ST37.4 is a high-precision seamless steel tube grade under the German standard DIN 1630/DIN 2391. In modern European standards, it is equivalent to EN 10305-1 E235.
NBK Condition: These tubes are typically delivered in the NBK (Normalized) state, performed in a non-oxidizing atmosphere. This results in a Bright Annealed surface that is silver-white, scale-free, and exceptionally clean.
Core Performance: Engineered specifically for hydraulic systems, it offers high dimensional accuracy, excellent cold-bending properties, and superior pressure resistance.
Superior Inner Surface Cleanliness – ST37.4 Precision Tubes for Zero-Contamination Hydraulics.
ST37.4 Seamless Hydraulic Tube Specification Table
| Item | Description |
| Standard | DIN 2391, DIN 1630, EN 10305-1 |
| Grade | ST37.4 / E235 |
| Delivery Condition | NBK (Normalized in protective atmosphere) |
| Outside Diameter (OD) | 4mm – 80mm |
| Wall Thickness (WT) | 0.5mm – 10mm |
| Surface Treatment | Phosphated, Galvanized, or Bright Annealed (Standard) |
| Length | 6000mm or customized lengths |
Chemical Composition of ST37.4 Seamless Tubes
| Grade | Carbon (C) max | Silicon (Si) max | Manganese (Mn) | Phosphorus (P) max | Sulfur (S) max |
| ST37.4 | 0.17% | 0.35% | 0.40% - 0.80% | 0.040% | 0.040% |
ST37.4 Tubes Mechanical Properties
Typical values in the NBK (Normalized) delivery condition:
| Grade | Tensile Strength (MPa) | Yield Strength (MPa) min | Elongation (%) min |
| ST37.4 | 340 – 480 | 235 | 25% |
St37.4 Cold Drawn Seamless Carbon Steel Pipe Common Dimension Table (Metric - mm)
Hydraulic tubes are specified by "OD x WT." Below are the most common sizes used in precision hydraulic piping:
| OD (mm) | WT 1.0mm | WT 1.5mm | WT 2.0mm | WT 2.5mm | WT 3.0mm |
| 6 | Available | Available | - | - | - |
| 10 | Available | Available | Available | - | - |
| 12 | Available | Available | Available | Available | - |
| 15 | Available | Available | Available | Available | - |
| 20 | - | Available | Available | Available | Available |
| 25 | - | - | Available | Available | Available |
ST37.4 Seamless Hydraulic Tubes Schedule Chart (Reference)
While precision tubes use Metric OD x WT, this chart provides a reference for engineering comparisons with NPS sizes:
| Metric OD (mm) | Approx. Inch Size | Equivalent Schedule (Reference) |
| 10.3 | 1/8" NPS | SCH 40 / 80 |
| 13.7 | 1/4" NPS | SCH 40 / 80 |
| 17.1 | 3/8" NPS | SCH 40 / 80 |
| 21.3 | 1/2" NPS | SCH 40 / 80 |
| 26.7 | 3/4" NPS | SCH 40 / 80 |
Pressure Rating of ST37.4 NBK Tubes
Note: Calculated based on DIN 2413 with a safety factor S=2.
| OD (mm) | WT (mm) | Allowable Working Pressure (Bar) | Burst Pressure (Ref. Bar) |
| 10 | 1.5 | 320 | 850 |
| 12 | 2.0 | 360 | 960 |
| 15 | 2.0 | 285 | 780 |
| 20 | 2.5 | 270 | 720 |
| 25 | 3.0 | 250 | 680 |
ST37.4 Seamless Hydraulic Tube Features
High Precision: Extremely tight tolerances on both ID and OD, ensuring perfect compatibility with ferrule-type fittings.
Oxide-Free Surface: The NBK heat treatment ensures the inner and outer surfaces are scale-free, preventing hydraulic valve blockage.
Superior Cold Bending: Capable of complex cold deformation without cracking, reducing the need for pipe joints and elbows.
High Pressure Resistance: High tensile strength allows smaller tubes to handle extreme system pressures safely.
ST37.4+NBK High Pressure Hydraulic Piping Typical Applications
Hydraulic Systems: Industrial presses, injection molding machines, and heavy construction equipment.
Automotive Industry: Fuel injection lines and power steering systems.
Marine Engineering: Hydraulic steering systems for vessels.
Railway Systems: Pneumatic and hydraulic braking systems.
ST37.4 Seamless Precision Steel Tubes Manufacturing Process
Raw Material: Use of high-quality killed carbon steel billets.
Cold Drawing/Rolling: Multiple passes of cold drawing to achieve precision dimensions.
NBK Heat Treatment: Normalizing in a controlled, oxygen-free furnace.
Non-Destructive Testing (NDT): 100% Eddy Current or Ultrasonic testing for internal flaws.
Finishing: Anti-rust oiling on internal and external surfaces.
ST37.4 Seamless Hydraulic Tubes factory
ST37.4 Seamless Hydraulic Tubes test and inspection
FAQ
What are hydraulics steel tubes used for
Hydraulic steel tubes are primarily used to transmit high-pressure fluids (oil or liquid) between various components in a hydraulic system. They act as the "veins" of a machine, connecting pumps, valves, and actuators.
Key applications include:
Construction Machinery: High-pressure lines in excavators, cranes, and forklifts.
Industrial Equipment: Connecting hydraulic presses, injection molding machines, and automation lines.
Automotive Industry: Used for fuel injection systems, power steering, and braking lines.
Marine & Offshore: Hydraulic steering systems and deck machinery on ships or oil rigs.
Aerospace: Control systems for landing gear and wing flaps.
What is difference Between Hydraulic Tubes and Hydraulic Hoses
The main difference lies in flexibility and durability.
| Feature | Hydraulic Hoses | Hydraulic Tubes |
| Material | Rubber & Steel Wire | Seamless Steel |
| Movement | For moving parts | For fixed/stationary parts |
| Weight | Heavier | Lighter |
| Heat Dissipation | Poor | Excellent |
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