Tubing Variables

• Wall Thickness
• Outside and Inside Diameter
• Type of Material
• Seamless or Welded
• Hardness
• Concentricity and Ovality
• Surface Finish

Wall Thickness

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

Hardness

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)
316	1.4404	90 max
316L	1.4435	90 max
Duplex	1.4462	95 max
S Duplex	1.4410	100 max
6Mo	1.4547	90 max
904L	1.4539	90 max
Monel 400	2.4360	75 max
825	2.4858	90 max
625	2.4856	93 max
C-276	2.4819	93 max

Concentricity and Ovality

• Non-concentric tubing has a lower pressure rating
• Oval tubing may not fit through the ferrules

Surface Finish

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)
AP	Ra≤3.2	Ra≤125
MP	Ra≤3.2	Ra≤125
BA	Ra≤o.38	Ra≤15
EP	Ra≤0.25	Ra≤10

For more information contact our sales team at sales@nvfcl.com or call 01942601209