What are the heat treatment conditions specified for EN10216-2 steel tube?

When you order seamless pressure tubes to EN 10216-2, the heat treatment condition is one of the first things a mill will confirm with you. It is not a minor detail: the heat treatment sets the microstructure of the steel, and the microstructure decides whether the tube can hold its strength, creep resistance and toughness at the elevated temperatures found in boilers, heat exchangers and high-pressure steam lines. This article explains the heat treatment conditions specified in EN 10216-2, what each symbol means, and how to specify them correctly on your order.

What EN 10216-2 covers

EN 10216-2 is the European standard for seamless steel tubes for pressure purposes, specifically the part covering non-alloy and alloy steel tubes with specified elevated temperature properties. It applies to seamless tubes of circular cross-section and defines two test categories that set the extent of inspection and testing. The current edition, EN 10216-2:2024, was published in November 2024 and supersedes EN 10216-2:2013+A1:2019.

The standard groups the steel grades into two families. P195GH, P235GH and P265GH are non-alloy quality steels, designated by the letter P for pressure purposes, the minimum yield strength in MPa for wall thickness up to 16 mm, and the symbols GH for elevated temperature. The remaining grades, such as 16Mo3, 13CrMo4-5 and 10CrMo9-10, are alloy special steels designated by their chemical composition.

Tubes to this standard are made by a seamless process, and the steel must be fully killed. Before heat treatment, tubes may be supplied hot finished or cold finished, and the purchaser can request cold finishing as an option.

The heat treatment conditions in Table 1

Clause 7.3.3 of EN 10216-2 states that tubes shall be supplied in the relevant heat treatment conditions specified in Table 1 of the standard. Table 1 lists every steel grade together with its required heat treatment, the austenitizing temperature range, the cooling medium, and the tempering temperature range where tempering applies.

Four heat treatment symbols are used across the standard:

• +N — Normalising. The tube is heated above the upper critical temperature and cooled in air, which refines the grain structure and improves toughness and ductility.
• +NT — Normalising followed by tempering. After normalising, the tube is reheated to a lower temperature to relieve internal stress and fine-tune the mechanical properties.
• +QT — Quenching and tempering. The tube is cooled in air or liquid from the austenitizing temperature, then tempered. This route develops higher strength.
• +I — Isothermal annealing. Used for martensitic grades, where the tube is held at a controlled temperature and cooled in a furnace atmosphere to soften the structure.

Where normalising is specified, it includes normalising forming. For several grades, when the wall thickness exceeds 25 mm or the T/D ratio exceeds 0.15, the manufacturer may need to apply quenching and tempering instead to achieve the required structure and properties; in that case the steel name is supplemented with the symbol +QT.

Heat treatment conditions by steel grade

The table below summarises the heat treatment conditions from Table 1 of EN 10216-2 for the main steel grades:

Reading the table: what each group of grades needs

The non-alloy grades P195GH, P235GH and P265GH, together with the low-alloy molybdenum grades 16Mo3 and 8MoB5-4, are supplied normalised. Normalising at roughly 880 to 960 °C refines the ferrite-pearlite structure and gives these grades a good balance of strength, ductility and weldability for boiler and pressure-vessel service.

The chromium-molybdenum grades such as 13CrMo4-5, 10CrMo9-10 and 14MoV6-3 are supplied in the normalised and tempered condition. The tempering step after normalising relieves stresses and stabilises the carbide structure, which is what gives these grades their creep resistance at elevated temperatures. The high-chromium grades X10CrMoVNb9-1 (often known as P91) and X20CrMoV11-1 are also normalised and tempered, but at higher austenitizing temperatures around 1040 to 1090 °C, reflecting their more highly alloyed composition.

Where higher strength is required, the grades 11CrMo9-10, 25CrMo4 and 20CrMoV13-5-5 are supplied in the quenched and tempered condition. Quenching in air or liquid from the austenitizing temperature produces a hardened structure, and the subsequent tempering restores toughness. The martensitic grades X11CrMo5 and X11CrMo9-1 are offered in several delivery conditions, including isothermal annealing, so the purchaser can ｓｅｌｅｃｔ the condition that best matches the fabrication route.

Why heat treatment matters for elevated-temperature service

Heat treatment is not just a production step; it is the mechanism that delivers the properties the standard guarantees. A correctly normalised tube has a uniform, fine-grained structure with predictable yield strength and good impact toughness. Tempering controls hardness and relieves the internal stresses that would otherwise make the tube brittle or difficult to bend. For grades used in creep service, the heat treatment determines the size and distribution of carbides, which directly influences long-term creep strength at operating temperature.

This is why the heat treatment condition is part of the steel designation itself. When you order an EN 10216-2 tube, the designation carries the heat treatment symbol, for example EN 10216-2 P265GH +N or EN 10216-2 13CrMo4-5 +NT, so there is no ambiguity about the delivery condition.

How to specify heat treatment when you order

When placing an order, give the mill the quantity, the dimensions (outside diameter and wall thickness), the full steel designation including the heat treatment symbol, and the test category. If the tube will be formed or welded after delivery, mention it, because the mill can advise whether a particular delivery condition is best suited to your fabrication route.

A few options in the standard are worth knowing about. Cold finishing can be requested as an option, which gives tighter dimensional control. Impact testing can be added, including longitudinal impact testing at -10 °C for the non-alloy grades. Tensile testing at elevated temperature is available where design data at operating temperature is required. If your wall thickness is above 25 mm or the T/D ratio is high, ask the mill directly whether quenching and tempering will be applied to achieve the required properties.

Verification and testing alongside heat treatment

Heat treatment is verified through the testing regime in the standard. Chemical analysis confirms the composition, and tensile testing at room temperature, and at elevated temperature when specified, confirms the mechanical properties produced by the heat treatment. Flattening, ring tensile, drift expanding and ring expanding tests check the soundness and ductility of the tube, while impact testing verifies toughness. Leak-tightness is confirmed by hydrostatic or electromagnetic testing, and non-destructive testing such as ultrasonic and flux leakage inspection detects internal and surface imperfections. Each tube is marked with the standard, steel grade, size, heat number and lot number, and is supplied with the appropriate inspection document.

Sourcing EN 10216-2 tubes with the right heat treatment

Getting the heat treatment right starts with a supplier that understands the standard and can control the process end to end. EZ Steel Industrial Co., Ltd. supplies EN10216-2 steel tube in the non-alloy and alloy grades covered by the standard, supplied in the normalised, normalised and tempered, or quenched and tempered conditions as required. The company also produces boiler tubing, alloy steel tube, heat exchanger and condenser tubes across its carbon, alloy and stainless steel lines, with heat treatment and full non-destructive testing available on every order.

If you are specifying tubes for a boiler, heat exchanger or high-temperature piping system and need to confirm the correct heat treatment condition for your design, contact the EZ Steel Industrial team with your steel grade, dimensions and service conditions. They will confirm the delivery condition, testing category and certification that match your project requirements.