ASTM B622 UNS N06022 Pipe

ASTM B622 UNS N06022 Pipe is a nickel-chromium-molybdenum alloy designed for the most aggressive mixed-acid environments in chemical processing. Compared with the more familiar C276, C22 carries higher chromium (20–22.5% vs 14.5–16.5%) and slightly lower molybdenum (12.5–14.5% vs 15.0–17.0%) - a deliberate trade that gives C22 stronger resistance to oxidizing acids (nitric, ferric, cupric) and mixed-acid streams, while C276 retains an edge in pure reducing acids (pure HCl, HF at high temperature).

Chemical Composition (ASTM B622 / DIN 2.4602)

Element	ASTM B622 Range (%)	Function in the Alloy
Nickel	Balance	Austenitic matrix, base element
Chromium	20.0–22.5	Oxidation resistance, passivation in oxidizing acids
Molybdenum	12.5–14.5	Reducing acid resistance, chloride pitting resistance
Iron	2.0–6.0	-
Tungsten	≤ 2.5	Localized corrosion resistance (lower than C276)
Cobalt	≤ 2.5	Residual from melt
Carbon	≤ 0.015	Low carbon for weldability and corrosion resistance
Manganese	≤ 0.50	Deoxidation residual
Silicon	≤ 0.08	-
Phosphorus	≤ 0.020	-
Sulfur	≤ 0.020	-
Vanadium	≤ 0.35	-

 

The composition comparison with C276 explains the application split:

Element	C22 (N06022)	C276 (N10276)	Effect on Service
Chromium	20.0–22.5%	14.5–16.5%	C22 better in oxidizing acids (HNO₃, Fe³⁺, Cu²⁺)
Molybdenum	12.5–14.5%	15.0–17.0%	C276 better in pure HCl, HF
Tungsten	≤ 2.5%	3.0–4.5%	C276 stronger reducing acid resistance
Iron	2.0–6.0%	4.0–7.0%	Similar

Selection rule for buyers: oxidizing acid or mixed acid service → C22; pure reducing acid (HCl, HF) → C276.

 

Mechanical Properties

Property	Value at 20°C	At 200°C	At 300°C	At 400°C
Tensile strength, min	690 MPa	~640	~615	~590
Yield strength (0.2% offset), min	310 MPa	~250	~230	~215
Elongation, min	45%	-	-	-
Hardness, max	HRB 100	-	-	-
Density	8,690 kg/m³	-	-	-
Elastic modulus	205 GPa	195 GPa	188 GPa	180 GPa

 

Note on pressure design: C22 yield strength (310 MPa) is lower than duplex 2205 (485 MPa) and 316L (220 MPa). For the same design pressure and diameter, C22 walls are typically 30–40% thicker than equivalent 2205 pipe. The trade is corrosion resistance, not strength.

 

Corrosion Resistance Data

The following data combines ASTM standard tests and Haynes International published isocorrosion data:

Test / Service	Condition	C22 Rate	C276 Rate	Notes
ASTM G48 Method A	6% FeCl₃, 50°C, 24h	No pitting	No pitting	Both alloys pass
ASTM G48 Method B	6% FeCl₃, ramped temperature	CPT 75–85°C	CPT 80–90°C	C276 slightly higher
ASTM G28 Method A	Boiling 50% H₂SO₄ + Fe₂(SO₄)₃	< 0.30 mm/yr	< 0.20 mm/yr	C276 slightly better in this test
Hydrochloric acid, 1%	Boiling	0.15 mm/yr	0.10 mm/yr	Both suitable
Hydrochloric acid, 5%	Boiling	0.25 mm/yr	0.20 mm/yr	Both suitable
Sulfuric acid, 10%	Boiling	0.08 mm/yr	0.10 mm/yr	C22 better
Sulfuric acid, 50%	Boiling	0.30 mm/yr	0.25 mm/yr	Both borderline
Nitric acid, 65%	Boiling	0.05 mm/yr	0.40 mm/yr	C22 clearly superior
Wet phosphoric acid (54% P₂O₅)	90°C	0.12 mm/yr	0.15 mm/yr	C22 better
Seawater	30°C	< 0.01 mm/yr	< 0.01 mm/yr	Both fully resistant

 

Application guidance:

