ASTM B366 — Factory-Made Wrought Nickel and Nickel Alloy Fittings
ASTM B366 (latest edition: B366-22) is the benchmark specification for wrought nickel and nickel alloy butt-welding pipe fittings for severe corrosion, high-temperature, and cryogenic service where stainless steel is insufficient. ASME SB-366 is adopted in BPVC Section II Part B. Products include elbows (LR/SR), tees, reducers, caps, and crosses to ASME B16.9 / ASME B16.28 dimensions, covering alloys from pure nickel to complex Ni-Cr-Mo-W superalloys.
1. Scope and Applicable Standards
| Standard |
Scope |
| ASTM B366 / ASME SB-366 |
Wrought nickel alloy butt-welding fittings (this specification) |
| ASTM B444 / ASME SB-444 |
Alloy 625 seamless pipe and tube (parent material for 625 fittings) |
| ASTM B622 / ASME SB-622 |
Hastelloy C-276 / C-22 seamless pipe and tube |
| ASTM B564 / ASME SB-564 |
Nickel alloy forgings (flanges and fittings) |
| ASME B16.9 |
Dimensional standard for factory-made fittings NPS ½–72 |
2. Grade Designations
| B366 Designation |
UNS No. |
Trade Name |
Alloy System |
Key Attribute |
| WPHC200 |
N02200 |
Nickel 200 |
Pure Ni (99.6%) |
Caustic soda, HF, food processing |
| WPHC201 |
N02201 |
Nickel 201 |
Low-C pure Ni |
Caustic >300 °C, eliminates graphite precipitation |
| WPMC400 |
N04400 |
Monel 400 |
Ni-Cu (63Ni-31Cu) |
Seawater, HF, dilute H₂SO₄, brine |
| WPHX |
N06002 |
Alloy X (Hastelloy X) |
Ni-Cr-Mo-Fe |
Gas turbine, high-temperature oxidising |
| WPNiCu30 |
N05500 |
Monel K-500 |
Ni-Cu age-hardened |
Seawater pump shafts, high strength |
| WPNCrFe (600) |
N06600 |
Inconel 600 |
Ni-Cr-Fe |
High-temperature oxidation, nuclear (dry conditions) |
| WPNCrMo3 (625) |
N06625 |
Inconel 625 |
Ni-Cr-Mo-Nb |
Most versatile: cryogenic, seawater, sour gas, high-temperature |
| WPNMH (B-2) |
N10665 |
Hastelloy B-2 |
Ni-Mo (28Mo) |
HCl, H₂SO₄ (reducing), H₃PO₄ |
| WPNC276 (C-276) |
N10276 |
Hastelloy C-276 |
Ni-Mo-Cr-W |
Broadest acid resistance: oxidising + reducing, FGD |
| WPNC22 (C-22) |
N06022 |
Hastelloy C-22 |
Ni-Cr-Mo-W |
Better oxidising resistance than C-276; Cl₂, bleach solutions |
| WPNiCrMo (825) |
N08825 |
Incoloy 825 |
Ni-Fe-Cr-Mo-Cu |
H₂SO₄, H₃PO₄, seawater, sour gas (cost-effective) |
3. Chemical Composition (Selected Grades)
| Grade |
Ni |
Cr |
Mo |
Fe max |
Cu |
Others |
| Nickel 200 |
≥99.0 |
— |
— |
0.40 |
0.25 |
C ≤0.15, Mn ≤0.35 |
| Monel 400 |
63.0 min |
— |
— |
2.50 |
28.0–34.0 |
Mn ≤2.0 |
| Inconel 600 |
72.0 min |
14.0–17.0 |
— |
10.0 |
0.50 |
C ≤0.15 |
| Inconel 625 |
58.0 min |
20.0–23.0 |
8.0–10.0 |
5.0 |
— |
Nb+Ta 3.15–4.15 |
| Hastelloy B-2 |
Balance |
1.0 max |
26.0–30.0 |
2.0 |
— |
Co ≤1.0 |
| Hastelloy C-276 |
Balance |
14.5–16.5 |
15.0–17.0 |
4.0–7.0 |
— |
W 3.0–4.5, Co ≤2.5 |
| Hastelloy C-22 |
Balance |
20.0–22.5 |
12.5–14.5 |
2.0–6.0 |
— |
W 2.5–3.5, Co ≤2.5 |
| Incoloy 825 |
38.0–46.0 |
19.5–23.5 |
2.5–3.5 |
22.0 min |
1.5–3.0 |
Ti 0.6–1.2 |
4. Mechanical Properties
| Grade |
UTS min (MPa) |
YS min (MPa) |
Elong. min (%) |
| Nickel 200 / 201 |
380 |
105 |
35 |
| Monel 400 |
485 |
170 |
35 |
| Inconel 600 |
550 |
240 |
30 |
| Inconel 625 |
690 |
275 |
30 |
| Hastelloy B-2 |
690 |
310 |
40 |
| Hastelloy C-276 |
690 |
280 |
40 |
| Hastelloy C-22 |
690 |
310 |
45 |
| Incoloy 825 |
586 |
241 |
30 |
5. Heat Treatment and Annealing
| Grade |
