| Instrumentation :: Tube Fittings :: Features& Installation |
| |
| RE-ASSEMBLY INSTRUCTIONS OF TUBE FITTINGS |
|
| With
PMT
tube fittings the connection can be disconnected and retightened many times and the same reliable, safe and
leak proof connection can be obtained. For re-assembly the following steps should be followed |
| |
| 1. Insert tube with pre-swaged ferrules into the tube fitting until front ferrule seats in fittings. |
| |
 |
| |
| 2. Holding the body with spanner, the nut is tightened to the original position and then given a slight extra effort to retain
positive sealing
|
| |
 |
| |
| PIPE THREAD CONNECTION |
| Most widely used NPT threads have been machined for connecting the threaded fittings. Leak tighteness is not achieved
by the thread alone without sealant. Commercially available Teflon tape/paste is to be used to provide sealing and
lubricating agent. Wrap the tape 4 to 5 layers around the male threads in a clockwise direction. Ensure that the tape/paste
does not over hang the first thread. |
| |
| SELECTION OF TUBING |
The
PMT
twin ferrule tube fitting is precision engineered to exacting standards. Careful selection of high quality tubing
together with appropriate
Super-lok fitting will ensure the installation of safe, leak free systems.
PMT
tube fittings are designed to work on line material. Stainless steel fittings should be used with S.S. tubing. The practice
of mixing material is strongly discouraged. The only exception is brass fittings with copper tubing.
Disimilar materials in contact may be susceptible to galvanic corrosion. Further different materials have different levels of
hardness, and can adversely affect the fittings ability to seal on the tubing.
The tubing wall thickness is decided based on maximum pressure rating. Thick walled tubing helps to provide resistance
Very low wall thickness of tubing may result in unreliable joints. For
PMT S.S. tube fittings seamless S.S. 316/316L/304L fully annealed tubing of high commercial quality as per ASTM-A-.269/ASTM-A-213 is recommended
PMT tube fittings are normally not recommended for tube wall thickness outside the ranges shown in Table I, II & III.
The key to proper tube hardness for use with PMT tube fitting is that the tubing should be softer than the fitting material
Based on this, preferred hardness of tubing is Rb 80 or less. If harder tube is used the maximum hardness should not
exceed Rb 90.
|
| |
| TUBING FOR GAS SERVICE |
Special care must be taken while selecting tubing for gas service. In gasses even a small surface defect may provide a leak
path. In order to achieve a gas tight seal, ferrules in instrument fittings must seal any surface imperfections. This is accomplished by the ferrules penetrating the surface of the tubing.
Penetration can only be achieved if the tubing provides radial resistance and if the tubing material is softer than the ferrules
Though maximum allowable hardness of S.S. tubing as per ASTM 269/213 is Rb 90, preferred hardness of tubing should
be Rb 80 or less for reliable and leak proof joints mainly in gas application.
The suggested minimum wall thickness of S.S. tubing for gas service for different sizes of tubing is given in following table
SUGGESTED MINIMUM WALL THICKNESS OF S.S. TUBING FOR GAS SERVICE |
| |
TUBE O.D
(Inch) |
SUGGESTED MINIMUM
WALL THICKNESS
(Inch) |
| 1/8 |
0.028 |
| 3/16 |
0.028 |
| 1/4 |
0.028 |
| 5/6 |
0.035 |
| 3/8 |
0.035 |
| 1/2 |
0.041 |
| 5/8 |
0.052 |
| 3/4 |
0.062 |
| 7/8 |
0.073 |
| 1 |
0.083 |
|
| |
| RECOMMENDED MAXIMUM WORKING PRESSURE FOR DIFFERENT TUBING |
The maximum allowable working pressure for different tubings (as given in following tables) have been calculated using the maximum allowable stress levels in accordance with ANSI B 31.3. The calculations are based on nominal wall thickness and at ambient temp. At higher temperature the maximum working pressure will be less as the allowable stress will be reduced. The maximum working pressure in the following tables have been given only for recommended minimum to maximum wall thickness for different sizes of tubing
