Black Phosphated Steel Tube | DIN 2391 & EN 10305-4 Supplier

Black phosphated steel tube is a precision cold drawn tube with a thin, dark phosphate layer on its surface. Hydraulic equipment makers, automotive suppliers and machinery builders choose it when they need tight dimensions, a clean surface and basic corrosion protection at a reasonable cost.
If you import steel tube, you compare more than price. You check standards, material grades, tolerances, surface finish, and whether a supplier can repeat the same quality on every order. This guide covers what you need to know before you send an inquiry for black phosphated steel tube: specifications, sizes, grades, production, applications, and how to order from a manufacturer in China.
Zhangjiagang Chewit International Co., Ltd. supplies precision steel tube from Jiangsu, China, including black phosphated steel tube made to DIN, EN, ASTM, SAE and BS standards.

What Is Black Phosphated Steel Tube?

 
Black phosphated steel tube is a seamless precision steel tube that has been bright annealed and then coated with a phosphate layer. The layer is thin, crystalline and bonded to the steel. It looks matte black or dark grey. Most suppliers add a light protective oil on top.
The phosphate coating does three jobs:
  • It slows surface rust during storage and shipping.
  • It lowers friction during assembly, bending and fitting.
  • It gives paint and adhesives a better surface to grip.
Buyers search for this product under several names, such as black phosphate hydraulic tube, phosphated hydraulic tubing, black phosphate steel tubing and DIN 2391 black tube. They all describe the same product family.

Black Phosphated Steel Tube Specifications (DIN 2391 / EN 10305-4)

Most orders for black phosphated steel tube follow a European or American standard. The table below shows the standards and material grades we list for this product.

Standard	Material grades	Delivery condition / note
DIN 2391 / DIN 1630 / DIN 2445	ST37.4, ST52.4	NBK (normalized)
EN 10305-4	E235, E355	+N (normalized)
ASTM A822 / A450	A822, 1010	Carbon steel hydraulic line tubing
SAE J524	1010, 1020	Low-carbon steel
BS 3602	CFS 360, CFS 450	Cold finished seamless grades

 
The base tube can be supplied with three surface options: bright annealed (BA), black phosphated, or galvanized. Please confirm the exact standard, grade and delivery condition with our team before you place an order, because small differences affect strength and bending behavior.

Black Phosphated Steel Tube Sizes: OD 2–60mm × WT 0.3–10mm

Our standard size range for black phosphated steel tube is:
  • Outside diameter (OD): 2 mm to 60 mm (0.079 to 2.36 inch)
  • Wall thickness (WT): 0.3 mm to 10 mm (0.012 to 0.394 inch)
Not every OD and wall thickness combination suits every grade or standard. A very thin wall on a large OD, for example, needs separate technical review. Send us your drawing or size list, and we will confirm what is possible.
To get an accurate quotation, include these details in your inquiry:
  • OD and wall thickness (with tolerance, if specified)
  • Standard and material grade
  • Delivery condition, such as +N or NBK
  • Surface finish: black phosphated, bright annealed or galvanized
  • Length and end finish (plain, capped or cut to size)
  • Order quantity and destination port

Key Advantages of Black Phosphated Precision Steel Tube

 
  • Corrosion resistance: The dense phosphate film helps keep moisture away from the steel. It performs better than uncoated tube, especially during storage and transport.
  • Lower friction: The smooth coated surface makes assembly with fittings easier and supports smooth fluid flow.
  • Better paint adhesion: The porous layer holds paint, oil and adhesives well, which helps when you need a second coating.
  • Precision stays intact: The phosphating process does not change the tight dimensional tolerances of the cold drawn tube.
  • Cost control: It costs less than galvanizing in most cases, which suits high-volume industrial parts.

How Is Black Phosphated Steel Tube Made? (Bright Annealing + Phosphating)

A typical production route for black phosphated steel tube has six steps:
1. Raw material: A seamless carbon or alloy steel hollow is selected to the required grade.
2. Cold drawing: The tube is drawn to the target OD and wall thickness. See our cold drawn or cold rolled seamless tube page for more on this process.
3. Heat treatment: Bright annealing or normalizing removes drawing stress and sets the mechanical properties.
4. Surface cleaning: The tube is cleaned so the coating bonds evenly.
5. Phosphating and oiling: The phosphate layer forms on the surface, then a light oil film is applied.
6. Inspection and packing: The tubes are checked, bundled and packed for shipping.

