Alloy 31 Seamless Tube

UNS N08031 | 1.4562 | ASTM B622

Chloride-containing acid streams that would defeat ordinary stainless grades are the reason the Alloy 31 seamless tube (UNS N08031) exists. This high-alloy austenitic nickel-iron-chromium material, with molybdenum and nitrogen, resists localized corrosion in chloride media and attack in selected aggressive acids, which makes it relevant to demanding chemical processing equipment. Acid coolers, chemical process exchangers and corrosive-service evaporators are typical applications. Where a heat-transfer surface sees mixed acidic and chloride-bearing fluids, assess the chemistry on both sides, cleaning solutions included, and give media composition, metal temperature and upset conditions so the duty can be checked against corrosion data. Both faces of the tube wall see service, so neither can be treated as secondary. ASTM B622 can be specified for this seamless tube, whose wall remains seamless through the tubesheet area. For replacement work, send the original dimensions and end details with the finish and inspection documents required, and we will quote the Alloy 31 seamless tube.

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At a glance — Alloy 31 Tube

Specification	ASTM B622 — the edition cited on the PO governs
Ordering basis	OD × wall × length, wall basis stated (minimum or average)
Sourcing range	OD 6 – 257 mm · wall 0.5 – 35 mm · length ≤ 18 m; each standard × OD × wall × length × condition confirmed in writing
Condition	Solution annealed; pickled & passivated, bright annealed or polished
Documents	EN 10204 3.1 MTC as standard (3.2 on request); hydrostatic or NDT electric test on every length

Sourcing capability, not a stock list — availability, MOQ and lead time are stated in the written quotation.

On this page

01Sizes 02Standards 03Chemistry 04Properties 05Dimensions 06Testing & MTC 07Applications 08Selection 09FAQ 10Related

Sizes, Wall Basis and Ordering

Two figures are kept apart here: the overall sourcing range — what we can supply ex-stock or source mill-direct — and the confirmed combination for your order (standard × OD × wall × length × manufacturing condition). The tables state the first; the written quotation fixes the second.

Supply combinations by outside diameter

OD band, mm	Wall range, mm	Supply route (ex-stock / mill-direct)	Order status
≤ 25	0.5 – 3.0	Cold-drawn / cold-pilgered	In stock · 3–7 days / mill-direct · 25–35 days
> 25 – 60	0.8 – 6.0	Cold-drawn	In stock · 3–7 days / mill-direct · 25–35 days
> 60 – 114.3	1.5 – 10.0	Cold-drawn; hot-finished above 8 mm wall	In stock · 3–7 days / mill-direct · 25–35 days
> 114.3 – 219.1	2.5 – 20.0	Hot-finished; cold-finished on request	In stock · 3–7 days / mill-direct · 25–35 days
> 219.1 – 257	4.0 – 35.0	Hot-finished (extruded)	In stock · 3–7 days / mill-direct · 25–35 days

Stock items are marked In stock; everything else is mill-direct with a stated lead time. Wall figures give the range that can be drawn or rolled for that OD band; the ordered wall is always stated with its basis. Above 225 mm OD the tabulated dimensional bands no longer apply and the basis is agreed in writing before the order is accepted.

Ordering options

Item	What can be ordered
Outside diameter	6 – 257 mm — drawn to the ordered OD, not to NPS
Wall thickness	0.5 – 35 mm — minimum or average basis, stated on the order
Length	Random 5–7 m, fixed up to 18 m, or cut to length
Ends	Plain, bevelled, or capped for export packing
Surface	Pickled and passivated, bright annealed, or polished
Delivery condition	Solution annealed; hardness and grain size reported on request

Sizes at the edge of a band, and anything above 225 mm OD, are quoted after technical review. If your enquiry is written in NPS and schedule, the quotation will restate it as OD × wall so both sides work from the same numbers.

Ordering Standards: B622 vs B619

Nickel alloys are not covered by A213 or A312. Each alloy carries its own B-series specification, and the mechanical values are set per alloy — so the specification and edition must be stated on the enquiry, not inferred from the grade name. B622 is the primary specification for this product; B619 is the companion specification that is sometimes cited instead.

