Steel Tube

Phosphated Hydraulic Tube

EN 10305-4 Black Phosphate Steel Tubes EN10305-4 E235+N/DIN1630 St37.4 Black Phosphate Steel Tubes Seamless precision steel tubes for hydraulic usages Description: galvanized or phosphated seamless cold drawn precision steel tubes for hydraulic and pneumatic lines with improved corrosion...
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EN 10305-4 Black Phosphate Steel Tubes

EN10305-4 E235+N/DIN1630 St37.4  Black Phosphate Steel Tubes

Seamless precision steel tubes for hydraulic usages



galvanized or phosphated seamless cold drawn precision steel tubes for hydraulic and pneumatic lines with improved corrosion protection.

Tolerances: according to EN 10305-4 “Steel tubes for precision applications – Technical delivery conditions- Part 4: Seamless cold drawn tubes for hydraulic and pneumatic power systems”.

Steel grade: E235 (St-35/37.4)

Delivery condition: +N (NBK) normalized under controlled atmosphere.

Surface treatments:

Internal and external phosphate coating;

Externally galvanized tubes with a zinc coating of 8 to 12 μm and subsequently chrome VI-free passivated (blue or iridescent silver).

Synopsis of Process Routing: quality carbon steel → cold drawing → bright heat treatment without oxidization (NBK status) → nondestructive testing. In the wall honing and inside flushing under the high pressure→ plastic capping on both ends→Phosphating→Antirust oiling outside surface→Bundles

Main Features: high accuracy, excellent brightness, no oxidization on the outer and inner walls after heat treatment, high cleanness inside wall. The steel tube is able to stand high pressure. No deformation after cold bending, no crack after flaring and flattening . The complicated geometrical forming and machining can be realized. bright black. Color is homogeneously distributed on the tube surface. The tube has good property of antirust

Main Application: to be used in hydraulic system, automobile and in the occasion where the high precision, brightness, cleanness and mechanical properties of the tube are required.

Main grades


Delivery Status:

NBK(+N) +Black Phosphating


Outer diameter x wall thickness

6~76 x 1~8mm

With high technology DIN pure drawn seamless steel tube of light steel products with a phosphate, with imports of environmental linhua liquid steel for internal and external wall phosphating film formation, black phosphating, through the phosphating film of microporous absorption oily-type rust, both for block as dustproof.

This type of steel tubes can meet the special requirements of high precision and fine finish steel tubes used in various trades;with the mechanical properties suitable to the bending at any angle and capable of bearing all types of high pressure,cold bending ,tube and expansion, bruising, tensile force, impact force,etc;without any occurrence of cracks or crackles,without oxidation scale on the interior or exterior wall of the tubes; without causing any blockage to the pneumatic, hydraulic and oil routes;the elongation and the strength of steel tubes are extremely ideal. OD range from 4MM to 76mm.WT range from 0.5MM to 6MM. The tolerance of OD of our mill can control in +-0.08mm to +_0.05mm,Our products are good quality,We are manufacturer of precision cold drawn seamless steel tube. For the best quality of the products we provided,We have already established long-term cooperative relationship with the world famous companies:Benteler and ContiTech AG,We are also desinated fuel pipes supplier for BMW, Audi, Volkswagen and other worldwide famous automoible manufacturers.Our products are widely used in hydraulic systems,automobile,machinery,engineering machinery,etc.Our main products: 1.DIN2391/C,SAEJ524,5050J,EN10305-4 cold drawn precision seamless steel tube 2.BK,BKS,GBK,NBK fuel pipe 3.Black Phosphated tube 4.Galvanized steel tubes Our mill have passed TS:16949.Free sample can be provided.


Product Feature

Steel with bright color, black, steel surface color uniformity, consistency is beautiful appearance, good performance, steel rust.

Product Specification/Models



Hydraulic Systems,Automotive,Machinery,Enineering Machinery,and etc.

Other Information

Delivery Staus: BK,BKW,BKS,GBK,NBK


Main Application:

Phosphated hydraulic tube is mainly used in hydraulic system.

Engineering machinery  Machine tool industry  Hydraulic industry  Special vehicle

Automobile pipeline  Heavy machinery   Compressor  Shipbuilding industry

Railway locomotive  Diesel engine  Utility boiler  Injection molding machine

Power equipment   Heavy duty automobile  Forging and stamping machine

Main Characteristics:

No Oxidation Layer on the Outer and Inner Walls

No Crack under Flaring and Flattening

No Leakage under High Pressure  

No Distortion after Cold Bending  

High Precision High Cleanness Excellent Brightness

Product name  DIN2391 10# 8.00*1.00mm cold drawn black phosphated pipe used for oil pipe of automobile

Material  10#, 20#, 45#, Cr-Mo alloy, 16Mn, SAE1010, SAE1020, SAE1045, ST35, ST52, SKTM11, 4130 alloy, etc

Standard  GB8163, GB8162, DIN2391, EN10305-1, EN10305-4, JIS-G3445, SAE J524, ASTM A519, ASTM A192, DIN1629

Main size OD: 4.0--75mm, WT: 0.70—10.0mm

Length  usually, 4000-5500mm length or random length 3000-5800mm, 12000mm length max

Heat treatment  BK, BKS, BKW, GBK, NBK

Surface treatment  Bare tube with oil; white ZN coated; olive green ZM coated, black phosphate


1) fuel injection lines/nozzles for diesel or gasoline engine;

2) compressed natured gas CNG tube

3) drive transmission: steering column elements

4) gear shafts, hand brake, front axles, airbag inflators, stabilizers, seat fasteners, front-wheel

drive shafts

5) mechanical structure pipe parts in automobile, motorcycles and vehicle

6) hydraulic circuits, pneumatic lines and hydraulic suspension

7) hydraulic cylinders


Precision seamless phosphated carbon steel tube:

▪ Standard:

DIN 2391, EN 10305-1, EN 10305-4

▪ Materials:

ST35, ST37.4, ST37, ST45, ST52, ST52.4, E235, E255, E355.

