UNS N08031|1.4562|Alloy 31 Seamless Tube

Seamless Alloy 31 Tubes (UNS N08031 / W.Nr. 1.4562) are high-performance iron-nickel-chromium-molybdenum solutions engineered for extreme resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC). As a premier manufacturer based in Wenzhou, China, XinZhe produces high-integrity seamless tubing that strictly adheres to ASTM B622 and ASME SB622 international standards.

Distinguished by a high Pitting Resistance Equivalent Number (PREN ≥ 48), our Alloy 31 tubing excels in aggressive environments containing hot concentrated phosphoric acid, sulfuric acid, and high-chloride media. With mechanical strength significantly surpassing standard austenitic steels, these tubes are indispensable for mission-critical applications in flue gas desulfurization (FGD), chemical reactors, and fine chemical processing. Through advanced cold-drawing and specialized solution annealing, XinZhe ensures every tube maintains a uniform microstructure and maximum durability for the most demanding industrial conditions.

PREN = %Cr + 3.3X(%Mo + 0.5X%W) + 16X%N≥ 48

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What Is a Seamless Alloy 31 Tube?

UNS N08031 (W.Nr. 1.4562), marketed as Alloy 31, is a super austenitic stainless steel with a Fe-Ni-Cr-Mo composition and a PREN of at least 48. It is engineered for extreme corrosive environments and serves as a cost-effective alternative to higher nickel alloys such as Alloy 625 and C276 in many aggressive chemical applications, while retaining good fabrication behaviour.

Seamless Alloy 31 tube (UNS N08031 / W.Nr. 1.4562) is a high-performance super austenitic stainless steel with a Fe–Ni–Cr–Mo composition, specifically engineered for extreme corrosive environments.

Manufactured through a seamless process from solid billets (piercing + cold drawing), it features a fully homogeneous, weld-free structure, ensuring superior pressure resistance and eliminating the risk of weld-related corrosion or failure.

With a high PREN value ≥ 48, Alloy 31 offers exceptional resistance to localized corrosion and serves as a cost-effective alternative to higher nickel alloys such as Alloy 625 and C276 in many aggressive chemical applications.

Key Features and Technical Advantages

Alloy 31 is specifically designed to maintain its strength and shape in high-stress, corrosive environments.

These physical properties highlight the material's ability to perform reliably under a wide range of conditions.

Outstanding Corrosion Resistance

Excellent resistance to pitting, crevice corrosion, and general corrosion in halide-containing media, sulfuric acid (H₂SO₄), and phosphoric acid (H₃PO₄).

High Resistance to Stress Corrosion Cracking (SCC)

Elevated nickel and molybdenum content significantly improves resistance to chloride-induced SCC.

Enhanced Performance in Reducing Acids

The addition of Copper (Cu) and Nitrogen (N) enhances corrosion resistance in strongly reducing environments.

Good High-Temperature Stability

Maintains mechanical integrity at elevated temperatures, outperforming conventional 300-series stainless steels.

Excellent Weldability

Low susceptibility to intergranular corrosion in the heat-affected zone (HAZ), ensuring reliable fabrication performance.

Cost-Effective Alternative to Nickel Alloys

Provides an optimal balance between performance and cost compared to high-grade nickel alloys (e.g., Alloy 625, C276).

Product Specifications and Data

The composition of Alloy 31 is carefully balanced to achieve its superior corrosion resistance and high strength.

