Ferritic stainless steels: 1.4520 and 1.4521

What the number says

Both numbers begin with “1.45”: stainless steels that owe their resistance to chromium alone – without nickel. The name makes the difference visible. X2CrTi17 (1.4520) is a high-alloy steel with very little carbon (2 = about 0.02 %), 17 % chromium and a titanium addition that binds the carbon. X2CrMoTi18-2 (1.4521) also carries about 2 % molybdenum – the element that separates 316 from 304 in the austenite world. That is why 1.4521 is often described as a “ferritic 316”: similar resistance to chloride-bearing water, but without nickel and with a different structure.

Characteristics according to the names in EN 10027-1; use and approvals as manufacturers’ information of the system manufacturers (Viega catalogue 2026, Viega media list, Sanha catalogue 2026). No analysis ranges – the composition in detail is in the mill certificate.

Why system tubes are ferritic

Nickel is the most expensive and most price-volatile alloying element of the austenites. A ferritic chromium steel does without it and remains resistant in drinking water if chromium and – for 1.4521 – molybdenum are right. That is why Viega offers its Sanpress tube in 1.4401 or 1.4521 and Sanha makes the NiroSan ECO from 1.4521: same dimension, same pressing, more economical tube. Two physical properties that ferritic steels share with unalloyed steel come on top: thermal expansion about one third lower than austenite and higher thermal conductivity. In the heating circuit this means less change in length between fixed and sliding point – the argument with which Viega justifies the Temponox tube made of 1.4520.

What ferritic steels cannot do: they are less tough than austenite, especially in the cold and in thick walls, and they cannot be cold formed as far. For thin-walled system tubes with press joints this plays no role – for welded process piping, austenite remains the rule. That is why we carry 1.4520 and 1.4521 only as system tube, not as tube to EN 10217-7 for general piping construction.

Source note: economy, thermal expansion and use as manufacturers’ information (Viega Temponox, Sanpress; Sanha NiroSan ECO); the classification “system tube, not process piping” is our range statement.

Examples of where the material is found in our range

The register of the materials world lists for each material where it sits in our range: in which system we carry it and which page describes it.

The approval for drinking water depends on the system, not on the number: according to the manufacturer, the system tubes in 1.4521 are approved for drinking water (DVGW), the Temponox tube 1.4520 expressly not – it carries the brown marking instead. The manufacturer also approves the Sanpress tube (1.4401 or 1.4521) for Temponox connectors; conversely, Temponox tube stays in the Temponox system. Which combination is permitted is stated on the respective system page; we combine only what the manufacturer approves.

Source note: system approvals and marking according to Viega catalogue 2026 and Viega media list, Sanha catalogue 2026; stock levels according to our ERP findings (as of 10/2026: Temponox tube in stock).

Recognising it on the part – in this order

1. Paper first. Certificate, delivery note and the tube marking state the material; system tubes carry it in the continuous printing. Every test on the part is only a second opinion.

2. The magnet. Ferritic steel sticks strongly to the magnet – like unalloyed steel. If the tube sticks, it is ferrite, duplex or carbon steel; if it does not, it is austenite. The magnet therefore says “not 1.4401”, but not “not stainless steel” – the most common misinterpretation on site.

3. Rust and colour. A ferritic stainless tube looks like austenite: bright, metallic, without mill scale. A galvanized or black carbon steel tube looks different – and rusts at the cut edge. Extraneous rust deceives; check at a fresh spot.

4. Spot test. The molybdenum test solution changes colour on 1.4521 (with molybdenum) and stays pale on 1.4520 (without) – the same test that separates 304 from 316. It names the family, not the material number.

Limit: identifying a material on the part names the probable family – not material number, heat, heat treatment or suitability, and it does not replace a document to EN 10204. How to read certificate and marking: Reading markings, Certificates EN 10204.

What the certificate must show

System tube made of 1.4521 or 1.4520 is not traded like tube to EN 10217-7 with an inspection certificate 3.1 per heat – its proof is the manufacturer’s system approval (DVGW registration number, material information in the catalogue) and the continuous tube printing with material, size, manufacturer and batch code. Anyone who needs a 3.1 on the tube for a project orders it expressly via the system; the certificate then states material number, heat, analysis and tensile test – and for ferritic steels not solution annealing but the annealed condition. A dual certificate with an austenite does not exist: Certificates EN 10204 · Certificate checklist.

Two worlds: EN number and ASTM type

1.4521 has a counterpart in the ASTM world: type 444 (UNS S44400), the ferritic chromium-molybdenum steel of heat exchanger and drinking water tubes. Same alloy, not the same material – analysis ranges and test programmes of the product standards differ, and dual certification is not usual for system tubes because the tube is only sold within the system anyway. For 1.4520 there is no ASTM counterpart common in the piping trade. Anyone finding a ferritic tube in an ASTM parts list asks the system manufacturer – our two-worlds table covers the austenites and duplex: Materials between the worlds.

The typical mix-ups

“The magnet sticks, so it is galvanized steel.” No – ferrite always sticks. The marking decides: if 1.4521 or 1.4520 is on the tube, it is a stainless steel.

“Stainless steel does not rust.” The most common misconception of all – in two stages. First, the German word “Edelstahl” does not mean “stainless”: by the steel definition, Edelstahl is any alloyed or unalloyed steel of special purity (little sulphur and phosphorus) – including tool and quenched-and-tempered steels that rust like any other. What is meant is stainless steel (at least 10.5 % chromium); the English word says it more honestly: stainless – low-staining, not rust-free. Second, even a stainless steel is only as resistant as its passive layer holds: chlorides from sea air, road salt or chlorinated water, sulphur dioxide in industrial air, dried-on deposits without cleaning, narrow crevices and the medium in the line can break through it – then 1.4521 or 1.4404 too show pitting, crevice corrosion or rust stains. Which material is resistant where is decided by the designer according to the corrosion resistance class and the manufacturer’s documents, not by the name.

“1.4521 is a 316L.” No. Both contain molybdenum, but 1.4521 is nickel-free and ferritic; strength, toughness and thermal expansion are different. In a parts list that calls for 1.4404, 1.4521 is no substitute – and vice versa.

“Temponox tube is fine for drinking water too, it is stainless steel after all.” No – the 1.4520 tube has no drinking water approval, the system is built for closed circuits and marked brown (Viega manufacturer’s information).

“Ferrite also comes as an L grade.” No – ferritic steels need no L variant: titanium binds the carbon, which is why the “2” for low carbon is already in the name.

More on the topic

The materials world: Austenitic stainless steels · Carbon and heat-resistant steels · Materials between the worlds · Materials overview.

From the knowledge base: Viega Sanpress · Sanpress Inox · Viega Temponox · Sanha NiroSan · Mixed installation and corrosion · Reading markings.