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#35625 - 05/25/10 11:27 AM square root(r*t)
M.SHUKLA Offline
Member

Registered: 06/05/08
Posts: 55
Loc: INDIA
Dear All,

This is a general question. Not related to PVElite

Ques) What is the significance of term square root(r*t) and from where it gets derived (basic behind it).


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#35653 - 05/26/10 07:08 AM Re: square root(r*t) [Re: M.SHUKLA]
Ray_Delaforce Offline
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Registered: 01/02/03
Posts: 743
Loc: Houston, TX
Hello there

The term Sqrt(R*t) represents the 'decay' length of the stress on a cylinder or head. Suppose you have an external load on a nozzle. Where you attach the nozzle to the shell, there is a small area of the shell that is subject to a high stress from the stress concentration factor. This stress decays, or dies away at a distance of Sqrt(R*t).
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Ray Delaforce
CADWorx & Analysis Solutions
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#35659 - 05/26/10 09:19 AM Re: square root(r*t) [Re: Ray_Delaforce]
kalra Offline
Member

Registered: 06/04/09
Posts: 17
Loc: india
HELLO RAYY.
REALLY AWESOME ANSWER

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#35666 - 05/26/10 10:20 AM Re: square root(r*t) [Re: Ray_Delaforce]
M.SHUKLA Offline
Member

Registered: 06/05/08
Posts: 55
Loc: INDIA
Thanks Ray,

Does this length of decay is applicable to thermal gradient (dt/dx).

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#35669 - 05/26/10 10:54 AM Re: square root(r*t) [Re: M.SHUKLA]
Ray_Delaforce Offline
Member

Registered: 01/02/03
Posts: 743
Loc: Houston, TX
Hello guys

This does not apply to thermal gradients. The temperature varies as a continuum over the surface (inside and outside), and also varies over the thickness of a shell section. Thermal stresses are extremely complex in nature and cannot be assessed accurately without knowing exactly where the temperatures exist at each discrete point. There is a simplified method (which is very crude) in the PD 5500 code, but its limitations must be recognised.
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Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM

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#35977 - 06/05/10 10:14 AM Re: square root(r*t) [Re: Ray_Delaforce]
M.SHUKLA Offline
Member

Registered: 06/05/08
Posts: 55
Loc: INDIA
Thanks,

But this question arose in my mind because, few clients in their specification dictate that top portion of skirt which would get welded with shell shall have a minimum length if 1.65 sqrt(r*t).

If thermal gradient is not the reason, then what else would be the reason for this.

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#35984 - 06/06/10 10:42 AM Re: square root(r*t) [Re: M.SHUKLA]
vishaltailor Offline
Member

Registered: 05/15/10
Posts: 56
Loc: Gujarat, india
Dear Mr. Shukla

I would like say that SQRT(r.t) is applicable for Nozzle, What Mr. Ray has explained in earlier post. If you like to know, from where this relation comes refer - Theory of Beam on Elastic Foundation.


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Vishal Tailor
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Vishal Tailor

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#35990 - 06/07/10 06:30 AM Re: square root(r*t) [Re: vishaltailor]
Ray_Delaforce Offline
Member

Registered: 01/02/03
Posts: 743
Loc: Houston, TX
Hi M

I am not certain of the reason, but if there are stress where the skirt is welded to the vessel, then any secondary stresses would decay (die out) in that distance.
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Sincerely,
Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM

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#35999 - 06/07/10 11:10 AM Re: square root(r*t) [Re: Ray_Delaforce]
tahirq Offline
Member

Registered: 12/08/09
Posts: 50
Loc: India
Hello there,

Can any body help by providing decay function for stress for the circular cylinder junction.

This is in interest to analyze decay of stress for Nozzle to shell junction.

Thanks in advance for your response.

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Tahir Quraishi
Technip

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#36396 - 06/24/10 11:51 AM Re: square root(r*t) [Re: tahirq]
Mak Offline
Member

Registered: 12/12/08
Posts: 82
Loc: india
HelLo Everybody,

As given in WRC 297 the width of the reinforcing pad or insert plate shall be at least 1.65*sqrt(rt) to consider its effect as a reinforcement & again to sustain the external loads.
But as you said that at a distance sqrt(rt) the stresses due to external loads will be die.
So, why the factor 1.65 is given in the WRC? Alos is this necessary to consider the factor 1.65 or the width can be only sqrt(rt)?
In some cases where we are using the self reinforced nozzles the hub outside diameter is much more & then again the width as per WRC 297 leads to increase the inert plate diameter to a very big dimension.
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Makrand Sakpal
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#36531 - 06/30/10 09:52 AM Re: square root(r*t) [Re: Mak]
Mak Offline
Member

Registered: 12/12/08
Posts: 82
Loc: india
Dear all,

can anyone please answer this?
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Regards,
Makrand Sakpal
Contact No: - 9967949656

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