Cr	Ni	Mo	Cu	N	Mn	Si	Fe	C
26.00 - 28.00	30.00 - 32.00	6.00- 7.00	1.00 - 1.40	0.15 - 0.25	≤ 2.00	≤ 0.30	Bal	≤ 0.015

Tensile Strength	Yield Strength	Elongation	Hardness	Brinell Hardness
≥ 650 MPa	≥ 275 MPa	≥ 40%	≤ 240 HBW	≤ 217 HB

Density	Melting Point	Thermal Expansion	Thermal Conductivity	Modulus of Elasticity	Electrical Resistivity
8.16 g/cm³	1350 - 1400 °C approx.	13.5 µm/m·°C (20-100°C)	11.5 W/m·K (20°C)	205 GPa	1.05 x 10⁻⁶ Ω·m (20°C)

Standard	OD(D)	Tolerance（MM)		Thickness(S)	Tolerance(MM)	Length	Tolerance
	MM	Common	High	MM			MM
EN 10216-5 HFD	30≤D≤219.1（D2)	±1.0% or ±0.5mm, whicever is the greater(取较大者)		T1, T≤4	±15% or ±0.6mm, whicever is the greater(取较大者)	L≤6M	+5/0
				T2	±12.5% or ±0.4mm, whicever is the greater(取较大者)
	219.1≤D≤610 (D1)	±1.5% or ±0.75mm, whicever is the greater (取较大者)		T≤0.05D	+22.5%/-15%	6≤12	+10/0
				T1, 0.05D≤0.09D	±15% or ±0.6mm, whicever is the greater(取较大者)
				T2, T>0.09D	±12.5% or ±0.4mm, whicever is the greater(取较大者)	L>12	+by agreement/0
EN 10216-5 CFD	D3(D≤219.1)	±0.75% or ±0.3mm, whicever is the greater(取较大者)		T3	±10% or ±0.2mm, whicever is the greater(取较大者)
	D4(D≤219.1)	±0.5% or ±0.mm, whicever is the greater(取较大者)		T4	±7.5% or ±0.15mm, whicever is the greater(取较大者)
ASTM A213 HFD	D≤100	+0.4/-0.8		D<100,S≤2.4	+40%/0	HFD, all size	+5.0/0
		+0.4/-1.2		D<100,2.4≤3.8	+35%/0
		+0.4/-1.6		D<100,3.8≤4.6	+33%/0
				D<100,S>4.6	+28%/0
	100≤200	+0.4/-1.2		D>100, 2.4≤3.8	+35%/0
	200≤225	+0.4/-1.6		D>100,3.8≤4.6	+33%/0
				D>100,S>4.6	+28%/0
ASTM A213 CFD	D<25	±0.10		D≤38.1	+20%/0	CFD, D<50.8	+3.0/0
	25≤D≤40	±0.15
	40	±0.20
	50≤D<65	±0.25
	65≤D<75	±0.30		D>38.1	+22%/0	CFD, D≥50.8	+5.0/0
	75≤D≤100	±0.38
	100≤200	+0.38/-0.64
	200≤225	+0.38/-1.14
ASTM A269	D≤13	±0.13		D≤13	±15%	D<38	+3.2/0
	13	±0.13		13	±10%
	38≤D<89	±0.25				D>38	+4.8/0
	89≤D<140	±0.38
	140≤D<203	±0.76
	203≤D<305	±1.01
	305≤D<356	±1.26
ASTM A270	D<25	±0.13		For weld pipe all size	±12.5%		+3.0/0
	25-50	±0.20
	50-75	±0.25
	75-100	±0.38		For CD SMLS pipe D≤38.1	+20%/0
	100-140	±0.38					+5.0/0
	140-200	±0.75		For CD SMLS pipe D>38.1	+22%/0
	200-300	±1.25

Dimensional Standards and Tolerances

Alloy 31 seamless tubes are supplied to the dimensional tolerances of ASTM B829 / B622 unless a tighter project specification applies.

