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Ferrule Fittings

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Double ferrule fittings are visually identifiable by the stepped shoulders on straight body and nut. It is commonly made from stainless steel SS316 and brass material. Straight body and nut are made through close grain forgings.

​It allows the connection of two straight tubes, either in inches or metric size. The size (OD – outer diameter) is available is 6mm to 42mm and 1/8” to 2”. Double Ferrule tube fitting, also know as instrumentation fittings, makes use of a two ferrule mechanical grip design to secure tubing connections. 
​Size
  • 1/8"OD to 2"OD
Material ​
  • Stainless Steel SS316
  • Carbon Steel
  • Brass
Working Pressure
  • Up to 670 bars
Connection Type
  • Compression end
CATALOGUE :

​Double Ferrule Fittings

HSME Double Ferrule


What are Double Ferrule Fittings

1. What are double ferrule tube fittings?
Double ferrule fittings are composed of four precision parts: body, nut, front and back ferrule. The addition of tubing makes it a five component upon installation. The two ferrules separate sealing and tube gripping functions. The front ferrule creates a seal against the fitting body and on the tubing outside diameter. As the nut is turned, the back ferrule compresses the front ferrule and forms an effective tube grip. The market well-known brands are Swagelok and Parker A-lok from United States. 
Union Coupling
Union Coupling
​Double ferrule fittings are supplied for installation in extensive applications: 
  • Onshore oil and gas
  • Shipbuilding 
  • Refinery 
  • Instrumentation 
  • Power generator
  • Pharmaceutical 
  • Chemical and Petrochemical 
  • Semiconductors 
  • Vacuum Application 
  • Gas Application
2. How are double ferrule tube fitting used?

​When the nut is screwed onto the body and is tightened against the tapered area of the body, the edge is compressed tightly against the tube by curling inward. The back ferrule that is located between the nut and body rolls up as the front ferrule rolls and bites into the tube and achieves the connection between fitting and tube as well as a non-leakage sealing effect. 
The ferrule fitting performs leak proof sealing with all assembly and reassembly motion being transmitted axially through the tube. This results in no radial movement of the tubing upon assembly and the tubing is not stressed. The mechanical integrity is maintained. The double ferrule fitting has a close tolerance control in machining, surface smoothness and hardness of each part.
Union Tee
Union Tee
3. How does a double ferrule fitting work?

There are various factors that affect the double ferrule fitting working pressure:

​3.1 Tubing wall thickness

Ferrule fittings are rated to the maximum working pressure according to its tubing wall thickness installed. The tube wall thickness governs the tubing working pressure.
Tube OD (inch)
WT (inch)
​0.028"
​WT (inch)
​0.035"
WT (inch)
​0.049"
WT (inch)
​0.065"
WT (inch)
​0.083"
WT (inch)
​0.095"
WT (inch)
​0.109"
WT (inch)
​0.120"
WT (inch)
​0.134"
WT (inch)
​0.156"
WT (inch)
​0.188"
1/8"
8500
10900
 
 
 
 
 
 
 
 
 
3/16"
5400
7000
10200
 
 
 
 
 
 
 
 
1/4"
4000
​5100
7500
10200
 
 
 
 
 
 
 
5/16"
 
4000
5800
8000
 
 
 
 
 
 
 
3/8"
 
3300
4800
6500
8600
 
 
 
 
 
 
1/2"
 
2600
3700
5100
6700
 
 
 
 
 
 
5/8"
 
 
2900
4000
5200
6000
 
 
 
 
 
3/4"
 
 
2400
3300
4200
4900
5800
6400
​ 
 
 
7/8"
 
 
2000
2800
3600
4200
4800
5400
6100
 
 
1"
 
 
 
2400
3100
3600
4200
4700
5300
6200
 
1  1/4"​
 
 
 
 
2400
2800
3300
3600
4100
4900
 
1  1/2"
 
 
 
 
 
2300
2700
3000
3400
4000
4900
2"
 
 
 
 
 
