EN 10305 Cold Drawn Precision Steel Tubes and Pipes (Part 1 & 4)

EN 10305 is a series of specifications for the technical delivery conditions of precision steel tubes developed by the European Committee for Standardization (CEN). It is mainly applicable to high-precision, high-quality cold-drawn or cold-rolled seamless steel tubes and welded steel tubes, which are widely used in hydraulic systems, automobile manufacturing, mechanical engineering and other fields.

EN 10305 Standard Classification

The EN 10305 standard is divided into several parts. While all cover precision tubes, they serve different applications. The most common parts are:

Main Features of EN 10305

The main features of this standard are:

● High precision: Strict control of outer diameter and wall thickness. Wall thickness tolerance: ±10% or ±0.1mm (whichever is greater), in accordance with EN 10305-1.
● High finish: The inner wall is smooth, reducing fluid resistance, suitable for hydraulic systems. (No oxide layer on the inner and outer surfaces, Ra ≤ 0.8μm).
● Excellent mechanical properties: No deformation during cold bending, no cracks during expansion and flattening, suitable for high-pressure environments.

Common Materials and Grades

Under EN 10305, the material grades have been modernized. The old DIN designations (St series) are now replaced by the European E-series. Common equivalents include:

Note: ST37.4 is the traditional DIN designation for the higher-purity E235 grade used in hydraulic systems. It is not a separate material but a specific quality variant of E235, often supplied in the NBK (+N) condition for excellent bendability.

Mechanical Properties

The mechanical properties of EN 10305 steel pipes vary depending on the material and heat treatment status. (Below are typical values for common grades in the normalized or cold-drawn condition):

Key performance features:
● High pressure resistance: Suitable for hydraulic systems. Maximum working pressure depends on the specific size and wall thickness (can reach up to 70 MPa for small-diameter, thick-wall tubes).
● Cold processing performance: Can withstand cold bending, flaring, flattening without cracking.

Note: The maximum working pressure depends on the outer diameter and wall thickness. For example, an E235 tube (EN 10305-4) with an OD of 20mm and a wall thickness of 2.0mm typically has a static design pressure of 282 bar (28.2 MPa) and a burst pressure of 900 bar (90 MPa) according to Parker's official data.

Specifications and Tolerances

Outer Diameter (OD): 4 mm to 80 mm (cold-drawn precision range).
Wall Thickness (WT): 0.5 mm to 12 mm.
Standard Length: Usually 6 m (custom lengths available).

Standard Tolerances (EN 10305-1):

OD Tolerances:

Outer Diameter (OD)	Tolerance (mm)
4 ≤ OD < 30 mm	± 0.08 mm
30 ≤ OD < 50 mm	± 0.15 mm
50 ≤ OD < 80 mm	± 0.20 mm

WT Tolerances:

Wall Thickness (WT)	Tolerance
All dimensions	± 10% (min. ± 0.1 mm)

Note: EN 10305-4 (hydraulic/pneumatic) tubes generally follow the same dimensional tolerance framework as EN 10305-1. However, -4 adds stricter requirements for surface cleanliness, non-destructive testing (eddy current), and suitability for hydraulic fittings. Tighter tolerances can be produced upon request. Please contact our technical team for specific dimensional tolerance tables or custom specifications.

Delivery Status (Delivery Conditions)

Common delivery statuses include:
● +C (BK): Cold drawn hard, high strength, no subsequent heat treatment.
● +N (NBK): Normalized, good comprehensive mechanical properties.
● +SR (BKS): Stress relieved, reduced internal stress.
● +A (GBK): Annealed, for softness and formability.
● +LC (BKW): Cold drawn / soft, for specific forming needs.

Choose the appropriate delivery status according to specific application needs.

Manufacturing Process & Surface Treatment

● Cold drawing/cold rolling process: Improve dimensional accuracy and surface finish.
● Non-oxidation bright heat treatment (NBK state): Eliminate stress, ensure that the steel pipe has no oxide layer during the manufacturing process, and improve the cleanliness and service life of the steel pipe.
● Surface treatment: Phosphating, galvanizing (white zinc, colored zinc) to enhance corrosion resistance.
● Non-destructive testing: The steel pipe will undergo NDT to ensure that the quality meets the standards.

Inner and Outer Wall Treatment:

Inner wall: Brushed and high-pressure flushed with special equipment to ensure good inner wall cleanliness.
Outer wall: Anti-rust oil treatment to effectively prevent rusting; dust-proof treatment at both ends to prevent pollution.

Application

EN 10305 steel pipes are widely used in hydraulic systems, automobile manufacturing, machinery manufacturing, petrochemicals, aerospace and other industries that have high requirements for steel pipe precision, finish, cleanliness and mechanical properties.

Typical examples include:

● Hydraulic and pneumatic systems: High-pressure cylinders, construction machinery, injection molding machines, ship hydraulic pipes. (Note: For precision hydraulic lines, ST37.4 / E235 in the +N condition is the standard material choice.)
● Automobile manufacturing: Brake oil pipes, fuel delivery pipes.

FAQ

Q1: What is the difference between EN 10305-1 and EN 10305-4?
A: EN 10305-1 specifies general cold-drawn seamless precision tubes for mechanical engineering. EN 10305-4 is specifically for hydraulic and pneumatic systems, requiring stricter tolerances, better inner surface cleanliness, and non-destructive testing.

Q2: Is EN 10305 the same as DIN 2391?
A: Yes, EN 10305 has replaced the older DIN 2391 standard. For example, the old DIN 2391 St 35 / St 37.4 materials are now designated as E235 in the EN 10305 standard.

Q3: Which delivery condition should I choose (+C, +N, or +SR)?
A: Choose +C (BK) for high strength and direct installation without further machining; choose +N (NBK) for good ductility when cold bending or flaring is required; choose +SR (BKS) to minimize internal stress after machining.

Q4: Can EN 10305 tubes be used for high-pressure hydraulic systems?
A: Yes, they are widely used in high-pressure hydraulics. The maximum working pressure depends on the outer diameter and wall thickness. 

Conclusion

EN 10305 is the core standard for high-precision steel tubes in Europe, especially suitable for hydraulics, automobiles, machinery and other fields. Its strict dimensional tolerances, excellent surface treatment and mechanical properties make it an ideal choice for high-end industrial applications.

Read more: 

●  DIN 17175 Heat-resistant Seamless Steel Pipe 

●  Cold Drawn ERW Pipe

●  Mechanical Tube Size Chart

●  Precision Hydraulic Seamless Tube

●  DIN 2391 Seamless Precision Tube: ST35, ST45, ST52

●  Cold Drawn Seamless Tube Size Chart for Mechanical and Hydraulic