TABLE-1
RECOMMENDED MAXIMUM WORKING PRESSURE FOR SS 304/316 TUBING (SEAMLESS) IN POUNDS PER SQUARE INCH. |
| |
TUBE O.D
(Inch) |
TUBE WALL THICKNESS (inch) |
| 0.028 |
0.035 |
0.049 |
0.065 |
0.083 |
0.095 |
0.109 |
0.120 |
| 1/8 |
8600 |
11200 |
- |
- |
- |
- |
- |
- |
| 3/16 |
5500 |
7000 |
10400 |
- |
- |
- |
- |
- |
| 1/4 |
4000 |
5100 |
7500 |
10500 |
- |
- |
- |
- |
| 5/6 |
- |
4100 |
5900 |
8100 |
- |
- |
- |
- |
| 3/8 |
- |
3300 |
4800 |
6600 |
- |
- |
- |
- |
| 1/2 |
- |
2500 |
3500 |
4800 |
6300 |
- |
- |
- |
| 5/8 |
- |
- |
3000 |
4000 |
5200 |
6100 |
- |
- |
| 3/4 |
- |
- |
2400 |
3300 |
4300 |
5000 |
5800 |
- |
| 7/8 |
- |
- |
2100 |
2800 |
3600 |
4200 |
4900 |
- |
| 1 |
- |
- |
- |
2400 |
3200 |
3700 |
4200 |
4700 |
|
| |
TABLE-2
RECOMMENDED MAXIMUM WORKING PRESSURE FOR STEEL (SEAMLESS! IN POUNDS PER SQUARE INCH) |
| |
TUBE O.D
(Inch) |
TUBE WALL THICKNESS (inch) |
| 0.028 |
0.035 |
0.049 |
0.065 |
0.083 |
0.095 |
0.109 |
0.120 |
| 1/8 |
8200 |
10900 |
- |
- |
- |
- |
- |
- |
| 3/16 |
5200 |
6700 |
10100 |
- |
- |
- |
- |
- |
| 1/4 |
3800 |
4900 |
7200 |
10100 |
- |
- |
- |
- |
| 5/6 |
- |
3800 |
5500 |
7700 |
- |
- |
- |
- |
| 3/8 |
- |
3100 |
4500 |
6200 |
- |
- |
- |
- |
| 1/2 |
- |
2300 |
3300 |
4500 |
6000 |
- |
- |
- |
| 5/8 |
- |
1800 |
2600 |
3500 |
4600 |
5400 |
- |
- |
| 3/4 |
- |
- |
2200 |
2900 |
3800 |
4400 |
5100 |
- |
| 7/8 |
- |
- |
1800 |
2500 |
3200 |
3700 |
4300 |
- |
| 1 |
- |
- |
1600 |
2100 |
2800 |
3200 |
3700 |
4100 |
|
| |
TABLE-3
RECOMMENDED MAXIMUM WORKING PRESSURE FOR COPPER (SEAMLESS) TUBING IN POUNDS PER |
| |
TUBE O.D
(Inch) |
TUBE WALL THICKNESS (inch) |
| 0.028 |
0.035 |
0.049 |
0.065 |
0.083 |
0.095 |
0.109 |
0.120 |
| 1/8 |
2800 |
3800 |
- |
- |
- |
- |
- |
- |
| 3/16 |
1600 |
2300 |
3600 |
- |
- |
- |
- |
- |
| 1/4 |
- |
1700 |
2600 |
3600 |
- |
- |
- |
- |
| 5/6 |
- |
1700 |
2000 |
2800 |
- |
- |
- |
- |
| 3/8 |
- |
1100 |
1600 |
2300 |
- |
- |
- |
- |
| 1/2 |
- |
800 |
1200 |
1600 |
2100 |
- |
- |
- |
| 5/8 |
- |
- |
900 |
1300 |
1700 |
2000 |
- |
- |
| 3/4 |
- |
- |
800 |
1000 |
1400 |
1600 |
1900 |
- |
| 7/8 |
- |
- |
600 |
900 |
1100 |
1300 |
1600 |
- |
| 1 |
- |
- |
550 |
800 |
1000 |
1200 |
1400 |
- |
|
| |
| QUALITY ASSURANCE PLAN |
PMT
Twin ferrule tube fittings are manufactured to conform with the applicable sections of the American standard code for
pressure piping (ASME codes). Manufacturing process is precisely controlled by a well established and approved quality assurance programme.
Manufacturing is started only after verifying the chemical composition and hardness of raw material. Unless otherwise
asked for special material, PMT
twin ferrule tube fittings are manufactured from S.S. 316 material. Ail bar stock items, i.e
nut ferrules and straight connectors, unions, etc. are manufactured from S.S. 316 meeting ASTM-A-479/276
requirements. All shaped fittings i.e. tees, elbows, etc. are manufactured from forgings meeting requirementsofASTM-A- 182.
Batch production of fittings is allowed only after qualification of sample fitting parts. Internal bores, seat angle, tube bore depth, ferrule and body inner dimensions and pipe threads are checked on 100% basis.
To check the mechanical conformance of the fittings/parts the following test are performed :
|
A) Material Test
B) Hydro Test
C) Vibration Test
D) Leak Test
E) Dimensional Conformance Test
F) Hardness test |
Hardness test on ferrules, pressure test, make remake test, vibration test, pull out tests, pressure & temp cycling tests are done on limited samples selected randomly from the lot and in case of any failure, full lot is tested for above tests.
In house Extensive test facility is being developed for performing different tests on tube fittings. |
| |
|
| |
