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#37181 - 08/01/10 09:33 AM Allowable stress as per ISO 14692 _CAESAR 5.2
prakash_26jan Offline
Member

Registered: 05/09/09
Posts: 19
Loc: oman
Hi
can some body help me how Caesar 5.2 will calculate the allowable stress as per ISO 14692.BECAUSE WHEN WE ARE CALCULATING THE allowable stress by hand using iso14692 part 3(technical corrugandum 1)is not matching with Caesar II 5.2 version calculated value.

Is there any specific file(supporting file) to be installed while installing the Caesar II 5.2 ?

prakash kumar
piping stress engineer
Composite pipes industry
muscat(oman)

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#37193 - 08/02/10 10:30 AM Re: Allowable stress as per ISO 14692 _CAESAR 5.2 [Re: prakash_26jan]
xlu Offline
Member

Registered: 07/10/07
Posts: 26
Loc: TX. USA
Kumar:

Could you send us (techsupport@coade.com) your case where the allowables for ISO-14692 from CAESAR II are not matching your hand calculation, please?

Thanks
_________________________
Xiaojun Lu
Intergraph CAS

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#39675 - 12/21/10 03:56 AM Re: Allowable stress as per ISO 14692 _CAESAR 5.2 [Re: prakash_26jan]
prakash_26jan Offline
Member

Registered: 05/09/09
Posts: 19
Loc: oman
Dear Sir

We are GRP manufacturer. We are manufacturing the GRP pipes and fitting as well as we are doing full engineering of GRP pipes. When we are performing the stress analysis of any system we found some node allowable stress is not matching with as per ISO 14692. We have two query regarding this
1) The formula mentioned for calculating the allowable stress in ISO 14692 part 3 (Equation 19 to 22) is not matching with the formula mentioned in the Caesar quick guide .please clarify.

2) As per Caesar quick guide some where the allowable stress is matching and some where it is not matching.

As per example: I mention the two scenarios in 1st scenario it is matching where as 2nd scenario it is not matching in the same report.
Input for calculating the allowable stress and code stress
As per our test value

Failure envelope for plain pipe

σ al (0:1) = 25.69 M Pa, σ al (2:1) = 49.67 M Pa, σ al (1:1) = 49.67 M Pa
σ hl (2:1) = 99.34 M Pa, σ hl (1:1) = 49.67 M Pa

Failure envelope for joints and fitting

Qs = 99.340

Biaxial stress ratio (r) =1

A1, A2, A3= 1

Scenario 1:

As per the Caesar extended o/p report

Axial Stress = 27.92 MPa, Bending stress = 0.85 MPa,
Torsion Stress = 0.02 MPa, Hoop Stress = 56.40 MPa

As per the Caesar Quick guide

σ a, sum = ((σ ap+σ ab)^2+ 4ξ^2)^0.5
= 27.93 MPa.
= code stress
σ h, sum = ((σ h)^2+ 4ξ^2)^0.5
= 56.41 MPa.

Also as per Caesar Quick guide
σ h, sum <= f2 *A1 *A2 *A3 *σ hl (2:1)
σ h, sum=56.40<= 82.45

&
σ h, sum >= f2*A1*A2*A3* σ hl (1:1)
56.40>= 41.2261

So use

σ a, sum <= f2*A1*A2*A3* σ al(1:1) + (σ al(2:1)- σ al(1:1))*( σ h, sum – f2*A1*A2*A3* σ h(1:1)) / (σ hl (2:1) - σ hl (1:1) )
= 41.23 MPa

And same allowable stress has mentioned in the extended stress Report.

Where as Scenario 2:

As per the Caesar extended o/p report

Axial Stress = 13.58 MPa, Bending stress = 0.13 MPa,
Torsion Stress = 0.03 MPa, Hoop Stress = 56.40 MPa

As per the Caesar Quick guide

σ a, sum = ((σ ap+σ ab)^2+ 4ξ^2)^0.5
= 13.59 MPa.
= code stress

But as per Caesar extended o/p report
The code Stress = 56.40 MPa

σ a, sum <= f2*A1*A2*A3* σ al(1:1) + (σ al(2:1)- σ al(1:1))*( σ h, sum – f2*A1*A2*A3* σ h(1:1)) / (σ hl (2:1) - σ hl (1:1) )
= 41.23 MPa
= Allowable Stress

But as per Caesar extended o/p report
The Allowable Stress = 82.47 MPa

Please clarify.

Your positive and quick reply is highly appreciated.


Best Regards,
Prakash Kumar,
Piping Stress Engineer,




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#39693 - 12/21/10 02:10 PM Re: Allowable stress as per ISO 14692 _CAESAR 5.2 [Re: prakash_26jan]
corne Offline
Member

Registered: 07/09/07
Posts: 392
Loc: The Netherlands
CAESAR II checks both the axial and hoop stress against the applicable allowables.
The stresses with the highest stress ratio are displayed.

Scenario 1:
Axial / axial allowable = 27,93 / 41,23 = 67,7 %
Hoop / hoop allowable = 56,40 / 82,45 = 68,4 %

Scenario 2:
Axial / axial allowable = 13,59 / 41,23 = 33 %
Hoop / hoop allowable = 56,40 / 82,47 = 68,4 %

In scenario 2 CAESAR II will display the hoop stress result and allowable and ratio.
In scenario 1, according to the info you gave CAESAR II should give the hoop, but maybe these are rounded figures so CAESAR II actually calculated a higher axial stress ratio in scenario 1.

The above (displaying the highest stress ratio) should be the issue I think.

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