20.0 – 22.0 |
Core alloying elements |
| Nickel (Ni) |
23.5 – 25.5 |
| Molybdenum (Mo) |
6.0 – 7.0 |
Key PREN drivers for chloride pitting resistance |
| Nitrogen (N) |
0.18 – 0.25 |
| Copper (Cu) |
0.75 max |
Sulfuric acid resistance |
| Iron (Fe) |
Balance |
Structural matrix |
Note: PREN = Cr + 3.3×Mo + 16×N = 20–22 + 3.3×(6–7) + 16×(0.18–0.25) ≈ 45–48. For comparison, 316L SS has PREN ~24.
4. Mechanical Property Requirements — Solution Annealed (ASTM B676 Table 2)
All values are minimum requirements per ASTM B676-19 (2024 reapproval).
| Property |
Value (Metric) |
Value (Imperial) |
Notes |
| Tensile Strength (UTS) |
655 MPa |
95 ksi |
Minimum, solution annealed |
| Yield Strength (0.2% offset) |
295 MPa |
43 ksi |
~2× that of 316L stainless steel |
| Elongation in 2 in. (50 mm) |
30% |
30% |
Minimum, in any direction |
| Low-Temperature Service |
Down to –196°C |
Down to –321°F |
LN₂, LPG, cryogenic service |
| Hardness (Rockwell B) |
≤ 100 HRB |
≤ 100 HRB |
Typical for solution annealed |
Yield Strength Comparison: UNS N08367 yield strength (295 MPa / 43 ksi) is approximately double that of conventional 316L stainless steel (~200 MPa / 29 ksi). This allows tube wall thickness reduction in pressure vessel and heat exchanger applications while maintaining equivalent burst pressure ratings.
5. Heat Treatment Requirements
| Condition |
Temperature Range |
Purpose |
| Solution Annealing (Standard) |
1121–1204°C (2050–2200°F) |
Dissolves carbides and intermetallics; maximizes corrosion resistance |
| Water Quench (preferred) |
Fast cool from temperature |
Prevents chromium carbide precipitation at grain boundaries |
Critical: UNS N08367 must be rapidly cooled (water quench preferred) from the solution annealing temperature to prevent sensitization. Slow cooling can allow chromium carbide precipitation at grain boundaries (580–870°C / 1075–1600°F "sensitization range"), degrading corrosion resistance. Mandatory intergranular corrosion test per ASTM B676.
6. Testing & Inspection Requirements
| Test |
Requirement |
Reference Standard |
| Chemical Analysis |
One per heat; all elements per Table 1 |
ASTM B676 Table 1 |
| Tensile Test |
One per lot; verifies UTS, YS, El% |
ASTM E 8 / ASTM E 370 |
| Flattening Test |
Mandatory for both welded joint and base metal |
ASTM B676 |
| Intergranular Corrosion Test |
Mandatory — copper-copper sulfate in sulfuric acid (HNO₃) method |
ASTM A 262 Practice E |
| Hydrostatic Test (Grade 1) |
100% of each tube; tested per agreed pressure |
ASTM B676 |
| Eddy Current Test (Grade 1) |
100% inspection of weld seam and tube body |
ASTM E 571 |
| Eddy Current Test (Grade 2) |
Batch sampling per agreement |
ASTM E 571 |
7. Tube Dimensions — ASTM B676 (OD & Wall Ranges)
ASTM B676 covers OD from 1/8" to 5" (3.2–127 mm) and wall thickness from 0.015" to 0.320" (0.38–8.13 mm). Standard tolerances per ASTM B829.
| NPS |
OD (in) |
OD (mm) |
0.020" Wall
(mm) |
0.035" Wall
(mm) |
0.049" Wall
(mm) |
0.065" Wall
(mm) |
0.083" Wall
(mm) |
| 1/4 |
0.250 |
6.35 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 3/8 |
0.375 |
9.53 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 1/2 |
0.500 |
12.70 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 3/4 |
0.750 |
19.05 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 1 |
1.000 |
25.40 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 1-1/2 |
1.500 |
38.10 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 2 |
2.000 |
50.80 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 2-1/2 |
2.500 |
63.50 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 3 |
3.000 |
76.20 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 4 |
4.000 |
101.60 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
| 5 |
5.000 |
127.00 |
0.51 |
0.89 |
1.24 |
1.65 |
2.11 |
Note: For common heat exchanger and instrumentation sizes. Full dimensional tables per ASTM B829 tolerances. Wall thickness tolerance: Average ±10–12.5% per OD range. OD tolerance: ±0.05–0.13 mm for small OD; ±0.25 mm for larger OD.
8. Industries & Applications
| Industry |
Recommended Grade |
Why N08367 / AL-6XN |
| Seawater Cooling Systems |
Grade 1 (100% NDT) |
PREN 45–48 withstands 35,000+ ppm Cl⁻ in seawater |
| Desalination Plants (MED/RO) |
Grade 1 or 2 |
High chloride in brine concentrate streams |
| Offshore Oil & Gas Platforms |
Grade 1 |
Subsea injection water, produced water handling |
| Pulp & Paper (Bleach Plants) |
Grade 2 |
Chloride-rich bleaching chemicals, acidic media |
| Pharmaceutical & Biotech |
Grade 1 (sanitary) |
CIP/SIP compatibility, no metal ion contamination |
| Chemical Processing |
Grade 2 |
Halide acids (HCl, HF), sour environments |
9. UNS N08367 (AL-6XN) vs 316L vs 904L — Comparison
| Property |
UNS N08367 (AL-6XN) |
316L Stainless |
904L Stainless |
| Molybdenum (Mo) |
6.0–7.0% |
2.0–3.0% |
4.0–5.0% |
| Nickel (Ni) |
23.5–25.5% |
10.0–14.0% |
23.0–28.0% |
| Nitrogen (N) |
0.18–0.25% |
0.10 max |
0.15 max |
| PREN (approx.) |
45–48 |
~24 |
~34 |
| Min. Yield Strength |
295 MPa (43 ksi) |
170 MPa (25 ksi) |
220 MPa (32 ksi) |
| Min. Tensile Strength |
655 MPa (95 ksi) |
485 MPa (70 ksi) |
490 MPa (71 ksi) |
| Seawater Resistance |
Excellent |
Limited |
Good |
| Cost Level |
Higher |
Lower |
Moderate |
Material Selection Guide: For seawater service (3.5% NaCl, up to 50°C), UNS N08367 is recommended. For moderate chloride environments (up to 1,000 ppm Cl⁻), 316L may suffice. For severe acid media or mixed acid, 904L or N08367 is preferred. Cost optimization: use N08367 only where 316L/904L cannot provide adequate service life.