Quality checks to ask your supplier about

Every buyer should ask which checks the factory performs. Useful items include:
  • OD, wall thickness and length measurement
  • Visual check of the surface and coating uniformity
  • Tensile test and other mechanical tests required by the standard
  • Flattening, flaring or bending tests when the application needs them
  • Material test certificates, such as EN 10204 3.1, if your project requires them
Confirm which documents are available for your order before production starts.

Black Phosphated Hydraulic Steel Tube for Fluid Power Systems

Hydraulic systems are the largest user of black phosphated steel tube. EN 10305-4 covers seamless cold drawn tubes for hydraulic and pneumatic power systems, and DIN 2445 covers precision tube for dynamic loads. Both are common in purchase specifications.
In these systems, the tube must fit accurately into connectors and hold pressure over many cycles. Tight tolerance on OD and wall thickness helps fittings seat and seal properly. A clean, evenly coated surface also makes bending and assembly easier.
Typical hydraulic uses include pressure lines, return lines and pneumatic actuator lines on construction machinery, industrial equipment and automation systems. Browse our full hydraulic pipe and tube range to compare surface options and related products.

Applications of Black Phosphated Steel Tube

  • Hydraulic and pneumatic systems: pressure lines, return lines and actuator tubing
  • Automotive industry: brake lines, clutch lines and engine hydraulic components
  • Precision machinery: guiding tubes, bearing sleeves and fluid tubes in CNC machines and linear actuators
  • Industrial equipment: hydraulic systems in mining, agricultural and material handling machines
  • Fluid transfer: low-pressure oil, water and air lines in industrial pipework
If your project needs a different surface or material, tell us the working environment. We can suggest a suitable option.

Black Phosphated vs Galvanized Steel Tube: Which Is Better?

Neither option is better in every case. The right choice depends on where the tube will work, how long it must last, and your budget.

Factor	Black phosphated tube	Galvanized tube
Appearance	Matte black or dark grey	Silver-grey zinc surface
Corrosion protection	Basic protection, best for indoor use, storage and transport (with oil)	Stronger barrier for damp or outdoor conditions
Paint adhesion	Very good	Good with correct surface preparation
Effect on dimensions	Very thin layer, minimal change	Zinc layer adds slightly more thickness
Typical cost	Generally lower	Generally higher
Common use	Hydraulic lines, automotive and machinery parts	Parts exposed to moisture or outdoor air

 
Choose black phosphated steel tube when you want a precise tube, low cost and a good base for paint. Choose galvanized tube when the tube will face moisture for a long time without extra coating. We also supply Cr6-free galvanized hydraulic tube, so you can compare both finishes in one inquiry.

Black Phosphated Steel Tube Material Grades: ST37.4, ST52.4, E235, E355

Your choice of grade sets the strength, ductility and bending behavior of the tube.
  • ST37.4 / E235: A low-carbon grade with good ductility. It suits bending, flaring and general hydraulic lines.
  • ST52.4 / E355: A higher-strength grade for lines that carry higher pressure or mechanical load.
  • 1010 and 1020 (SAE, ASTM): Low-carbon grades often called out in American specifications.
  • CFS 360 and CFS 450 (BS 3602): Grades used in British Standard orders.
ST37.4 and E235 are close equivalents, as are ST52.4 and E355. Check your drawing to see which standard your buyer or end user requires. The tubes themselves are made from carbon steel; you can also view our full carbon steel tube range for other carbon steel options.

Black Phosphated Steel Tube Standards: DIN, EN, ASTM, SAE, BS

 
Here is a short guide to the standards you will see in inquiries:
  • DIN 2391: seamless cold drawn precision steel tube
  • DIN 1630: seamless tube with special quality requirements
  • DIN 2445: seamless precision tube for dynamic loads
  • EN 10305-4: seamless cold drawn tube for hydraulic and pneumatic power systems
  • ASTM A822 / A450: cold drawn carbon steel hydraulic tubing and its general requirements
  • SAE J524: seamless low-carbon steel tube, annealed for bending and flaring
  • BS 3602: carbon steel pressure tube
Send us the standard printed on your purchase order or drawing. Mixing two standards in one order often causes delays, so confirm the exact one early.