 
2000
2200
2500
2900
3600
Table 1: Fractional Seamless Stainless Steel SS316 Tubing (ASTM A269/A213)
*Working pressure are shown in psi
Weldable Bulkhead
Weldable Bulkhead
Allowable pressure calculations are calculated with maximum outer diameter and minimum wall thickness. For an example, stainless steel SS316 tubing size outer diameter 1/2"OD x 0.035 thickness can withstand working pressure up to 2600 PSI. Therefore, double ferrule fittings used to compress the tube are able to withstand up to 2600 PSI. ​
Tube OD (mm)
WT (mm)
1.0
WT (mm)
1.2
WT (mm)
1.5
WT (mm)
1.8
WT (mm)
2.0
WT (mm)
2.2
WT (mm)
2.5
WT (mm)
2.8
WT (mm)
3.0
WT (mm)
3.5
WT (mm)
4.0
WT (mm)
4.5
WT (mm)
5.0
6
420
520
670
 
 
 
 
 
 
 
 
8
310
380
490
 
 
 
 
 
 
 
 
10
240
300
380
 
 
 
 
 
 
 
 
12
200
240
310
380
430
 
 
 
 
 
 
14
180
220
280
340
390
430
 
 
 
 
 
15
170
200
260
320
360
400
 
 
 
 
 
16
 
190
240
300
330
370
 
 
 
 
 
18
 
170
210
260
290
320
370
Value
​ 
 
 
20
 
150
190
230
260
290
330
380
Value
 
 
22
 
130
170
210
230
260
300
340
Value
Value
 
25​
 
 
 
180
200
230
260
300
320
Value
 
28
 
 
 
 
180
200
230
260
280
330
Value
30
 
 
 
 
170
190
210
240
260
310
Value
32
 
 
 
 
160
170
200
230
240
290
330
38
 
 
 
 
 
140
170
200
230
240
280
310
42
 
​ 
 
 
​
 
 
170
180
210
250
280
Value
50
 
 
 
 
 
 
 
Value
150
180
200
230
260
Table 2: Metric Seamless Stainless Steel SS316 Tubing (ASTM A269/A213)
​*Working pressure are shown in bar
Another example as follows, stainless steel SS316 tubing size outer diameter 10mm x 1.5mm thickness can withstand working pressure up to 380 Bar. Therefore, double ferrule fittings used to compress the tube are able to withstand up to 380Bar. ​
3.2 Ferrule Fitting material ​
Temperature °F (°C)
Stainless Steel SS316
Brass
100 (38)
1.00
​1.00
200 (93)
​1.00
0.80
300 (149)
​1.00
0.78
400 (204)
0.97
​0.50
500 (260)
0.90
0.13
600 (316)
0.85
-
700 (371)
​0.82
-
800 (427)
0.80
-
900 (482)
0.78
-
1000 (538)
0.77
-
1200 (649)
0.37
-
Table 3: Elevated Temperature de-rating factors
For an example, the same tube with outer diameter of size 10mm x 1.5mm thickness and ferrule fitting can withstand working pressure up to 380 Bar under room temperature. However, under the temperature 700°F or 371°C, due to de-rating factor of 0.82, the ferrule fitting working pressure will drop to 311.6 Bar and it would affect the would system running pressure. 
3.3 Fitting seal (optional)
​

When rubber elastomer seal is used in ferrule fitting, the temperature rating of the O-ring may be the limiting factor on fitting’s temperature rating.
Elastomer Seal Material
Working Temperature
NBR (Perbunan)
-25°C to 110°C (-13°F to 230°F)
FKM (Viton)
-28°C to 204°C (-20°F to 400°F)
PTFE (Teflon)
-30°C to 315°C (-22°F to 600°F)
Table 4: O-ring temperature ratings
For an example, the same tube with outer diameter of size 10mm x 1.5mm thickness, with NBR seal, the ferrule fitting can work under temperature from -25°C to 110°C.
​4. What are the purposes of a double ferrule fitting?
Reducer
Reducer
Double ferrule fittings can be easily installed. The connections do not require welding or threaded ends. It turns to cost reducing which leads to lesser fabrication on manpower. They can be re-used and keep a low material cost. The benefits of using double ferrule fitting are: 
  • Offer maximum strength and ductility 
  • Chemical resistant and high corrosion resistance
  • Hold extreme temperatures
  • High pressure resistant in harsh or high stress nuclear environment
5. How do you use a double ferrule compression fitting?

