Re: Another Trick

Dear Kaustubh

you have fallen into exactly the same hole that I did when I started this, and I am satisfied that for thin wall pipes I was wrong and Ben is right. Explanation? Here goes:
Consider your 0.005mm/mm or 0.5% thermal strain. All dimensions will increase by 0.5%, including bend radii, and pipe diameter, which I overlooked. The bend centreline radius will increase as well. Suppose, for ease of visualisation the strain was increased to 5% or even 50%. The bend will simply be a larger version of the pre-strained version, but geometrically similar. If you are still unsure, draw it out on paper; it only takes a minute.
However, if the effect of significant wall thickness is added then I am unsure, and would think some secondary stress could possibly be generated. However I have difficulty in visualising the effect. A finite element study would put my mind at rest.

Sorry about the Red Herring. I'll start taking the pills again.

Cheers

Steve McK

• Original Message ----- From: "KAUSTUBH JOSHI" <kvj@epc.ltindia.com> To: <PipingDesign@yahoogroups.com> Sent: Saturday, April 20, 2002 7:14 PM Subject: RE: [PipingDesign] Another Trick

> Dear Ben,
>
> When the temperature of the outer surface is more than the inner one, then
the thermal bowing comes into picture.
>
> I try to explain what I think, I may also be wrong:
> Take a 12"NB, 1.5D 90 Deg. bend. The outer radius is 619mm, while inner
radius is 295mm. The outer surface developed length is 973mm, while the inner surface developed length is 464mm. Now let us take a thermal strain of 0.005mm/mm.
> The expansion of the outter surface is 4.86mm, whereas that of the inner
surface is 2.32mm.
> What happens when the bend is subjected with this temperature? Since the
outer surface wants to expand more than that of the inner surface, and there is a connecting piping at start and end of bend, then bend bends inward. There is always a end rotation associated with start & end of the bend. At the same time there is ovalization of the bend (flatter from top & bottom surfaces).
> And this happens at all the temperatures increase. Am I sounding logical?
>
> Regards,
> Kaustubh
>
>
>
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Received on Sat Apr 20 05:12:00 2002