Why Choose Black Phosphated Tube for Corrosion Resistance and Paint Adhesion?

The phosphate layer is made of fine crystals. These crystals hold oil, which protects the steel from moisture. They also give paint a rough, porous surface to grip. This is why painted or lacquered parts often start with a phosphated tube.

Where phosphate works well

It works well for tube stored in warehouses, shipped by sea in protective packing, and installed in equipment that is painted or sealed after assembly.

When phosphate alone is not enough

For tubes exposed to rain, salt air or constant moisture, phosphate and oil alone will not last as long as a zinc layer or a full paint system. Tell us the working environment, and we will help you choose between black phosphated, galvanized or painted options.

Black Phosphated Steel Tube for Automotive and Precision Machinery

Automotive and machinery buyers care about surface quality and repeatable dimensions. Brake lines, clutch lines and engine hydraulic parts need tube that bends cleanly and fits connectors without leaks. Our automotive steel tube range covers related products for vehicle applications.
In CNC machines, linear actuators and similar equipment, the tube often works as a guide, a sleeve or a fluid line. Here, dimensional accuracy and wear resistance matter more than cosmetic finish. If you have a special bend radius, cut length or end finish, share the drawing, and we will review it.

Custom Black Phosphated Steel Tube Manufacturer in China

Zhangjiagang Chewit International Co., Ltd. is based in Zhangjiagang, Jiangsu Province. We supply high-precision seamless steel tube in carbon, alloy and stainless steel, and hydraulic tube in black phosphated, Cr6-free galvanized or stainless condition. Our company has more than ten years of experience in this field.
For custom orders, you can discuss these options with our team:
  • Outside diameter and wall thickness
  • Standard and material grade
  • Surface finish: bright annealed, black phosphated or galvanized
  • Cut length and packing method
  • Technical documents needed for your market

How to choose a reliable supplier

  • Ask for the exact standards and grades the factory can supply.
  • Compare the full specification, not only the price.
  • Request sample information and test report details.
  • Check how the tubes are packed for sea transport, including end protection and oil film.
  • Test the supplier’s response speed. Clear, quick answers to technical questions usually signal a well-run factory.

How to Order Black Phosphated Steel Tube (Quote, Samples, Delivery)

 
1. Send your requirements. Share the size, standard, grade, surface and quantity.
2. Review the quotation. We confirm technical details and quote based on your specification.
3. Discuss samples. Ask our team about sample availability and conditions for your project.
4. Confirm the order. Once price, specification and documents are agreed, production begins.
5. Inspection and packing. The tubes are checked and packed for export.
6. Shipping. We arrange delivery to your port or agreed location. Please confirm lead time and shipping terms when you request your quote.

Black Phosphated Steel Tube FAQs

What is black phosphated steel tube used for?

Black phosphated steel tube is mainly used for hydraulic and pneumatic lines, automotive brake and clutch lines, precision machinery parts, and industrial fluid transfer lines.

Is black phosphated tube the same as hydraulic tube?

Not always. Hydraulic tube describes the use, while black phosphated describes the surface. Many hydraulic tubes are black phosphated, but they can also be bright annealed or galvanized.

What sizes of black phosphated steel tube can you supply?

Our standard range is OD 2–60 mm and wall thickness 0.3–10 mm. Send your drawing or size list, and we will confirm availability.

Which is better: black phosphated or galvanized tube?

Black phosphated tube costs less and gives a good base for paint. Galvanized tube gives stronger protection in damp or outdoor conditions. Your working environment decides the best choice.

Which standards do you follow?

We supply to DIN 2391, DIN 1630, DIN 2445, EN 10305-4, ASTM A822 / A450, SAE J524 and BS 3602. Please confirm the exact standard and grade for your order.

What should I include in my inquiry?

Include OD, wall thickness, standard, grade, delivery condition, surface finish, length, quantity and destination port. A drawing helps us respond faster and more accurately.

Conclusion

Black phosphated steel tube gives buyers a practical balance of precision, corrosion protection, paint adhesion and cost. It is a proven choice for hydraulic systems, automotive parts and precision machinery, as long as you match the grade, standard and surface to the working environment.
If you are comparing suppliers or preparing a purchase, contact our sales team for product details, a quotation, customization or technical support. Send your drawing or size list to sale@chewit.cn, or message us on WhatsApp at +86 18962244644.