10. Related Standards
| Standard |
Scope |
Relationship to B676 |
| ASTM B690 |
UNS N08367 Seamless Pipe (OD > 5 in) |
Seamless complement for larger OD pipe |
| ASTM B829 |
General Requirements for Nickel and Nickel Alloy Seamless Pipe and Tube |
Mandatory general requirements document |
| ASME SB676 |
ASME Section II Part B — Welded Tube adoption |
Identical requirements; ASME Code compliance |
| ASTM A 262 E |
Practice E — Intergranular Corrosion Testing |
Mandatory corrosion test method |
| ASTM E 571 |
Eddy Current Testing of Nickel Alloy Tube |
Grade 1 mandatory; Grade 2 per agreement |
| ASTM E 8 |
Tensile Testing of Metallic Materials |
Mechanical test method |
| ASTM B673 |
UNS N08367 Welded Tube (Sanitary Applications) |
Sanitary/BPE tube variant of B676 |
| EN 10216-5 |
Seamless Stainless Steel Tube — EN equivalent |
European standard for 6Mo seamless tube |
11. How to Order — Required Information
| No. |
Item |
Requirement / Example |
| 1 |
Specification |
ASTM B676 / ASME SB676 |
| 2 |
Grade |
UNS N08367 (AL-6XN) — Grade 1 (100% NDT) or Grade 2 |
| 3 |
Outside Diameter & Wall Thickness |
e.g., 1/2 in OD × 0.035 in wall; or 25.40 mm × 0.89 mm |
| 4 |
Length |
Single random (~6 m); Double random (~12 m); Cut-to-length |
| 5 |
Finish |
Bright annealed (BA), pickled, or mill finish |
| 6 |
End Preparation |
Plain end (PE), beveled end (BE), or with couplings |
| 7 |
Supplementary Tests |
Intergranular corrosion test (mandatory), PMI, hydrostatic, PMI verification |
| 8 |
Certification |
EN 10204 3.1 Certified Mill Test Report (CMTR) |
| 9 |
Quantity |
Lineal meters or pieces |
12. Frequently Asked Questions
Q: What is the difference between ASTM B676 and ASTM B690?
ASTM B676 covers welded tube (OD 1/8 to 5 in). ASTM B690 covers seamless pipe in the same alloy (UNS N08367) for larger OD applications (typically NPS 1/8 to NPS 10+). For applications requiring seamless construction or diameters above 5 inches, specify ASTM B690 (ASME SB690). Both share identical chemical composition and mechanical property requirements.
Q: Why is UNS N08367 called "6Mo" stainless steel?
"6Mo" refers to the approximately 6% molybdenum content — the defining feature distinguishing super austenitic stainless steels from standard austenitic (316L has 2–3% Mo). The high Mo, combined with high nitrogen (0.18–0.25%), gives UNS N08367 a PREN of 45–48 — roughly double that of 316L. This enables service in seawater and chloride media where 316L would pit and fail prematurely.
Q: Is ASTM B676 welded tube suitable for high-pressure applications?
Yes. ASTM B676 welded tube is suitable for pressure-boundary applications in heat exchangers, condensers, and piping systems. The weld seam must pass flattening tests and eddy current inspection (Grade 1: 100% inspection). Hydrostatic test pressure is calculated per agreed formula. Design pressure-temperature ratings per applicable code (ASME B31.1, B31.3, or ASME BPVC).
Q: What filler metal is used for welding UNS N08367 tube?
For matching filler metal, AWS A5.14 ERNiCrMo-3 (Inconel 625) or ERNiCrMo-4 is commonly used. ERNiFeCr-2 (Alloy 617) is also acceptable. Post-weld heat treatment is generally not required. The welded joint retains the corrosion resistance of the base metal if proper welding procedures (controlled heat input, interpass temperature < 150°C/300°F) are followed.
Q: Can UNS N08367 tube replace 904L stainless steel?
Yes, in most cases. UNS N08367 has superior pitting resistance (PREN 45–48 vs ~34 for 904L) and higher mechanical strength (YS 295 MPa vs 220 MPa). For seawater service or chloride concentrations above ~2,000 ppm, N08367 is recommended. For moderate chloride service, 904L may be a cost-effective alternative. The decision should be based on life-cycle cost analysis including expected service conditions and required service life.
Request a Quote — ASTM B676 UNS N08367 Welded Tube
Zhengzhou Huitong (HT Pipe) supplies ASTM B676 / ASME SB676 UNS N08367 (AL-6XN) welded tube in Grade 1 (100% NDT) and Grade 2. Full EN 10204 3.1 CMTRs, intergranular corrosion test reports, and competitive lead times from stock and mill.
