Stainless Steel capillary tubes are long, thin, cylindrical tubes with a small internal diameter. The word capillary refers to the flow of liquids and gases within a small internal diameter tube. These stainless-steel capillary tubes are used in medical, aerospace, and chemical processing industries. The following properties make it suitable to use in these industries:
- High strength: These tubes have excellent strength with the ability to provide resistance to pressure.
- Corrosion resistance: These tubes resist the chemicals and have stability at extreme temperatures.
- Smooth surface finish: These tubes have a smooth internal surface, which minimizes friction and maintains the excellent fluid within the tubes.
- Dimensional tolerances and stability: These stainless-steel capillary tubes have high dimensional tolerances and maintain their dimensions at extreme temperatures.
- Hygienic: Due to its non-porous properties, it is hygienic and easy to clean, making it suitable for use in the food processing, chemical, and medical industries.
Size Range & Dimensional Precision
The stainless-steel capillary tubes have a wide size range with tight dimensional precision to achieve a consistent liquid flow. Table 1 shows the size ranges and precise dimensional tolerances of thickness, length, outer, and inner diameter.
Table 1: The size range and precise dimension tolerance of different parameters
Parameter | Range / Value | Dimensional Tolerances |
Outer Diameter (OD) | 0.30 mm – 12.70 mm | ±0.02 mm to ±0.05 mm |
Inner Diameter (ID) | 0.10 mm – 8.00 mm | ±0.02 mm to ±0.04 mm |
Wall Thickness | 0.05 mm – 1.50 mm | ±10% of wall thickness |
Length | Up to 30 meters | ±0.5% of ordered length |
Material Grades & Types
Depending upon the application, different grades of stainless steel are used, but austenitic stainless steel is the most common material used in capillary tubes. These austenitic stainless steel capillary tubes provide excellent corrosion resistance, high ductility, and strength.
Table 2: Common types and material grades used in capillary tubes
Material Grade | Common Types | Typical Applications |
321 | Austenitic (non-magnetic) | High-temperature applications |
316 / 316L | Austenitic (non-magnetic) | Medical devices, marine environments, and chemical processing. |
304 / 304L | Austenitic (non-magnetic) | General-purpose fluid transfer, food and beverage processing lines. |
17-4 PH | Precipitation-Hardening (magnetic) | High-pressure hydraulic lines |
410 | Martensitic (magnetic) | Precision mechanical parts, pins |
Manufacturing & Quality Standards
To manufacture high-quality stainless steel capillary tubes, it is important to maintain both a small internal diameter with excellent mechanical properties and surface finishing. There are some international standards to produce quality stainless steel capillary tubes. Below, the manufacturing of stainless-steel capillary tubes is discussed in detail:
- Hot extrusion is done to form the hollow shell from the billet.
- The small diameters of capillary tubes can be made by cold drawing.
- The annealing is done to relieve the material from stress after applying too much cold working process on it.
- To ensure the smooth internal surface of the capillary tube, pickling and polishing are done.
- The long-manufactured tubes are cut according to the required dimension without deforming the tube dimension.
- Eddy current, hydrostatic testing, and ultrasonic testing are used to ensure the properties of capillary tubes.
To ensure consistency in properties during the manufacturing of capillary tubes, different international standards should be followed strictly. Some of them are discussed below:
1) ASTM A269: It specifies the specifications for capillary tubing made from both seamless and welded austenitic stainless steel.
2) ASTM A 213: This standard specifies the chemical, mechanical properties for seamless ferritic and austenitic alloy steel tubes.
3) ASTM E213: It talks about ultrasonic testing regulations to detect internal flaws.
4) ASTM E209: It specifies the specifications for eddy current testing to detect the surface and subsurface cracks in the tubes.
5) A623: It specifies the specifications for both seamless and welded austenitic stainless-steel tubes, especially for small diameter tubes.
How to Choose the Right Tube
The right stainless steel capillary tubes can be chosen according to the requirements for applications. The following key points should be considered when choosing the right stainless steel capillary tube:
1) If tubes are used in a corrosive environment, then tubes should be made from the 316L stainless steel material. While other stainless steel material grades like 304 can be considered if they carry the inert gases.
2) The low-thick tube can be made if the tube is carrying low pressure. The thickness of the stainless-steel capillary tube should be increased to avoid the failure of the tube.
3) If a rigid stainless-steel tube is required, then a thicker wall should be used.
4) Surface finishing should be considered for some applications. For example, bright annealed tubes are preferred for the medical industry.
5) If the tube is carrying the high-temperature liquid, then thermally stable materials like 321 should be selected to avoid the deformation of the tube.
Pricing Considerations
The price of stainless steel varies according to different application requirements. A cheaper and uncertified tube can fail during application. The following important factors should be considered before deciding on the budget for stainless steel tubes:
1) The addition of molybdenum in 316 makes it cost more compared to 304 stainless steel tubes.
2) The tight tolerance of dimensions with small diameters requires expensive equipment, and the cost of production will increase automatically.
3) The non-destructive testing can increase the cost of stainless-steel capillary tubes to get a defect-free tube.
4) The market trends can increase the price of tubes due to fluctuations in the price of nickel and chromium.
5) The bulk order of stainless-steel tubes can reduce the cost due to a reduction in the setup cost of the manufacturer.
Conclusion
It is not always necessary to bear the load and maintain liquid pressure with thicker tubes. Stainless steel capillary tubes can be considered in applications where low thickness and small internal diameter are required, such as aerospace systems and medical devices. Different grades of stainless-steel tubes can be manufactured according to the application requirements. Different international standards should be strictly followed while manufacturing stainless steel capillary tubes. The more corrosion-resistant material grade, precise dimension tolerances, and smooth surface finishing can increase the price of the tubes. Contact us now for tailored stainless steel capillary tube solutions at favorable prices!