Double ferrule fittings do their job effectively when assembled correctly. Often, leakages may still occur due to a loose connection or an incorrect tube fitting. Fittings assembly is easy to learn and initiate. 
​​
  • First, cut your tube to the required length neatly, make sure that you have squared ends without any burr. 
  • Then, one must push the tube inside the twin ferrule fitting firmly, till it reaches a stop inside. 
  • Next, mark the starting point at 6 o’clock position before tightening nut.
  • Follow by simply turning the nut 1-1/4 times and make sure the tube is strongly secured. The starting point is placed at a 9 o’clock position. 
  • The best part about twin ferrule fittings is that they are durable, and so they can be used many times. The parts may be disassembled and reassembled for a different tube. A twin ferrule fitting ensures that the pieces never lose shape or strength due to any excessive fluid pressures. ​

CATALOGUE :

​RFS Double Ferrule Fittings

HSME Double Ferrule Fittings


​Ask a Question

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  • About
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      • High Pressure Ball Valves
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    • High Pressure Fittings >
      • Compression Fittings
      • Ferrule Fittings
      • Forged Pipe Fittings
      • JIC Fittings
      • Quick Release Couplings
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    • Low Pressure Valves >
      • Ball Valves >
        • 1 Piece Ball Valve
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        • 3 Piece Ball Valve
        • L-Port Ball Valve
        • T-Port Ball Valve
        • Brass Ball Valve
        • Brass Mini Ball Valve
        • Stainless Steel Mini Ball Valve
      • Flange End Ball Valves >
        • PN10/16 SS316 Flange End Ball Valve
        • ANSI 150# SS316 Flange End Ball Valve
        • ANSI 300# SS316 Flange End Ball Valve
        • JIS 10K SS316 Flange End Ball Valve
        • ANSI 150# Cast Steel Flange End Ball Valve
        • ANSI 300# Cast Steel Flange End Ball Valve
      • Swing Check Valves >
        • ANSI 150# SS316 Swing Check Valves
        • JIS 10K SS316 Swing Check Valves
        • ANSI 150# Cast Steel Swing Check Valve
        • Threaded End SS316 Swing Check Valves
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      • Single Plate Check Valves
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      • Y-Strainers >
        • ANSI 150# SS316 Y-strainer
        • JIS 10K SS316 Y-strainer
        • Threaded End SS316 Y-strainer
        • ANSI 150# Cast Steel Y-strainer
        • JIS 10K Cast Steel Y-strainer
      • Gate Valves >
        • ANSI SS316 150# Gate Valve
        • JIS 10K SS316 Gate Valve
        • Threaded End SS316 Gate Valve (200 PSI)
        • Threaded End SS316 Gate Valve (800 PSI)
        • ANSI 150# Cast Iron Gate Valve
        • JIS 10K Cast Iron Gate Valve
        • ANSI 150# Cast Steel Gate Valve
        • ANSI 150# Forged Steel Gate Valve
        • Threaded End Forged Steel Gate Valve
        • Welded End Forged Steel Gate Valve
      • Globe Valves >
        • ANSI 150# SS316 Globe Valve
        • JIS 10K SS316 Globe Valve
        • Threaded End SS316 Globe Valve (200 PSI)
        • Threaded End SS316 Globe Valve (800 PSI)
        • ANSI 150# Cast Iron Globe Valve
        • JIS 10K Cast Iron Globe Valve
        • ANSI 150# Cast Steel Globe Valve
        • ANSI 150# Forged Steel Globe Valve
        • Threaded End Forged Steel Globe Valve
        • Welded End Forged Steel Globe Valve
      • Butterfly Valves >
        • ANSI 150# Cast Iron Butterfly Valve
    • Low Pressure Fittings >
      • Class 150 Fittings
      • Camlock Fittings
    • Accessories >
      • Pressure Gauges
      • Stauff Test Couplings
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      • GS Retain Ring
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  • Catalogues
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    • Accessories
  • Contact
  • MYREWARDS
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