UNS N06022|2.4602|Hastelloy C22 Seamless Pipe

Seamless Hastelloy C22 pipe (UNS N06022 / W.Nr. 2.4602), to ASTM B622 / ASME SB622, ordered by nominal pipe size and schedule.

Seamless Hastelloy C22 pipe (UNS N06022 / W.Nr. 2.4602) is the pipe form of the nickel–chromium–molybdenum–tungsten alloy that resists both oxidising and reducing media. In pipe form it is ordered the way process piping is bought: by nominal pipe size and schedule — for example NPS 2 in. SCH 40 — to ASTM B622 / ASME SB622, with the end preparation, inspection scope and documents agreed on the order.

This page is written for that buying decision: what the standard requires, what our quotation covers, what we can normally supply, and what has to be asked for separately.

What Hastelloy C22 (UNS N06022) is

HASTELLOY® C-22® alloy is a nickel–chromium–molybdenum–tungsten alloy, designated UNS N06022 / W.Nr. 2.4602 / NiCr21Mo14W. Its distinguishing feature is that it performs on both sides of the redox divide: the chromium content (20.0–22.5 %) maintains a passive film in oxidising media, while molybdenum (12.5–14.5 %) and tungsten (2.5–3.5 %) carry the reducing side. That combination is why it is chosen for mixed and contaminated process streams, and why it is the usual upgrade when a C276 line has suffered from an oxidising upset.

How we supply C22 seamless pipe

We are a China-based stockist and supplier of seamless stainless steel, duplex, super duplex and nickel alloy pipe and tube, working from Wenzhou, Zhejiang. That role is worth stating plainly, because it decides what you can expect from a quotation: the heat is melted and the tube is made by the mill, the material test certificate is issued for that heat, and our job is to make sure the grade, dimensions, condition, inspection scope and documents you receive are the ones you specified. Common sizes are quoted from stock of the sizes we normally hold; everything else is sourced mill-direct from qualified producers. Availability and price move with mill schedules and stock, so both are confirmed in the quotation rather than published as a fixed list.

C22 or C276 — how the choice is actually made

The two alloys are not ranked against each other, they cover different media. The usual starting point:

• Oxidising or mixed duty → C22. Nitric acid, ferric chloride, cupric chloride, wet chlorine, chlorine dioxide, hypochlorite, and process streams that swing between oxidising and reducing. The higher chromium content is what buys this.
• Strongly reducing duty → C276. Pure hydrochloric acid and similar strongly reducing streams, where the higher molybdenum (15.0–17.0 % against 12.5–14.5 %) and tungsten (3.0–4.5 % against 2.5–3.5 %) content matters more.

Past that, the decision depends on the medium, its concentration, the operating temperature, whether oxidisers or chlorides are present, and which form of attack you are designing against — general thinning, pitting, crevice attack or stress corrosion cracking. A statement that one grade is simply “better” is not usable for selection. Send us the medium, concentration and temperature, and we will quote the suitable grades side by side.

Corrosion performance, with the test conditions attached

The figures below are laboratory screening results, and they are only meaningful with their conditions. They are useful for comparing alloys; they are not a service life.

Seamless construction — what it does and does not guarantee

Seamless pipe is made from a solid billet by hot working and then cold finishing, so there is no longitudinal weld seam in the wall. That is a genuine difference from welded pipe, and for some duties it is the reason seamless is specified. It is not by itself a pressure rating, and it is not a blanket guarantee of a more uniform structure.

• Pressure capability is a function of the specified outside diameter, the wall thickness and its tolerance, the delivered condition, the design temperature, the design code applied and the inspection performed. The word “seamless” does not set any of those numbers.
• Grain structure and cleanliness follow from the mill’s melting, working and annealing practice, not from the absence of a weld. Two seamless tubes from different mills will not necessarily be equivalent.
• If wall integrity matters, specify it. Ask for the non-destructive examination and the document you need — hydrostatic or eddy current testing per the standard, ultrasonic testing, PMI, or witnessed inspection — rather than relying on the manufacturing route to imply it.

Temperature — three different limits, not one

A single “maximum service temperature” figure is the kind of number that causes trouble, because it mixes up three separate things. Keep them apart when you specify:

• Melting range (a physical property): 1357–1399 °C for C-22. This is solidus to liquidus for the alloy and is not a service limit of any kind.
• Design-code limit: the maximum temperature at which the applicable construction code approves the alloy for the product form you are buying. It differs from code to code, as the table below shows — the same alloy is approved to 677 °C under one code and to 343 °C under another.
• Service temperature: set by corrosion. For aqueous process duty this is normally far below the code limit, because what limits the alloy is the corrosion rate in that medium at that concentration and temperature — not the alloy’s strength.

