we dont know if the inner nozzle to vess wall was weaker and fractured
preferentially to a stronger outer noz/repad weld.
Could this explain the "wrinkle" in the theory about the inward 6"
deflection??. ie it flared in 6" being weaker at rupture.
remember its the older and corroding side. The doubler plate was new and newly welded to the outside of the nozzle therfore perhaps stronger there, although the repad weld at the periphery was compromised. Interesting but short on facts..
> Okay, let's accept (for sake of argument), that the fillet welds cracked
due
> to some embrittlement problem.
>
> But that does not explain the bulging of reinf. pad with some sort of
> explosion, neither it solves the inward movement of shell plates in that
> location after the explosion. The physical evidence suggests some sort of
> pressure development between reinf. pad & the vessel shell plates. From
the
> arguments put forward, I understand that the explosion can not take place
> due to volumetric expansion of air.
>
> But with water entrapped between the plates, formation of steam &
consequent
> volumetric expansion at 320 C ( approx 600 F) should be enough. Sufficient
> time for build up of pressure was there. The vessel obviously did not
reach
> 320 C in a minute. Any commissioning has to be a gradual practice.
>
> With regards
>
>
>
> -----Original Message-----
> From: <a href="/group/PipingDesign/post?postID=nNM7UxxG_G441pPG0h46FxgaEOUCbHlErBWKoOFX1Y5sF1o0s70ZcOl8c44nP2fdDl_ttMSRI6ee4MdLX5sr464n7A">PipingDesign@yahoogroups.com</a>
> [mailto:PipingDesign@yahoogroups.com]On Behalf Of Christopher Wright
> Sent: Thursday, September 15, 2005 2:10 AM
> To: <a href="/group/PipingDesign/post?postID=nNM7UxxG_G441pPG0h46FxgaEOUCbHlErBWKoOFX1Y5sF1o0s70ZcOl8c44nP2fdDl_ttMSRI6ee4MdLX5sr464n7A">PipingDesign@yahoogroups.com</a>
> Subject: Re: [PipingDesign] Re: Reinforcement Pad Weep hole
>
>
> I couldn't stand it, I wasted 20 minutes or so making a brief
> assessment of what kind of pressures you'd have to build up to bulge a
> doubler plate. You can make a few assumptions and get a pretty good
> idea of what needs to happen. Assume--
>
> --the doubler behaves as a flat annular plate
>
> --The doubler OD, Do, is about twice the ID, based on reinforcement
> boundary requirements, and that the ID and OD are fully connected to
> the nozzle wall and the vessel wall respectively. The stress in the
> doubler (Timoshenko, Strength of Materials) due to pressure, Pi, over
> the faying surface is S = 0.185Pi(Do/td)^2 with td as the doubler
> thickness.
>
> --The opening diameter is half the vessel diameter, D, and the doubler
> thickness equals the vessel thickness, t. The ratio of vessel diameter
> to thickness, D/t, is about 2xAllowable stress/internal pressure, which
> works out to be about 100 for a design pressure of 400 psi and an
> allowable stress of 20000 psi. For ordinary vessels the ratio ranges
> from 20 to 100 or more.
>
> --For the opening size specified, Do = D so Do/td = D/t. The pressure,
> Pi, required to yield the doubler is Sy/0.185(Do/td)^2 =
> Sy/0.185(D/t)^2. A vessel carrying an allowable stress of 20 ksi and a
> yield stress of 40 ksi with D/t = 100 and Do = D (corresponds roughly
> to an internal pressure of 400 psi) requires roughly 22 psi to bulge
> the pad. if D/t = 50 the pad requires 86 psi to bulge.
>
> If air were trapped between the wall and the doubler the internal
> absolute pressure is proportional to the absolute temperature. To go
> from atmospheric pressure to 22 psi requires a temperature rise to 675F
> from atmospheric if the volume remains constant. If D/t = 50 the
> doubler gets thicker and the pressure to bulge is 86 psi. That would
> take a temperature rise to just over 2600F. Note the trapped volume
> will increase as the doubler deforms, so the required temperature to
> achieve a given pressure gets higher. The high temperature has to occur
> throughout the entire volume of air and be maintained long enough for
> yielding to occur.
>
> The situation is about the same if the area inside the pad contains
> steam or any other gas. Water remains liquid at higher temperatures
> than 212F if the pressure goes up, so any liquid trapped between the
> requires a higher temperature to become steam at the required pressure.
>
> I conclude that it's not likely that gas can be heated high enough to
> bulge the doubler under ordinary conditions. I don't think this is a
> likely cause of the doubler deformation or the cracking that
> Chakraborty describes. Given that Chakraborty's vessel didn't get the
> proper Q/A and was welded wet, I daresay the weld broke because it was
> embrittled. Although the pressure (4 kg/cm^2 = 60 psi) is the right
> order of magnitude, it's hard to imagine that the volume change to a 6
> inch dent would allow such a pressure build-up.
>
> So now I've stuck my neck out, just waiting for someone to point out
> the hidden flaw in my work...
>
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw@skypoint.com | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania
> 1864)
> <a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a>
>
>
>
>
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Received on Thu Sep 15 23:13:00 2005
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