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Performance valuation cum destructive (type) tests

Life Cycles (Fatiuge life) testing
Yield Rupture
Salt Mist
Spring Rate
Inspection

 

 

 

 


LIFE CYCLES (FATIGUE LIFE) TESTING
a) Summary
Fatigue life testing is a verification of the ability of a Bellows to withstand a given no. of flexing cycles. The theoretical evaluations is related to the material, manufacturing constants and the sums of meridional stress range & total meridional deflection stress range owing to imposed movement on the Bellows. EJMA-designed Bellows are not subjected to any form of heat treatment since its residual forming stresses/work hardening of cold forming practices improve the cycle life to a greater level than that of a normalized Bellows.

b) Test Procedure
Place the Bellows in a life cycle testing fixture. Both side to be joined/bolted to the top and bottom plate of the fixture gently. The bottom plate is fixed type and top plate is sliding type through a plunger/piston cylinder arrangement through which hydraulic pressure is applied. Limit switch is provided on the plunger to arrest the maximum axial compression to which the specified value is met. Through the sliding rods the top plate gets closer to the bottom plate and returns to original position by load on piston/plate. Electronic meter having contact limit switch measures each upward movement and counts as one cycle.


Compression Position
Expansion Position
c) Conclusions
First D. P. Test & Air Pressure Test was carried out after 7550 cycles and no crack or leakage found. Second D. P. & Air Pressure Tests carried out after15584 cycles, no crack or leakage found in bellow. Bellow found satisfactory.

 

 

 

 

 

 

 

 

 

 

 


YIELD RUPTURE
Yield Rupture Testing
a) Summary
The objective of a meridional yield rupture test is to determine the internal pressure, which will cause yielding, and rupture of a Bellows. An accurate evaluation of the yield pressure is quite important since it is this value, rather than rupture, which usually provides the limiting criteria for establishing suitable operating pressure. The test specimen should have a minimum of three convolutions to minimize the effects of the end attachments. Identification of the Bellows should be established as per parameters of prototype specified.

b) Test Procedure
Place the Bellows in any suitable fixture, the Bellows fixed in the straight position, which will effectively seal the ends during pressurization, and most importantly, will prevent any movement of the ends during testing. The fixture must also safely restrain the Bellows when rupture occurs. The test medium should be limited to water as a safety precaution.
Pressurize the specimen in steps, returning to zero pressure after each step, up to at least twice the yield pressure. There after the specimen may be pressurized continuously until rupture occurs. The initial pressure intervals should not exceed 10% of the anticipated yield pressure. A constant holding time at pressure should be established for each step throughout the yield point determination. As a minimum, the width or space between each convolution at the pitch diameter, should be measured and record before and after each pressure step. Instrumentation, such as a pressure time recorder, strain gauges, or other conventional means may be used to get valuable information.

c) Conclusions
Both meridional yielding (bulging of flat sides of the convolutions and circumferential yielding of the root diameter will be experienced in test of this type. Although a plot of permanent deformation versus pressure will resemble that of a simple tensile stress-strain curve, a well defined yield point does not usually appear. Beyond the yield point gross distortion, root collapse and ultimate failure will occur.


 

 

 

 

 

 

 

 

 

 

 


Salt Mist
 

 

 

 

 

 

 

 

 

 

 

 

 


Spring Rate
a) Summary
Spring rate is defined as the force required to deflect a Bellows axially by 1 mm. Since there exists a significant variation in value of theoretical elastic spring rate and actual Bellows working spring rate with resistance factors, the probable value during testing vary with manufacturer to manufacture and has to be individually evaluated. The generally considered, allowable variation is within the range of ± 15% of theoretical value of spring rate.


b) Test Procedure in
The Bellows to be placed on a spring rate testing fixture or a simple flat surface. Measure the overall length at four different places in 0°, 90°, 180°, 270° plane and record it. Place a circular ring on top after measuring its dead weight. Check the variation in overall length. Continue placing additional similar weights until the Bellows reaches its designed axial compression value. Measure the overall length and take the average value of deflection. Check the total weight applied and divide this load by deflection, to get the working spring rate. This value should be within the range of ±15% of theoretical value.

 

 

 

 

 

 

 

 

 

 

 


Inspection
INSPECTION CUM DIMENSIONAL REPORT
Sr. No.
:
33 Date
:
18.12.2003
Client
:
Inox India Ltd.  
 
P.O.No.
:
---  
 
P.O.Date
:
---  
 
Item
:
Bellows DRG. No.
:
ABPL/172/02-03 REV.4
SIZE
:
20 NB x 210 long QTY.
:
5 Nos.
Sr. No.
DESCRIPTION
SPECIFIED
ACTUAL
REMARKS
1.
BELLOW ELEMENT
(a) Raw Material
SA240 TP316L
SA240 TP316L
 
  Chemical
CTC No. 241KE/2003 DTD.12.01.2003
 
Physical
PTC No. 28XH/2003 DTD. 22.01.2003
 
(b) Bellows Thickness
0.3 x 1 PLY
0.3 x 1 PLY
 
(c) Bellows I.D.
19.5
19.4
 
(d) Bellows O.D.
29.5
29.6
 
(e) No. of Convolutions
26
26
 
(f) Active Length
104
105
 
2.
COVER
(a) Raw Material
SA312 TP304
SA479 TP316L
 
  Chemical
CTC No. 388KE/2003 DTD.30.01.2003
 
  Physical
PTC No. 61XG/2003 DTD. 20.01.2003
 
(b) O.D. x Thickness
38 x 1.5
38.3 x 1.52
 
3.
NIPPLE
  (a) Raw Material      
    Chemical
CTC No. 377KE/2003 DTD. 25.01.2003
 
    Physical
PTC No. 61XG/2003 DTD. 20.01.2003
 
  (b) O.D. x Length
26.6 x 1.5
26.5 x 53.5
 
4.
Overall Length
210
210
 
D.P. Test
All weld joints
All weld joints
Satisfactory
Hydro Test
39.75 kg / cm2
39.75 kg / cm2
No Leakage Found
Pneumatic Test
28.62 kg / cm2
28.62 kg / cm2
No Leakage Found
Painting & Packing
As per specs
All S.S. parts buffing & bellows packed in corrugated paper
Note :
Bellows have been tested as above for designed performance and recommended to use in systems. Guarantee shall be void if it is used improperly.

Q.C. Department.

 

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