Common Industrial Applications

Chemical Processing

Reactors and heat exchangers
Sulphuric and phosphoric acid service
Halide-containing process streams

Petrochemical Processing

Process piping and vessels
Acid handling equipment
Heat recovery systems

Pollution Control and FGD

Flue gas desulphurisation scrubbers
Absorber internals
Waste-gas handling pipework

Pulp and Paper Industry

Bleach plant equipment
Digester and liquor lines
Heat exchangers

Quality Assurance and Manufacturing Process

Certification

All Alloy 31 (UNS N08031) tubes are supplied to ASTM B622 / ASME SB622 and ASTM B619 / ASME SB619 with EN 10204 3.1 mill test certificates. Third-party inspection (SGS, BV, TUV, Lloyd's), PMI reports and full heat-number traceability can be provided on request.

Non-Destructive Testing (NDT)

Hydrostatic or eddy-current testing is performed on 100% of tubes. Ultrasonic testing (UT) and dye-penetrant inspection (PT) are available for critical service, with records retained for each production lot.

Material Verification

Positive Material Identification (PMI) and spectrometric analysis confirm that the chemical composition matches the ordered grade and that the ferrite/austenite balance is within the specified range.

Mechanical Testing

Tensile, yield, elongation and hardness tests are carried out per heat. Impact testing can be supplied at the project design temperature for subsea and low-temperature service.

Dimensional Inspection

Outside diameter, wall thickness, ovality and straightness are measured against ASTM A1016 / A1016M or ASTM A789 tolerances. Length, square-cut ends and end-finish conditions are verified before packing.

Alloy 31 vs Alloy 625 / C276 – Technical Comparison

Alloy 31 is a super austenitic stainless steel positioned between the duplex grades and the nickel alloys. Comparing it with Alloy 625 and C276 clarifies where it belongs.

Chemistry and PREN

Alloy 31 (N08031): Fe-Ni-Cr-Mo, PREN ≥ 48, nickel about 31%
Alloy 625 (N06625): Ni-Cr-Mo-Nb, much higher nickel, PREN around 50
C276 (N10276): Ni-Mo-Cr-W, the broadest corrosion envelope of the three

Corrosion Performance

Alloy 31 resists pitting, crevice corrosion and general corrosion in halide-containing media, sulphuric acid and phosphoric acid, with a PREN approaching the nickel alloys. It does not match C276 in reducing acids or in wet chlorine service, and does not match 625 in high-temperature oxidation.

Cost and Fabrication

Alloy 31 costs substantially less than Alloy 625 or C276 because of its lower nickel content, and its austenitic structure is readily formed and welded by standard procedures. That combination makes it the economic answer where the nickel alloys would be over-specified.

Selection Guide

Choose Alloy 31 for aggressive chemical service where a PREN around 48 is sufficient and cost matters
Choose Alloy 625 for high-temperature oxidation and chloride pitting beyond the stainless range
Choose C276 where reducing acids, wet chlorine or mixed chemistry require the broadest envelope

Frequently Asked Questions

What is Alloy 31 tube?

Alloy 31 (UNS N08031 / W.Nr. 1.4562) is a super austenitic stainless steel tube with a Fe-Ni-Cr-Mo composition and a PREN of at least 48, engineered for extreme corrosive environments.

What is the difference between Alloy 31 and Alloy 625?

Alloy 625 is a nickel-based superalloy with much higher nickel content, giving it superior high-temperature oxidation and chloride pitting resistance. Alloy 31 offers a PREN approaching 48 at substantially lower cost, making it the economic answer where the nickel alloys would be over-specified.

What standard covers Alloy 31 tube?

Alloy 31 seamless tube is supplied to ASTM B622 / ASME SB622, with ASTM B829 covering general requirements and ASTM B619 / ASME SB619 applying to welded pipe.

What is Alloy 31 tube used for?

Alloy 31 is used for reactors and heat exchangers in chemical processing, sulphuric and phosphoric acid service, halide-containing process streams, flue-gas desulphurisation equipment and pulp and paper bleach plants.

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Send your Seamless Alloy 31 Tube enquiry with grade, application, size (OD and wall thickness or schedule), quantity, length, end finish and inspection requirements. Our technical team will confirm availability, testing scope and lead time.

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