Ordering tube instead? Seamless Hastelloy C22 tube is the same alloy ordered by outside diameter and wall thickness — the route for heat exchanger, condenser and instrument tubing. Also available in the same family: Hastelloy C276 seamless pipe, B2 seamless pipe and B3 seamless pipe.

Equivalent Grade

Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. See the grade designation index.

Chemical Composition (ASTM B622)

Composition limits for UNS N06022 as required by ASTM B622 / ASME SB622, Table 1. These are acceptance limits verified on the heat analysis — not a description of the alloy and not the analysis of one particular heat.

Mechanical Properties (ASTM B622)

These are the room-temperature acceptance requirements of ASTM B622, Table 2 for UNS N06022 in the solution-annealed condition. They are minimum requirements, not typical values.

Physical Properties (typical values)

Typical published properties for the alloy, each with the temperature it was measured at. ASTM B622 does not specify physical properties, so these are for engineering reference and are not certified per batch.

Electrical resistivity, thermal conductivity and modulus vs temperature

Properties like these change with temperature, so a single figure is only valid at the temperature at which it was measured. The published series for C-22 is:

Size, Schedule & Tolerances

What ASTM B622 covers, and how pipe is ordered

• ASTM B622 covers seamless pipe and tube of nickel and nickel-cobalt alloys, including UNS N06022 (this page’s grade), and requires the product to be supplied solution annealed and descaled (§1.2).
• The specification is limited to tubes up to and including 3.5 in. (88.9 mm) outside diameter (§1.3). NPS 1/4 to NPS 3, quoted on this page, sits inside that limit.
• Pipe is ordered by nominal pipe size and schedule, so the outside diameter is fixed for a given NPS and the wall comes from the schedule. Tube is ordered by outside diameter, minimum or average wall thickness, and length. The schedule table in Appendix X2 is non-mandatory information; the dimensions themselves follow the ANSI/ASME B36.10M schedule system.
• Pipe and tube are not interchangeable on a purchase order. If you are not sure which you need, send the drawing or the service and we will indicate the ordering route.

Pipe schedules — Appendix X2, Table X2.1 (inches)

Pipe schedules — Appendix X2, Table X2.1 (millimetres)

Dimensional tolerances

ASTM B622 requires the material to conform to the applicable general requirements of ASTM B829 unless the order provides otherwise, so the permissible variation in outside diameter, wall thickness, length and straightness comes from that document. The tolerance that applies to your order is the one in the edition of the standard named on your purchase order, and it differs between cold-finished and hot-finished product and between outside diameter ranges. Duplex stainless tolerances such as ASTM A790/A999 have no application to this nickel alloy.

Where the tolerance is not stated, we confirm it in writing at quotation, referencing the standard and edition — do not design around a tolerance taken from a web page, including this one.

Standard reference vs. what we normally supply

Applications of Hastelloy C22 pipe

C22 seamless pipe is normally specified where the medium is aggressive and the line is not easily replaced. Typical duties, in pipe rather than tube form:

• Chemical and petrochemical process lines — reactors, columns, acid handling, mixed-acid and chloride-bearing streams, and pipework subject to oxidising upsets.
• Flue gas desulfurisation and pollution control — scrubber circuits, recycle and spray headers, quench lines and ducting connections.
• Pharmaceutical and high-purity service — process pipework that has to survive cleaning chemicals and organic catalysts without contaminating the product.
• Pulp, paper and bleaching — chlorine dioxide and hypochlorite circuits, bleach plant piping.
• Seawater and brine handling — lines and headers where chloride attack and crevice corrosion govern the material choice.

Pipe ends, marking and length are part of the specification, not details to be left to the supplier: plain ends are our standard, bevelled ends are prepared on request, and both are stated on the purchase order along with the inspection scope.

Inspection and testing — what is standard and what is optional

Several tests listed on alloy pages are not part of the default supply. The matrix below separates what ASTM B622 requires on every order from what has to be asked for, because the difference changes price, lead time and sometimes the manufacturing route.

Documents, traceability and delivery

• Material test certificate. EN 10204 3.1 as standard, issued for the heat actually supplied and stating grade, heat number, chemical analysis, tensile results, dimensions, condition and the tests performed.
• 3.2 certificate and witnessed inspection. On request. These are performed and signed by the third-party agency — nominated by you or proposed by us — and are not a certificate issued by our company.
• Traceability. Heat number is marked on each length and carried onto the MTC, so a piece can be traced back to its heat. Inspection records held by the mill for your order can be passed on where you need them.
• Marking and packing. Grade, size, standard and heat number stencilled or tagged; ends protected; packed for sea freight. Special marking, tagging or packing against your specification on request.
• Documents and photographs before you order. On request we can send a redacted MTC for a comparable order, dimensional inspection records, and photographs of the actual material being offered, so the paperwork can be checked before the order is placed.