Wet phosphoric acid (WPA) production → C22 is the standard specification

FGD absorber spray headers and slurry recycle → C22 (C276 also acceptable)

Waste incineration flue gas treatment → C22 per NORSOK M-630 Grade 2

Pure HCl / HF at high temperature → C276 preferred

Hot concentrated H₂SO₄ (>30%, >100°C) → consider C276 or higher-nickel alloys

 

Dimensions, Standards, and Tolerances

Parameter	Range
Outside diameter	6.0–406.4 mm (1/8″ – 16″)
Wall thickness	Sch 5S – Sch 160, custom walls on request
Standard (seamless)	ASTM B622 / ASME SB622
Standard (welded)	ASTM B619 / ASME SB619
Surface finish	Pickled & annealed (standard), bright annealed (BA) on request
Length	Random 4–12 m, cut-to-length ± 3 mm
OD tolerance	± 0.5% per ASTM B622 Table 3
Wall tolerance	± 12.5%
Straightness	≤ 1.5 mm/m

 

HUITONG stocking program covers the most-requested specifications:

Size	Schedule	Length	Typical Application
DN15 – DN50 (1/2″ – 2″)	Sch 40S, Sch 80S	6 m	Sample lines, instrument tubing
DN65 – DN150 (2½″ – 6″)	Sch 40S, Sch 80S	6 m / cut-to-length	Process piping, FGD spray headers
DN200 – DN300 (8″ – 12″)	Sch 40S	6 m / cut-to-length	Main process lines, slurry recycle
DN350 – DN400 (14″ – 16″)	Sch 20 – Sch 40	Cut-to-length	Large-diameter flue gas ducts

 

Applications

1. Wet Process Phosphoric Acid (WPA) Production

Major WPA producers - OCP (Morocco), Ma'aden (Saudi Arabia), Yuntianhua (China), IFFCO (India) - specify C22 for the 30–54% P₂O₅ concentration section and the defluorination piping. WPA contains 1–2% free sulfuric acid plus dissolved fluoride and SiF₆²⁻ complexes; this mixed-acid environment is exactly where C22 outperforms C276.

Typical specification: ASTM B622 seamless, DN50–DN150, Sch 40–Sch 80, pickled & annealed, solution-annealed after fabrication welds.

 

2. FGD Scrubber Systems

Coal-fired power plant FGD absorbers circulate CaCl₂/MgCl₂ slurry with residual HCl and HF at 40–60°C. Chloride content reaches 30,000–50,000 ppm. C22 is the standard specification for absorber spray headers, slurry recycle piping, and mist eliminator wash headers in European and Chinese coal-fired plants.

 

Operating data from German RWE and EnBW coal-fired units: duplex 2205 in FGD slurry typically requires replacement after 8–12 years; C22 in the same service has documented service life exceeding 20 years. For operators running 30+ year plant lives, C22 delivers lower life-cycle cost despite higher initial material cost.

 

3. Waste Incineration Flue Gas Treatment

Municipal waste incinerators in Switzerland, Germany, the Nordics, and Japan treat flue gas containing HCl, SO₂, HF, and heavy metal vapors at 200–350°C. C22 pipe is specified for the wet scrubber circulation loop, the quench piping, and the gas-to-gas heat exchanger (GGH) tubing.

Reference standards: NORSOK M-630 (offshore flue gas), VDI 2452 (German incinerator standard), and the operator-specific specifications of major European utilities.

 

Welding Procedure

C22 weldability is good when the heat input and interpass temperature are controlled. The recommended procedure:

Parameter	Recommendation
Welding process	GTAW (TIG) for root, GMAW (MIG) for fill
Filler metal	ERNiCrMo-10 (AWS A5.14)
Heat input	≤ 1.0 kJ/mm (stringent for corrosive service)
Interpass temperature	≤ 100°C
Pre-weld cleaning	Acetone degrease, dedicated stainless wire brush, no carbon steel tooling cross-contamination
Post-weld treatment	Solution anneal 1120°C / water quench for severe corrosive service; pickle + passivate as minimum
Avoid	SMAW (stick) with cellulosic-coated electrodes - moisture pickup risk; no preheating above 100°C

For fabricated pipe spools in C22, the typical practice is shop fabrication with GTAW root + GMAW fill, full solution anneal after welding, then hydrostatic test and PMI verification before despatch.

 

 

 

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