Item	ASTM B622	ASTM B619
Scope	Primary B-series specification for this alloy in the ordered form	Companion specification; confirm which one the purchase order cites
Ordering basis	OD × wall × length for tube, NPS × schedule or OD × wall for pipe	Same dimensional notation, different acceptance clauses
Chemical limits	Per the alloy table of the primary specification	May differ; the order must name the standard and edition
Testing	Integrity test plus the mechanical tests the specification requires	Same intent, different sampling and frequency
Documents	EN 10204 3.1 with heat-number traceability	3.1 or 3.2 as ordered

B163 covers seamless tube for several nickel alloys; B161, B165, B167, B407, B423, B444 and B622 cover pipe and tube by alloy family. The certificate cites the standard named on the order — mixing them after the fact is not possible.

Chemical Composition (Alloy 31 Heat-Analysis Limits)

Chemical composition, % by weight:

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

Values are the heat-analysis limits of the specification named above. Product analysis on the finished tube or pipe may differ within the tolerances the standard permits, and the actual heat analysis is printed on the mill test certificate.

Mechanical Properties and Physical Data

Mechanical properties:

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

Typical physical properties:

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)

Tensile and yield values are specification minima at room temperature; hardness and grain size are reported when the purchase order asks for them. Design values at service temperature must be taken from the applicable code, not from this table.

Permissible Variations in Dimensions (B622)

Dimensional acceptance follows the tables of the B-series specification named above, with B829 as the general tolerances reference where the product standard is silent. The bands below are representative; the edition cited on the purchase order governs.

Outside diameter

Outside diameter, mm	Permissible variation
≤ 25	± 0.13 mm
> 25 – 50	± 0.20 mm
> 50 – 100	± 0.38 mm
> 100 – 200	± 0.76 mm
>200	± 0.5 % of OD

Variations apply to the individual measurement. For cold-drawn tube the ovality is included in the OD band, not added to it.

Wall thickness

Condition	Permissible variation
Cold-finished	± 10 % of ordered wall
Hot-finished	+ 22.5 % / − 0 % of ordered wall
Minimum wall ordered	No point below the ordered minimum

The wall basis must match the design calculation; nickel-alloy tube is normally ordered on a minimum basis.

Fixed lengths: + 3 mm / − 0 mm. Random lengths 5–7 m unless a fixed length is ordered; straightness 1 in 600, and end squareness is inspected before packing.

Inspection, Testing and Mill Test Certificates

Three groups of evidence are separated here, because only the first is inside the base price. Anything in the second and third groups has to be written on the purchase order — it cannot be added after the mill test certificate has been issued.

Group	Content	How it is triggered
1 — Included	Chemical analysis, tensile test, flattening or bend test, hydrostatic or nondestructive electric test, dimensional check, EN 10204 3.1 certificate	Standard supply; no extra instruction needed
2 — Written on the PO	Ultrasonic or eddy-current testing to a stated acceptance level, PMI on each heat, intergranular corrosion test, grain size, hardness survey, 3.2 certificate	Must appear on the purchase order; priced per order
3 — Third party	TPI witness (SGS, BV, TÜV, Lloyd's), destructive sampling, third-party laboratory, packing inspection, pre-shipment photographs	Arranged per order; extends the lead time

The test route is not interchangeable after the fact: if the certificate has to show ultrasonic testing, say so on the enquiry, because a hydrostatic-only pipe cannot be re-certified as ultrasonically tested.

What the mill test certificate records

Heat number	The melt the item came from, traceable to the raw-material certificate
Grade and specification	Grade designation plus the standard and edition the order cites
Chemical analysis	Actual values for each element, not the range
Mechanical results	Tensile, yield, elongation and hardness as tested
Test route	Hydrostatic or nondestructive electric test, plus any agreed NDT with the method reference
Heat treatment	Solution-annealing temperature range and cooling method
Dimensions	Ordered OD, wall and length, with the measured values on request

Alloy 31 Tube Applications and Points to Confirm

Each application below names the duty the grade is normally chosen for, and what should be settled before the order is placed — the third column decides whether this grade is the right one:

Industry	Typical duty
Chemical processing	aggressive reaction and transfer duty
Petrochemical & refining	hydrocarbon and sour-service duty
Pulp & paper	cooking liquor and bleaching duty
Fertilizer	ammonia, nitric and phosphoric duty
Marine & offshore	salt-laden marine duty
Water treatment	water and wastewater duty

Points to confirm before ordering

Medium, concentration and chloride content — the figures that decide whether this grade holds
Design temperature and pressure, including upset and cleaning cycles
Whether the joint is welded, and the post-weld condition required
Inspection and document scope: NDT level, PMI, third-party witness

Send the medium, concentration, temperature, pressure and chloride level, and we will confirm the grade — or propose the next one up if the margin is narrow.

Grade Selection: Alloy 31 vs 254SMO

Property	Alloy 31	254SMO
PREN, typical	48	43
Molybdenum	6.00–7.00	6.00–6.50
Yield strength, min.	≥ 280 MPa	≥ 300 MPa
Service temperature	≈ 400 °C	≈ 400 °C
Choose when	The acid, alkali or temperature exceeds what stainless steels hold	Lower alloy content is enough for the duty

PREN is indicative only and is calculated from the composition ranges above — it is not an acceptance value. Where the duty sits between two grades, the deciding factors are usually chloride content, temperature and whether the joint is welded.

Frequently Asked Questions

What sizes can be supplied in Alloy 31 tube?

The overall sourcing range is OD 6 – 257 mm, wall 0.5 – 35 mm, length 18 m. The band table shows the wall range normally held or supplied for each OD band; the exact combination of standard, OD, wall, length and manufacturing condition is confirmed in the quotation. Sizes at the edge of a band are quoted after technical review.

Is this page a stock list?

In part. Stocked sizes are marked In stock and ship in 3–7 days; everything else is mill-direct with a 25–35 day lead time, confirmed per item in the quote.

Should the wall be ordered minimum or average?

Either, but it must be stated. A213-type tube is normally ordered on a minimum-wall basis, which is what the tolerance table in the dimensional section assumes. If your design code calls for average wall, say so on the enquiry and the quotation changes basis.

Which specification applies — B622 or B619?

ASTM B622 is the primary specification for this tube and the one the page describes. ASTM B619 is the adjacent specification; whether it applies depends on the ordered form, the test regime and the design code. State the standard and edition on the enquiry and the certificate will cite the same one.

Which tests and documents are included?

Mandatory: one integrity test per length (hydrostatic or nondestructive electric), tensile test per lot, dimensional check and an EN 10204 3.1 mill test certificate. Optional and only when written on the order: ultrasonic or eddy-current testing to a stated level, PMI, intergranular corrosion test, grain size, third-party witness and 3.2 certification.

How does Alloy 31 compare with 254SMO?

254SMO is the usual comparison grade. Alloy 31 carries PREN of about 48 against 43 for 254SMO, with a minimum yield of 280 MPa. The change is normally made when the duty — chloride level, temperature or pressure — leaves 254SMO without margin over the design life.

Request an Alloy 31 Tube Quotation

Send: specification and edition, OD or NPS, wall and wall basis, length, quantity, surface finish, inspection scope and documents, and destination port. The quotation will restate the confirmed size combination, delivery condition, documents included and lead time for Alloy 31 Tube.

Request an Alloy 31 Tube quotation

Related Product Forms and Grades

Other forms and neighbouring grades, each with its own specification — confirm the applicable standard on every order:

254SMO seamless tube — 254SMO — the grade normally compared with Alloy 31 on this duty
254SMO seamless pipe — 254SMO — the grade normally compared with Alloy 31 on this duty
TP904L seamless tube — UNS N08904 · W-Nr 1.4539
Incoloy 028 seamless tube — UNS N08028 · W-Nr 1.4563
Contact the sales team — Sizes outside the range, non-standard lengths and third-party inspection

Technical data compiled from the ASTM/ASME specification tables cited above and from published mill data. Page reviewed by the Xinzhe technical team, 09–11-2026. All values must be confirmed against the edition current at the time of order and against the heat certificate.