Anneal Temperature (°C) |
Cooling |
| Nickel 200 / 201 |
700–925 |
Air cool or water quench |
| Monel 400 |
760–870 |
Air cool |
| Inconel 600 |
980–1065 |
Rapid air cool or water quench |
| Inconel 625 |
1095–1175 (solution anneal) |
Water quench |
| Hastelloy B-2 / C-276 / C-22 |
1065–1175 (solution anneal) |
Water quench (mandatory) |
| Incoloy 825 |
930–980 |
Water quench or rapid cool |
PMI requirement: ASTM B366 strongly recommends Positive Material Identification (PMI) via XRF or OES for all nickel alloy fittings. Visual appearance and weight are insufficient to distinguish alloys — e.g., C-276 and 316L stainless steel look identical. Hastelloy B-2 is particularly hazardous if misidentified in oxidising-acid service (immediate corrosion failure).
6. Corrosion Environment — Alloy Selection Guide
| Corrosive Medium |
Recommended Grade(s) |
Note |
| Hot concentrated NaOH (caustic) |
Nickel 200 / 201 |
Use 201 (low-C) above 300 °C to avoid graphite precipitation |
| Hydrofluoric acid (HF) |
Monel 400 |
Best cost-effective option; Ni 200 also suitable |
| Seawater (ambient) |
Inconel 625, Monel 400 |
625 for highest pitting resistance; 400 for lower cost |
| Hydrochloric acid (HCl, reducing) |
Hastelloy B-2 / B-3 |
Do NOT use B-2 in oxidising acids — catastrophic corrosion |
| Mixed oxidising/reducing acids |
Hastelloy C-276, C-22 |
C-22 better for highly oxidising; C-276 for reducing-heavy media |
| Flue gas desulfurisation (FGD) |
Hastelloy C-276, C-22 |
Hot Cl⁻ + SO₄²⁻ + HF attack; C-276 widely proven |
| H₂SO₄ (moderate) |
Incoloy 825, C-276 |
825 cost-effective for dilute/moderate H₂SO₄ |
| Sour gas (H₂S + CO₂) |
Inconel 625, Incoloy 825 |
NACE MR0175 compliance required; both permitted |
7. How to Order
| # |
Item |
Example |
| 1 |
Standard |
ASTM B366-22 or ASME SB-366 |
| 2 |
Grade / UNS No. |
Inconel 625 / UNS N06625, or Hastelloy C-276 / N10276 |
| 3 |
Fitting type & NPS |
90° LR Elbow, NPS 4, Sch 40S |
| 4 |
Dimensional standard |
ASME B16.9 |
| 5 |
Heat treatment |
Solution annealed (state temperature range) |
| 6 |
PMI |
100% XRF PMI required (specify in PO) |
| 7 |
Certificate |
EN 10204 3.1 MTR; NACE MR0175 compliance if applicable |
HT PIPE supplies ASTM B366 nickel alloy fittings in Alloy 625, C-276, C-22, Monel 400, and Incoloy 825 with full EN 10204 3.1 and PMI certification. Contact us for dimensional and material specifications.
8. Frequently Asked Questions
Q1: Why is Hastelloy B-2 dangerous in oxidising environments?
Hastelloy B-2 (Ni-28Mo) lacks chromium and therefore has no passive oxide film in oxidising environments. In the presence of oxidising agents (Fe³⁺, Cu²⁺, dissolved O₂, HNO₃), B-2 corrodes rapidly at rates exceeding 25 mm/year. Even a small amount of oxidising contamination in an HCl stream can cause catastrophic failure. Always verify process chemistry is strictly non-oxidising before specifying B-2.
Q2: Can Inconel 625 fittings be used in cryogenic service?
Yes. Inconel 625 (N06625) retains excellent ductility and toughness at cryogenic temperatures down to –196 °C, making it suitable for LNG, liquid oxygen, and liquid nitrogen piping systems where simultaneous corrosion resistance and low-temperature performance are required. It is one of few materials approved for both cryogenic and elevated-temperature (to 816 °C) service under ASME BPVC.
