- Wall Thickness
- Outside and Inside Diameter
- Type of Material
- Seamless or Welded
- Concentricity and Ovality
- Surface Finish
The wall thickness is directly related to the pressure rating of the system. If the wall thickness is too thick, it will not allow the ferrules to deform the tube. If the wall thickness is too thin, it can result in a blowout.
Outside & Inside Diameter
When designing a fluid system the Outside Diameter and Inside Diameter need to be carefully selected to ensure sufficient flow and pressure rating. SS tubing (Type 304, 304L, 316, 316L) by EN ISO 1127 (D4, T4 tolerance for 3 to 12mm; D4, T3 tolerance for 14 to 50 mm) or equivalent.
Type of Material
Seamless or Welded
- Seamless tube gives a 20% higher pressure rating
- Welded seams can reduce the corrosion resistance of the tube
Tubing must be softer than the fitting material. Hardness of SS Tubing used with twin ferrule tube fittings should be 90 HRB (200 HV) or less.
|Alloy||EN Number||Hardness (HRB)|
|S Duplex||1.4410||100 max|
|Monel 400||2.4360||75 max|
Concentricity and Ovality
- Non-concentric tubing has a lower pressure rating
- Oval tubing may not fit through the ferrules
Pipes: Acid Pickling (AP)
Tubes: Acid Pickling (AP), Mechanical Polishing (MP), Bright Annealing (BA) and Electro Polishing (EP).
Surface Finish is very important for proper sealing. Tubing with any kind of depression, scratch, raised portion, or other surface defect will be difficult to seal, particularly in gas service.
|Surface Condition||Surface Roughness (μm)||Surface Roughness (μinch)|
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