Pressure vessel steel grades are special steel grades that are designed for the manufacture of vessels that must be able to withstand high pressure and temperature loads and must not show any cracks or other damage. Here we take a look at the strict regulations that define the requirements for the manufacture, testing and use of pressure vessel steel grades.
Pressurized vessels must be made of steel that has the required strength, ductility, toughness and corrosion resistance to ensure the safety of users. The regulations for the manufacture of pressure vessel steel grades contain regulations that define the requirements for the composition, properties and production of steel used for the manufacture of pressure vessels.
The regulations specify the following requirements for pressure vessel steel grades:
- Chemical composition: The chemical composition of a steel determines its properties. The regulations therefore specify certain limit values for the content of alloying elements.
- Mechanical properties: The mechanical properties of a steel are its compressive strength, elongation at break and toughness. The regulations therefore specify minimum values for these properties.
- Manufacturing process: The manufacturing processes for pressure vessel steel grades must be such that the required properties of the steel are achieved. The regulations therefore specify certain requirements for the manufacturing processes.
- Testing: The testing of pressure vessel steel grades is necessary to ensure that the required properties of the steel are met. The regulations therefore specify certain requirements for testing.
Compliance with the regulations for the manufacture of pressure vessel steel grades is required by law. Manufacturers of pressure vessels must therefore ensure that the steel gradesused meet the requirements of the regulations.
Internationally recognized standards
In the USA, the ASME regulations are important, such as the ASME Boiler and Pressure Vessel Code (ASME BPVC). This code defines standards for the design, manufacture and testing of pressure vessels and pressure vessel components. When steel is exported to the USA, steel grades such as SA516Gr60, SA516Gr65 and SA516Gr70, SA537CL1 and heat-resistant variants such as SA387Gr11CL2 and SA387Gr22CL2 are used.
The EN standards of the European Commission are relevant for Europe. These standards define the requirements for materials used in the manufacture of pressure vessels and cover various steel grades that are suitable for different operating conditions and temperatures.
The EN 10028 series is a European standard for the specification of the chemical composition and mechanical properties of steel grades for pressure vessels for flat products. It comprises the individual chapters
- General requirements
- Unalloyed and alloyed steel grades with specified properties at elevated temperatures
- Weldable fine-grained structural steel grades, normalized
- Nickel-alloyed low-temperature steel grades
- Weldable fine-grained structural steel grades, thermomechanically rolled
- Weldable fine-grained structural steel grades, quenched and tempered
- Stainless steel grades
Certification for pressure equipment according to PED
Manufacturers who wish to place pressure equipment on the market in a country of the European Union require a certificate of conformity from a notified body in accordance with the European Pressure Equipment Directive (Directive 2014/68/EU) – known as the Pressure Equipment Directive ( PED ).
This applies to the following pressure equipment and assemblies:
- Steam boiler
- Pressure vessel
- Equipment parts with safety function
- Pressure-retaining equipment parts
- Pressure equipment assemblies
The Pressure Equipment Directive states that an approval in accordance with PED 2014/68/EU is required for the manufacture of plates in a plant. In addition, the steel parts used in the pressure vessel, including flanges, pipes, plates, shell joints, dished ends, etc., must be manufactured in accordance with a harmonized standard.
However, PED 2014/68/EU is considered insufficient or not strict enough in some EU countries. Therefore, country-specific regulations apply in some cases. In France, for example, the CODAP (Code de construction des appareils à pression) is used, while in the UK pressure vessels are manufactured in accordance with BS 5500 (Specification for unfired, fusion welded pressure vessels).
AD-2000 – the most important set of regulations in Germany
The AD-2000 set of rules is the most widely used set of rules in Germany for the manufacture and testing of pressure vessels. It specifies all the basic safety requirements that must be observed in accordance with the Pressure Equipment Directive. AD-2000 is the result of cooperation between the Pressure Vessels Working Group and working groups from associations such as FDBR, DGUV, VCI, VDMA, VDEh, VGB Power Tech and VdTÜV.
Various material properties are covered in the AD-2000 regulations. AD2000W0 specifies the general properties, while AD2000W1 deals with flat products made of unalloyed and alloyed steel grades.
Section 2.1 of this code deals with steel grades according to EN 10025-2:2019-10, specifically structural steel grades such as S235JR+N (1.0038), S235J2+N (1.0117), S355J2+N (1.0577) and S355K2+N (1.0596). Interestingly, these steel grades can be used up to a temperature of 300 °C in unfired pressure vessels, but with reduced yield strength and certain restrictions regarding internal pressure and diameter.
Section 2.3 in AD2000W1 is dedicated to plate grades according to EN 10028-2:2017-10 for pressure vessel steel grades. Steel grades such as P265GH (1.0425), P295GH (1.0481), P355GH (1.0473) are listed here. For alloyed steel grades such as 16 Mo3 (1.5415), 13CrMo4-5 (1.7335) and 10CrMo9-10 (1.7380), an additional confusion test is required.
Section 2.4 of AD2000W1 describes flat products made of pressure vessel steel grades in accordance with DIN EN 10028-3:2017-10. These include steel grades such as P355N (1.0562), P355NH (1.0565), as well as low-temperature variants such as P275NL2 (1.1104), P355NL1 (1.0566), P355NL2 (1.1106) and P460NL2 (1.8918), which are also approved for higher stresses with increased impact energy. A certificate in accordance with EN 10204 3.2 is required here.
In 2020, thermomechanically rolled variants (section 2.6 according to EN 10028-5:2017-10) and quenched and tempered steel grades with a maximum yield strength of 500 MPa in section 2.7 according to DIN EN 10028-6:2017-10 were added.
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