▪ Delivery condition:

Black Phosphated after bright annealed.

▪ Size Range:

Outer Diameter: 4 mm - 60 mm    Wall thickness: 0.5 mm - 10 mm

▪ Main Features:

Bright black color is homogeneously distributed on the tube surface. with good anti-rust and corrosion resistance performance.

▪ Main Application:

Used in hydraulic systems, mechines and facilities, other applications which require good rust proof and corrosion resistance performance.


We maintains a large stock of hydraulic tubes in steel material. These steel tubes are in accordance to DIN 2391, the standard specification of steel tubes for precision application such as hydraulic and pneumatic power systems, and DIN 2445, the standard specification of seamless steel tubes for dynamic loads.

Steel tubes are available in two kinds of steel material, ST37.4 (E235N) and ST52.4 (E355N). Different materials result from differences in the working pressure that the material can withstand. Grade ST52.4 is a higher grade compared to grade ST37.4, and a higher grade of material quality can reduce wall thickness and weight while maintaining the same working pressure.


Steel Tube Attributes:

Different material grades will lead to differences in attributes. For ST37.4, tensile strength ranges from 340 N/mm² to 480 N/mm², while for ST52.4, the tensile strength ranges from 490 N/mm² to 630 N/mm². Higher tensile strength means higher working pressures with reduced wall thickness, thus leading to reduced tube weight.


The two different steel grades also lead to different yield strengths. The minimum yield strength for ST37.4 is 235 MPa and for ST52.4 it is 355 MPa. However, for steel tubes with an outside diameter that is less than 30MM and a thickness that is less than 3.0MM, the minimum yield strength is 10 MPa lower.


There are also differences in chemical composition between ST37.4 and ST52.4. For example, the maximum carbon content for ST37.4 is 0.17%, while the maximum carbon content for ST52.4, is 0.22%. The high carbon content will make the steel harder and stronger through heat treatment. However, it will also cause the steel material to be less ductile and reduce the melting point.

Steel Tube Finishing:

The finishing of tubes under ST37.4 and ST52.4 are NBK, where tubes are normalized, phosphated, and oiled inside and outside. Normalizing is a type of heat treatment process. Heat treatment done to change its the mechanical properties such as hardness, yield strength, and ductility.


In the normalizing process, steel is heated to a temperature about 55˚C. This process will be continued over a period of time for a transformation namely grain refinement to occur. The steel then will be air-cooled in a room temperature. This results in the steel becoming stronger and harder. 


Outer Diameter and Tube Thickness Specifications:

The specifications of the tube outer diameter and tube wall thickness are according to EN 10305-4. Below Hydraulic Steel Tubes Literature will  shows the preferred outside diameter, inside diameter, and wall thickness.


Surface condition of zinc coated tubes             

First layer electrolitically leached zinc (Zn) – acts as anode and in a corrosive environment it corrodes first and the base metal is cathodically protected against corrosion. The zinc layer thickness may be in the range of 5 to 30 micrometers (µm).


Second layer based on the valency of used chrome is called either: passivation or chromating. For chromating in the past the Cr+6 salts were used. Nowadays the term chromating is no longer used, but passivation, or based on the number of chromites (salts Cr3+) we are talking about chromiting.


Third layer for the overall increase of coating resistance, we use as the last layer the layer of organic substances on the Si base that stabilizes the chrome layer. This process is called impregnation or sealing.


Norm: DIN2391  DIN2445  EN10305  DIN1630  DIN1629  ASTM A179 ASTM A106  JIS G3445

Steel Grade: ST35(E235)  ST45(E255)  ST52(E355)  ST37.4

Delivery condition: NBK(+N)  GBK(+A)  BK(+C)  BKW(+LC)  BKS(+SR)

Outside Diameter (mm): 4~200(mm)      Wall Thickness(mm): 1~20(mm)

Main Purpose: Hydraulic System, Automobile

Main customer: famous end user Hydraulic System, Automobile, Heavy Equipment and so on.


TS offers three types of seamless metric tubes for hydraulic, pneumatic and instrumentation applications: Steel seamless cold drawn tube, phosphate and oil dipped for corrosion resistance, Steel seamless cold drawn tube, zinc Chromium-6 free plating for corrosion resistance, Stainless steel cold drawn tube, Conformance and Material Specifications

Tests and Certificates

All tubes are subjected to a non-destructive leak test and marked accordingly. This marking is used in lieu of a works certificate DIN EN 10204-2.2. Test Class 1 DIN EN 10216-5 Table 7 applies

for tubes made of 1.4571 material. Materials and Mechanical Properties Steel Types, mechanical properties and conditions are listed below.

Welding Suitability and Weldability:  Steel tubes of St. 37.4, R Series, are weldable according to usual techniques. Not recommended to weld St. 37.4, R-VZ series,

Zinc Chromium-6 Free plated tubes. Stainless steel tubes of 1.4571 are suitable for arc welding.

The welding filler should be selected in accordance with DIN EN1600 and DIN EN12072 Part 1 taking into account the type of application and the welding technique.

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