• ByRouging Solutions Editorial Team  ·  20 October 2026

EN 10088 Explained: Stainless Steel Grades for Plant Engineers

A new tank arrives from a European maker. Your drawings say 316L, but the mill paperwork says 1.4404, and nobody on the receiving team is sure they match. That number comes from EN 10088, Europe's standard for stainless steels. It is easy to read once you know the pattern.

This guide shows what EN 10088 covers and how its numbers match the grades Indian plants use. It also shows why the grade matters when you plan passivation or deal with rouge.

What Is EN 10088?

EN 10088 is the European set of standards for stainless steel. Part 1 lists each grade and what it is made of. The later parts set the terms for each form the steel comes in, such as sheet, plate, strip and bar. Mills, makers and buyers in Europe use it to name and order a grade.

You will meet it most often on kit built or bought in Europe. Pumps, valves and vessels from European suppliers often carry EN numbers on their papers. Indian drawings, on the other hand, often use the American names, such as 304 and 316L.

Neither system is better. They are two ways of naming steels that are very close to each other. The trouble starts when the buyer, the maker and the quality team each use a different one, and each one assumes the others will translate.

What Do the Parts of EN 10088 Cover?

Part 1 is the list of grades, and the other parts deal with how each form of the steel is supplied. Part 2 covers sheet, plate and strip. Part 3 covers semi-finished products, bars, rods, wire, sections and bright products. All the parts carry the EN 10088 name, so a mill paper quotes whichever part matches the form you bought.

The Swiss standards body sums up Part 1 in one line. It says the document "lists the chemical composition of stainless steels" (SNV, SN EN 10088-1:2024). It puts them in three groups, for steels made to resist rust, heat or creep, which is slow stretching under load at high heat. An annex also gives a formula for "pitting resistance ranking", which matters where salts such as chlorides are present.

Part 2 is the one most process plants touch, because tanks and vessels are made from sheet and plate. Its scope note says "General purposes include the use of stainless steels in contact with foodstuffs" (SNV, EN 10088-2:2024). That line is worth knowing if you run a food or drinks plant and buy from Europe.

Part 2 also points to EN 10021, a general standard for steel deliveries, which applies alongside it. Part 1 was revised in 2023, and the new edition replaced the 2014 one. So ask your supplier which edition their paper follows.

How Do EN 10088 Numbers Like 1.4404 Work?

Each EN grade has two labels: a steel number and a steel name. The number, such as 1.4404, is short and easy to type. The name, such as X2CrNiMo17-12-2, spells out the main metals mixed into the steel. So the name tells you at a glance if a grade has molybdenum in it. The number alone does not.

Both labels follow a separate pair of European standards. EN 10027-1 sets the rules for steel names, using "symbolic letters and numbers" (EVS, EN 10027-1:2016). EN 10027-2 sets the steel numbers, which it calls "complementary to steel names" (EVS, EN 10027-2:2015).

Take two grades that pharma and food plants see often. 1.4301 is named X5CrNi18-10. Its letters show chromium (Cr) and nickel (Ni) as the main added metals. 1.4404 is named X2CrNiMo17-12-2, and it adds "Mo", the symbol for molybdenum.

That one extra symbol is the quickest check your receiving team can make. If the drawing asks for a grade with molybdenum and the name has no "Mo", stop. Ask the supplier before the steel goes any further.

How Do EN Grades Match 304 and 316L?

Closely, but not exactly. TWI, the UK welding research body, has a table that pairs 1.4301 with 304 and 1.4404 with 316L. It also warns that the table "is intended to give comparisons only; these may not represent direct equivalents" (TWI).

Here is the part of that table most process plants need:

Keep two points in mind. First, TWI says its table follows BS EN 10088-1:2005, an older edition, so check the current limits for anything critical. Second, the European and American standards set their limits on their own. A batch of steel can meet one and just miss the other.

When a drawing and a mill paper use different systems, write both names on the purchase order. Our guide to writing a passivation scope of work shows where the grade belongs in that document.

Why Does the Grade Matter for Passivation and Rouging?

Because the mix of metals decides how the surface behaves. Chromium forms the thin film that keeps stainless steel from rusting. Molybdenum helps that film hold up against salts, and low carbon helps the steel near welds keep its guard. Pick the wrong grade for the job and it can rouge, pit or rust early, even with good passivation.

A study on 316L says molybdenum "suppresses a susceptibility to the localized corrosion, such as pitting and crevice corrosion" (Materials journal, via PubMed Central). In plain words, it helps stop tiny pits from forming where salts are present. EN 10088-1 even has a formula for ranking how well each grade resists pitting.

Low carbon matters most at welds. The same study explains why. When chromium carbides form along the grain edges inside the steel, the metal next to them loses chromium, and it can then corrode. This happens between 500 °C and 800 °C with slow cooling, a range that welding passes through. Thermo Fisher says the "L" grades "are used to provide extra corrosion resistance after welding" (Thermo Fisher on L and H grades).

The right grade still needs care. Rouge forms on 316L in hot water systems too, as our article on rouging and corrosion in SS316L pipes explains. Passivation helps the chromium-rich film form again on whatever grade you have. Our ASTM A967 guide covers how that work is specified and tested.

What Should You Check on a Mill Certificate?

Check five things: the grade, the standard, the heat number, the type of paper and the make-up. EN 10204 is the European standard that "specifies the different types of inspection documents supplied to the purchaser" for metal products (EVS, EN 10204:2004). The type tells you if the test results come from the steel you actually got.

EN 10204 has four types. Types 2.1 and 2.2 come from the maker. Type 2.1 is a declaration that the steel meets the order, with no test results. Type 2.2 gives "non-specific" test results, from the same grade but not always your heat or lot (Project Materials). Types 3.1 and 3.2 report "specific inspections". An inspector who does not work in production signs them (Wermac summary of EN 10204). Type 3.2 adds a second sign-off, by the buyer's inspector or an official one.

When a delivery arrives, go through the paper in this order:

1. Grade. Find the EN number or name, and check it against your drawing with the grade table earlier in this guide.
2. Standard and part. Note which part of EN 10088 the paper quotes, and which edition.
3. Heat number. Match the heat or batch number on the paper to the mark on the steel itself.
4. Paper type. Confirm it is the EN 10204 type your order asked for.
5. Make-up. For a grade with molybdenum, check that molybdenum shows up in the test results.

Keep the paper in the equipment file. Auditors who ask about passivation documentation often want the steel records too.

Putting EN Grades to Work in Your Plant

Here is an illustration, with made-up details. A formulation plant in Baddi orders a mixing vessel from a European maker. The drawing says 316L, and the mill paper says 1.4404 with a 3.1 type. The receiving engineer checks the name for "Mo", matches the heat number on the shell and files the paper.

That quick check heads off a much bigger problem. A wrong grade found after start-up means replacing the vessel or its parts, or living with a weak spot that touches the product. The same habit works for food, drinks and chemical plants in the Vapi-Ankleshwar belt and beyond.

Once the right steel is in place, the surface still needs care. New equipment is often passivated before first use. Our passivation services cover work at your plant or at our own site, with the records your QA team needs.

Where to Start

Remember one thing: an EN 10088 number and an American grade are two names for steels that are very close. Check that they match before any new stainless equipment goes into use. A wrong grade is much harder to fix once it is installed.

This week, pull the paper for your newest stainless vessel. Read the EN name, and look for "Mo" if the drawing says 316L. Then match the heat number on the paper to the mark on the shell.

If you would like help with passivation or derouging after the vessel is in, our team responds within 24 hours.

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